Introduction to the Structure and Function of the Nervous System

Chapter 3 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Introduction to the Structure and Function of the Nervous System © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

STRUcTURE AnD FUncTIOn Of THE makes possible complex activities, such NERVOUs SYsTEM as walking, running, playing a piano, and © Jones & BartlettThe Learning, nervous system LLC is a complex regulatory© Jones using& Bartlett a computer, Learning, as well as simpleLLC activi- NOT FOR SALE ORsystem DISTRIBUTION that, along with the endocrine system (seeNOT FORties, SALE such as OR maintaining DISTRIBUTION muscle tone and Chapter 23), controls and coordinates activities posture while at rest. and functions throughout the body, internally • Monitoring and recognizing stimuli (and and externally, by sending, receiving, and sort- information) within the environment, and ing electrical impulses. Disruption of any part of then directing an appropriate response to the nervous© system Jones affects & bodyBartlett function Learning, in some LLC the stimuli. This function© Jonesmakes possible & Bartlett Learning, LLC way, either NOTinternally FOR or externally. SALE OR DISTRIBUTIONreflex actions, such as NOTpulling FOR away SALEone’s OR DISTRIBUTION The nervous system consists of the central hand from a hot surface, as well as perceiv- nervous system, which includes the brain and ing music being played in the next room. spinal cord, and the peripheral nervous system, • Monitoring and coordinating internal body states so that internal organs function as a © Joneswhich & includes Bartlett nerve Learning, fibers extending LLC from the © Jones & Bartlett Learning, LLC brain and spinal cord that carry information unit, internal body constancy (homeosta- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION between the central nervous system and the rest sis) is maintained, and protective action is of the body. The peripheral nervous system is fur- taken. For example, in response to a lack of ther divided into two parts: the afferent (sensory) oxygen, more rapid breathing occurs; the system, which carries messages from other parts body shivers in response to cold; and when of the body to the central nervous system, and the threat or danger is encountered, the heart © Jones & Bartlett Learning, LLC © Jones beats& Bartlett more rapidly. Learning, LLC NOT FOR SALE ORefferent DISTRIBUTION (motor) system, which carries messagesNOT FOR SALE OR DISTRIBUTION from the central nervous system to other parts of Other functions, such as display of personality the body (see Table 3-1). traits, language, speech, learning, remembering, feeling emotion, reasoning, and generating and Function of the Nervous System relaying thoughts, are also controlled by the ner- Functions of© Jonesthe nervous & Bartlett system include Learning, the LLCvous system—specifically, by© the Jones brain. & Bartlett Learning, LLC following: NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION • Organizing and directing motor responses Nerve Cells of the voluntary muscle system, enabling Specialized cells called neurons are the func- the body to move more effectively as a tional units of the nervous system. Neurons © Jones &whole Bartlett and to achieve Learning, purposeful LLC movement. transmit messages© Jones to and & fromBartlett the brain. Learning, They LLC NOT FORThis SALE coordination OR DISTRIBUTION of voluntary muscles consist of NOTa cell FORbody andSALE processes OR DISTRIBUTION (nerve

