The Brain and Cranial Nerves

14 The Brain and Cranial Nerves

PowerPoint® Lecture Presentations prepared by Jason LaPres Lone Star College—North Harris

• Learning Outcomes • 14-1 Name the major brain regions, vesicles, and ventricles, and describe the locations and functions of each. • 14-2 Explain how the brain is protected and supported, and discuss the formation, circulation, and function of cerebrospinal fluid. • 14-3 Describe the anatomical differences between the medulla oblongata and the spinal cord, and identify the main components and functions of the medulla oblongata.

• Learning Outcomes • 14-4 List the main components of the pons, and specify the functions of each. • 14-5 List the main components of the cerebellum, and specify the functions of each. • 14-6 List the main components of the midbrain, and specify the functions of each. • 14-7 List the main components of the diencephalon, and specify the functions of each.

• Learning Outcomes • 14-8 Identify the main components of the limbic system, and specify the locations and functions of each. • 14-9 Identify the major anatomical subdivisions and functions of the cerebrum, and discuss the origin and significance of the major types of brain waves seen in an electroencephalogram. • 14-10 Describe representative examples of cranial reflexes that produce somatic responses or visceral responses to specific stimuli.

© 2012 Pearson Education, Inc. • In the pre-synaptic neuron, an Synapse electrical signal comes in, opens up to voltage-gated channels, and signals the vesicles containing neurotransmitters (chemical signal) to be released into the synaptic cleft. Pre-synaptic neuron • Receptors on the post-synaptic neuron bind to the neurotransmitter signaling it to open its gate and let ions flow through. • The flow of ions will generate a current that changes the resting Synaptic cleft membrane potential. If the membrane Glutam potential passes the threshold, then ate an action potential is produced. • The action potential is then propagated to the next neuron, and Post-synaptic the communication continues from neuron neuron to neuron. AMP NMD AR AR

An Introduction to the Brain and Cranial Nerves

• The Adult Human Brain

• Ranges from 750 cc to 2100 cc

• Contains almost 97% of the body’s neural tissue

• Average weight about 1.4 kg (3 lb)

© 2012 Pearson Education, Inc. Brain Summary • Important component of the CNS. • Site for coordination and integration of sensations, emotions, memory, and behavior. • Divided into 6 regions (cerebrum, cerebellum, diencephalon, mesencephalon, pons, and medulla oblongata) • Protected by 3 connective tissue meninges: dura mater, arachnoid, and the pia mater—just like the spinal cord. • Large blood vessels called dural sinuses can be found between 2 layers of dura mater. • The subarachnoid space is filled with CSF • Cranial nerves emerge from various parts of the brain • The brain contains both gray matter and white matter • Gray = interneurons and neuroglia • White = fiber tracts © 2012 Pearson Education, Inc.

14-1 The Brain

• Six Regions of the Brain 1. Cerebrum 2. Cerebellum 3. Diencephalon 4. Mesencephalon (midbrain)

5. Pons Brain Stem 6. Medulla oblongata

• Cerebrum

• Largest part of brain

• Controls higher mental functions

• Divided into left and right cerebral hemispheres

• Surface layer of gray matter (neural cortex)

• Cerebrum

• Neural cortex

• Also called cerebral cortex

• Folded surface increases surface area

• Elevated ridges (gyri)

• Shallow depressions (sulci)

• Deep grooves (fissures)

• Cerebellum

• Second largest part of brain

• Coordinates repetitive body movements

• Two hemispheres

• Covered with cerebellar cortex

Left cerebral hemisphere Gyri

CEREBRUM Sulci

• Conscious thought processes, Fissures intellectual functions • Memory storage and processing • Conscious and subconscious regulation of skeletal muscle contractions

CEREBELLUM • Coordinates complex Spinal somatic motor cord patterns • Adjusts output of other somatic motor centers in brain and spinal cord

• Diencephalon

• Located under cerebrum and cerebellum

• Links cerebrum with brain stem

• Three divisions of the diencephalon

1. Epithalamus

2. thalamus

3. Hypothalamus

• Diencephalon

• Thalamus

• Relays and processes sensory information

• Hypothalamus

• Hormone production

• Emotion

• Autonomic function

• Diencephalon

• Pituitary gland

• Major endocrine gland

• Connected to hypothalamus

• The Brain Stem

• Processes information between:

• Spinal cord and cerebrum or cerebellum

• Includes:

• Midbrain

• Pons

• Medulla oblongata

• Midbrain

• Also called mesencephalon

• Processes sight, sound, and associated reflexes

• Maintains consciousness • Pons

• Connects cerebellum to brain stem

• Is involved in somatic and visceral motor control

• Medulla Oblongata

• Connects brain to spinal cord

• Relays information

• Regulates autonomic functions

• Heart rate, blood pressure, and digestion

THALAMUS • Relay and processing centers for sensory information

HYPOTHALAMUS • Centers controlling emotions, autonomic functions, and hormone production

MIDBRAIN Brain • Processing of visual stem and auditory data • Generation of reflexive somatic motor responses • Maintenance of consciousness

PONS • Relays sensory MEDULLA OBLONGATA information to cerebellum and • Relays sensory information to thalamus and thalamus to other portions of the brain stem • Subconscious • Autonomic centers for regulation of visceral somatic and visceral function (cardiovascular, respiratory, and motor centers digestive system activities) © 2012 Pearson Education, Inc. 14-1 The Brain

• Ventricles of the Brain

• Within the brain are 4 spaces called ventricles

• 2 lateral ventricles • Third ventricle • Fourth ventricle

• Connects with third ventricle via narrow canal in midbrain called the cerebral aqueduct

Lateral ventricles

Third ventricle

Cerebral aqueduct

Fourth ventricle Pons Medulla oblongata Spinal cord Central canal Ventricular system, lateral view © 2012 Pearson Education, Inc. Figure 14-2b Ventricles of the Brain Ventricles of Cerebral hemispheres the Brain

Lateral ventricles

Third ventricle

Fourth ventricle

Central canal Cerebellum

Ventricular system, anterior view

• The Brain

• The brain is a large, delicate mass of neural tissue • Containing internal passageways and chambers filled with cerebrospinal fluid • Each of the six major brain regions has specific functions • Ascending from the medulla oblongata to the cerebrum, brain functions become more complex and variable • Conscious thought and intelligence • Are produced in the neural cortex of the cerebral hemispheres

• Physical Protection of the Brain

• Bones of the cranium

• Cranial meninges

• Cerebrospinal fluid

• Biochemical Isolation

• Blood–brain barrier

• The Cranial Meninges

• Have three layers

1. Dura mater

2. Arachnoid mater

3. Pia mater

• Are continuous with spinal meninges

• Protect the brain from cranial trauma

• Dura mater

• Inner fibrous layer

• Arachnoid mater

• Covers brain

• Contacts epithelial layer of dura mater

• Subarachnoid space between arachnoid mater and pia mater

• Pia mater

• Attached to brain surface by astrocytes

14-2 Brain Protection and Support

• Dural Folds

• Folded inner layer of dura mater

• Extend into cranial cavity

• Stabilize and support brain

• Contain collecting veins (dural sinuses)

© 2012 Pearson Education, Inc. Figure 14-3a The Relationship among the Brain, Cranium, and Meninges Dura mater (endosteal layer) Dural sinus Cranium (skull) Dura mater (meningeal layer) Subdural space Arachnoid mater Subarachnoid space Arachnoid trabeculae Pia mater Cerebral cortex

Cerebral cortex

Cerebellum Medulla oblongata Spinal cord

• Cerebrospinal Fluid (CSF) – subarachnoid space is filled with CSF

• Surrounds all exposed surfaces of CNS

• Interchanges with interstitial fluid of brain

• Functions of CSF

• Cushions delicate neural structures

• Supports brain

• Transports nutrients, chemical messengers, and waste products

• Cerebrospinal Fluid (CSF)

• Choroid plexus—site of CSF production

• Specialized ependymal cells and capillaries

• Secrete CSF into ventricles

• Remove waste products from CSF

• Adjust composition of CSF

• Produces about 500 mL of CSF/day

• Cerebrospinal Fluid (CSF)

• CSF circulates:

• From choroid plexus

• Through ventricles

• To central canal of spinal cord

• Into subarachnoid space via two lateral apertures and one median aperture around the brain, spinal cord, and cauda equina

• Blood Supply to the Brain

• Supplies nutrients and oxygen to brain

• Delivered by internal carotid arteries and vertebral arteries

• Removed from dural sinuses by internal jugular veins

• Blood–Brain Barrier (BBB)

• Isolates CNS neural tissue from general circulation

• Formed by network of tight junctions

• Between endothelial cells of CNS capillaries

• Lipid-soluble compounds (O2, CO2) and steroids • Diffuse into interstitial fluid of brain and spinal cord • Astrocytes control blood–brain barrier by:

• Releasing chemicals that control permeability of endothelium

• Blood–CSF Barrier

• Formed by special ependymal cells

• Surrounds capillaries of choroid plexus

• Limits movement of compounds transferred

• Allows chemical composition of blood and CSF to differ

• Protection and Support

• Meninges stabilize brain in cranial cavity

• Cerebrospinal fluid protects against sudden movement

• CSF provides nutrients and removes wastes

• Blood–brain barrier and blood–CSF barrier

• Selectively isolate brain from chemicals in blood that might disrupt neural function

• The Medulla Oblongata

• Allows brain and spinal cord to communicate

• Coordinates complex autonomic reflexes

• Controls visceral functions

• Sensory and Motor Nuclei of the Medulla Oblongata

• Associated with 5 of 12 cranial nerves (VIII, IX, X, XI, XII)

Figure 14-5a The Diencephalon and Brain Stem

Diencephalon Cerebral peduncle Lateral geniculate nucleus Thalamus Optic tract Medial geniculate nucleus

Cranial nerves Midbrain N II Superior colliculus Inferior colliculus N III N IV Cerebellar peduncles Superior cerebellar peduncle N V

Pons Middle cerebellar peduncle N VI N VII Inferior cerebellar peduncle N VIII N IX N X N XI Medulla oblongata N XII Spinal

nerve C1

Spinal Spinal cord nerve C2

• The pathway from spinal cord to brain through which all ascending (sensory) and descending (motor) fibers pass. Many of the nuclei involved in basic survival processes such as coughing, sneezing, sweating, and chewing are found here as well as nuclei that control the heart rate, respiratory rate, and blood pressure.

• The Pons

• Sensory and motor nuclei of cranial nerves (V, VI, VII, VIII) • “the bridge” contains fiber tracts that connect the medulla and midbrain as well as transverse tracks between left and right cerebellar hemispheres.

Tracts Respiratory Centers Ascending tracts Descending tracts Pneumotaxic center Apneustic center

Transverse fibers Cerebellum Midbrain Fourth ventricle

Pons Medulla oblongata

Reticular formation Medulla Olivary nucleus oblongata

Spinal cord

Lateral view

• Located in the posterior part of the brain, it plays an important role in motor control, interpreting textures of objects, some spatial perception, understanding some aspects of speech, and time keeping.

• It is the second largest part of the brain and externally exhibits gyri and folia

• Functions of the Cerebellum

1. Adjusts postural muscles

2. Fine-tunes conscious and subconscious movements

Vermis

Primary Anterior fissure lobe

Posterior lobe Folia

Left Hemisphere Right Hemisphere of Cerebellum of Cerebellum

The posterior, superior surface of the cerebellum, showing major anatomical landmarks and regions

Midbrain

Anterior lobe

Cerebellar Arbor Peduncles Pons vitae Superior cerebellar Cerebellar peduncle nucleus

Middle cerebellar Cerebellar peduncle cortex Inferior cerebellar Posterior peduncle lobe Choroid plexus of the fourth ventricle Medulla oblongata Flocculonodular lobe

• Structures of the Midbrain

• Two pairs of sensory nuclei (corpora quadrigemina)

• Superior colliculus (visual)

• Inferior colliculus (auditory) • Summary

• The corpora quadrigemina control reflexes of the eye and ear. Fiber tracts extend between the pons and cerebrum and between the midbrain and the cerebellum. Contains nuclei of cranial nerves III and IV. © 2012 Pearson Education, Inc. Figure 14-8a The Midbrain

Pineal Thalamus gland

Red nucleus Substantia nigra

Corpora quadrigemina Cerebral Superior peduncle colliculus Inferior colliculus

• The Diencephalon

• Integrates sensory information and motor commands

• Thalamus, epithalamus, and hypothalamus

• Thalamus: site of some aspects of emotion and memory; relay and filter to the cerebrum for the special senses and motor activity

• Hypothalamus: Inferior to the thalamus. The major controller of the autonomic nervous system and the link between the nervous system and much of the endocrine system via its connection with the pituitary gland. It is also involved in memory, thermoregulation, satiety, thirst, sleep, and emotion.

• Epithalamus: contains the pineal gland (endocrine in function) and a relay from the limbic system to the midbrain.

