Chapter 8:

Nervous System

Jan Carver, MSHS, RDH

NERVOUS SYSTEM OVERVIEW

Central Nervous System

Peripheral Nervous System

Cranial Nerves

Nervous System Outline

1. Define and pronounce all the key terms

and anatomic terms in this lecture.

2. Describe the components of the nervous

system and outline the actions of nerves.

3. Discuss the divisions of the central and

peripheral nervous systems.

4. Integrate an understanding of head and

neck nerves into clinical dental practice.

Learning Objectives

6. Discuss the nervous system pathology

associated with the head and neck region.

7. Correctly complete the review questions and

activities for this lecture.

8. Integrate an understanding of head and neck

nerves into clinical dental practice.

Learning Objectives

(cont.)

It adds to the general background of

pathology involving head and neck muscles,

the temporomandibular joint, and the

salivary glands.

The dental professional involved in the

administration of local anesthesia must have

a sufficient understanding of the nervous

system of the head and neck.

Why Study the Nervous

System?

Nervous SystemOverview

Nerve tissue is a separate classification of

body tissue.

Contains a network of specialized cells

(neurons) that coordinate actions and

transmit signals between different parts of

the body

The nervous system:

– Regulates body systems

– Causes muscles to contract

– Stimulates glands to secrete

– Allows sensation to be felt

The Nervous System

Two Divisions: Central Nervous

System (CNS) =

brain, spinal cord

Peripheral Nervous

System (PNS) =

nerves

The Nervous System

Nervous System Overview

Descriptive

Terminology

NerveNerve—a bundle of neural processes outside the CNS

and within the PNS

NeuronsNeuron—a nerve cell containing:A nucleus

Dendrites—conduct impulses toward the cell body

Axons—conduct impulses away from the cell body

Afferent and Efferent Nerves Afferent (sensory) neurons—transmit impulses from the

periphery of the body toward the CNS (e.g. taste, pain,

proprioception)

Efferent (motor) neurons—transmit information from the

brain to the periphery of the body, toward a body

structure

Carries information to the muscles to activate them

A nerve cell leading from the eye to the brain and carrying visual information is a part of the afferent nervous system.

A nerve cell leading from the brain to the muscles controlling the eye’s movement is a part of the efferent nervous system.

Afferent and Efferent Nerves

Myelin SheathMyelin sheath—fatty tissue wrapped around the axons

that insulates and protects the nerve fibers

NodesNodes—small spaces between the sheaths for

speeding the conduction of an impulse

{

Synapse

Synapse—A

junction point

where the

transmission of

nerve impulses

occurs between

two neurons or

between a

neuron and an

effector organ

GanglionGanglion—A collection of nerve cells outside the CNS

(pl. ganglia)

Perception—3 Types

Exteroception—receives stimuli from outside the

body (pain, sight, hearing, etc.)

Intraception—stimuli from inside the body (thirst,

hunger, etc.)

Perception—3 Types

Proprioception—muscle sense

Perception—3 Types

Nervous System:

How it Works

Resting Potential

Action Potential

Neurons Have a “Charge”

Plasma membrane has a resting potential of -70mv

fluid outside cell = positive charge

fluid inside cell = negative charge

Sodium ions more concentrated outside the cell

Potassium ions more concentrated inside the cell

imbalance is maintained by the sodium-potassium pump

which actively* transports ions against their concentration

gradients

Resting Potential

• 3 Na+ ions out

for every 2 K+

ions in

* Actively =

requiring

the use of

ATP

Action Potential—a temporary

reversal of the electric potential

along the membrane for a brief

period

Na channels open and Na floods

into the cell (depolarization).

Then the sodium gates close and

the potassium channels open,

flooding K ions out of the cell

(repolarization).

happens in less than a millisecond

the sodium-potassium channel will

reestablish the resting potential

Action Potential

+ 40 mv

Refractory Period =

brief period after the

action potential where

a membrane cannot be

stimulated

Action Potential (cont.)

+ 40 mv

The neurotransmitter released from the neuron will initiate an action depending on the type of neurotransmitter released. Excitatory

Neurotransmitters (ex: acetylcholine, norepinephrine)

InhibitoryNeurotransmitters (ex: dopamine, seratonin)

Action Potential (cont.)

Local anesthetics mimic inhibitory neurotransmitters by decreasing the sensory neurons’ ability to create an action potential, thus producing localized anesthesia Block the Na channel, so Na can’t rush in, so can’t

depolarize!