31 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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process begins again (see Figure 3-1). After neu- Table 3-1 TThe Nervous System rotransmitters are released, they are either taken (Central and Peripheral) © Jones & Bartlett Learning, LLCup again by the neuron or destroyed.© Jones & Bartlett Learning, LLC I. Central nervous system NOT FOR SALE OR DISTRIBUTIONLonger axons are generallyNOT grouped FOR in bun-SALE OR DISTRIBUTION A. Brain dles. When they are transmitting impulses within B. Spinal cord the central nervous system, these bundles are referred to as tracts. Those bundles located out- II. Peripheral nervous system side the central nervous system are referred to © Jones A. &Aff Bartletterent (sensory) Learning, LLC as nerves. © Jones & Bartlett Learning, LLC NOT FORB. Eff SALEerent (motor) OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1. Somatic nervous system The Central Nervous System 2. Autonomic nervous system The central nervous system is made up of the a. Sympathetic nervous system brain and spinal cord. Bony coverings protect © Jones & Bartlett Learning, b. Parasympathetic LLC nervous system © Jonesboth the & brainBartlett and the Learning, spinal cord. LLC On the inte- rior of these bony coverings are three membranes NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION (meninges) that provide additional protection: • The dura mater is the outer membrane, fibers) that extend beyond the cell body. In most lying closest to the bony covering of the cases, a single long nerve fiber called an axon brain and spinal cord. conducts nerve© Jones impulses & (and Bartlett information) Learning, away LLC © Jones & Bartlett Learning, LLC • The arachnoid membrane is the middle from the cell body to other neurons. Smaller, NOT FOR SALE OR DISTRIBUTIONmembrane, a cobweb-appearingNOT FOR membrane. SALE OR DISTRIBUTION shorter nerve fibers called dendrites conduct • The pia mater is the inner membrane, which nerve impulses toward the cell body after receiv- lies closest to the brain and spinal cord. ing information from other neurons. Fibers that carry information from parts of the body to the Between each of the membrane layers are spaces. © Jonesbrain &are Bartlett called afferent Learning, neurons LLC(sensory neu- The space between© Jones the dura& Bartlett mater and Learning, the inner LLC NOT rons).FOR FibersSALE that OR carry DISTRIBUTION information from the surface of NOTthe bony FOR covering SALE is ORthe epiduralDISTRIBUTION brain to other parts of the body are called effer- space. T; the space between the dura mater and ent neurons (motor neurons). the arachnoid membrane is the subdural space; Surrounding neurons is a fatty sheath called and the space between the arachnoid membrane myelin, which, much like the covering of elec- and the pia mater is the subarachnoid space. © Jones & Bartletttrical Learning, cords, provides LLC insulation, ensuring that© JonesThe & central Bartlett nervous Learning, system is alsoLLC protected NOT FOR SALE ORelectrical DISTRIBUTION impulses are able to flow smoothly andNOT and FOR cushioned SALE by OR cerebrospinal DISTRIBUTION fluid (CSF), reliably. Information is passed from neuron to which is formed by specialized capillaries called neuron by both electrical and chemical impulses. the choroids plexus in inner chambers within the The electrical impulse, which has been picked up brain called ventricles. The cerebrospinal fluid by the dendrites,© Jones is passed & Bartlettthrough the Learning, cell body LLCbathes the brain and spinal cord,© circulatingJones & from Bartlett Learning, LLC to the axon. The electrical impulse then moves the ventricles into the subarachnoid space (see NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION down the full length of the axon until it reaches Figure 3-2). From the subarachnoid space it the its tip. At the tip of the axon are tiny processes, CSF flows to the back of the brain, down around which release chemicals known as neurotrans- the spinal cord, and then back to the brain, mitters. Neurotransmitters, through chemical where it is reabsorbed into the blood through the © Jonesmeans, & transferBartlett the Learning, impulse from LLC one neuron arachnoid membrane.© Jones The & Bartlettamounts of Learning, cerebro- LLC NOT toFOR another SALE across OR a space DISTRIBUTION between the two neu- spinal fluidNOT produced FOR and SALE absorbed OR are DISTRIBUTION equally rons called the synapse. The electrical impulse, balanced, so that under normal conditions, the through the vehicle of neurotransmitters, then amount of CSF within the central nervous system moves to the next neuron’s dendrites and the remains constant. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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Figure 3-1 Neurons

© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC Another protective device is the blood–brain harmful substances, such as toxins, are prevented barrier, a structuralNOT FOR arrangement SALE ORof capillaries DISTRIBUTION from crossing into the brain. NOT FOR SALE OR DISTRIBUTION that selectively determines which substances can The central nervous system is composed of move from the blood into the brain. While sub- white matter and gray matter. White matter stances such as oxygen and glucose are necessary makes up the inner part of the brain and the outer © Jonesto brain & Bartlettsurvival and Learning, consequently LLC move freely portion of the© spinalJones cord & and Bartlett consists ofLearning, myelin- LLC NOT acrossFOR theSALE blood–brain OR DISTRIBUTION barrier, other potential ated coveredNOT axons FOR that conduct SALE nerve OR impulses. DISTRIBUTION

