Basic Brain Anatomy

Chapter 2 Basic Brain Anatomy

Where this icon appears, visit The Brain http://go.jblearning.com/ManascoCWS to view the corresponding video. The average weight of an adult human brain is about 3 pounds. That is about the weight of a single small To understand how a part of the brain is disordered by cantaloupe or six grapefruits. If a human brain was damage or disease, speech-language pathologists must placed on a tray, it would look like a pretty unim- first know a few facts about the anatomy of the brain pressive mass of gray lumpy tissue (Luria, 1973). In in general and how a normal and healthy brain func- fact, for most of history the brain was thought to be tions. Readers can use the anatomy presented here as an utterly useless piece of flesh housed in the skull. a reference, review, and jumping off point to under- The Egyptians believed that the heart was the seat standing the consequences of damage to the structures of human intelligence, and as such, the brain was discussed. This chapter begins with the big picture promptly removed during mummification. In his and works down into the specifics of brain anatomy. essay On Sleep and Sleeplessness, Aristotle argued that the brain is a complex cooling mechanism for our bodies that works primarily to help cool and The Central Nervous condense water vapors rising in our bodies (Aristo- tle, republished 2011). He also established a strong System argument in this same essay for why infants should not drink wine. The basis for this argument was that The nervous system is divided into two major sec- infants already have Central nervous tions: the central nervous system and the peripheral too much moisture system The brain and nervous system. The central nervous system (CNS) in their heads. None- spinal cord. consists of the brain and spinal cord. The peripheral theless, thanks to ad- Peripheral nervous nervous system (PNS) consists of the nerve tracts vancements in the system The nerve tracts outside of the central that connect the rest of the body to the central ner- fields of science, med- nervous system that work vous system. An easy way to differentiate the CNS icine, and the birth of to connect the central and the PNS is to remember that the CNS is entirely the fields of psychol- nervous system to the rest of the body. encased in bone whereas the PNS is not (Figure 2-1). ogy and neurology, we

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Cranial Nerves (12 Pairs) Brain

PNS CNS

Spinal Nerves Spinal Cord (31 Pairs)

Figure 2-1 The central and peripheral nervous systems.

now know that the brain is much more than an inert mass of head stuffing. And though we know Aristotle was correct in stating that infants should not drink Cerebrum wine, we know that it is not because infants are born with copious amounts of head vapors. We know now that the brain is the organ that coordinates and regu- lates all functions and other organs in our bodies. It is Cerebellum the seat of consciousness, intelligence, and language. Midbrain The brain has three gross divisions, the cerebrum, the Brain Pons stem brain stem, and the cerebellum (Figure 2-2). Medulla oblongata Spinal cord When asked to describe a brain, most individuals describe the cerebrum of the brain. This is the most Figure 2-2 Cerebrum, brain stem, and recently evolved and most easily recognizable part of cerebellum. the brain. The cerebrum is the rounded gray section of the brain riddled with tiny ridges and valleys that makes so many appearances in zombie movies. The as produce language and cognition and organize cerebrum rests on top of the brain stem. The cere- body movements. The surface tissue of the cerebrum brum houses our highest Cerebrum The rounded is known as the cerebral cortex. The cortex is the gray section of the brain and most complex cog- most superficial layer of the cerebrum (Figure 2-3). with gyri and sulci. nitive functions. This is Cerebral cortex The where our consciousness The cerebral cortex is gray and folded and marked most superficial layer of originates as well as our by various ridges and valleys. The cerebrum is folded the cerebrum. ability to do things such in on itself so that more neural tissue can be packed

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connecting different areas and structures of the brain to one another and enabling them to communicate.

The myelinated axons of neurons make white mat- ter appear white and the lack of myelin makes gray matter gray. There are three primary types of white matter tracts in the CNS: association fibers, com- missural fibers, and projection fibers. Association fibers are the pathways of white matter that connect different structures and areas of the brain in a single hemisphere. Commissural fibers are white matter pathways that connect analogous areas between the Figure 2-3 Cerebral cortex. two cerebral hemispheres. Projection fibers are white matter tracts that project from the brain to the spinal cord and transmit motor (movement) signals from into a much smaller space. The gray coloration of the the CNS out to the PNS and sensory signals from the surface of the cerebral cortex results from the gray PNS back up through the lower CNS to be processed color of the cell bodies of the neurons and is therefore in the brain. said to consist of gray matter. Gray matter is where Certain diseases attack and break down the myelin processing and regulating of information occurs in sheath of white matter. These are known as demyelin- the CNS. Gray matter is found in the cortex and some ating illnesses. Demyelinating illnesses degrade the subcortical structures such as the cerebellum, thala- potential of neurons to conduct neural impulses. This mus, basal ganglia (to be discussed), in addition to degradation of the myelin inhibits appropriate neural the spinal cord. This is in contrast to white matter. functioning by disrupt- The white matter of the CNS consists of the axons Association fibers ing communication be- of neurons that are covered in a white sheath of a White matter pathways tween different areas of that connect different protein and fatty sub- Gray matter the CNS or PNS, or structures and areas of Unmyelinated neurons stance called myelin. the brain within a single both. Amyotrophic lat- responsible for the Myelin insulates the hemisphere. processing and regulating eral sclerosis (ALS) and axons of neurons (like Commissural fibers of information within the multiple sclerosis are nervous system. a rubber sheath insu- White matter pathways two such de­myelinating that connect analogous lates the copper wire in White matter diseases. See the areas between the two Myelinated neurons electrical wiring) and al- cerebral hemispheres. video, Living with Mul- responsible for the trans­ lows electrical chemical mission of impulses from tiple Sclerosis for a dis- Projection fibers White impulses of the nervous matter pathways that one area of the brain to cussion of this disease as another. system to be conducted project from the brain well as an interview with to the spinal cord at approximately 100 Myelin An insulating an individual living with and transmit motor layer of protein and fatty meters per second. Un- (movement) signals from multiple sclerosis. substances that forms a myelinated neurons are the CNS out to the PNS layer around the axons and also transmit sensory of certain neurons, which able to conduct neural The folds on the cere- signals from the PNS back allows for the fast and impulses only at about 1 bral cortex are created up through the lower CNS effective transmission of meter per second. White by small convolutions to be processed in the neural impulses. brain. matter is responsible for and furrows, or ridges

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and valleys. The ridges are known as gyri (singu- Clinical Note lar: gyrus). The valleys are known as sulci (singular: sulcus). (See the following Clinical Note on lissen- Lissencephaly cephaly for a discussion of the clinical relevance of As mentioned, the human cerebrum is folded in on the gyri and sulci.) Deeper grooves that make more itself to allow far more cortical tissue to be packed pronounced divisions in the anatomy of the brain into the skull. If you smoothed out the gyri and sulci are referred to as fissures. Knowledge of the major of the human cortex, the surface area would be far gyri, sulci, and fissures is important to learning about greater than that of the inside of the skull. This sys- tem of folding allows the body to fit as much corti- the rest of the anatomy of the brain because they cal tissue within the skull as possible. It is this great are important landmarks for describing the location amount of cortex that allows for normal cognitive of many other areas and functioning. However, there is a group of congenital Gyri Ridges forming the visible portion of the structures of the brain. malformations categorically referred to as lissen- cerebral cortex. The following sections cephaly, or smooth brain syndrome, in which the Sulci Inward folds of the on the cerebral hemi- brain develops in the mother’s womb without these folds in the cortex (Figure 2-4). There are many dif- cerebral cortex. spheres and the major ferent etiologies that account for the varying types Fissure A deep groove cerebral lobes revisit that creates major of lissencephaly. Some etiologies are viral infection divisions in the anatomy the importance of these and gene mutation. Children who are born this way of the brain. structures. usually have profound neurologic impairments, Lissencephaly A feeding difficulties, and can have a very short life group of congenital Between the surface of span. Nonetheless, lissencephaly does occur on a malformations that create spectrum and the long-term medical and develop- the brain and the skull a lack of appropriate gyri mental prognosis of an affected child depends on and sulci of the cortex and are three anatomic layers the level of severity of the brain disorder. a consequent reduction in of tissue known as the cortical tissue. cerebral meninges. The Cerebral meninges Three layers of tissues outermost of these layers with various functions is the dura mater. The that encase and envelope dura mater (Latin for the brain and spinal cord. tough mother) is a dense, Dura mater A dense, fibrous protective layer fibrous protective layer of tissue that envelopes of tissue enveloping the the brain and spinal brain and spinal cord. cord. This is the superficial-most layer of Beneath the dura mater the cerebral meninges. is the arachnoid mater. Arachnoid mater A The arachnoid mater is layer of the cerebral a far more delicate layer Figure 2-4 Imaging scan of a normally meninges that exists between the dura mater of tissue than the dura developed brain and cortex alongside a and the pia mater that mater. The arachnoid lissencephalic brain. Missing from the plays a large role in mater wraps the brain lissencephalic brain are the many folds supplying blood to the and spinal cord and of cortical tissue seen in the normally surface of the brain developing brain. through the many blood plays a large role in sup- vessels it contains. Source: Courtesy of Dr. Joseph G. Gleeson, University of California plying blood to the sur- San Diego face of the brain by the

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many blood vessels that it contains. The arachnoid The Cerebral Hemispheres mater is so named because of the dense spider-web- Observable on the surface of the brain is a deep like appearance of the blood vessels in this layer. The groove running front to back. This groove is known pia mater (Latin for gentle mother) is the innermost as the longitudinal fissure and it runs the length of and most delicate meningeal layer. The pia mater the brain and divides the brain into left and right closely hugs the surface of the brain and spinal cord halves. These halves are known as the left and right as it rises and falls along the gyri, sulci, and fissures cerebral hemispheres (Figure 2-6). of the brain. Blood vessels from the arachnoid mater pass through the pia mater to nourish the surface Generally speaking, each cerebral hemisphere is of the brain and spinal cord. Figure 2-5 shows the responsible for different cognitive and motor func- dura mater as it is being pulled back from the brain tions. For instance, the right hemisphere is respon- below to expose the leptomeninges (i.e., the arach- sible for movement of the left side of the body and noid mater and the pia mater). See Figure 2-14 for processing sensory information coming up to the an image depicting the meningeal layers. brain from the left side of the body. The left hemi- sphere is responsible for moving the right side of the body and processing sensory information coming up to the brain from the right side of the body. Although the hemispheres are often spoken of as discrete and separate units that operate indepen- dently, it is a false and outdated assumption that each hemisphere performs its own functions in isolation without input Pia mater The from the other. The two innermost and most hemispheres work in delicate layer of the tandem and communi- cerebral meninges that hugs the surface of the cate with one another brain and spinal cord by a mass of white mat- closely as it rises and falls ter tracts known as the along the gyri, sulci, and fissures of the brain. corpus callosum. The corpus callosum is lo- Leptomeninges The thin layers of the meninges cated between the cere- including the arachnoid bral hemispheres and is mater and the pia mater. found deep within the Longitudinal fissure A longitudinal fissure, at deep groove running front to back along the brain its very base. The cor- that divides the brain into pus callosum houses the right and left cerebral the largest white matter hemispheres. pathways responsible Corpus callosum A for connecting the left mass of white matter tracts located at the Figure 2-5 Head autopsy revealing dura and right hemispheres. base of the longitudinal mater and leptomeninges. See the following Clini- fissure that connects the cal Notes on split-brain analogous areas between Courtesy of Department of Health and Human Services, Centers for the two hemispheres. Disease Control and Prevention. Dr. Edwin P. Ewing, Jr. syndrome.