No action potential No impulse No sensation

Anesthesia = loss of feeling or sensation resulting from the use of drugs or gasses

Anesthetics

1. Resting Potential: -70mv

2. Depolarization: Na floods in

3. Action Potential: +40mv —

*Nerve impulse

4. Repolarization: K floods out

5. Refractory Period: break time

6. Resting Potential: -70mv

3 Na pumped out for every 2 K in

In Summary

Central Nervous System

Made up of the:

• Brain

• Spinal column

Brain

Divisions

• Cerebrum

• Cerebellum

• Diencephalon

• Brainstem

Cerebrum

5 Lobes

• Frontal—controls

abstract thought &

voluntary muscles

• Parietal—integrates

incoming stimuli;

contains center for

speech and conscious

sensations

• Temporal—hearing

• Occipital—vision

• Insula—function

unknown

Cerebellum

Made up of

two

hemispheres

Controls

muscle

coordination

DiencephalonContains the thalamus & hypothalamus

– Thalamus—serves as a central relay point for

incoming nerve impulses

– Hypothalamus—regulates homeostasis

» Thirst, hunger, body temperature, blood pressure

Brain Stem3 Divisions

• Midbrain—includes relay

stations for hearing,

vision, and motor

pathways

• Pons—contains nuclei of

various nerves, including

the facial & trigeminal

nerves

• Medulla oblongata—

contains center for

certain vital functions

such as breathing,

vascular control, and

heart rate

Imaging: Brain and Spinal Cord

Dissection: Brain and Spinal

Cord

Nervous SystemPeripheral Nervous System

Peripheral Nervous System

All of the nerves outside of the central nervous

system

The PNS is further divided into the

afferent nervous system or sensory

nervous system, which carries

information from receptors to the brain

or spinal cord, and the efferent

nervous system or motor nervous

system, which carries information from

the brain or spinal cord to muscles or

glands.

Peripheral Nervous System

Nervous

System

PNS: Somatic and Autonomic

The efferent

division of the

PNS is further

subdivided into

the somatic

nervous system

and the

autonomic

nervous

system.

Autonomic Nervous System

Operates without conscious control

Efferent for smooth & cardiac muscle &

glands

Afferent

Impulses carried by both spinal and

cranial nerves

Subdivisions:Sympathetic—“fight or flight” stress

response, such as the shutdown of salivary

gland secretion

Parasympathetic—returns the body to

normal after “fight or flight”

A subdivision of the efferent division of the PNS

Includes all nerves controlling the muscular system

and external sensory receptors

Involves both receptors and effectors

Spinal nerves

• Both afferent and efferent

• 31 pairs of nerves designated by the spinal

foramen by which they exit

C1 to C8 T1 to T12 L1 to L5 S1 to S5 Coccygeal

Cranial nerves

Somatic Nervous System

Chapter 8:

Nervous System: Cranial Nerves

Jan Carver, MSHS, RDH

1. Define and pronounce all the key terms and anatomic terms in this lecture.

2. Identify and trace the routes of the cranial nerves on a diagram and skull.

3. Discuss the innervation of each of the cranial nerves.

4. Discuss the nervous system pathology associated with the head and neck region.

5. Correctly complete the review questions and activities for this lecture.

6. Integrate an understanding of head and neck nerves into clinical dental practice.

Learning Objectives

Cranial Nerves12 paired cranial

nerves connected

to the brain at its

base

Passes through the

skull by way of

fissures or foramina

Designated by both

Roman numerals (I

to XII) and

anatomic terms

Either afferent,

efferent, or both

Cortical Homunculus

Afferent component Sensory perception—Pain, touch,

temperature, and pressure

Proprioception—sense of movement

Skeletal muscle, skin, oral mucosa,

alveolar bone, teeth, and TMJ

Efferent component Provides motor function to the muscles of

mastication & muscles of facial expression

Both efferent and afferent

Cranial Nerves

Entrances & Exits

Afferent

Transmits smell from nasal mucosa to brain

Enters skull through cribriform plate (ethmoid)

Cranial Nerve I (Olfactory)

Olfactory Bulb

w/ olfactory

Nerves

Afferent

Transmits sight from retina to brain

Enters skull through optic canal (sphenoid)

Cranial Nerve II (Optic)

Efferent

Transmits to muscles of the eye

Exits skull through superior orbital fissure (sphenoid)

Cranial Nerve III (Oculomotor)

Efferent

Transmits to one muscle of the eye

Exits skull through superior orbital fissure (sphenoid)

Cranial Nerve IV (Trochlear)

Largest Cranial Nerve

Efferent AND Afferent Components Sensory Root

Motor Root = tomuscles of mastication

3 divisions enter/exit skull through different openings

*The trigeminal nerve will be covered in greater detail later.

