Cranial nerves VIII to XII.pptx

CRANIAL NERVES
MADE BY - DR. NIKITA SAINI- PG 1ST YEAR (2022)
DEPARTMENT OF PAEDIATRIC AND PREVENTIVE DENTISTRY

CONTENT
◦ CRANIAL NERVE VIII – VESTIBULO-COCHLEAR NERVE
◦ CRANIAL NERVE IX – GLOSSOPHARYNGEAL NERVE
◦ CRANIAL NERVE X – VAGUS NERVE
◦ CRANIAL NERVE XI – ACCESSORY NERVE
◦ CRANIAL NERVE XII – HYPOGLOSSAL NERVE

VESTIBULO-COCHLEAR NERVE (VIII)

◦ It is the eight cranial nerve.
◦ It is a sensory cranial nerve since it is responsible for balance and orientation in space and auditory
function.

◦ It contains 2 different parts: (a) a vestibular part, referred to as the
vestibular nerve and (b) a cochlear part, named the cochlear
nerve.
◦ The vestibular nerve is concerned with the maintenance of
equilibrium, while the cochlear nerve is concerned with hearing.

FUNCTIONAL COMPONENT AND NUCLEI

Special somatic afferent fibres: They carry sensory information essential for
the maintenance of equilibrium and hearing from the membranous labyrinth of
the internal ear.
◦ The fibres carrying the sensory info for equilibrium terminate in the vestibular
nuclei inside the brainstem.
◦ The fibres carrying the sensory info for hearing terminate in the dorsal and
ventral cochlear nuclei which are found, respectively, on the dorsal and
ventral aspects of the inferior cerebellar peduncle.

COURSE AND RELATIONSHIPS
◦ The vestibular nerve originates from the lateral aspect of the
pontomedullary junction, goes through the pontocerebellar angle
and enters the internal acoustic meatus together with the facial
nerve and labyrinthine vessels.

◦ The vestibular ganglion (also named Scarpa’s ganglion) lies on the vestibular
nerve in the lateral part of the internal acoustic meatus. It contains bipolar
sensory neurons. In the lateral part of the internal acoustic meatus, the nerve
splits into 3 distinct branches: superior and inferior divisions and remarkable
nerve.

◦ These branches go through the foramina in the fundus of the meatus and
innervate the sensory receptors for equilibrium (cristae ampullaris and
maculae) in the membranous labyrinth of the internal ear.

◦The cochlear nerve also originates from the lateral aspect of the
pontomedullary junction and requires a quite similar course to go
into the internal acoustic meatus.

◦ At the medial end of the internal acoustic meatus, it enters into bony
labyrinth of the middle ear via tractus spiralis foraminosus in the fundus of
the meatus and reaches the modiolus of the internal ear.

◦ In the modiolus, the cochlear nerve possesses a sensory ganglion referred to as
the spiral ganglion made of bipolar neurons. The peripheral process of these
neurons innervates the sensory receptor of hearing- the organ of Corti.

CLINICAL SIGNIFICANCE
The lesions of the vestibulo-cochlear nerve medically
present as:
◦Tinnitus
◦Damage or loss of hearing
◦Decline of balance
VESTIBULAR NERVE is normally damaged by Acoustic
Neuroma

◦ It’s a mixed nerve, i.e., composed of both the motor and sensory
fibres but mainly it’s sensory.
◦ Glossopharyngeal nerve is the 9th cranial nerve.
◦ It derives its name from the truth that it gives sensory innervation to
the tongue and pharynx.

FUNCTIONAL COMPONENT AND NUCLEI
Special visceral
efferent fibres:
They supply the
stylopharyngeus
muscle. They
originate from
nucleus ambiguus.

Special visceral
afferent fibres:
They carry taste
sensations from the
posterior one-third
of tongue consisting
of vallate papillae
and terminate in the
nucleus tractus
solitarius.