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ANTERIOR

Left hemishere Right hemishere

Frontal Lobe Longitudinal Fissure

Precentral Gyrus Central Sulcus

Postcentral Gyrus

Parietal Lobe

POSTERIOR

Figure 2-6 A superior view of the cerebral hemispheres.

See the Split Brain Demonstration video for a live situation where the language-dominant hemisphere demonstration. (most often the left hemisphere) also controls a person’s writing hand (most often the right hand). Typically, the left cerebral hemisphere is the hemi- More often than not, the right cerebral hemisphere sphere that houses most language abilities. Also, is not the language-dominant hemisphere. Even in most individuals are right handed. This creates the left-handed individuals the left hemisphere usually

Clinical Note

Split-Brain Syndrome All brains operate using electricity. Electrical chemi- the two cerebral hemispheres by cutting the corpus cal impulses are how our brains communicate with callosum. This surgery, known as a corpus commi- themselves and our bodies. However, it is possible to surotomy, decreases seizures but results in what is have too much electricity generated in the brain. A known as split-brain syndrome. Individuals with split- seizure is a result of an excess and pathologic amount brain syndrome have cerebral hemispheres that are of electricity in the brain. Seizures can be very dan- unable to communicate with one another. This makes gerous and can create severe and permanent dam- perception sometimes difficult and creates motor age to the brain and even death. The most common problems as well. With the modernization and perfec- group of seizure disorders are categorized as forms of tion of this surgery in the 1960s and 1970s, scientists epilepsy. In some very severe forms of epilepsy, sei- were able to study the functioning and abilities of the zure activity is so threatening to an individual’s brain individual cerebral hemispheres in isolation from one that it is deemed necessary to perform a surgery on another.

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Clinical Note

Split-Brain Demonstration Find a friend and try this little experiment to dem- each of you has one hand that will attempt to work onstrate to yourself the value of communication together with the other to tie the shoe. Now there is between your right and left cerebral hemispheres. a left and a right hand each controlled by a separate You need a friend and a shoe with laces. cerebral hemisphere. This is almost just like when you tied your shoe yourself but with an important To begin, take the shoe in your own hands, close difference. The difference is that when you were by your eyes, and tie the laces with your eyes closed. yourself, the two cerebral hemispheres controlling Probably this isn’t a difficult task for you. Your brain the hands were connected. With your friend, the two can draw on years of motor memory developed by cerebral hemispheres controlling the hands are not the thousands of times you have tied your shoes. connected at all and, therefore, cannot communicate As you are tying the shoe, your left cerebral hemi- with one another (you are not allowed to talk to your sphere is controlling your right hand and your right friend or open your eyes as you do this experiment). cerebral hemisphere is controlling your left hand. Therefore, one hemisphere does not know what the Your hands probably move dexterously together as other hemisphere’s hand is doing. if they know exactly what the other is doing, even though you have your eyes closed. In fact, each In this side-by-side position where each of you contrib- hand does know what the other is doing because ute the use of one hand, hold the untied shoe, both your left and right cerebral hemispheres are com- of you close your eyes, and attempt to tie the shoe. municating with each other by the corpus callosum Probably you’ll find it far more difficult than when and telling each other what the other is doing with you attempted this task by yourself. Why is this? It is each hand. because each hand does not know exactly what the Now, sit side by side with your friend. The two of you other is going to do and when. Individuals with split- should be shoulder to shoulder. One of you lace your brain syndrome face these motoric problems on all arm under the arm of the other (Figure 2-7) so that tasks requiring more than one side of the body.

Figure 2-7 Split-brain demonstration.

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houses language or a greater part of it. Although cer- us to give the words we Prosody The changes tainly not always the case, in the rest of this book, say an emotional com- in pitch, stress, timbre, cadence, and tempo a unless otherwise stated, it is assumed for the sake of ponent. Usually most of person uses to infuse brevity that the term left hemisphere is synonymous the emotional content of utterances with emotional with language-dominant hemisphere and right hemi- speech (the mood and content. sphere is synonymous with nondominant hemisphere emotional state of the for language. person) is conveyed in prosody. For instance, when a person is angry, a listener often does not really need to hear the actual words said to know that the speaker Right Cerebral Hemisphere is angry. The listener will probably be able to detect If the brain was neglected as an important organ for anger in the speaker’s prosody, their tone of voice. Or most of known history, then the right hemisphere when a person produces a verbal insult, a listener can has suffered almost the same fate since the inception tell the utterance is meant to be an insult even if they of serious study of the brain. For most of the history don’t understand the language or have never heard of neuroscience, the right hemisphere was deemed the insult. Another example is of two people arguing most insignificant and such terms as silent, minor, in a closed room. Listeners in adjacent rooms might unconscious, or subordinate were almost universally hear the muffled sound of these two people arguing. applied when describing the right hemisphere. Only Even though the listeners might not hear the actual in the last 20 to 30 years (really beginning with the words spoken, they cannot mistake the angry tone of split-brain studies of the 1960s and 1970s) has the the voices as two people having a pleasant conversa- scientific community come to acknowledge the tion. The right hemisphere allows people to perceive right hemisphere as a truly significant structure in emotions through interpretation of prosody. cognition and language. In fact, damage to the right hemisphere produces some of the most bizarre and The ability to comprehend the information embed- noteworthy deficits in neurology. ded within prosody and other nonlinguistic signals during communication is especially important in As it is understood now, the right hemisphere plays social interactions because, often, the words that some very important roles in communication. Com- a person says do not reflect the true intent of the munication not only involves language but facial utterance. For example, when a person says, “It is expressions, body language, gestures, and prosody a beautiful day” accompanied by a pleasant smile, of speech. It is these nonlinguistic aspects of com- she probably is communicating that it is, in fact, a munication that the right hemisphere specializes in. beautiful day. However, by using a sarcastic tone, The right hemisphere deals heavily in the perception furrowing her brows, and snarling her upper lip, she of emotion by processing these nonlinguistic com- can use the words “It is a beautiful day” to commu- ponents of communication. The appropriate pro- nicate very effectively that she does not believe that cessing of nonlinguistic aspects of communication the day is beautiful in any way, shape, or form. The can facilitate effective communication and mutual right hemisphere enables listeners to know that the understanding between speakers, whereas a failure to literal interpretation of a person’s words does not process nonlinguistic information appropriately can always accurately reflect the thoughts the speaker completely derail efforts at communication. intends (or does not intend) to communicate. Due In regard to speech, the right hemisphere is responsible to the loss of these abilities, individuals with right for our perception of prosody. Prosody is the changes hemisphere damage tend to be very concrete in their in tone and intensity we use when we speak that allow comprehension of language. For example, if asked

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to explain the phrase “She is warm-hearted,” an in- to certain areas in the right hemisphere might result dividual with right hemisphere damage might state in a lack of ability to discern the meaning of non- that the person in question has a heart temperature speech sounds that occur in the environment such as that is much higher than most other people’s hearts. a door slamming, a car driving by, or a bird singing (Joseph, 1988). This can happen in the absence of Processing and recognizing faces and facial expres- any difficulty interpreting speech sounds. See the sions are also right hemisphere responsibilities. A following discussion on the temporal lobe for more loss of the ability to perceive and recognize faces specific information regarding this function of the often follows damage to the right occipital area right hemisphere. (Luria, 1973). Difficulty with the visual processing of the faces of others is known as prosopagnosia. In Also significant is that the right hemisphere has a severe cases, individuals with lesions in the occipital role in processing the macrostructure, or gestalt. area of the right hemisphere might have difficulty Macrostructure processing is the ability to ef- recognizing the faces of their loved ones or even their fectively piece together many smaller details (mi-

own face. In less severe cases, they might simply be crostructure) to arrive Prosopagnosia A unable to interpret facial expressions appropriately. at the correct percep- neurologic deficit in Their understanding of the communicative intent of tion of the big picture the specific ability to cognitively process others can be affected by this. (the macrostructure). sensory information An example of macro- regarding the faces of The right hemisphere is responsible not only for com- structure processing is others for the purposes of prehending emotion in speech and on faces, but also recognition. being able to perceive for producing appropriate prosody and facial expres- four wheels, doors, Amusia An acquired sion to convey emotion. Individuals who have dam- deficit in the ability to trunk, hood, and head- age to the right cerebral hemisphere can often appear interpret and recognize lights and from that music. expressionless and sound monotone and emotionless being able to perceive to listeners. Hence, listeners might not be able to per- Macrostructure The that the object is a car. bigger picture composed ceive that a person with right hemisphere damage is Individuals with defi- of many details. Also in a highly agitated state or experiencing some other known as the gestalt. cits of macrostructure strong emotion as it is occurring because of these def- processing tend to per- Macrostructure icits. Clinically, this can make the treatment of cog- processing The severate on details and nitive deficits in individuals with right hemisphere ability to generate a cannot piece together correct perception of damage difficult as the speech-language­ pathologist the details and perceive macrostructure. may have no idea of the frustration or enthusiasm the whole. Therefore, Visuospatial level of the patient. individuals with right processing The ability to understand visual The right hemisphere is also responsible for process- hemisphere lesions are information, visual ing melody and rhythm in music. Individuals who often known as being representations, and have experienced right hemisphere damage can dis- unable to see the forest spatial relationships among objects. play amusia, or the loss of the ability to recognize and for the trees. interpret music (Luria, 1973). Amusia can also affect The spatial component of math skills as well as the ability of the person to produce music as well as ­visuospatial processing is also a primary responsibil- hear and interpret it correctly. ity of the right hemisphere. Examples of some specific The right hemisphere also is largely responsible for visuospatial skills are perception of depth, distance, the perception of environmental sounds. Damage and shape; localizing targets in space; and identifying