Figure 3-2 Circulation of Cerebrospinal Fluid

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It is called white matter because of its whitish • The associational cortex is involved in cog- appearance due to the myelin covering. Gray nitive functions such as memory, reasoning, matter makes© Jonesup the thin & outerBartlett layer of Learning, the brain LLC abstract thinking, and consciousness.© Jones & Bartlett Learning, LLC and the inner portion of the spinal cord. Small NOT FOR SALE OR DISTRIBUTIONThe cerebrum is divided into NOTtwo halves, FOR called SALE OR DISTRIBUTION segments of gray matter are also embedded deep the right hemisphere and the left hemisphere. within certain parts of the white matter of the These two hemispheres communicate with each brain. Gray matter consists of groups of neuron other. Dividing the hemispheres and connecting cell bodies; it gets its name from . It is called gray specific areas of the two hemispheres are bundles © Jonesmatter & because Bartlett of its Learning, grayish appearance. LLC Gray © Jones & Bartlett Learning, LLC of nerve fibers called the corpus callosum. Each matter of the brain receives, sorts, and processes NOT FOR SALE OR DISTRIBUTION hemisphereNOT has centers FOR for SALE receiving OR informa- DISTRIBUTION nerve messages, while gray matter of the spinal tion and for initiating responses. The left hemi- cord serves as a center for reflex action (automatic sphere mostly receives information from and response to stimuli). sends information to the right side of the body, © Jones & Bartlett Learning, LLC © Joneswhereas & theBartlett right hemisphere Learning, mostly LLC receives NOT FOR SALE ORSTRU DISTRIBUTIONcTURE AnD FUncTIOn Of NOTinformation FOR SALE from OR and DISTRIBUTION sends information to the THE BRAIn left side of the body. Deep within the cerebral hemispheres are The brain is directly connected to the spinal cord groups of gray matter called basal ganglia, which and serves as the primary center for the integra- are part of the extrapyramidal system. (“Extrapy- tion, coordination, initiation, and interpretation © Jones & Bartlett Learning, LLCramidal” denotes nerve fiber tracts© Jones that lie &outside Bartlett Learning, LLC of most nerve messages. It regulates and moni- the pyramidal tract, a relatively compact group of tors many unconsciousNOT FOR body SALE functions, OR DISTRIBUTION such as NOT FOR SALE OR DISTRIBUTION nerve fibers that originate from cells in the outer heart and respiratory rate, and coordinates most layer of the brain.) Extrapyramidal function is voluntary movements. In addition, it is the site concerned with postural adjustment and gross of higher cognitive processes such as learning, voluntary and automatic muscular movements. generating and relaying thoughts, reasoning, © Jones & Bartlett Learning, LLC The basal ganglia© Jones help to& maintain Bartlett tone Learning, in mus- LLC judgment, memory, consciousness, and emotion. NOT FOR SALE OR DISTRIBUTION cles in the trunkNOT and FOR extremities, SALE enablingOR DISTRIBUTION indi- The brain also has a sensory function, which is viduals to maintain balance and posture and to responsible for vision, hearing, touch, taste, and engage in movements such as walking. The basal smell. Language function, including the ability ganglia also play a role in enabling individuals to to communicate and to comprehend, is also con- react swiftly, appropriately, and automatically to trolled by the brain as well. Finally, the brain con- © Jones & Bartlett Learning, LLC © Jonesstimuli & that Bartlett demand anLearning, immediate response,LLC such trols basic behavior patterns and the display of NOT FOR SALE OR DISTRIBUTION NOTas FOR after tripping,SALE enablingOR DISTRIBUTION the individual to adjust general personality traits, which are characteris- his or her movement to avoid a fall. tic of how each individual responds to stimuli. Each hemisphere of the cerebrum is divided The brain is protected by the bony covering of into lobes that contain areas related to specific the skull (cranium or cranial bones). The largest functions (see Figure 3-3). The frontal lobe is part of the brain,© Jones the cerebrum & Bartlett, is covered Learning, with a LLC © Jones & Bartlett Learning, LLC located in the front of each hemisphere and con- thin outer layer of gray matter called the cortex, NOT FOR SALE OR DISTRIBUTIONtains motor areas that initiateNOT voluntary FOR move- SALE OR DISTRIBUTION which contains billions of nerve cells. The cortex ment and skilled movements, such as those, has three specialized areas, which serve three involved in handwriting. Other areas in the fron- major areas of function: tal lobe control higher intellectual functions such © Jones• &The Bartlett motor cortex Learning, coordinates LLC voluntary as foresight,© analytical Jones thinking,& Bartlett and Learning,judgment. LLC NOT FORmovements SALE OR of the DISTRIBUTION body. The parietalNOT lobe FOR is located SALE in theOR middle DISTRIBUTION of • The sensory cortex is responsible for the each hemisphere and is primarily the sensory recognition or perception of sensory stim- area, integrating and interpreting sensation such uli, such as touch, pain, smell, taste, vision, as touch, pressure, pain, and temperature. Some and hearing. memory functions are also located in the parietal © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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Figure 3-3 Areas of Brain Function

