CHAPTER 3 BASIC NEUROANATOMY AND CRANIAL NERVES

Nervous Tissue 66

Central Nervous System 68

Peripheral Nervous System 72

Cranial Nerves 74

Clinical Correlates 103

CHAPTER 3

BASIC NEUROANATOMY ANDCRANIAL NERVES

Nervous TissueGENERAL INFORMATIONNervous tissue is divided into 2 major cell types:● Neurons● Neuroglial cells (the neuroglia)

NEURONS

The structural and functional cells in the nervous system

Respond to a nervous stimulus and conduct the stimulus along the length of the cell

A neuron’s cell body is called the perikaryon, or soma

Cell bodies are classified by their location:● Ganglion—a collection of nerve cell bodies located in the peripheral nervous system

(e.g., dorsal root ganglion, trigeminal ganglion, ciliary ganglion)● Nucleus—a collection of nerve cell bodies located in the central nervous system (e.g.,

Edinger-Westphal nucleus, chief sensory nucleus of cranial nerve V, motor nucleus ofcranial nerve VII)

Neuron’s cell bodies contain typical cellular organelles within their cytoplasm:● Mitochondria● Nucleus● Nucleolus● Ribosomes● Rough endoplasmic reticulum (Nissl substance)● Neurotubules● Golgi apparatus● Lysosomes

Neurons have 2 types of processes that extend from the nerve cell body:● Dendrite—process that carries nerve impulses toward the nerve cell body; neurons may

have multiple dendrites● Axon—process that carries nerve impulses away from the nerve cell body; neurons can

have only 1 axon

3 major types of neurons:● Unipolar—has only 1 process from the cell body (sensory neurons)● Bipolar—has 2 processes from the cell body: 1 dendrite and 1 axon (sensory neurons;

located only in the retina, olfactory epithelium, and the vestibular and cochlear ganglia)● Multipolar—has 3 or more processes from the cell body: 2 or more dendrites and 1

axon (motor neurons and interneurons)

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66 NETTER’S HEAD AND NECK ANATOMY FOR DENTISTRY

Axon

DendritesDendritic spines(gemmules)

Rough endoplasmic reticulum

(Nissl substance)Ribosomes

Mitochondrion

NucleusNucleolus

Axon hillock

NeurotubulesGolgi apparatus

Lysosome

Cell body(soma)

Satellite cellsSchwann cellMyelinated fibersFree nerve endingsEncapsulated ending

Specialized ending

Muscle spindle

Multipolar neuron

Oligodendrocyte

Multipolar somatic motor cell

Myelinated somatic motor fiberMyelin sheath

Striated (voluntary) muscle Motor endplate with Schwanncell cap

AstrocyteCollateral

Blood vessel

Bipolar cell of cranial n. VIIIUnipolar cell ofsensory ganglia

Red: Motor neuronBlue: Sensory neuron

Purple: InterneuronGray: Glial and

neurilemmalcells and myelin

Interneurons

Nervous TissueNEUROGLIANeuroglia is the supporting nervous tissue for neurons, although neuroglial cells alsohave assistive roles in neuron function

Neuroglial cells have only 1 type of process

Classification:● Astrocytes—located in the central nervous system; help keep neurons in place, provide

nutritional support, regulate the extracellular matrix, form part of the blood-brainbarrier

● Oligodendrocytes—located in the central nervous system; responsible for axonmyelination in the central nervous system; 1 oligodendrocyte can myelinate 1 segmentof multiple axons

● Microglia—located in the central nervous system; responsible for phagocytosis toremove waste

● Schwann cells—located in the peripheral nervous system; responsible for axonmyelination in the peripheral nervous system; 1 schwann cell can myelinate 1segment of 1 axon

● Satellite cells—located in the peripheral nervous system; surround the nerve cell bodiesof ganglia

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BASIC NEUROANATOMY AND CRANIAL NERVES 67

Neuron

Ventricle

Ependyma

AxonAstrocyte

Perivascularpericyte

Oligodendrocyte

Microglialcell

Astrocyte foot process

CapillaryPia mater

Tanycyte

Central Nervous SystemGENERAL INFORMATIONThe central nervous system is composed of the:● Brain● Spinal cord

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Short gyri

Occipital pole

Inferior temporal gyrus

Superior temporal gyrusTemporal pole

Anterior ramusAscending ramusLateral (sylvian) fissure

Frontal pole

Inferior frontal gyrus

Middle frontal gyrus

Superior frontal gyrus

Precentral sulcusPrecentral gyrus

Central sulcus

Superior parietal lobule

Intraparietal sulcus

Inferior parietallobule

Angular gyrus

Postcentral gyrus

Posterior ramus

Circular sulcus of insulaCentral sulcus of insula

Occipital lobe

Parietal lobe

Frontal lobe

Temporal lobe

LimenInsulaLong gyrus

Central Nervous SystemBRAINCEREBRUM

The surface of the cerebral cortex of the brain is divided by:● Gyri (singular gyrus)—the elevations of brain tissue on the surface● Sulci (singular sulcus)—the grooves or fissures located between the gyriThere are 3 large sulci that help divide the cerebral hemispheres into 4 of its lobes:● Central sulcus (of Rolando)—divides frontal lobe from parietal lobe● Lateral sulcus (of Sylvius)—divides the frontal and parietal lobes from the temporal lobe● Parieto-occipital sulcus—divides the parietal lobe from the occipital lobeThe brain is divided into 5 lobes:● Frontal—motor movement, motor aspect of speech (Broca’s area), reasoning,

emotions, personality, and problem solving● Parietal—sensory perceptions related to pain, temperature, touch and pressure, spatial

orientation and perception, sensory aspect of language (Wernicke’s area)● Temporal—auditory perceptions, learning, and memory● Occipital—vision● Insula—associated with visceral functions including taste