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Broca’s area The figure–ground relation- are responsible for expressive and receptive language inferior, posterior region ships (Joseph, 1988). skills cued researchers in the late 1800s to begin ex- of the frontal lobe of the amining the relationship between brain and cogni- left hemisphere that is Visuospatial processing a specialized area of the skills are used to piece tion more closely. cerebrum responsible for together a jigsaw puzzle, finding and assembling In 1861, Paul Broca published the results of his stud- sink a basket in a basket- words for the appropriate ies indicating that the inferior, posterior region of the expression of thought. ball game, and success- frontal lobe of the left hemisphere is responsible for fully navigate your body Wernicke’s area A finding and assembling words for the appropriate specialized portion of from place to place past expression of thought. This area is now known as the cerebrum located at and around innumerable the superior marginal Broca’s area (Figure 2-8). Damage to this area can obstacles. gyrus of the left produce what is known as Broca’s aphasia. Individu- hemisphere’s temporal als with this disorder usually know what they want lobe that is responsible for The right hemisphere interpreting and deriving to say but cannot find the right words. meaning from the speech also plays a great role of others. in the ability to attend A few years later in 1874, Carl Wernicke localized receptive language to the superior marginal gyrus Central sulcus A deep to stimuli. There are groove that runs down the various levels of at- of the left hemisphere’s temporal lobe. This area is middle lateral surface of tention, and the right now known as Wernicke’s area (Figure 2-8). Wer- each cerebral hemisphere. hemisphere plays a nicke’s area is responsible for interpreting and deriv- Lateral sulcus A deep role in regulating most ing meaning from the speech of others. Damage to groove that begins at the this area produces a condition known as Wernicke’s lower frontal aspect of kinds. Specifically, the each of the two cerebral right hemisphere spe- aphasia. Individuals with this disorder cannot com- hemispheres and travels cializes in the ability prehend the speech of others, and their own speech at an upward angle, is often nonsensical and nonstop. passes the central sulcus, to keep attention on and then terminates. a single stimulus for an extended period of time (sustained attention) and the ability to ignore The Major Cerebral Lobes unimportant stimuli while sustaining attention on Two important sulci are the central sulcus and the important stimuli (selective attention). An example lateral sulcus (Figure 2-8). The central sulcus, also of sustained attention is paying attention to a lec- known as the fissure of Rolando or the central fis- ture in a classroom. If a lawn mower is running sure, runs down the middle lateral surface of each outside the classroom during the lecture, then stu- cerebral hemisphere. The lateral sulcus, also known dents must actively block out the distracting sound as the sylvian fissure, begins at the lower frontal as- of the lawn mower to focus on the lecture, which is pect of each of the two cerebral hemispheres, travels an example of selective attention. at an upward angle, passes the central sulcus, and then terminates. The central and lateral sulci create Left Cerebral Hemisphere important divisions among the major sections, or lobes, of the cerebrum. The lobes of the cerebrum As mentioned, the left cerebral hemisphere has been are each named for the bones of the cranium that the subject of study more than the right hemisphere overlay them. has. This is mostly because the left hemisphere typi- cally is the hemisphere that houses language. The As the central sulci run down the side of each cere- discovery that certain locations in the left hemisphere bral hemisphere they create a division between the

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Primary Primary Central sensory motor sulcus cortex cortex Parietal Lobe Visual association cortex

Prefrontal association cortex Occipital Lobe Wernicke’s Broca’s area Frontal area Lobe

Primary visual Primary auditory cortex cortex Lateral Temporal sulcus Lobe

Figure 2-8 External surface of the left cerebral hemisphere.

frontal lobes and the parietal lobes (Figure 2-8). The motor cortex is responsible for issuing motor plans lateral sulci create a division between the temporal for volitional movement. More surface area of the lobes and the above frontal and parietal lobes (Figure cortex within the primary motor cortex is devoted 2-8). These are both unlike the longitudinal fissure, to body parts that are capable of producing deli- which divides the brain into right and left cerebral cate or fine motor movements, including the face, hemispheres. lips, mouth, and hands. Less cortical tissue in the primary motor Each cerebral lobe houses different major functions cortex is dedicated Frontal lobes The most of the brain and specializes in certain functions. to the control of anterior sections of the cerebral hemispheres that The left frontal lobe (Figure 2-8) houses expressive body parts that are delineated posteriorly ­language in Broca’s area in the inferior and poste- execute only gross by the central sulcus and rior sections. The frontal lobes also play a large motor functions. inferiorly by the lateral sulcus and that houses role in motor movement. All voluntary movement The knee, for in- expressive language and originates in the anterior portion of the brain (i.e., stance, has less deals heavily in motor the frontal lobes). The frontal lobes house cortical surface area dedi- movement. areas responsible for the initiation and construction cated to its control Primary motor cortex of plans for motor movement such as the primary within the primary A strip of tissue oriented vertically along the last motor ­cortex, which is also known as the motor motor cortex than gyrus of each frontal strip (Figure 2-8). The primary motor cortex is lo- does the mouth or lobe that plays a large cated on the most posterior gyrus of the frontal hands. The spatial role in voluntary motor movement. lobe, just in front of the central sulcus. The primary representation of

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Motor homunculus A the amount of space in and clothing preferences. See the following Clinical visual illustration of the brain dedicated to Notes on Phineas Gage and frontal lobotomies. the amount of cortical the movement of each tissue dedicated to the The parietal lobes are located behind the frontal movement of each body body part is repre- lobes (Figure 2-8) and are responsible for receiving part within the primary sented by an illustration motor cortex. and processing sensory information concerning the known as the motor body. The first gyrus of the parietal lobes house the Parietal lobes A section homunculus. The word of the cerebrum located primary sensory cortex (Figure 2-8), also known homunculus is Latin for posterior to the frontal as the sensory strip. This section of cortex receives lobes and anterior to little man (Figure 2-9). the occipital lobes that and processes tactile information coming from the is largely responsible for The left primary motor body as well as proprioceptive information. The left receiving and processing cortex is responsible for primary sensory cortex receives sensory information sensory information concerning the body. issuing motor move- from the right side of the body, and the right primary ments for speech. Dam- sensory cortex receives sensory information from the Primary sensory cortex A section of age at or near Broca’s left side of the body. Proprioception is an individu- cortex along the first area, near the base of the al’s sense of where their extremities and their body is gyrus of the parietal lobes left primary motor cor- in space. For instance, when an individual closes his dedicated to receiving and processing sensory tex, disrupts the brain’s eyes and extends his arms in front of himself, he can information. ability to execute appro- feel his arms out there and knows exactly where they

Proprioception An priate motor plans for are in space, despite having his eyes closed. individual’s sense of where speech. This condition More cortical tissue within the primary sensory cor- their extremeties and is known as apraxia of their body is in space. tex is dedicated to body parts that have higher num- speech. Sensory homunculus A bers of sensory receptors than those that have fewer. visual illustration of The frontal lobes, spe- For instance, the mouth and lips are very sensitive the amount of cortical cifically the prefrontal to touch and to temperature. Accordingly, very large tissue within the primary sensory cortex dedicated regions (the very front sections of the primary sensory cortex are dedicated to processing sensory of the frontal lobes), to receiving and processing sensory information information from each also store personal- coming from the mouth and lips. In contrast, the body part. ity and some memory. skin on the back has far fewer sensory receptors and Frontal lobotomy A Damage to the prefron- therefore has very little representation in the primary procedure of damaging or removing tissue from tal regions of the fron- sensory cortex. As in the primary motor cortex, the the prefrontal area of tal lobes can produce topographical arrangement of cortical tissue repre- the frontal lobes for the changes in personality senting the associated body parts creates an arrange- supposed remediation of psychological problems. ranging from mild to ment that is referred to as the sensory homunculus. drastic. Examples of On the sensory homunculus, body parts that have Temporal lobe A section of the cerebrum located these changes include the most cortical tissue dedicated to processing their inferior to the parietal a sudden lack of social sensory information are represented as being larger lobes that is largely inhibitions leading to than those body parts that have little cortical tissue responsible for memory and processing of auditory inappropriate sexual dedicated to processing their tactile and propriocep- stimuli. advances or physical/ tive information (Figure 2-9). Extending the previous verbal aggression, or example, the mouth and lips on the sensory homun- impulsivity. However, less obvious changes in per- culus are quite large, while the trunk of the sensory sonality can also take place, such as changes in food homunculus is very small.

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A.

Hip Leg

w runk

Neck T Foot Head Arm t

arm Toes Elbo ris

Shoulder W Hand Fore r Genitals

Little finger Ring fingerx finger humb T e MiddleInde finge Ey Nose Face

Lips, teeth, w gums, and ja

Tongue Pharynx Intr aabdominal

Primary motor Central sulcus cortex (precentral gyrus) Primary sensory cortex (postcentral gyrus) Frontal Parietal lobe lobe

Occipital Temporal lobe lobe

B.

Hip w

Trunk Knee t Arm Elbo ris

Shoulder W Hand Ankle Upper arm

tle finger

Lit Ring fingerx finger humb Toes T Middle finger Inde Neck

eball Eyelid and ey Face

w Lips and ja

Tongue

Swa llowing

Figure 2-9 A. Sensory homunculus. B. Motor homunculus.