Cranial Nerve V (Trigeminal)

Efferent

Transmits to muscle of the eye

Exits skull through superior orbital fissure

(sphenoid)

Cranial Nerve VI (Abducens)

Efferent AND Afferent

Component

Transmits to muscles of facial

expression & lacrimal gland

Transmits sensation from skin

behind ear, and the tongue’s

taste sensation

Exits cranial cavity through the

internal acoustic meatus (71),

travels through the facial canal

(temporal bone), then exits the

skull through the stylomastoid

foramen (73)

*The facial nerve will be covered

in greater detail later.

Cranial Nerve VII (Facial)

Afferent

Transmits signals from

inner ear to brain

Vestibular Portion:

balance (semicircular

canals)

Cochlear Portion:

hearing (cochlea)

Enters skull through

internal acoustic

meatus (temporal)

Cranial Nerve VIII

(Vestibulocochlear)

Efferent AND Afferent

Component

Transmits to

stylopharyngeus muscle

and parotid gland

Transmits sensation from

middle ear, pharynx AND

sensation/taste from base

of tongue

Passes through jugular

foramen (occipital/

temporal)

Cranial Nerve IX

(Glossopharyngeal)

GP

Efferent AND Afferent

Component

Transmits to muscles of the

soft palate, pharynx, larynx

Parasympathetic fibers to:

thymus, heart, stomach, and

more

Transmits sensation from skin

around ear, and taste

sensation of epiglottis

Passes through skull via

jugular foramen

(occipital/temporal)

Cranial Nerve X (Vagus)

Efferent

Transmits to muscles of

neck, soft palate, and

pharynx

Two roots (and only

partly a cranial nerve)

One arising from brain

One arising from spinal

cord

Exits skull through

jugular foramen

(occipital/temporal)

Cranial Nerve XI (Accessory)

Efferent

Transmits to

intrinsic/extrinsic

tongue muscles

Exits skull through

hypoglossal canal

(occipital)

Cranial Nerve XII (Hypoglossal)

Out On Our Table Top Are Fruits, Very Green Veggies,

And Hamburgers

Oh, Once One Takes The Anatomy Final, Very Good

Vacations Are Heavenly

Odor Of Orangutan Terrified Tarzan After Forty

Voracious Gorillas Viciously Attacked Him

On Occasion Our Trusty Truck Acts Funny, Very Good

Vehicle Any How

Olfactory, Optic, Oculomotor, Trochlear, Trigeminal,

Abducens, Facial, Vestibulocochlear, Glossopharyngeal,

Vagus, Accessory, Hypoglossal

Cranial Nerve Name

Mnemonics

S=Sensory M=Motor B=Both

SSMMBMBSBBMM

Some Say Mary Money But My Brother

Says Big Brains Matter More

Some Say Marilyn Monroe But My

Brother Says Bridget Bardot Mmm,

Mmm

Some Say Money Matters, But My

Beloved Says Being Beloved Matters

More

Afferent vs. Efferent

Mnemonics

Cleaners Only Spray Smelly Stuff Right On Smelly Idiots

In J. Jonah Jameson High

Carl Only Swims South. Silly Roger Only Swims In Infiniti

Jacuzzis. Jane Just Hitchhikes.

Mnemonics for Foramina

• Cribriform plate (Olfactory)

• Optic canal (Optic)

• Superior Orbital Fissure (Oculomotor)

• Superior Orbital Fissure (Trochlear)

• Superior Orbital Fissure (Trigeminal - Ophthalmic)

• Foramen Rotundum (Trigeminal -Maxillary)

• Foramen Ovale (Trigeminal -

Mandibular)

• Superior Orbital Fissure (Abducens)

• Internal Acoustic Meatus (Facial)

• Internal Acoustic Meatus (Vestibulocochlear)

• Jugular Foramen (Glossopharyngeal)

• Jugular Foramen (Vagus)

• Jugular Foramen (Accessory)

• Hypoglossal Canal (Hypoglossal)

You have one nose, so the olfactory nerve is CN I, and it

controls the sense of smell and innervates the nose.

You have two eyes, so the optic nerve is CN II, which

functions to produce vision.

CN VII: A mnemonic for the names of the five branches

of the Facial nerve is To Zanzibar By Motor Car, where

the five branches are the Temporal, Zygomatic, Buccal,

Mandibular and Cervical branches.