DIENCEPHALON

Composed of 4 parts:● Thalamus—major relay center of the somatosensory system and parts of the motor system● Hypothalamus—controls the autonomic nervous system and endocrine system● Epithalamus—major structures include the pineal gland (which controls circadian

rhythms) and the habenula● Subthalamus—an extrapyramidal nucleus of the motor system; if lesioned, will result in

a contralateral hemiballismus

BRAINSTEM

Composed of 3 parts:● Midbrain● Pons● Medulla

CEREBELLUM

Part of the motor systemReceives sensory input of all forms that use the deep cerebellar nucleiAssociated with:● Equilibrium● Posture● Tone of axial muscles● Gait

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Corpus callosum

Lingual gyrus

Pineal gland

Cerebellum

Interthalamic adhesion

Hypothalamic sulcus

Optic chiasm

Pituitary gland (anterior and posterior)Midbrain

Medulla oblongataPons

AP

CuneusThalamus

SPINAL CORDThe caudal continuation of the central nervous system

Begins at the caudal end of the medulla and ends at vertebral level L1–2, tapering intothe conus medullaris

Has 2 enlargements associated with the limbs:● Cervical—associated with the upper limb and found between the spinal cord at levels

C4 to T1● Lumbosacral—associated with the lower limb and found between the spinal cord at

levels L1 to S2

Composed of:● Gray matter—location of nerve cell bodies and neuroglial cells● White matter—location of the axons and neuroglial cells

Has 5 levels:● Cervical—8 spinal nerves● Thoracic—12 spinal nerves● Lumbar—5 spinal nerves● Sacral—5 spinal nerves● Coccygeal—1 spinal nerve

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Central Nervous System

C11st cervical n.

Cervical enlargementC78th cervical n.

T11st thoracic n.

Spinal dura materFilaments of nerve root

T12Lumbosacral enlargement12th thoracic n.L11st lumbar n.Conus medullarisCauda equinaL55th lumbar n.S11st sacral n.Filum terminale5th sacral n.

CoccyxCoccygeal n.

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Rami communicantes

Dura mater

Dorsal root

Dorsal root (spinal) ganglion

Arachnoid

Subarachnoid space

Pia mater (overlying spinal cord)

Filaments of dorsal root

Denticulate ligament

Gray matter

Anterior view

Posterior view

Filaments of dorsal root

White matterDorsal root

Dorsal root (spinal) ganglion

Spinal nerveVentral root

Filaments of ventral root

Anterior median fissure

C5 T2 T8

L1 L3S1

S3

Sections through spinal cord at various levels

Central Nervous SystemSPINAL CORD CONTINUED

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Peripheral Nervous SystemGENERAL INFORMATIONPeripheral nervous system is that portion of the nervous system located external to thecentral nervous system

Consists of:● Cranial nerves—12 pairs● Spinal nerves—31 pairs

Can be subdivided into:● Somatic nervous system—voluntary system associated with afferent (sensory) and

efferent (motor) fibers● Autonomic nervous system—involuntary system associated with homeostasis of the

body

Dorsalcolumn

Dorsalroot

Ventral root

Sensory neuron ofabdominal viscera

Neuroeffector junctions on smoothmuscle, cardiac muscle, secretoryglands, metabolic cells, immune cells

Preganglionic sympathetic neuronspassing to synapse in anothersympathetic chain ganglion

Vascular smoothmuscle, sweatglands, andarrector pili

muscles in skin

White ramuscommunicans

Gray ramus communicans

Sympathetic chain ganglion

Splanchnic nerve

Collateralsympathetic

ganglion

Dorsalramus

Paciniancorpuscle

Ventral ramus

Freeendings

Skeletalmuscle

Skeletalmuscle

Dorsal rootganglion

Sympathetic chain

SensoryMotor

Preganglionicsympathetic

Postganglionicsympathetic

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Oculomotor (III) n.

Facial (VII) n.

Glossopharyngeal (IX) n.

Medulla oblongata

Vagus (X) n.

C1C2

C3C4C5C6C7C8

Sweat gland

T1T2T3T4

Peripheral vessel

T5

T6

T7

T8

T9

T10

T11

Hairfollicle

T12

L1

L2

L3

L4

L5

S1

S2S3S4S5

Coccyx

Ciliary ganglion

Pterygopalatineganglion

Otic ganglion

Submandibularganglion

Greaterthoracicsplanchnic n.

Celiacganglion

Lesse

r tho

racic

splan

chnic

n.

Lowes

t tho

racic

splan

chni

c n.

Sup. mesenteric

ganglion

Lumbarsplanchnic nn.

Hypogastricnn.

Sup.hypogastric

plexus

Inf.mesentericganglion

Pelvic splanchnic nn.

Inf. hypogastric(pelvic) plexus

Sympathetictrunk

Intracranial vessels

Eye

Lacrimal gland

Parotid gland

Sublingual andsubmandibular glands

Peripheral cranialblood vessels

Larynx

Trachea

Bronchi and lungs

Heart

Stomach

LiverGallbladderBile ducts

Pancreas

Adrenal glands

Kidneys

Intestines

Distal colon

Bladder

External genitalia

Parasympathetic fibers

preganglionicpostganglionic

Shownfor only

1 segment

Brown fat

Lymphoid organs

Gra

y

Ram

i com

mun

ican

tes

gray

and

whi

teG

ray

Sympathetic fiberspreganglionic postganglionic

Peripheral Nervous SystemSPINAL NERVES AND CRANIAL NERVES

CHAPTER 3 BASIC NEUROANATOMY AND CRANIAL NERVES

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