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Clinical Note

Frontal Lobotomy

In the 1940s and 1950s, the frontal lobotomy, a abandoned the surgical suite, the surgical team, and procedure of damaging or removing tissue from the general anesthesia. In his office, he began knocking prefrontal area of the frontal lobes for the supposed his patients out with electroshock (electric currents to remediation of psychological problems, was at its the brain) and inserting ice picks through the orbital height. This procedure was popularized in the United process of their skull behind their eyes and moving States by Dr. Walter Freeman, whose name is closely the ice picks back and forth in a lateral (side-to-side) associated with the procedure though use of the fron- fashion, effectively damaging the prefrontal areas tal lobotomy was widespread (Acharya, 2004). of the frontal lobes. Thousands and thousands of individuals were lobotomized in this manner dur- The frontal lobotomy began as a surgical procedure ing the 1940s and 1950s in assembly-line-like pro- to treat those with profound schizophrenia. At this cedures. Eventually, Freeman abandoned the use of point, the frontal lobotomy was still considered a ice picks, which occasionally broke off in the skulls of highly experimental procedure (Kucharski, 1984). his patients, and had custom instruments made that Freeman and most other medical professionals of the were far stronger than the average ice pick. time initially used the frontal lobotomy as only a last- resort treatment. However, Freeman eventually came Despite grossly inconsistent results from the proce- to believe that once psychological problems got to a dure, varying from improvement of conditions to certain level of severity, patients became unrespon- extreme worsening of conditions and severe side sive to other treatments. Following this belief, he effects, Freeman continued advocating for the pro- shifted his position to using the frontal lobotomy as cedure well after pharmaceutical treatments in the a more general treatment to be applied earlier to a mid-1950s had been developed to target the same range of problems including depression, criminal- psychological conditions (Acharya, 2004). The frontal ity, schizophrenia, alcoholism, obsessive-compulsive lobotomy was a product of its time and part of the disorder, and hysteria among others (Acharya, 2004; scientific zeitgeist of the 1940s and 1950s. In retro- Kucharski, 1984). spect, it is seen as being accepted too enthusiastically and blindly as an effective procedure by not only the To perform this treatment as often and as efficiently scientific community but the popular culture at large as necessary to meet his new criteria, Freeman willing to subject their loved ones to the procedure.

Clinical Note Phineas Gage Perhaps the most famous case documenting person- frontal lobes of his brain and out through the top of ality change following damage to the frontal lobes his skull (Figure 2-10). This injury damaged both his is that of Phineas Gage. Mr. Gage was a railway con- frontal lobes and took out his left eye. It is generally struction worker who lived in the mid-1800s. He was accepted that he might not have lost consciousness known to those around him to be moderate in his from the injury. He is said to have sat upright in the habits and possessing self-restraint and was rarely cart that drove him to see a doctor (MacMillan, 2000). known to be profane (MacMillan, 2000). In 1848, while Mr. Gage was packing explosive powder into a Despite the severity of the injury, Mr. Gage lived and hole to clear away rock for a railway, the explosives had generally recovered after 3 months (MacMillan, ignited unexpectedly and blew the metal tamping rod 2000). However, it was noted by friends and rela- he was using beneath his cheekbone up through the tives that his personality changed dramatically after

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his accident. He was reported to have become very his death his skull was exhumed and it was deter- uninhibited and had difficulties not indulging in all mined that the areas of Mr. Gage’s brain that were his desires. He also had significant memory loss. His damaged by the metal rod were within the frontal employers found that he could no longer complete cortex, parts of the brain responsible for inhibiting his previous duties in railway construction. Years after socially inappropriate behavior.

Figure 2-10 Phineas Gage. Source: © National Library of Medicine.

The temporal lobes are located inferior to the pos- Individuals who have damage to the hippocampal terior portion of the frontal lobes and inferior to the regions in both tempo- anterior portion of the parietal lobes (Figure 2-8). ral lobes display severe Hippocampus A The temporal lobes house more memory than any to profound deficits in region of the temporal lobe responsible for other cerebral lobes. Most of the memory ability of short-term memory be- storing and creating the temporal lobes can be attributed to the hippo- cause they cannot create memories. (Plural: campi (plural). Hippocampus (singular) is Latin for new memories (Scoville hippocampi.) seahorse. The hippocampi are located within the in- & Milner, 1957), and Primary auditory ferior and medial section of the temporal lobe where long-term memory abil- cortex A region of cortex located within the cortex curls up into itself (Figure 2-11). ities might be destroyed the temporal lobes as well. See the following responsible for receiving The hippocampi of the temporal lobes are so named Clinical Note about Pa- and processing neural because of their curled shape, which early anato- impulses related to sound. tient H.M. mists thought resembled a seahorse. The hippocam- pal region takes new experiences and turns them The primary auditory cortex is located on the supe- into memories that can be stored and accessed later. rior temporal gyrus, anterior to Wernicke’s area in the

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Clinical Note

Patient H.M. The role of the hippocampus in creating new mem- ories was brought to the attention of the medical community in the 1950s. A patient now known as H.M. was experiencing epileptic seizures to the point of being unable to work. Medications were ineffec- Hippocampi tive in controlling his seizures (Scoville & Milner, 1957). Drastic action was considered to be war- ranted given H.M.’s severe epileptic condition. Dr. William Beecher Scoville decided to attempt a radi- cal surgery on H.M.’s temporal lobes to relieve the patient of his seizures. Dr. Scoville removed sections of both H.M.’s temporal lobes extending into the Figure 2-11 Hippocampi displayed on a hippocampal regions. This operation was performed coronal section of the brain. in 1953 and was successful in relieving the patient of most of his seizures. However, an unexpected result of the surgery was a profound deficit in the ability to create new memories (Scoville & Milner, 1957). Although his memory of events prior to the surgery left hemisphere (Figure 2-8). The primary auditory was mostly intact, Scoville and Milner (1957) report cortex is the section of the temporal lobes that first that 2 years after his surgery H.M. was still incapa- receives neural impulses of sound from the ears. ble of storing new information in his memory. This form of amnesia is known as anterograde amnesia. In the left temporal lobe, the left primary auditory Scoville and Milner (1957) give some examples of cortex receives impulses of speech sounds and then the daily impact of H.M.’s memory deficit: After liv- passes these impulses on to Wernicke’s area for pro- ing in a new house for 10 months, H.M. still could not cessing so that, as mentioned earlier, the individual find his way around it; he would complete the same jigsaw puzzles and read the same magazines each can comprehend spo- day “without finding their contents familiar” (p. 14). Anterograde amnesia ken language. The right An inability to create new hemisphere’s primary Although he possessed no conscious recollection memories. of it, H.M. allowed a steady stream of scientists and auditory cortex mostly students to study him and his memory continually Occipital lobes The passes impulses of envi- throughout his life (Corkin, 2002). H.M.’s contribu- most posterior section of the cerebrum that is ronmental sounds and tion to the understanding and science of memory dedicated to receiving music to the area in the and the brain is monumental. He also arranged for and processing neural right hemisphere analo- his brain to be exhumed for examination upon his impulses related to vision. gous to Wernicke’s area death so that his case could continue to help oth- ers (Corkin, 2002). In 2008, Patient H.M., widely (Bhatnagar, 2008) for the regarded as one of the most important individuals interpretation of meaning. Hence, the left hemisphere in the history of neuroscience, died at 82 years of is responsible for auditory comprehension of verbal age (Carey, 2008). language while the right hemisphere is responsible for comprehension of the meaning of environmental sounds, such as a car starting or tree falling, as well The occipital lobes are the most posterior of the as our appreciation of music. cerebral lobes. They are located behind the parietal

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Primary visual cortex and temporal lobes (Fig- the digestive system, Visual association The posterior-most ure 2-8). The occipital and regulating level of cortex A section of cortex within the section of the occipital lobes are concerned arousal (this includes lobes dedicated to occipital-parietal region receiving neural impulses mostly with vision. The the sleep–wake cycle). responsible for processing of vision from the eyes. occipital lobes house the The following subsec- and interpreting visual information received from primary visual cortex tions discuss four pri- the primary visual cortex. (Figure 2-8), which receives visual information from mary structures of the Subcortex The portion the eyes. The primary visual cortex is located on the subcortex: the brain of the brain located most posterior section of each occipital lobe. The stem, cerebellum, thala- beneath the cortex that right and left divisions of the primary visual cortex mus, and basal ganglia. deals less in reasoning abilities and higher-level receive and process information from the contralat- cognition and more in eral visual field. autonomic, life-sustaining The Brain Stem functions. Just anterior to the primary visual cortex is the ­visual In evolutionary terms, Brain stem A association cortex (Figure 2-8). This is the section subcortical structure of the brain that processes and interprets visual in- the brain stem is the old- that connects the spinal formation received from the primary visual cortex est part of the brain. As cord to the rest of the a species, we were sleep- brain and houses many allowing for appropriate visual perception (i.e., the structures involved in visual association cortex allows people to make sense ing, breathing, and mat- autonomic functions. ing long before we were with the brain of what they are seeing with their Medulla The superior- eyes). This area performs much the same function enjoying Shakespeare or most section of the for vision that Wernicke’s area performs for spoken learning the Pythagorean spinal cord that connects theorem. Higher levels the spinal cord to the language. Just as a lesion at Wernicke’s area creates pons and is the site of a condition (an aphasia) in which the person might of cognition came only decussation of a large be able to hear spoken words but cannot deduce the with the more recent portion of the motor evolution of the huge ce- tracts descending through meaning of the sounds, bilateral lesions at the visual the brain stem. association cortices often create a condition known rebrum that sits on top of as visual agnosia in which a person can see but can- our brain stems. not comprehend what she is seeing. In a basic sense, the brain stem is the structure that connects the spinal cord to the brain. There are three main divisions of the brain stem. From top to bottom Subcortical Structures these are the midbrain, the pons, and the medulla Beneath the cortex is the subcortex, its name liter- (Figure 2-12). The medulla is the superior-most sec- ally meaning below the cortex. Unlike the cortex, tion of the spinal cord that connects the spinal cord which is responsible for very high-level reasoning to the pons. The medulla is the place where many and cognitive abilities, the subcortex is responsible of the motor fibers that transmit impulses of motor for performing functions that are more automatic movement cross over or decussate to the other side and usually beneath the level of our awareness. Ex- of the body (Figure 2-13). amples of subcortical functions are refining and Because of the decussation of these motor fibers, monitoring motor plans, regulating automatic life- the left side of the body is controlled by the right sustaining body functions such as heartbeat as well cerebral hemisphere and vice versa. Because of as automatic breathing, coordinating functions of the decussation of these fibers, a lesion to the

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Thalamus

Midbrain

Pons Medulla

Figure 2-12 Sections of brain stem shown in midsaggital section.

Hemiplegia A unilateral descending motor tracts above the medulla creates spinal cord), the result- spastic paralysis of the a hemiplegia (one-sided paralysis) or a hemipa- ing hemiplegia or hemi- body. resis (one-sided weakness) on the side of the body paresis is on the side Hemiparesis A unilateral contralateral (opposite) the lesion. If a lesion occurs of the body ipsilateral spastic weakness of the body. below the level of decussation (such as within the (same) to the lesion.

Cortex

Corona radiata

Internal capsule

Thalamus

Basal ganglia Pons

Motor tract crossing at pyramids

Figure 2-13 Coronal section of the brain showing decussation of descending motor tracts at the level of the medulla.

