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
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