lobe, especially those responsible for storage of articulation. This area contributes to expressive sensory memory. The temporal lobe is located function (speech formation), or the ability to inte- under the frontal and parietal lobes and is pri- grate and coordinate words so that the meaning © Jonesmarily & responsible Bartlett forLearning, the interpretation LLC of and can be comprehended.© Jones & Bartlett Learning, LLC NOT distinctionFOR SALE between OR auditory DISTRIBUTION stimuli. The occipi- A structureNOT known FOR as the SALE thalamus OR lies DISTRIBUTION within tal lobe is located at the back or posterior por- the center of the brain. The thalamus acts as a tion of each hemisphere; i. It is the primary area relay station that sorts, interprets, and directs for reception and interpretation of visual stimuli. sensory information. Below the thalamus is the Several parts of the cerebrum are involved hypothalamus, which coordinates neural and © Jones & Bartlettin Learning,the language LLCfunction, which consists of the© Jonesendocrine & Bartlett activities. ItLearning, This structure LLC helps regu- NOT FOR SALE ORprocess DISTRIBUTION of receiving, interpreting, and integrat-NOTlate FOR the body’sSALE internal OR DISTRIBUTION environment and behav- ing visual and auditory stimuli as well as the iors that are important to survival, such as eating, ability to express thoughts in a coordinated way drinking, and reproduction. Below the hypothala- so that others can comprehend them. Language mus is the pituitary gland, an endocrine gland that function is ©located Jones in the & leftBartlett hemisphere Learning, of the LLCwill be discussed in more detail© in Jones a later chapter. & Bartlett Learning, LLC cerebrum in most individuals, whether they are The limbic system is comprises a group of right- or left-handed.NOT FOR An SALE area located OR DISTRIBUTIONover the structures consisting of bothNOT gray FORand white SALE OR DISTRIBUTION temporal and parietal lobes, called Wernicke’s matter that surround the thalamus. The limbic area, is the major area responsible for receptive system plays a role in expression of instincts, function (speech understanding), or the ability to drives, and emotions and as in the formation of © Jonesintegrate & Bartlett visual and Learning, auditory information LLC so as memories. A© band Jones of gray & matterBartlett called Learning, the hip- LLC NOT toFOR understand SALE communication OR DISTRIBUTION received. An area pocampus isNOT involved FOR in learningSALE andOR long-term DISTRIBUTION located in front of the temporal lobe and in the memory, helping to determine where important frontal cortex, called Broca’s area, is responsible and relevant aspects of facts will be stored. for speaking ability and is closely associated with Beneath the occipital lobe of the cerebrum is motor areas that control the muscles needed for a structure called the cerebellum. The cerebellum © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