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Pons The middle and Located above the me- formation regulates arousal (i.e., level of wakeful- slightly bulbous portion dulla is the pons (Fig- ness), respiration, and blood pressure (Seikel, King, of the brain stem that ure 2-12). The pons is a & Drumright, 2010). provides an attachment between the cerebellum slightly bulbous portion (not cerebrum) and the of the brain stem that rest of the CNS. provides an attachment The Cerebellum Midbrain The superior­ between the cerebellum Hanging off the back of the brain stem under the most section of the brain (not cerebrum) and the stem that houses the occipital lobes is the cerebellum (Figure 2-15). The substantia nigra. rest of the CNS. The cerebellum is known as the little brain because of its pons also connects the Substantia nigra A resemblance to the cerebral hemispheres. The cere- structure located within medulla below to the bellum resembles the cerebral hemispheres because it the midbrain responsible midbrain above. for the production of also is divided into right and left hemispheres (Figure the neurotransmitter The superior-most sec- 2-14), each with a tightly packed and folded gray mat- dopamine. tion of the brain stem ter layer superficial to white matter coursing below. Reticular formation A is the midbrain (Figure These are the cerebellar hemispheres. Students must series of nuclei stretching 2-12). The midbrain among the midbrain, pons, be sure not to confuse the cerebellar hemispheres and medulla that regulates houses the substantia with the cerebral hemispheres. arousal, respiration, and nigra. The substantia When cut through at Cerebellum A blood pressure. nigra is where the brain midline in a saggital subcortical structure produces a neurotrans- hanging off the back of (front to back) fashion, mitter known as dopamine. When the substantia the pons and under the the distinctive plant- occipital lobes that is nigra fails to produce enough dopamine, the symp- like shape of the white known as an error control toms of Parkinson’s disease begin to arise. device for body movement matter fibers of the cer- and ensures that body Stretching between the midbrain, pons, and me- ebellar hemispheres is movements are smoothly dulla is a series of nuclei called the reticular forma- apparent (Figure 2-15). coordinated and as error free as possible. tion or the reticular activating system. The reticular This plant-shaped

A. B. Scalp Scalp Periosteum Bone of skull Dura mater Arachnoid mater Subarachnoid space Cerebral hemispheres Pia mater Brain tissue

Cerebellar hemispheres Blood vessel

Figure 2-14 A. The cerebellar and cerebral hemispheres. B. The meningeal layers.

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Arbor vitae

Cerebellum

Figure 2-15 The cerebellum attached to the pons.

structure is known as the arbor vitae (Latin for tree The cerebellum is known as an error control device of life). The right and left cerebellar hemispheres are for body movement. It makes sure that body move- connected to each other at midline by the unpaired ments are smoothly coordinated and error free. After vermis. The vermis is motor plans are assembled in the primary motor cor- Arbor vitae The the midline gray matter tex they are sent to the cerebellum to be checked for distinctive plantlike shape of the fibers of the that connects the cere- errors. The cerebellum monitors the intended move- cerebellar hemispheres bellar hemispheres and ments of the motor plan and compares those plans evident upon dissection receives somatosensory with what the body is actually doing (Duffy, 2005). If and some imaging studies. information about the there are any discrepancies between the motor plan Vermis The midline body through projec- and the body’s execution of the motor plan, which gray matter that connects the two cerebellar tions coursing through are errors, the cerebellum makes corrections in the hemispheres and the pons. body’s movements to match the motor plan to avoid receives somatosensory the error. It does this by altering force, timing, and information about the The cerebellum is at- body through projections sequencing of muscle contractions (Diener & Di- coursing through the pons. tached to the pons and chgans, 1992). Although this discussion makes this communicates with the Peduncles Attachments process sound like it occurs in a step-by-step manner, between the cerebellum rest of the CNS by the the monitoring of the body’s appropriate execution of and the pons. cerebellar peduncles. motor plans by the cerebellum is an ongoing activity The word peduncle is that continues in time as body movements continue. used primarily to refer to the stalk that a piece of fruit hangs from. The word is used here because early Each cerebellar hemisphere receives and monitors anatomists perceived that the cerebellum resembled motor plans from the contralateral cerebral hemi- a piece of fruit hanging off the pons under the cere- sphere (Duffy, 2005). This means that motor signals brum. In order from top to bottom, there are three from the left cerebral hemisphere are checked for er- cerebellar peduncles: the superior, middle, and infe- rors in the right cerebellar hemisphere and motor sig- rior cerebellar peduncles. nals from the right cerebral hemisphere are checked

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for errors in the left cerebellar hemisphere. Because relay station. Specifically, all afferent (sensory) in- of this arrangement each cerebellar hemisphere is formation (excluding olfaction) passes through the

Thalamus A subcortical responsible for monitor- thalamus before arriving at the correct portion of the structure that rests on ing movement occurring cerebral cortex for processing. For example, the optic top of the brain stem on the ipsilateral side of nerve from the eyes passes through the thalamus on beneath the cerebrum and functions as a relay the body (Duffy, 2005). its way to the occipital lobes. Afferent impulses of station for neural impulses proprioception and taction coming up from the body of sensation (excluding The more rapid and pre- pass up the spinal cord, through the brain stem, and olfaction). cise a body movement through the thalamus to the primary sensory cortex Basal ganglia A group is, the greater the like- in the parietal lobes. The thalamus also takes the of subcortical structures lihood that an error in motor plans that the cerebellum has checked for er- located deep within the the execution of motor cerebral hemispheres rors and sends those motor plans to the appropriate on either side of the plans will occur and the places for execution (Duffy, 2005). thalamus that works to harder the cerebellum regulate body movement. will work to minimize The Basal Ganglia Spinal cord A bundle of that risk. For example, white matter tracts and as a professional pianist The term ganglia refers to a collection of nerve cells. gray matter housed within The basal ganglia is a group of subcortical struc- the bony vertebral column performs a complicated that enables afferent piece, the cerebellum tures located deep within the cerebral hemispheres (sensory) impulses coming works much harder to on either side of the thalamus (Figure 2-13). The from the body to be structures of the basal ganglia include the cau- transmitted to brain and monitor for errors the efferent (motor) impulses motor plans of finger date nucleus, the putamen, and the globus palli- from the brain to be movements than it does dus (Duffy, 2005). These structures have complex transmitted to the body. if the pianist simply circuitry and interconnections among themselves waved her arm in the air. A far more common activity and other portions of the CNS. The basal ganglia that also requires a great deal of rapidity and preci- and its connections and circuitry are far from being sion in motor execution and that is used by almost perfectly understood. Nonetheless, it is clear that everyone every single day is speech. Because the act the basal ganglia play a strong role in motor move- of producing smoothly articulated speech requires a ment. Lesions to the basal ganglia create problems great deal of cerebellar input, difficulties in articula- with initiation of movement, muscle tone, and extra tion can be a first indicator of cerebellar pathology. movements. These are all the symptoms of Parkin- Pathology of the cerebellum often produces a speech son’s disease, which is created by dysfunction of the problem known as ataxic dysarthria. basal ganglia. Parkinson’s disease occurs when the substantia nigra fails to produce dopamine, which the basal ganglia requires to operate properly. The Thalamus The thalamus sits on top of the brain stem and under The Spinal Cord the cerebral hemispheres (Figure 2-12, Figure 2-13). The spinal cord is a bundle of white matter tracts This is a perfect location for the thalamus because and gray matter housed within the bony vertebral the thalamus is responsible for taking sensory signals column. It allows afferent (sensory) impulses coming from one part of the nervous system and directing from the body to be transmitted to brain and efferent them to another part of the nervous system. The (motor) impulses from the brain to be transmitted tag line associated with the thalamus is that it is a to the body.

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The spinal cord originates superiorly at the medulla. The spinal cord then passes inferiorly through the vertebral column until it narrows at a section known as the conus medullaris. The spinal cord terminates inferiorly at the conus Conus medullaris ​ medullaris in the lum- Conical point of inferior termination of the spinal bar region of the lower cord in the lumbar region back. Below the level of the lower back. of the conus medullaris Cauda equina The loose the spinal cord breaks strands of spinal nerves up into loose strands of that separate from the inferior termination of the spinal nerves called the spinal cord. cauda equina, or horse’s tail, so named because of the resemblance of the loose strands of nerves to the hairs of a horse’s tail (Figure 2-16).

In a cross section or transverse cut of the spinal cord, a gray butterfly or H shape appears in the middle (Figure 2-17). The grayness of the butterfly shape stands out in contrast to the whiteness of the sur- rounding tissue. This gray tissue is spinal nerve mat- ter and can be thought of as the location where the spinal nerves enter and leave the spinal cord. The Figure 2-16 Cauda equina of the spinal cord. topmost wings of the butterfly shape are known as the dorsal horns. The nerve cells of the dorsal horns (efferent) information from the associated white deliver the sensory (afferent) information from the matter tracts in the spinal cord to the spinal nerves to spinal nerves to the surrounding white matter tracts be delivered to the organs and muscles. In the usual to be transmitted to the brain. The bottom wings of orientation of the spinal cord within the vertebral the butterfly shape are known as the ventral horns. column the dorsal horns point posteriorly while the The nerve cells of the ventral horns deliver motor ventral horns point anteriorly.

Posterior median sulcus Gray White matter matter Ganglion Posterior (dorsal) root Spinal nerve

Anterior Central canal (ventral) root

Anterior median fissure

Figure 2-17 Cross section of spinal cord.