◦ General visceral
efferent fibres:
They supply the
secretomotor fibres
to the parotid gland
They originate
from the inferior
salivatory nucleus
and are
preganglionic
parasympathetic
fibres.

◦ General visceral
afferent fibres:
They carry general
sensations of pain, feel
and temperature from
the mucous membrane
of the pharynx, tonsil,
soft palate and the
posterior one-third of
tongue and terminate
in the dorsal nucleus
of the vagus.

General somatic afferent fibres:
They carry proprioceptive sensations from the stylopharyngeus and
skin of the auricle and terminate in the nucleus of the spinal tract of
5th nerve.

Sensory: Innervates the oropharynx, carotid body and sinus, posterior 1/3 of the
tongue, middle ear cavity and Eustachian tube.
Special sensory: Provides taste sensation to the posterior 1/3 of the tongue.
Parasympathetic: Provides parasympathetic innervation to the parotid gland.
Motor: Innervates the stylopharyngeus muscle of the pharynx.
Embryologically, the glossopharyngeal nerve is associated with the derivatives of the
third pharyngeal arch.

The glossopharyngeal nerve
originates in the medulla
oblongata of the brain. It
emerges from the anterior
aspect of the medulla,
moving laterally in the
posterior cranial fossa.
The nerve leaves the
cranium via the jugular
foramen. At this point, the
tympanic nerve arises. It has
a mixed sensory and
parasympathetic
composition.

Immediately outside the
jugular foramen lie two
ganglia (collections of nerve
cell bodies). They are known
as the superior and inferior
(or petrous) ganglia – they
contain the cell bodies of the
sensory fibres in the
glossopharyngeal nerve.

Now extracranial, the
glossopharyngeal nerve
descends down the neck,
anterolateral to the internal
carotid artery.
At the inferior margin of the
stylopharyngeus, several
branches arise to provide
motor innervation to the
muscle. It also gives rise to
the carotid sinus nerve,
which provides sensation to
the carotid sinus and body.

The nerve enters the pharynx
by passing between the
superior and middle
pharyngeal constrictors.
Within the pharynx, it
terminates by dividing into
several branches – lingual,
tonsil and pharyngeal.

SENSORY FUNCTIONS
provides sensory innervation a
variety of structures in the head
and neck.
The tympanic nerve arises as
the nerve traverses the jugular
foramen. It penetrates the
temporal bone and enters the
cavity of the middle ear. Here,
it forms the tympanic plexus –
a network of nerves that
provide sensory innervation to
the middle ear, internal surface
of the tympanic membrane and
Eustachian tube.

At the level of the
stylopharyngeus, the
carotid sinus nerve
arises. It descends
down the neck to
innervate both the
carotid sinus and
carotid body, which
provide information
about blood pressure
and oxygen saturation
respectively.

terminates by splitting into several
sensory branches:
Pharyngeal branch – combines
with fibres of the vagus nerve to
form the pharyngeal plexus. It
innervates the mucosa of the
oropharynx.
Lingual branch – provides the
posterior 1/3 of the tongue with
general and taste sensation
Tonsillar branch – forms a
network of nerves, known as the
tonsillar plexus, which innervates
the palatine tonsils.

Special Sensory Functions
The glossopharyngeal nerve provides taste sensation to the posterior
1/3 of the tongue, via its lingual branch

Motor Functions
The stylopharyngeus muscle of the pharynx is innervated by the
glossopharyngeal nerve. This muscle acts to shorten and widen the
pharynx and elevate the larynx during swallowing.

PARASYMPATHETIC FUNCTIONS
The glossopharyngeal nerve provides parasympathetic innervation to the parotid
gland. These fibres originate in the inferior salivatory nucleus of CN IX. These
fibres travel with the tympanic nerve to the middle ear. From the ear, the fibres
continue as the lesser petrosal nerve, before synapsing at the otic ganglion.

The fibres then hitchhike on the auriculotemporal nerve to the parotid
gland, where they have a secretomotor effect.
Remember – although the facial nerve splits into its five terminal
branches in the parotid gland, it is the glossopharyngeal nerve that
actually supplies the gland.