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is primarily responsible for the coordination and fused (joined) bone. At the tip of the sacrum is integration of voluntary movement and for the the coccyx, or tailbone (see Figure 3-4). maintenance© of Jones equilibrium, & Bartlett posture, and Learning, balance LLCThe spinal cord conducts© impulses Jones to& andBartlett Learning, LLC of the body.NOT It also FORregulates SALE and coordinates OR DISTRIBUTION fine from the brain. The outer whiteNOT matter FOR of SALE the OR DISTRIBUTION movements of the extremities, which are initiated spinal cord, which consists of bundles or tracts of by the frontal lobe. myelinated fibers of sensory afferent( ) and motor The brain stem, which is located beneath (efferent) neurons, conveys electrical impulses up the cerebellum at the base of the brain just above and down the spinal cord between the peripheral © Jonesthe spinal & Bartlett cord, acts Learning, as a relay station, LLC transmit- nervous system© Jones (those nerves& Bartlett lying outside Learning, the LLC NOT tingFOR nerve SALE impulses OR between DISTRIBUTION the spinal cord and central nervousNOT system) FOR andSALE the brain. OR DISTRIBUTIONIn most the brain. It is the primary center of involuntary instances, sensory information traveling up the functions. Control of vital organ functions, such right side of the spinal cord crosses over to the as regulation of heartbeat or respiration, occurs in left side of the brain, so the left hemisphere of the brain stem. Areas in the brain stem also regu- the brain would, for example, interpret pain in © Jones & Bartlettlate Learning, the diameter LLC of blood vessels, contributing to© Jonesthe right & hand.Bartlett Conversely, Learning, motor impulses LLC origi- NOT FOR SALE ORthe controlDISTRIBUTION of blood pressure. Reflex actions, suchNOT nating FOR in SALE the left ORbrain DISTRIBUTION cross to the right side of as coughing and swallowing, are controlled in the the spinal cord and initiate a response to the right brain stem as well. Finally, the brain stem con- side of the body. Because of this crossover effect, tains scattered groups of cells, called the reticu- damage on one side of the brain typically causes lar formation, which are involved in the initiation manifestations itself on the opposite side of the © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC and maintenance of wakefulness and alertness. body. The brainNOT requires FOR both SALE oxygen OR and DISTRIBUTIONnourish- NOT FOR SALE OR DISTRIBUTION ment in the form of glucose in order to function and to survive. Oxygen and glucose are trans- Figure 3-4 The Spine ported to the brain by blood carried by four major © Jonesarteries: & Bartletttwo carotid Learning, arteries and LLCtwo vertebral © Jones & Bartlett Learning, LLC NOT arteriesFOR SALE. The vertebral OR DISTRIBUTION arteries join to form the NOT FOR SALE OR DISTRIBUTION basilar artery. The carotid and basilar arteries then connect at the base of the brain to form the circle of Willis, from which cerebral arteries branch out to carry blood to the rest of the brain. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE ORSTRU DISTRIBUTIONcTURE AnD FUncTIOn NOT FOR SALE OR DISTRIBUTION Of THE SpInAL CORD AnD PERIpHERAL NERVOUs SYsTEM The Spinal Cord The spinal ©cord Jones is part & of Bartlett the central Learning, nervous LLC © Jones & Bartlett Learning, LLC system andNOT extends FOR from SALE the brain OR stem DISTRIBUTION to the NOT FOR SALE OR DISTRIBUTION lower part of the back. Bony coverings called vertebrae surround the spinal cord and protect it. Taken as a whole, this bony covering, as a whole, forms the vertebral column. The vertebral © Jonescolumn & consistsBartlett of 7Learning, cervical vertebrae LLC, located © Jones & Bartlett Learning, LLC NOT inFOR the neckSALE area; OR 12 thoracicDISTRIBUTION vertebrae, located NOT FOR SALE OR DISTRIBUTION in the upper and middle back; and 5 lumbar vertebrae, located in the lower back. The sacrum, located below the lumbar vertebrae, consists of Copyright Jane Tinkler Lamm. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONStructure and Function of theNOT Spinal FOR Cord SALEand Peripheral OR DISTRIBUTION Nervous System 37