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In addition to being a major highway between the yet no instructions came down from the brain telling brain and body for afferent and efferent signals, the that muscle in the leg to do so. The spinal cord knows spinal cord is also involved in basic reflexes. A re- that it is problematic for a body part to be moving flex is the production of a physical movement that with no commands from the brain to do so. occurs automatically in response to a stimulus and is initiated below the level of awareness. Perhaps the The spinal cord here is a mediator between the body most salient example of a reflex is the pain with- and the brain. The spinal cord monitors the motor drawal reflex. Accidentally laying a hand on a hot plans for the muscles as they come down from the stove produces this reflex: When a person’s hand brain, and then it sends those motor plans out along touches the hot surface, he pulls his hand away from the cranial and spinal nerves to the muscles for ex- the stove very quickly. In ecution. When a muscle behaves in a way contradic- Reflex The production of fact, he begins pulling tory to the motor plans sent down from the brain, the a physical movement that the hand away before spinal cord is the first to know. It is problematic for occurs automatically in survival if a person’s muscles or body parts are not response to a stimulus and he realized his hand was is initiated below the level being burned or that where the brain wants them to be and doing what the of awareness. he was even in pain. In brain has told them to do. In evolutionary terms, this Stretch reflex A other words, the rest of could mean the difference between a narrow escape contrac­­tion of a muscle this person’s CNS does with a saber-tooth tiger or a saber-tooth tiger tearing in response to a passive off an arm. Fortunately, the spinal cord doesn’t wait stretching of a muscle not wait for the cerebral spindle within a muscle. cortex (which is the por- for information concerning this discrepancy to travel This reflex enables the tion of the CNS farthest all the way up to the cerebral cortex and rise to the body to correct any level of conscious awareness. It recognizes the situ- unintended changes in away from the burning body position in a timely hand) to realize the hand ation as an emergency and takes immediate action manner without waiting is burning before decid- without consulting the brain. for input from the cerebral cortex as well as keep ing to get it off the hot Now back to the knee. When a muscle is lengthened appropriate tone in the stove. This is a survival passively, as when a doctor tests the patellar reflex, muscles. mechanism that allows the spinal cord recognizes the discrepancy between people to react much the motor plans sent by the brain and the afferent faster than they would be able to if they had to wait signal coming from the muscle informing the spinal for the sensation of pain to travel all the way up to cord that the muscle has moved out of place (i.e., the the cerebral cortex, which is the farthest section of spinal cord recognizes that no signal came from the the CNS from the extremities. brain telling the muscle that just moved to move). The spinal cord then originates and sends its own One very important reflex of concern to speech-­ efferent (motor) signal out to the muscle to correct language pathologists is the stretch reflex. The most the situation and contract the muscle into its original well known example of this is the kick a leg makes and intended position. This contraction causes the unintentionally after the knee is tapped, the patellar leg to kick in response to the tap on the knee. In reflex. When a doctor taps an individual’s knee, she short, before the brain realizes there is a problem the is momentarily stretching a muscle in the person’s spinal cord steps in and tells the offending muscle leg. A sensory receptor in that muscle called a mus- or body part to get to where it is supposed to be to cle spindle is stretched as well and sends an afferent correct the situation. signal to the spinal cord indicating that the muscle has moved. The spinal cord receives this signal and Normally, the stretch reflex is a good thing. In healthy recognizes that the leg muscle has been moved and individuals, the stretch reflex allows their bodies to

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correct any unintended changes in body position in and glucose used by the Internal carotid arteries a timely manner without waiting for input from the body. In other words, up Paired arteries that course superiorly from the thorax cerebral cortex as well as keeps appropriate tone in to a fourth of the body’s within the anterior portion the muscles. However, the stretch reflex can be prob- oxygen and energy sup- of the neck to the base of lematic when it becomes hyperactive. In some clini- plies is used to power the brain to link with the circle of Willis. cal scenarios, the spinal cord overapplies the stretch this single organ. Any reflex and uses this hyperactive stretch reflex to create interruption of blood Circle of Willis A series of anastomoses that hypertonia in affected musculature which, combined flow to the brain, such connects the internal with the weakness discussed previously, inhibits the a stroke, has immediate carotid and vertebral/ individual's ability to move the affected body parts. and possibly dire conse- basilar system, acts to ensure equal blood flow This overactive stretch reflex also resists passive quences. To keep up the to all areas of the brain, muscle movement. In these cases, a person’s muscles supply of blood to the and acts as a safety valve might tighten, accomplish volitional movement with brain necessary to meet if an occlusion occurs within the circle of Willis difficulty, and be resistant to movement when the cli- these massive require- or below the circle of nician attempts to passively move the affected limbs ments the body must Willis.

or musculature. This resistance to passive movement get blood first from the Anterior cerebral arteries brought about by an overactive stretch reflex is a big heart to the head. Paired arteries that part of producing spasticity in musculature. originate from the internal carotid arteries at the The two pairs of large Spasticity is a combination of hypertonia (over- circle of Willis and course arteries whose function anteriorly to supply blood tightness of muscles) and the resistance to passive it is to deliver blood su- to the frontal and parietal movement caused by a hyperactive stretch reflex lobes, basal ganglia, and periorly to the brain to that makes movement of a body part difficult (i.e., corpus callosum. be distributed through- it creates a spastic weakness). A clinical example is Middle cerebral arteries out the brain by other spastic cerebral palsy. Paired arteries that arteries are the internal originate from the internal Spasticity A combina­ Spastic cerebral palsy is tion of hypertonia and carotid arteries and the carotid arteries at the the most common form circle of Willis and course the resistance to passive vertebral arteries. The movement caused by a of cerebral palsy and can laterally to supply blood paired right and left in- flow to Broca’s area, hyperactive stretch reflex be mild, affecting only a that makes movement of a ternal carotid arteries Wernicke’s area, the single extremity, or se- temporal lobes, and the body part difficult. course superiorly from vere enough to affect an primary motor cortex. the thorax in the ante- individual’s entire body. If an individual’s laryngeal, rior portion of the neck oral, or thoracic musculature is spastic, then the abil- (Figure 2-18). The pulse in the neck is felt by palpat- ity to move those structures is weakened, which can ing the internal carotid. The internal carotid arter- affect production of speech. This communication ies course through the neck to the base of the brain disorder is termed spastic dysarthria and occurs as a to link with the circle of Willis. Once the internal result of bilateral damage to motor tracts within the carotid arteries reach the circle of Willis, the paired CNS usually by stroke. left and right anterior cerebral arteries and middle cerebral arteries branch off from the internal carotids (Figure 2-19). The anterior cerebral arteries course Blood Supply to the Brain anteriorly to supply blood to the frontal and parietal Although the average human brain is only about lobes, basal ganglia, and corpus callosum (Seikel et 2% of total body weight, the brain consumes be- al., 2010). The middle cerebral arteries course later- tween 20% and 25% of the total amount of oxygen ally to supply blood flow to Broca’s area, Wernicke’s

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Basilar artery Circle of Willis Vertebral arteries Paired arteries that course Internal carotid artery superiorly through the cervical vertebrae of the spinal column in the posterior aspect of the neck and come together Vertebral arteries to form the basilar artery at the pons.

Basilar artery A single unpaired artery that joins the circle of Willis Subclavian artery posteriorly and branches into the paired posterior cerebral arteries.

Posterior cerebral artery Paired arteries that branch off the basilar artery at the circle of Willis to course posteriorly and deliver blood to the occipital Figure 2-18 Major arteries supplying blood flow to the brain. lobes, cerebellum, and the inferior temporal lobes.

Anastomosis A area, the temporal lobes, the circle of Willis (Figure 2-19). Once the basilar connection between blood vessels. (Plural: and the primary motor artery reaches the circle of Willis, it branches into anastomoses.) cortex. the posterior cerebral arteries (Figure 2-19), which Anterior communicating delivers blood to the occipital lobes, cerebellum, and artery An unpaired Meanwhile, the paired the inferior temporal lobes (Seikel et al., 2010). anastomosis between right and left verte- the right and left The circle of Willis is a set of anastomoses (i.e., bral arteries course anterior cerebral arteries connections between arteries) between the anterior, that forms the anterior superiorly through the middle, and posterior cerebral arteries that together portion of the circle of cervical vertebrae of Willis. form a circle at the base of the brain. The anterior the spinal column in communicating artery connects the left and right Posterior communicating the posterior aspect of arteries Paired anterior cerebral arteries. The posterior communi- the neck (Figure 2-18). anastomoses coursing cating arteries link the posterior cerebral arteries to from the left posterior The vertebral arteries the middle cerebral arteries. cerebral artery to the left come together to form middle cerebral artery and also coursing from the the basilar artery at the The circle of Willis is highly important be­cause by right posterior cerebral pons. The basilar artery connecting the internal carotid and vertebral/basilar artery to the right middle then proceeds to join to systems it acts to ensure equal blood flow to all areas cerebral artery. the posterior section of of the brain and acts as a safety valve if an occlusion

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Anterior communicating artery

Anterior cerebral artery

Frontal Lobe

Carotid Artery

Middle cerebral artery

Posterior communicating artery Posterior cerebral artery Temporal Lobe

Basilar Artery Vertebral artery

Cerebellum

Figure 2-19 Circle of Willis.

(i.e., a clot) occurs within the circle of Willis or below Afferent signals originating with the body are trans- the circle of Willis. For instance, if there is a sudden mitted along the PNS on their way back to the CNS reduction in blood flow from the left internal carotid for processing. Afferent information is analyzed artery, blood can course through communicating and interpreted by the CNS in the cerebrum. For arteries from the basilar and right internal carotid example, the sensory information about the way an arteries to sustain blood flow to those areas of the individual feels following striking his thumb with a brain dependent on the internal carotid artery for hammer is transmitted along the nerves of the PNS blood supply. In this way, brain tissue can be saved to the CNS where that afferent signal is processed from oxygen deprivation and tissue death. and understood as pain. The two primary divisions of the PNS are the cranial The Peripheral Nervous nerves and spinal nerves. System The Spinal Nerves The PNS is composed of the nerves that connect As their name implies, spinal nerves are associated the CNS to the rest of the body. These nerves can with the spinal cord. Whereas the cranial nerves con- be thought of as wires that connect at one end to a tribute to control of the head and neck, the spinal muscle, organ, or gland and at the other end to the nerves contribute to control of the rest of the body. brain, brain stem, or the spinal cord. The spinal cord and spinal nerves are associated with Efferent signals from the brain travel along the PNS movement and control of the trunk of the body and to reach the muscles to command them to move. Ex- the arms and legs. There are 31 pairs of spinal nerves. amples of efferent information sent from the CNS are Each spinal nerve arises commands to muscles to contract or relax to move a within the gray matter Spinal nerves Nerves body part or to make the heart beat as well as com- of the spinal cord and that course between the spinal cord and the body. mands regulating body metabolism. then courses out from