Clinical testing of Glossopharyngeal nerve
The glossopharyngeal nerve can be examined medically by:
◦ Evoking the gag reflex (i.e., on tickling the posterior wall of the
pharynx, soft palate, or tonsillar fossa, there’s reflex contraction of
pharyngeal muscles causing gagging and retching) and
◦ Examining the taste sensations in the posterior one-third of the
tongue.

The lesion of the glossopharyngeal nerve is uncommon in isolation since
there’s frequently related engagement of the vagus nerve. Yet, the complete
lesion of the glossopharyngeal nerve results in:
oThe loss of flavor and general sensations over the posterior one-third of the
tongue,
oTrouble in swallowing,
oThe decrease of the salivation from the parotid gland and
oThe unilateral reduction of the gag reflex.

GLOSSOPHARYNGEAL NEURALGIA
Glossopharyngeal neuralgia, in spite of the fact that uncommon, may happen.
It’s characterized by paroxysmal episodes of intractable pain in the area of the
sensory distribution of the glossopharyngeal nerve, example, throat, tongue and
ear, precipitated by consuming.

• The vagus nerve is the 10th cranial nerve (CN X).
• It is a functionally diverse nerve, offering many different modalities of innervation
( WANDERING NERVE)
• It is associated with the derivatives of the fourth and sixth pharyngeal arches.
• It’s a mixed nerve, i.e., composed of both the motor and sensory fibres but mostly it
is motor.
• It’s the longest and most widely distributed cranial nerve.

◦ Vagus nerve is also known as
pneumogastric nerve.
◦ It supplies nerves to the pharynx,
esophagus, larynx, trachea,
bronchi, heart, stomach and liver.
◦ Like glossopharyngeal nerve, it
influences the action of
swallowing, it also sends and
transmits signals to our
autonomous system, to help the
regulate activation and control
stress levels or send signals
directly to our sympathetic
system.

ANATOMICAL COURSE
The vagus nerve has the longest course of all the cranial nerves, extending from the
head to the abdomen.
In the Head
The vagus nerve originates from the medulla of the brainstem. It exits the cranium via
the jugular foramen, with the glossopharyngeal and accessory nerves (CN IX and XI
respectively).
Within the cranium, the auricular branch arises. This supplies sensation to the posterior
part of the external auditory canal and external ear.

In the neck
In the neck, the vagus nerve passes into the carotid sheath, travelling inferiorly with
the internal jugular vein and common carotid artery.
At the base of the neck, the right and left nerves have differing pathways:
The right vagus nerve passes anterior to the subclavian artery and posterior to the
sternoclavicular joint, entering the thorax.
The left vagus nerve passes inferiorly between the left common carotid and left
subclavian arteries, posterior to the sternoclavicular joint, entering the thorax.

Several branches arise in the neck:
Pharyngeal branches – Provides motor innervation to the majority of the muscles of
the pharynx and soft palate.
Superior laryngeal nerve – Splits into internal and external branches. The external
laryngeal nerve innervates the cricothyroid muscle of the larynx. The internal laryngeal
provides sensory innervation to the laryngopharynx and superior part of the larynx.
Recurrent laryngeal nerve (right side only) – Hooks underneath the right subclavian
artery, then ascends towards to the larynx. It innervates the majority of the intrinsic
muscles of the larynx.

In the Thorax
In the thorax, the right vagus nerve forms
the posterior vagal trunk, and the left
forms the anterior vagal trunk. Branches
from the vagal trunks contribute to the
formation of the oesophageal plexus,
which innervates the smooth muscle of
the oesophagus.

Two other branches arise in the thorax:
Left recurrent laryngeal nerve – it
hooks under the arch of the aorta,
ascending to innervate the majority of the
intrinsic muscles of the larynx.
Cardiac branches – these innervate
regulate heart rate and provide visceral
sensation to the organ.
The vagal trunks enter the abdomen via
the oesophageal hiatus, an opening in the
diaphragm.