The inner gray matter of the spinal cord, Many types of neurons work together to trans- which is composed of cell bodies and unmy- mit impulses through the spinal cord. Sensory elinated neurons,© Jones acts as& aBartlett coordinating Learning, center LLCimpulses entering the spinal cord© Jones at the lumbar & Bartlett Learning, LLC for reflex andNOT other FOR activities, SALE such OR as DISTRIBUTIONvoluntary region are relayed vertically toNOT the brain FOR through SALE OR DISTRIBUTION movements and control of internal functions. A a number of connecting sensory neurons. Motor reflex center in the gray matter of the spinal cord impulses from the brain to the peripheral nerves, is where sensory and motor neurons connect; this however, are conducted through two separate cat- part of the spinal cord serves as a center for spinal egories of motor neurons. Upper motor neurons © Jonesreflexes. & BartlettA reflex can Learning, be defined asLLC an automatic originate in ©the Jones brain and & are Bartlett contained Learning, entirely LLC NOT responseFOR SALE to a given OR stimulus. DISTRIBUTION Spinal reflexes con- within the centralNOT nervousFOR SALE system. ORLower DISTRIBUTION motor trol not only muscle reflexes, but also the reflexes neurons, although originating in the central ner- of internal organs. vous system, have fibers extending to the periph- The gray matter within the spinal cord resem- eral nerves in voluntary muscles. Alteration of bles the letter “H.” The projections of the H are function of either upper or lower motor neurons © Jones & Bartlettnamed Learning, according LLC to the direction to which they© Jonescan generally & Bartlett affect Learning,the voluntary LLCmuscles. The NOT FOR SALE ORproject. DISTRIBUTION The posterior horns extend toward theNOT location FOR SALEof the alteration OR DISTRIBUTION of function determines back, and the anterior horns project toward the nature of the manifestations. the front. Cerebrospinal fluid, which nourishes and protects the spinal cord, fills both the cen- Structure and Function of the Peripheral tral canal, located within the center of the gray Nervous System © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC matter, and the subarachnoid space surrounding A nerve is a bundle of fibers outside the cen- the outer portionNOT of FOR the spinal SALE cord. OR DISTRIBUTIONtral nervous system that transmitsNOT informationFOR SALE OR DISTRIBUTION Motor (efferent) impulses originate in the between the central nervous system and vari- motor cortex of the brain, extend down the spinal ous parts of the body. The peripheral nervous cord through descending tracts, and exit through system consists of all nerves that extend from © Jonesmotor & spinal Bartlett nerve Learning, roots that extend LLC through the brain and© spinal Jones cord. & To Bartlett function effectively, Learning, LLC NOT openingsFOR SALE between OR the DISTRIBUTIONvertebrae that surround the the peripheralNOT nerves FOR must SALE be connected OR DISTRIBUTION to the spinal cord. Sensory (afferent) impulses from the central nervous system. Some peripheral nerves body enter the spinal cord through spinal nerve connect directly to the brain (cranial nerves); roots that also extend through openings between others connect directly to the spinal cord (spinal vertebrae and then travel up ascending tracts in nerves). Cranial and spinal nerves are essential © Jones & Bartlettthe Learning, spinal cord to LLC the brain. © Joneslinks between & Bartlett the rest Learning, of the body and LLC the central NOT FOR SALE OR SpinalDISTRIBUTION nerve roots are named for the verte-NOTnervous FOR SALEsystem. OR DISTRIBUTION bral level from which they exit. For example, the The 12 pairs of peripheral nerves that con- nerve roots that leave the spinal cord at the cervi- nect and transmit messages directly to the brain cal level are labeled C1 through C8, and the nerve are called cranial nerves. Some cranial nerves roots that leave at the thoracic level are labeled contain only sensory fibers, whereas others con- T1 through© T12 Jones (see Figure & Bartlett 3-5). The Learning, sensory LLCtain both sensory and motor fibers.© Jones Cranial &nerves Bartlett Learning, LLC (afferent) nerveNOT fibers FOR from SALE outside OR the DISTRIBUTION central mediate many aspects of sensationNOT and FOR muscular SALE OR DISTRIBUTION nervous system carry body sensations into the activity in and around the head and neck. Cranial sensory nerve roots (posterior roots) at the back nerves and their related functions are described of the spinal cord, where they are then carried in Table 3-2). up the spinal cord to the brain. Motor (efferent) The 31 pairs of peripheral nerves that con- © Jonesimpulses & Bartlett travel from Learning, the brain down LLC the spinal nect and transmit© Jones messages & Bartlett directly to Learning,the spinal LLC NOT cordFOR and SALE exit from OR motor DISTRIBUTION nerve roots (anterior cord are calledNOT spinal FOR nerves SALE. Each OR nerve DISTRIBUTION divides roots) at the front of the spinal cord. Motor nerve and then subdivides into a number of branches. fibers then carry impulses to the voluntary mus- Nerves at each level travel to specific parts of cles of the body. the body, conveying information between those © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR38 DISTRIBUTION Chapter 3 • Introduction to the StructureNOT and FunctionFOR SALE of the NervousOR DISTRIBUTION System