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between the 33 individual bones of the vertebral col- in nature transmit Phrenic nerve A spinal umn (the vertebrae) to innervate the body (Figure only afferent impulses nerve that provides inner­ vation to the diaphragm. 2-17). Each spinal nerve connects the spinal cord to from the body back to a muscle, organ, or gland of the body. the CNS. The cranial Diaphragm The primary muscle of inspiration. nerves that function Most spinal nerves do not play a direct role in speech. both as sensory and Cranial nerves Nerves However, the phrenic nerve innervates the dia- that course between motor nerves relay phragm. The diaphragm is the muscle that is primar- the brain stem and the both efferent and af- head/neck/face and are ily responsible for the inspiration of air into the lungs. ferent information be- either motor/efferent, Of course, respiration is necessary to life, but it also is sensory/afferent, or mixed tween the CNS and the essential for the production of phonation for speech. sensory-motor in function. body. See Table 2-1 Ophthalmic branch A for a complete listing branch of the trigeminal The Cranial Nerves of the cranial nerves nerve that is sensory and their function. in nature and transmits As their name implies, the cranial nerves are associ- afferent information from ated with the cranium. The cranium is the bony part Although all the cra- the upper face, forehead, and scalp to the central of the skull that encases and protects the brain. The nial nerves are very nervous system. cranial nerves connect muscles and structures of the important to know, Maxillary branch A head, face, and neck to the CNS. There are 12 cranial this book focuses on branch of the trigeminal nerves. Each of the cranial nerves is a paired nerve, those whose func- nerve that is sensory in meaning that there is one for the right side of the body tion is important for nature and is responsible for transmitting afferent and an analogous one for the left side of the body. communication. The information from the cranial nerves that are teeth, upper lip, buccal Thorough knowledge of the function and location of most directly impor- and nasal cavities, as well the cranial nerves is a powerful diagnostic tool for the as the sides of the face to tant to speech are tri- speech-language pathologist. Based on the presence the CNS. geminal V, facial VII, of certain speech, voice, or swallowing difficulties, a Mandibular branch A glossopharyngeal IX, speech-language pathologist often can discern the branch of the trigeminal vagus X, accessory XI, nerve with both sensory presence of pathology in the PNS and, using knowl- and hypoglossal XII. and motor functions. The edge of the function of the cranial nerves, can deter- afferent portion of this mine with which nerve(s) the problem originates. nerve carries sensory information from the The cranial nerves are numbered by roman numer- The Trigeminal V lower teeth, lower gums, bottom lip, as well as als in the order that they synapse, or connect, to the The fifth cranial somatic information from CNS from superior to inferior. The olfactory nerve portions of the tongue. nerve, the trigeminal, is numbered I because, from superior to inferior, it The efferent component is one of the largest innervates muscles of is the first cranial nerve to synapse with the CNS. In cranial nerves and one mastication. contrast, the hypoglossal nerve is XII because the of the most important other 11 cranial nerves attach to the portions of the cranial nerves for speech (see Figure 2-20.) It is a brain and brain stem above it. mixed motor and sensory nerve. The trigeminal The cranial nerves are all either motor nerves, sen- emerges from the pons and splits into three primary sory nerves, or mixed sensory-motor. Cranial nerves branches: the ophthalmic branch, the maxillary that are motor in nature carry only efferent impulses branch, and the mandibular branch (Seikel et al., from the CNS out to the body. Those that are sensory 2010). The ophthalmic branch is sensory in nature

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Table 2-1 Cranial Nerves

Roman Numeral Cranial Nerve Origin Type Function

I Olfactory Cerebral hemispheres Sensory Smell

II Optic Thalamus Sensory Vision

III Oculomotor Midbrain Motor Movement of the eyes

IV Trochlear Midbrain Motor Movement of the eyes

V Trigeminal* Pons Sensory Somatic sensation from face, lips, jaw

Motor Movement of the mandible

VI Abducens Pons Motor Movement of the eyes

VII Facial* Pons Sensory Gustation (taste) from the anterior two-thirds of the tongue

Motor Movement of the lips and face

VIII Cochleovestibular Pons, medulla Sensory Hearing and balancing

IX Glossopharyngeal* Medulla Sensory Gustation (taste) from the posterior one-third of the tongue

Motor Movement of superior portion of pharynx

X Vagus* Medulla Sensory Sensation from larynx, pharynx, abdominal viscera

Motor Movement of the larynx, pharynx, velum

XI Accessory* Medulla, spinal cord Motor Movement of the muscles of shoulder and neck (trapezius)

Assisting vagus on movement of the larynx, pharynx, and velum

XII Hypoglossal* Medulla Motor Movement of the tongue

* Necessary for speech production.

and transmits afferent information from the upper regarding pathology of the trigeminal refer to the face, forehead, and scalp to the CNS (Figure 2-20). video Trigeminal Neuralgia. The maxillary branch is also a sensory nerve and is responsible for transmitting afferent information from the teeth, upper lip, buccal and nasal cavities, as well as the sides of the face to the CNS (Figure The Facial Nerve VII 2-20). In contrast, the mandibular branch has both The seventh cranial nerve, the facial, is a mixed sen- sensory and motor functions. The afferent portion sory-motor nerve. The facial nerve emerges from of this nerve carries sensory information from the the inferior pons. The primary motor function of the lower teeth, lower gums, and bottom lip and somatic facial nerve is to provide motor innervation to the information from portions of the tongue (Figure muscles of the face. The primary sensory function 2-20). The efferent component of the mandibular of the facial nerve is to transmit afferent information branch of the trigeminal nerve innervates muscles of concerning taste from the anterior two-thirds of the mastication. For an interview with an individual tongue to the CNS (Gertz, 2007).

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Ophthalmic zone

Maxillary zone

Mandibular zone Trigeminal nerve

Figure 2-20 Areas of the face and scalp innervated by the Mandibular, Maxillary, and Opthalmic branches of the trigeminal nerve.

The facial nerve has four branches. From superior of the lower face receive Bilateral innervation An to inferior these are the temporal branch, the zygo- motor plans only from innervation pattern that matic branch, the buccal branch, and the mandibular occurs when one side the contralateral cere- of a paired nerve (the branch. A distinctive feature of the facial nerve is that bral hemisphere (Figure right or the left) receives the temporal and zygomatic branches, which inner- 2-21). Therefore, when motor plans from both vate the muscles of the upper face, receive plans of the right and left cerebral an individual twitches hemispheres. volitional motor movement for the upper face from the right side of her the contralateral as well as the ipsilateral cerebral Unilateral mouth, that motor plan innervation An hemispheres (Figure 2-21). When one side of a paired comes only from the left innervation pattern that nerve (the right or the left) receives motor plans from cerebral hemisphere. occurs when a nerve both the right and left cerebral hemispheres, it is receives motor plans from Other cranial nerves only the contralateral termed bilateral innervation. cerebral hemisphere. besides the facial nerve In contrast, the inferior branches of the facial nerve, are also bilaterally in- Protective the buccal and the mandibular branches, which in- redundancy When nervated, though some- the body duplicates nervate the muscles of the lower face, are unilaterally times inconsistently systems to protect proper innervated. Unilateral innervation of a nerve indi- between individuals. functioning. cates that the nerve receives motor plans from only the The facial nerve presents contralateral cerebral hemisphere. More simply: The a unique opportunity to learn unilateral and bilateral muscles of each side of the upper face receive motor innervation because the superior branches receive plans from both the right cerebral hemisphere and bilateral innervation whereas the inferiorly located the left cerebral hemisphere (Figure 2-21). So, when branches receive only unilateral innervation. an individual moves one side of her upper face and forehead, those motor plans come from both cere- There is a protective redundancy in bilateral inner- bral hemispheres. However, the muscles of either side vation. With bilateral innervation, a lack of motor

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Lower motor neuron lesion Corticobulbar tract

Upper motor neuron lesion

Facial (VII) nucleus Facial (VII) nucleus for lower face Facial (VII) nucleus for upper face

Figure 2-21 Bilateral innervation of the facial nerve.

plans coming from one cerebral hemisphere does would incapacitate the entire contralateral half of not completely incapacitate a body part if that body the diaphragm. However, due to the protective re- part can still receive motor plans from the oppo- dundancy of bilateral innervation, an individual site hemisphere. So, why is this important? Take the can suffer damage to a cerebral hemisphere and still phrenic nerve, which innervates the diaphragm, for retain some function in the contralateral portion example. The diaphragm is the primary muscle for of the diaphragm. Because moving the diaphragm respiration and the phrenic nerve, which supplies is important to sustaining life, the significance of motor commands to the diaphragm, is bilaterally bilateral innervation becomes evident. Figure 2-21 innervated. If the phrenic nerve was not bilaterally shows an illustration of the bilateral innervation of innervated, then damage to one cerebral hemisphere the superior portions of the facial nerve.

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Glossopharyngeal IX Upon leaving the medulla, the first branch of the The ninth cranial nerve, the glossopharyngeal, has vagus innervating a structure important for speech both sensory and motor functions. The primary is the pharyngeal plexus. This branch of the vagus sensory function of the glossopharyngeal is trans- innervates most of the muscles of the inferior phar- mitting taste from the posterior one-third of the ynx as well as most of the muscles of the velum. The tongue and also from a portion of the soft palate. muscles of the inferior pharynx are responsible for The motor function of the glossopharyngeal nerve pharyngeal constriction, which is used during swal- is to deliver efferent signals to the superior muscles lowing, while the muscles of the velum are impor- of the pharynx, which are involved in swallowing, as tant for sealing off the nasal cavity for production well as to the parotid gland, which produces saliva of nonnasal phonemes and also for avoiding nasal (Gertz, 2007). regurgitation during swallowing. Continuing inferiorly, the second branch of the vagus important for speech is the superior laryngeal Vagus X branch, or the superior laryngeal nerve (SLN). The The 10th and largest cranial nerve, the vagus, is SLN has an intrinsic and an extrinsic branch. The perhaps the most important cranial nerve for the intrinsic branch of the SLN is sensory in nature and speech-language pathologist. The vagus is a long responsible for transmitting sensory information and complex nerve with both sensory and motor from the inside of the larynx to the CNS. The extrin- functions. The vagus exits the medulla and travels sic portion of the SLN is responsible for innervating inferiorly to innervate the muscles of the soft palate, the cricothyroid muscle (the primary tensor of the pharynx, and larynx. Figure 2-22 is an illustration of vocal folds). the sections of the vagus. The vagus then courses and passes inferiorly into the thorax. The right vagus nerve passes under the X Vagus Medulla right subclavian artery within the right side of the thorax. The left vagus passes under the arch of aorta Pharyngeal Intrinsic plexus Velum branch of of the heart within the left side of the thorax. Both of superior these branches then immediately change course and Pharynx laryngeal Superior nerve pass superiorly back, recurring, into the neck and to laryngeal nerve the larynx to innervate all the remaining intrinsic (SLN) larynx muscles of the larynx (those muscles responsible for

l adduction and abduction of the vocal folds). These Extrinsic branch of branches of the vagus are known appropriately as the superior laryngeal recurrent laryngeal nerve (RLN). nerve

e (RLN)

ent laryngea

nerv curr Accessory XI bclavi Re Su an ar The 11th cranial nerve, the accessory, is an efferent te r y Aorta nerve and as such is only motor in function. The ac- cessory nerve has a spinal component responsible for innervating muscles of the shoulders such as the tra- Figure 2-22 Sections of the vagus nerve. pezius, but also has a cranial component. The cranial

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component of the accessory nerve and the functional in nature. The primary role of the hypoglossal nerve differences between it and the vagus nerve are poorly is to innervate all the intrinsic muscles of the tongue understood. The cranial component of the accessory and most of the extrinsic muscles of the tongue. The nerve works alongside the vagus (as an accessory). intrinsic muscles of the tongue are the muscles that The spinal component of the accessory nerve inner- comprise the actual body of the tongue and are re- vates some of the muscles of the shoulders. sponsible for the more fine motor movements of the tongue involved in articulation. The extrinsic muscles of the tongue are those muscles responsible Hypoglossal XII for gross movements of the tongue, such as the ex- The 12th and last cranial nerve is the hypoglos- tension and retraction of the tongue. These gross sal. The hypoglossal nerve exits the brain stem at motor movements of the tongue are more likely to a more inferior location off the medulla than any be used during mastication and swallowing than other cranial nerve. The hypoglossal nerve is motor during speech.