In the Abdomen
In the abdomen, the vagal trunks terminate by dividing into branches
that supply the oesophagus, stomach and the small and large bowel
(up to the splenic flexure).

SENSORY FUNCTIONS OF VAGUS NERVE
1) Somatic refers to sensation from the skin and muscles. This is provided by
the auricular nerve, which innervates the skin of the posterior part of the
external auditory canal and external ear.
2) Viscera sensation is that from the organs of the body. The vagus nerve
innervates:
• Laryngopharynx – via the internal laryngeal nerve.
• Superior aspect of larynx (above vocal folds) – via the internal laryngeal nerve.
• Heart – via cardiac branches of the vagus nerve.
• Gastro-intestinal tract (up to the splenic flexure) – via the terminal branches of
the vagus nerve.

SPECIAL SENSORY FUNCTIONS OF
VAGUS NERVE
The vagus nerve has a minor role in taste sensation. It carries afferent fibres
from the root of the tongue and epiglottis.

MOTOR FUNCTIONS OF VAGUS NERVE
The vagus nerve innervates the majority of the muscles associated with the
pharynx and larynx. These muscles are responsible for the initiation of
swallowing and phonation.

Pharynx
Most of the muscles of the pharynx are
innervated by the pharyngeal branches of
the vagus nerve:
Superior, middle and inferior pharyngeal
constrictor muscles
Palatopharyngeus
Salpingopharyngeus
An additional muscle of the pharynx, the
stylopharyngeus, is innervated by the
glossopharyngeal nerve.

Larynx
Innervation to the intrinsic muscles of the larynx is achieved via the recurrent
laryngeal nerve and external branch of the superior laryngeal nerve.
Recurrent laryngeal nerve:
◦ Thyro-arytenoid
◦ Posterior crico-arytenoid
◦ Lateral crico-arytenoid
◦ Transverse and oblique arytenoids
◦ Vocalis
External laryngeal nerve:
◦ Cricothyroid

Other Muscles
In addition to the pharynx and larynx, the vagus nerve also innervates the
palatoglossus of the tongue, and the majority of the muscles of the soft palate.

PARASYMPATHETIC FUNCTIONS OF VAGUS
NERVE
In the thorax and abdomen, the vagus nerve is the main parasympathetic outflow to the heart
and gastro-intestinal organs.
The Heart
Cardiac branches arise in the thorax, conveying parasympathetic innervation to the sino-atrial
and atrio-ventricular nodes of the heart.
These branches stimulate a reduction in the resting heart rate. They are constantly active,
producing a rhythm of 60 – 80 beats per minute. If the vagus nerve was lesioned, the resting
heart rate would be around 100 beats per minute.

Gastro-Intestinal System
The vagus nerve provides parasympathetic innervation to the majority of the abdominal
organs. It sends branches to the oesophagus, stomach and most of the intestinal tract – up to
the splenic flexure of the large colon.
The function of the vagus nerve is to stimulate smooth muscle contraction and glandular
secretions in these organs. For example, in the stomach, the vagus nerve increases the rate of
gastric emptying, and stimulates acid production
.

Clinical testing of vagus nerve
◦ The vagus nerve can be analyzed medically by requesting the
patient to open his mouth and say ‘ah’ and after that comparing the
palatal arches of the 2 sides.
◦ If the vagus is undamaged, the soft palate rises (is elevated) in the
midline.
◦ In bilateral lesions, the soft palate falls.
◦ In the unilateral lesion, there’s flattening (drooping) of palate arch
on the side of paralysis and uvula pulled to the normal side.

LESIONS OF VAGUS NERVE
The bilateral lesions of vagus nerve cause:
◦nasal regurgitation of the swallowed liquids,
◦nasal twang of voice,
◦hoarseness of voice,
◦flattering of palatal arches
◦dysphagia and
◦reduction of cough reflex.