Figure 3-5 Spinal Nerves

areas and the© Jones central nervous& Bartlett system. Learning, Spinal LLCThe autonomic nervous system© Jones integrates & Bartlettthe Learning, LLC nerves and NOTtheir related FOR functions SALE ORare described DISTRIBUTION work of vital organs, such as theNOT heart FOR and lungs. SALE OR DISTRIBUTION in Figure 3-5. Its primary function is to coordinate the activity Nerves control both voluntary and involun- of internal organs so that they can make adap- tary functions in the body. Nerves that control tive responses to changing external situations, voluntary functions (such as movement of the thereby maintaining internal equilibrium. Nerve © Jonesmuscles & Bartlettin the extremities) Learning, are called LLC somatic fibers monitor© Jones the activities & Bartlett of internal Learning, organs LLC NOT nervesFOR .SALE Nerves thatOR are DISTRIBUTION concerned with the con- as well as changesNOT FOR in the SALEexternal ORenvironment. DISTRIBUTION trol of involuntary functions are part of a subcat- When changes are necessary to maintain inter- egory of the peripheral nervous system called the nal homeostasis (equilibrium) or to protect the autonomic nervous system. body, the autonomic nervous system stimulates © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION

© Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTIONBibliography 39

Table 3-2 Cranial Nerves and Related Functions

Cranial Nerve© Jones & BartlettArea of Learning,Function LLC © Jones & Bartlett Learning, LLC I. OlfactoryNOT FOR SALESmell OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION II. Optic Vision III. Oculomotor Movement of eye muscles IV. Trochlear Eyelids © Jones V. &Tri Bartlettgeminal Learning,Sensation LLC in head, face, and teeth, motor© activityJones of &chewing Bartlett Learning, LLC NOT FORVI. AbdSALEucens OR DISTRIBUTIONPupil dilation, focusing of lens NOT FOR SALE OR DISTRIBUTION VII. Facial Taste, sensation of external ear, control of salivary glands, tears, muscles in facial expression VIII. Vestibulocochlear Sensation of sound, balance, orientation of head © Jones & Bartlett IX. Learning, Glossopharyngeal LLC Swallowing, sensation© Jones of pain, taste,& Bartlett touch from Learning, tongue and throat LLC NOT FOR SALE OR X. DISTRIBUTION Vagus Heartbeat, digestion,NOT speech, FOR swallowing, SALE respiratory OR DISTRIBUTION function, gland functions XI. Accessory Movement of head and shoulders, muscles of pharynx and larynx in throat, production of voice sounds XII. Hypoglossal Tongue movement, speech, swallowing © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION an immediate, involuntary response. For exam- In contrast, the parasympathetic nervous ple, in response to a speck of dust in the eye, tears system dominates when the body is a rest. It are produced; i. In response to a fearful situation, activates those mechanisms that focus on body the heart beats faster. conservation, such as decreasing the heart rate © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC The autonomic nervous system is divided into and constricting the pupils of the eye. The para- NOT twoFOR subsystems: SALE OR DISTRIBUTION sympatheticNOT nervous FOR system SALE is also OR an important DISTRIBUTION component of sexual arousal in both males and • The sympathetic nervous system females. • The parasympathetic nervous system

© Jones & BartlettThese Learning, two systems LLC work both together and in© Jones & Bartlett Learning, LLC opposition to control internal organs and regu- BIbLIOGRApHY NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION late their function. Hormones and emotions can Falvo, R. E. (2001). Human physiology physiology 201 core affect both systems. curriculum. Champaign, IL: Stipes Publishing L.L.C. The sympathetic nervous system becomes Sherwood, L. (2007). Human physiology: From cells to sys- active during periods of stress and in emergen- tems (6th ed.). Australia:. Thomson Brooks/Cole. cies. It prepares© Jones the body & forBartlett action, deepeningLearning, LLCTortora, G. J., & Derrickson, B. H. (Eds.).© Jones (2011).(13th & Bartletted) Learning, LLC respirations, making the heart beat faster, dilating Principles of anatomy and physiology (13th ed.). Hobo- NOT FOR SALE OR DISTRIBUTIONken, NJ:. John Wiley and Sons. NOT FOR SALE OR DISTRIBUTION the pupils, stimulating production of stress hor- Widmaier, E., Raff, H., & Strang, K. (Eds.). (2010). Vander’s mones, and increasing blood supply to the large human physiology: The mechanisms of body function. muscles of the body. New York: McGraw-Hill.