• The Cerebrum

• Is the largest part of the brain

• Controls all conscious thoughts and intellectual functions

• Processes somatic sensory and motor information

• The Cerebrum Summary

• Forms the bulk of the brain, is folded superficially to form ridges (gyri) and grooves (sulci).

• A longitudinal fissure divides the cerebrum into 2 cerebral hemispheres. Each hemisphere is further subdivided into 5 lobes: frontal, parietal, temporal, insula, and occipital.

Central sulcus

FRONTAL LOBE PARIETAL LOBE

OCCIPITAL LOBE Lateral sulcus

TEMPORAL LOBE Cerebellum Pons Medulla oblongata Lateral view, cadaver brain

Precentral Central Postcentral gyrus sulcus gyrus

FRONTAL PARIETAL LOBE LOBE

OCCIPITAL LOBE

TEMPORAL Lateral sulcus LOBE Cerebellum Pons Medulla oblongata Lateral view

Insula

Retractors along the lateral sulcus showing the insula

Precentral gyrus Central sulcus Postcentral gyrus

Cingulate gyrus PARIETAL LOBE

FRONTAL LOBE Parieto- occipital sulcus

OCCIPITAL LOBE

Pons TEMPORAL LOBE Cerebellum

Medulla oblongata Midsagittal section

• The cerebrum receives sensory information from both internal and external stimuli. Within the cerebral gray matter, this information is evaluated in conjunction with memory and is used to coordinate motor output .

• The fiber tracts (white matter) of the brain serve to receive or send information to the rest of the body (projection tracts), cross from one cerebral hemisphere to the other (commissural tracts such as the corpus collosum), or connect different regions within one hemisphere (association tracts).

• Three Functional Principles of the Cerebrum

1. Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of the body

2. The two hemispheres have different functions, although their structures are alike

3. Correspondence between a specific function and a specific region of cerebral cortex is not precise

Projection fibers of internal capsule

Anterior commissure

Anterior view

Primary motor cortex Central sulcus Primary sensory cortex (precentral gyrus) (postcentral gyrus)

Somatic motor association area (premotor cortex) PARIETAL LOBE

Somatic sensory association area FRONTAL LOBE Visual association area Prefrontal cortex OCCIPITAL LOBE Gustatory cortex Visual cortex Insula Auditory association area Lateral sulcus Auditory cortex TEMPORAL Olfactory cortex LOBE

Major anatomical landmarks on the surface of the left cerebral hemisphere. The lateral sulcus has been pulled apart to expose the insula.

• Hemispheric Lateralization

• Functional differences between left and right hemispheres

• Each cerebral hemisphere performs certain functions that are not ordinarily performed by the opposite hemisphere

• The Left Hemisphere • In most people, left brain (dominant hemisphere) controls: • Reading, writing, and math • Decision making • Speech and language • The Right Hemisphere • Right cerebral hemisphere relates to: • Senses (touch, smell, sight, taste, feel) • Recognition (faces, voice inflections)

Left Cerebral Hemisphere

LEFT HAND

Prefrontal cortex

Speech center

C O R P U Writing S C A Auditory cortex L L O S U General interpretive center M (language and mathematical calculation)

Visual cortex (right visual field)

Right Cerebral Hemisphere

RIGHT HAND

Prefrontal cortex

Anterior commissure C O R P U S Analysis by touch C A Auditory cortex L L O S U M Spatial visualization and analysis

Visual cortex (left visual field)

• Cranial Nerves

• 12 pairs connected to brain

• Four Classifications of Cranial Nerves

1. Sensory nerves carry somatic sensory information, including touch, pressure, vibration, temperature, and pain

2. Special sensory nerves carry sensations such as smell, sight, hearing, balance

3. Motor nerves: axons of somatic motor neurons

4. Mixed nerves: mixture of motor and sensory fibers

• Cranial Nerves • Are classified by primary functions • May also have important secondary functions • Distributing autonomic fibers to peripheral ganglia • The 12 cranial nerve groups are identified by: • Primary function • Origin • Pathway • Destination