◦ Accessory nerve is sometimes also named as the spinal nerve or spinal
accessory nerve. It is a motor nerve and controls the movements of the head
and shoulders by supplying the sternocleidomastoid and trapezius muscles.

◦ It is composed of 2 roots, cranial and spinal.
◦ The cranial root is accessory to the vagus and its fibres are dispersed via the
vagus nerve.
◦ The spinal root has a separate course and is normally regarded as spinal
accessory nerve, or merely as accessory nerve.

ANATOMICAL COURSE
Spinal Component
◦ The spinal portion arises from neurons
of the upper spinal cord, specifically
C1-C5/C6 spinal nerve roots. These
fibres coalesce to form the spinal part
of the accessory nerve, which then
runs superiorly to enter the cranial
cavity via the foramen magnum.
◦ The nerve traverses the posterior
cranial fossa to reach the jugular
foramen. It briefly meets the cranial
portion of the accessory nerve, before
exiting the skull (along with the
glossopharyngeal and vagus nerves).

Outside the cranium, the spinal part
descends along the internal carotid
artery to reach the sternocleidomastoid
muscle, which it innervates. It then
moves across the posterior triangle of
the neck to supply motor fibres to the
trapezius.
Note: The extracranial course of the
accessory nerve is relatively
superficial (it runs between the
investing and prevertebral layers of
fascia), and thus leaves it vulnerable
to damage.

ANATOMICAL COURSE
Cranial Component
The cranial portion is much smaller and arises from the lateral aspect of the medulla
oblongata. It leaves the cranium via the jugular foramen, where it briefly contacts the
spinal part of the accessory nerve.
Immediately after leaving the skull, cranial part combines with the vagus nerve (CN X)
at the inferior ganglion of vagus nerve (a ganglion is a collection of nerve cell bodies).
The fibres from the cranial part are then distributed through the vagus nerve. For this
reason, the cranial part of the accessory nerve is considered as part of the vagus nerve.

Motor Function of Accessory N.
◦ The spinal accessory nerve innervates two
muscles – the sternocleidomastoid and trapezius.
Sternocleidomastoid
◦ Attachments – Runs from the mastoid process of
the temporal bone to the manubrium (sternal
head) and the medial third of the clavicle
(clavicular head).
◦ Actions – Lateral flexion and rotation of the
neck when acting unilaterally, and extension of
the neck at the atlanto-occipital joints when
acting bilaterally.

TRAPEZIUS
◦ Attachments – Runs from the base of the skull
and the spinous processes of the C7-T12
vertebrae to lateral third of the clavicle and the
acromion of the scapula.
◦ Actions – It is made up of upper, middle, and
lower fibres. The upper fibres of the trapezius
elevate the scapula and rotate it during abduction
of the arm. The middle fibres retract the scapula
and the lower fibres pull the scapula inferiorly.

Clinical testing of Accessory Nerve
◦ The sternocleidomastoid muscle is examined by asking the patient to turn his
face to the reverse against the opposition given by the examiner’s hand. In a
normal state, someone can do it and sternocleidomastoid stands out
conspicuously.
◦ The trapezius muscle can be examined by asking the patient to shrug his
shoulder against the resistance.

Injury (causes?) to the accessory nerve can be clinically presented as:
◦ Shoulders develop the inability to shrug because the trapezius muscle gets paralyzed.
◦ Head rotation becomes really difficult due to paralysis of the sternocleidomastoid
muscle.
◦ Spasmodic torticollis: It might result from irritative central lesions of the spinal
accessory nerve. It’s defined by clonic spasms of the sternocleidomastoid muscle.

◦ Hypoglossal nerve is the 12th cranial nerve and originates from the
medulla oblongata.
◦ Its name is derived from ancient Greek, ‘hypo‘ meaning under, and
‘glossal‘ meaning tongue.
◦ The nerve has a purely somatic motor function, innervating all the
extrinsic and intrinsic muscles of the tongue (except the palatoglossus,
innervated by vagus nerve).