Main Points

• The nervous system is divided into the central The right and left cerebral hemispheres are con- nervous system (CNS), which is made up of the nected by a thick band of commissural fibers brain and spinal cord, and the peripheral ner- called the corpus callosum. vous system (PNS), which is made up of the • The right cerebral hemisphere is responsible for cranial nerves and spinal nerves. the interpretation of nonlinguistic stimuli such • The brain is grossly composed of the cerebrum, as facial expressions, body language, gestures, brain stem, and cerebellum. prosody, melody, rhythm, and environmental • The surface of the cerebrum is the cerebral cor- sounds; understanding macrostructure; visuo- tex and is composed of folded tissue that cre- spatial processing; and attention (sustained and ates gyri and sulci. These folds of cortical tissue selective). enable more neural tissue to be packed into a • The left cerebral hemisphere is primarily re- smaller space. sponsible for expressive and receptive language • The brain is made up of gray and white mat- abilities. Broca’s area is primarily responsible ter. Gray matter lacks myelin, a fatty substance for expressive language, and Wernicke’s area is used to facilitate the conduction of electrical primarily responsible for receptive language. impulses along tracts of white matter. Gray mat- • The cerebrum is divided into four paired lobes: ter is responsible for processing information. frontal, parietal, temporal, and occipital. The White matter is responsible for transmitting frontal lobes’ functions include expressive and information. White matter is made up of three receptive language, as well as motor movements. types of fibers. These include association fibers, The parietal lobes’ functions include receiving commissural fibers, and projection fibers. and processing sensory information regarding • The cerebrum is divided into right and left ce- the body such as taction and proprioception. rebral hemispheres by the longitudinal fissure. The temporal lobes’ functions include memory

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as well as receiving and processing auditory in- certain pathologic situations, such as damage to formation through the primary auditory corti- the motor pathways within the CNS, and result ces. Last, the occipital lobes’ functions include in spasticity. receiving afferent signals of vision as well as • The brain consumes 25% of all oxygen and glu- processing visual information. cose brought into the body. • The frontal and parietal lobes are divided by the • The internal carotid arteries and the basilar central sulci, which run laterally down the side artery transmit blood from the thorax to the of each cerebral hemisphere in a vertical fash- brain. ion. The frontal and parietal lobes are divided • The anterior cerebral arteries, middle cerebral from the temporal lobes by the lateral sulci, arteries, and posterior arteries transmit blood which run anteriorly to posteriorly at an up- out to certain portions of the brain. ward angle through each cerebral hemisphere. • The anterior communicating artery and the • Structures of the subcortex are the brain stem, posterior communicating arteries link up the cerebellum, thalamus, and basal ganglia. The internal carotid system with the vertebral/ subcortex is responsible for less volitional and basilar system to form the circle of Willis. The more automatic/visceral functions such as circle of Willis acts as a safety valve to protect heartbeat, breathing, and sleep–wake cycles. the brain from a lack of blood supply. • The brain stem is composed of (from superior to • The 31 paired spinal nerves connect the spinal inferior) the midbrain, pons, and medulla. The cord to muscles, organs, and glands that usually brain stem connects the spinal cord to the brain. do not play a direct role in speech production. • The cerebellum is made up of two hemispheres However, the phrenic nerve is a spinal nerve connected by the vermis at midline. The cer- that innervates the diaphragm, the muscle pri- ebellum is attached to the pons by the inferior, marily responsible for inspiration of air into the medial, and superior peduncles. The cerebel- lungs. lum is as an error control device and works to • The 12 paired cranial nerves connect the mus- create smoothly coordinated and errorless body cles and structures of the head, face, and neck to movements. the CNS and function as sensory, motor, or both • The thalamus rests on top of the brain stem and sensory and motor nerves. Important cranial is the relay station for afferent signals. nerves for speech include the trigeminal (V), • The basal ganglia is made up of the caudate facial (VII), glossopharyngeal (IX), vagus (X), nucleus, putamen, and globus pallidus and is accessory (XI), and hypoglossal (XII). responsible for regulation of motor movement, • The trigeminal (V) nerve is a paired sensory- muscle tone, and inhibition of extraneous motor nerve that transmits sensory information movements. from the upper and lower face to the CNS and • The spinal cord, which begins at the medulla, transmits motor information from the CNS to narrows and terminates at the conus medullaris the muscles of the mandible. The trigeminal is and divides into in loose strands of nerves. The divided into ophthalmic, maxillary, and man- spinal cord transmits afferent information from dibular branches. the PNS to the brain and transmits efferent in- • The facial (VII) nerve is a paired sensory-motor formation from the brain to the PNS. The spi- nerve that provides motor to the face and sen- nal cord is also responsible for originating the sation (taste) from the anterior two-thirds of stretch reflex, which can become hyperactive in the tongue and is divided into the temporal and

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zygomatic branches, which are bilaterally inner- viscera through its many branches, including vated, and the buccal and mandibular branches, the pharyngeal plexus, superior laryngeal nerve which are unilaterally innervated. (intrinsic and extrinsic branches), and recurrent • The glossopharyngeal (IX) nerve is a paired laryngeal nerve. sensory-motor nerve that provides sensory • The accessory (XI) nerve is a paired motor-only information to the posterior one-third of the nerve whose cranial portion works alongside tongue and motor information to the pharynx the vagus for innervation of the larynx, phar- for swallowing. ynx, and velum and whose spinal portion in- • The vagus (X) nerve is a paired sensory-motor nervates some of the muscles of the shoulders. nerve that provides motor information to the • The hypoglossal (XII) nerve is a paired motor soft palate, pharynx, and larynx and sensory nerve that innervates the intrinsic and extrinsic information from the pharynx, larynx, and muscles of the tongue.

Review Questions

1. Describe the two major sections of the nervous 11. List the three sections of the brain stem and de- system, including each section’s anatomy and scribe functions of each. functions. 12. What structures of the cerebellum attach it to 2. What three gross structures constitute the brain? the pons and the CNS? 3. What are the ridges and valleys of the cerebral 13. What is the location and primary function of cortex called and why are they there? the thalamus? 4. What is myelin? What is the function of myelin 14. Describe the function of the basal ganglia. and what type of neurons have myelin? 15. Why is the circle of Willis an important 5. Which fissure separates the left and right cere- structure? bral hemispheres? What major band of commis- 16. Describe the location, anatomy, and role of the sural fibers connects the right and left cerebral spinal cord. hemispheres? 17. Describe how a healthy stretch reflex occurs 6. List five functions of the right hemisphere. and describe how a hyperactive stretch reflex 7. List two functions of the left hemisphere. contributes to spasticity. 8. Name the four lobes of the cerebral hemispheres 18. In your opinion, which cranial nerve is the most and describe the function and any important important for speech production and why? areas of each lobe that enable those functions 19. What are the six most important cranial nerves to occur. that are central to the production of speech? 9. Which sulci run laterally and divide the frontal 20. What is bilateral innervation? What is unilat- and temporal lobes? Which sulci run superiorly eral innervation? Why is bilateral innervation to inferiorly and divide the frontal and parietal a good thing? lobes? 10. List three structures of the subcortex and iden- tify the main functions of those structures.

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References

1. Acharya, H. (2004). The rise and fall of the frontal 9. Joseph, R. (1988). The right cerebral hemisphere: Emo- lobotomy. Proceedings of the 13th Annual History of tion, music visual-spatial skills, body-image, dreams, Medicine Days. and awareness. Journal of Clinical Psychology, 44(5), 2. Aristotle. (2011). On sleep and sleeplessness (I. Beare, 630–673. Trans.). Amazon Digital Services. 10. Kucharski, A. (1984). History of frontal lobotomy in 3. Bhatnagar, S. (2008). Neuroscience for the Study of the United States, 1935–1955. Neurosurgery, 14(6), Communicative Disorders. Philadelphia, PA: Wolters 765–772. Kluwer/Lippincott Williams & Wilkins. 11. Luria, A. (1973). The working brain: An introduction to 4. Carey, B. (2008). H.M., an unforgettable amnesiac, neuropsychology. New York, NY: Basic Books. dies at 82. New York Times. http://www.nytimes. 12. MacMillan, M. (2000). Restoring Phineas Gage: A com/2008/12/05/us/05hm.html?pagewanted=al&_ 150th retrospective. Journal of the History of the Neu- rmoc.semityn.www rosciences, 9(1), 46–66. 5. Corkin, S. (2002). What’s new with the patient H.M.? 13. Scoville, W. B., & Milner, B. (1957). Loss of recent mem- Nature Reviews: Neuroscience, 3, 153–160. ory after bilateral hippocampal lesions. Journal of 6. Diener, H., & Dichgans, J. (1992). Pathophysiology of Neurology, Neurosurgery, and Psychiatry, 20(11), 11–21. cerebellar ataxia. Movement Disorders, 7(2), 95–109. 14. Seikel, J., King, D., & Drumright, D. (2010). Anatomy and 7. Duffy. J. (2005). Motor speech disorders: Substrates, physiology for speech, language, and hearing (4th ed.). differential diagnosis, and management (2nd ed.). St. Clifton Park, NY: Delmar Cengage. Louis, MO: Mosby. 8. Gertz, S. (2007). Liebman’s neuroanatomy made easy and understandable (7th ed.). Austin, TX: Pro-Ed.

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