The number 8 resembles an ear, so CN VIII, the

vestibulocochlear/acoustic nerve is a sensory nerve for

hearing.

Mnemonics for Function

The number 11 can resemble a pair of arms or

shoulders, and CN XI innervates the sternocleidomastoid

and trapezius muscles and controls shoulder and neck

movements.

The saying The tongue licks the wound is a reminder

that when the hypoglossal nerve (CNXII) is damaged, the

tongue deviates to the same side of a lesion to the

cranial nerve. (eg, if the tongue deviates to the right,

the right side of CNXII is damaged).

Mnemonics for Function

Nervous SystemNerves to Oral Cavity and Associated

Structures

Nerves to Oral

Cavity and

Associated

Structures

VII Facial Nerve

Sensory Skin around the ear & anterior tongue; taste

Proprioception

Pathology: loss of taste to the anterior 2/3 of tongue

Motor Muscles of facial expression

Though embedded in the parotid gland, it does not

innervate it.

Pathology: facial paralysis (Bell’s palsy). Causes drooping

of the lower eyelid, sagging of the mouth, & lack of

expression on the affected side. Damage to the parotid

gland can cause facial paralysis.

Autonomic Submandibular & sublingual glands

Pathology: decreased saliva production

Facial Nerve

Facial paralysis is the loss of muscular action of the muscles of facial expression.

Can be unilateral or bilateral, transient or permanent, depending on the nature of the nerve damage

Known as Bell’s palsy

Clinical Note:

Facial Paralysis

Can occur because the facial nerve

branches are superficially located and

vulnerable to trauma

Can occur secondary to a brain injury

by way of a stroke, with other muscles

of the head and neck also affected

May also have no known cause.

Clinical Note:

Facial Paralysis (cont.)

Facial NerveEmerges from the

brain and enters

the internal

acoustic meatus

in the petrous

part of the

temporal bone

Location: It continues

anteriorly, passing

through the parotid

gland, and separates.

Stapedius—a small

efferent branch to

the middle ear (not

shown)

Greater petrosal—

parasympathetic

fibers

Chorda tympani—

parasympathetic

fibers

Facial Nerve

Facial Nerve The main trunk emerges from the skull through the

stylomastoid foramen (73) of the temporal bone and

gives off two branches, the posterior auricular nerve

and a branch to the posterior belly of the digastric

and stylohyoid muscles (not shown).

Facial Nerve It then passes into

the parotid salivary

gland and divides

into numerous

branches to supply

the muscles of facial

expression, but not

the parotid salivary

gland itself.

Greater Petrosal Nerve

Efferent area: fibers

carry through the

pterygopalatine

ganglion in the

pterygopalatine

fossa to the lacrimal

gland, nasal cavity,

& minor salivary

glands of the hard &

soft palate

Afferent area: taste

sensation for the

palate

Chorda Tympani Nerve

Branches

off within

the

petrous

part of the

temporal

bone

Chorda Tympani Nerve Exits the skull by the petrotympanic fissure,

located immediately posterior to the

temporomandibular joint

Chorda Tympani Nerve Then travels with

the lingual nerve

along the floor of

the mouth in the

same nerve bundle

In the

submandibular

triangle, the chorda

tympani nerve,

appearing as part of

the lingual nerve,

communicates with

the submandibular

ganglion.

Chorda Tympani Nerve

• Parasympathetic

efferent:

submandibular &

sublingual salivary

glands

• Afferent area:

taste sensation

from the body of

the tongue

Muscular Branches of the

Facial Nerve

Branches originate

within the parotid

salivary gland to

muscles of facial

expression

Temporal branch Anterior to ear

Frontal belly of

epicranius

Part of orbicularis

oculi

Corrugator supercilii

Muscular Branches of the

Facial Nerve

Zygomatic branch Inferior

orbicularis oculi

Zygomatic major

& minor muscles

Buccal branchMuscles of upper

lip & nose,

buccinator,

risorius, &

orbicularis oris

Muscular Branches of the

Facial Nerve

Mandibular branchLower lip

Mentalis muscle

Cervical branchPlatysma muscle

Clinical Note: Facial Nerve and

Local Anesthesia

Anesthesia of the facial

nerve at its location in

the parotid salivary

gland is a possible

consequence when

administering an

inferior alveolar block

because it may result in

transient facial

paralysis if given

incorrectly.

Clinical Note:

Facial Pain and Parotid Gland Cancer

A neoplastic growth in the parotid salivary

gland may be painful due to the presence of

the facial nerve.

Parotid Gland Cancer