ANATOMICAL COURSE
◦ The hypoglossal nerve arises from the hypoglossal nucleus in the medulla oblongata of the
brainstem. It then passes laterally across the posterior cranial fossa, within the
subarachnoid space. The nerve exits the cranium via the hypoglossal canal.
◦ Now extracranial, the nerve receives a branch of the cervical plexus that conducts fibres
from C1/C2 spinal nerve roots. These fibres do not combine with the hypoglossal nerve –
they merely travel within its sheath.
◦ It then passes inferiorly to the angle of the mandible, crossing the internal and external
carotid arteries, and moving in an anterior direction to enter the tongue.

MOTOR FUNCTIONS
◦ The hypoglossal nerve is responsible for motor innervation of the vast majority of the
muscles of the tongue (except for palatoglossus). These muscles can be subdivided into
two groups:
i) Extrinsic muscles
◦ Genioglossus (makes up the bulk of the tongue)
◦ Hyoglossus
◦ Styloglossus
{NOTE - Palatoglossus (innervated by vagus nerve)}

ii) Intrinsic muscles
◦ Superior longitudinal
◦ Inferior longitudinal
◦ Transverse
◦ Vertical
Together, these muscles are responsible for all movements of the tongue.

Role of the C1/C2 Roots
◦ The C1/C2 roots that travel with the
hypoglossal nerve also have a motor
function. They branch off to innervate the
geniohyoid (elevates the hyoid bone) and
thyrohyoid (depresses the hyoid bone)
muscles.
◦ Another branch containing C1/C2 fibres
descends to supply the ansa cervicalis – a
loop of nerves that is part of the cervical
plexus. From the ansa cervicalis, nerves
arise to innervate the omohyoid, sternohyoid
and sternothyroid muscles. These muscles
all act to depress the hyoid bone.

Clinical Testing of Hypoglossal Nerve
◦ To check the integrity of the hypoglossal nerve, the functions of genioglossus
muscles are evaluated. The patient is requested to protrude the tongue. If the
hypoglossal nerves of both sides are complete, the protruded tongue is located
in the midline.
◦ If the hypoglossal nerve of 1 side is damaged, the tongue deviates to the side of
the lesion/paralysis.
◦ If the hypoglossal nerves of both sides are damaged, the patient cannot
protrude his tongue. It is located motionless in mouth causing trouble in
language and swallowing.

Clinical Significance
Hypoglossal Nerve Palsy
Damage to the hypoglossal nerve is a relatively
uncommon cranial nerve palsy. Possible causes
include head & neck malignancy and penetrating
traumatic injuries. If the symptoms are accompanied
by acute pain, a possible cause may be dissection of
the internal carotid artery.
Patients will present with deviation of the tongue
towards the damaged side on protrusion, as well as
possible muscle wasting and fasciculations
(twitching of isolated groups of muscle fibres) on
the affected side.

REFERENCES
• Garg K. Mittal PS, Chandragupta M.BD Chaurasia’s Human Anatomy.CBS
publishers;7th edi:114-20.
• Tortura G, Grabowski S. Principles of Anatomy and Physiology. John Wiley and sons;
10th edi:273-99.
• Snell RS; Clinical Anatomy: Lippincott Williams and Wilkins: 7th edi:780-3.
• Laskin D, Clinician’s handbook of Oral and Maxillofacial Surgery; 2nd edi: 161-83.
• Ryan S, Blyth P, Duggan N, Wild M, Al-Ali S. Is the cranial accessory nerve really a
portion of the accessory nerve? Anatomy of the cranial nerves in the jugular foramen.
Anat Sci Int. 2007 Mar;82(1):1-7
• Riggs JE. Distinguishing between extrinsic and intrinsic tongue muscle weakness in
unilateral hypoglossal palsy.J.Neurol.1984 Oct;34(10):1367-8.

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