© 2012 Pearson Education, Inc. Cranial Nerve Nerve Type Major Functions I: Olfactory sensory smell II: Optic sensory vision III: Oculomotor primarily motor eyeball and eyelid movement; lens shape eyeball movement; proprioception (superior oblique IV: Trochlear primarily motor muscle) sensations of touch and pain from facial skin, nose, V: Trigeminal: sensory mouth, teeth, and tongue; proprioception motor control of chewing VI: Abducens primarily motor eyeball movement; proprioception (lateral rectus muscle) movement of facial muscles; tear and saliva secretion; VII: Facial mixed sense of taste and proprioception VIII: Vestibulocochlear: cochlear branch sensory hearing VIII: Vestibulocochle-ar: vestibular branch sensory sense of equilibrium sensations of taste, touch, and pain from tongue and pharynx; chemoreceptors (that monitor O and CO ); IX: Glosso-phayrngeal mixed 2 2 blood pressure receptors; movement of tongue and swallowing; secretion of saliva parasympathetic sensation and motor control of smooth X: Vagus mixed muscles associated with heart, lungs, viscera; secretion of digestive enzymes XI: Accessory primarily motor head movement; swallowing; proprioception tongue movement, speech, and swallowing; XII: Hypoglossal primarily motor proprioception

Olfactory bulb: termination of olfactory nerve (I)

Olfactory tract

Optic nerve (II)

Infundibulum

Oculomotor nerve (III)

Pons

Basilar artery

Vertebral artery

Cerebellum

Medulla oblongata

Spinal cord

Optic chiasm

Optic tract

Mamillary body

Trochlear nerve (IV)

Trigeminal nerve (V)

Abducens nerve (VI)

Facial nerve (VII)

Vestibulocochlear nerve (VIII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)

Hypoglossal nerve (XII)

Accessory nerve (XI)

Superior OPTIC Optic OCULOMOTOR TROCHLEAR Superior rectus NERVE (N II) chiasm NERVE (N III) NERVE (N IV) oblique muscle muscle

Trochlea

Levator palpebrae superioris muscle Trigeminal nerve (N V), cut

Inferior Vestibulocochlear oblique nerve (N VIII), cut muscle

Facial nerve Inferior Medial (N VII), cut rectus Ciliary rectus Lateral rectus ABDUCENS muscle ganglion muscle muscle (cut) NERVE (N VI)

Superior orbital fissure Supra-orbital Ophthalmic nerves branch Semilunar Ciliary ganglion ganglion Pons TRIGEMINAL Foramen NERVE (N V) rotundum Maxillary branch Infra-orbital nerve Foramen ovale Lingual nerve Otic ganglion

Submandibular Mandibular ganglion branch

Pterygopalatine ganglion Mental nerve

Pterygopalatine Greater petrosal Geniculate FACIAL ganglion nerve ganglion NERVE (N VII)

Temporal branch

Pons

Zygomatic Posterior branches auricular branch Buccal branch Stylomastoid foramen Chorda tympani nerve Mandibular (with mandibular branch branch of N V) Lingual branch Cervical (with lingual nerve branch of N V)

Submandibular ganglion The origin and branches of the facial nerve

Tympanic cavity Semicircular Vestibular Facial nerve Internal VESTIBULOCOCHLEAR (middle ear) canals branch (N VIII) (N VII), acoustic NERVE (N VIII) cut meatus

N V

Pons

N VI N VII

N IX N XII N X Medulla oblongata N XI

Tympanic membrane Auditory tube Cochlea Cochlear branch (N VIII)

Pons N V N VII N VIII N VI GLOSSOPHARYNGEAL NERVE (N IX) Otic ganglion Medulla oblongata Inferior Superior (jugular) (petrosal) ganglion ganglion Parotid salivary gland Lingual branch Pharyngeal branches

Carotid sinus branch Carotid body

Carotid sinus

Common carotid artery

Superior VAGUS pharyngeal NERVE (N X) branch Pons

Medulla oblongata Auricular branch to external ear Superior ganglion Inferior of vagus nerve ganglion Pharyngeal branch of vagus nerve Superior laryngeal nerve Internal branch Superior laryngeal nerve External branch

HYPOGLOSSAL NERVE (N XII)

ACCESSORY NERVE (N XI) Trigeminal nerve (N V)

Internal branch: to palatal, Medulla oblongata pharyngeal, and laryngeal muscles with vagus nerve Cranial root of N XI

Intrinsic muscles of tongue Spinal root of N XI Styloglossus muscle External Genioglossus muscle branch of N XI

Geniohyoid muscle Spinal cord Hyoglossus muscle Hyoid bone Trapezius muscle

Thyrohyoid muscle Sternocleidomastoid muscle Sternohyoid muscle Ansa cervicalis Sternothyroid muscle (cervical plexus)

Omohyoid muscle