Transcript Cranial Nerve II - Maryville University

Cranial Nerve II
Cranial Nerve VII: Facial Nerve
• CN-VIII is a mixed nerve. It sensory
component serves the external ear and a
small area behind the ear, and also
transmits taste sensations from the
anterior two-thirds of the tongue. It's motor
component regulates the muscles of facial
expression and the secretion of sublingual
salivary gland and lacrimal gland.
Brancial motor
(special visceral efferent)
Supplies the muscles of facial
expression; posterior belly of digastric
muscle; stylohyoid, and stapedius.
Visceral motor
(general visceral efferent)
Parasympathetic innervation of the
lacrimal, submandibular, and sublingual
glands, as well as mucous membranes
of nasopharynx, hard and soft palate.
Special sensory
(special afferent)
Taste sensation from the anterior 2/3 of
tongue; hard and soft palates.
General sensory
(general somatic afferent)
General sensation from the skin of the
concha of the auricle and from a small
area behind the ear.
General somatic afferent fibers
carry sensory impulses to CNS
from skin and skeletal muscles
General somatic efferent fibers
carry motor impulses from CNS to
skeletal muscles
General visceral afferent fibers
carry sensory impulses to CNS
from blood vessels and internal
organs
General visceral efferent fibers
carry motor impulses away from
CNS to smooth muscles and glands
Special somatic efferent fibers
carry motor impulses from brain to muscles used in
chewing, swallowing, speaking, and forming facial
expressions
Special visceral afferent fibers
carry sensory impulses to brain from olfactory and
taste receptors
Special somatic afferent fibers
carry sensory impulses to brain from receptors of sight,
hearing, and equilibrium
Branchial Motor Component
• The largest component of the facial nerve.
• Provides voluntary control of the muscles
of facial expression (including buccinator,
occipitalis and platysma muscles), as well
as the posterior belly of the digastric,
stylohyoid and stapedius muscles.
Motor
• Facial motor nucleus also receives afferent
fibers from other sources for reflexes. for
instance, fibers from superior colliculus provides
a pathway for closure of eyelids in the event of
intense light or rapidly approaching objects.
Fibers from trigeminal sensory nuclei completes
corneal reflex, etc.
• Descending innervations are provided by
corticobulbar tract which is mainly crossed
except fibers that innervate frontalis and
orbicularis oculi muscles. Therefore, upper
motor neuron lesion (i.e., corticobulbar tract)
only affects lower facial muscles contralaterally
(drooling, unsymmetrical smile, cannot whistle,
OK frown).
Control of the Muscles of Facial Expression
• The portion of the nucleus that innervates
the muscles of the forehead receives
corticobulbar fibers from both the
contralateral and ipsilateral motor cortex.
The portion of the nucleus that innervates
the lower muscles of facial expression
receives corticobulbar fibers from only the
contralateral motor cortex.
Lower Motor Neuron (LMN) Lesion
• Results from damage to the motor nucleus
of CN VII or its axons.
• A LMN lesion results in the paralysis of all
muscles of facial expression (including
those of the forehead) ipsilateral to the
lesion.
Upper Motor Neuron (UMN) Lesion
• Results from damage to neuronal cell bodies in
the cortex or their axons that project via the
corticobulbar tract
• Voluntary control of muscles of the forehead will
be spared due to the bilateral innervation of the
portion of the motor nucleus of CN VII that
innervates the upper muscles of facial
expression.
• UMN lesions are usually the result of a stroke.
Upper motor neuron lesions spare forehead; lower motor
neuron lesions cause paralysis in upper and lower face.
Gustatory fibers
• Originate from taste receptors located on soft palate,
epiglottis, and the tongue, enters brain by two branches.
Taste receptors from soft palate together with
preganglionic terminate into geniculate ganglion via
greater petrosal nerve of facial nerve (A motor branch
innervates stapedius muscle). Anterior two thirds of the
taste buds on the tongue terminates in geniculate
ganglion by the choda tympani branch of the facial
nerve. These two nerves synapse at Geniculate
Ganglion, axons from geniculate ganglion enter the brain
stem in the nervus intermedius and then turn in the
solitary tract. Other gustatory axons from
glossopharyngeal and vagus nerves also join this
fasciculus. Fibers from all three sources then terminate
into the rostral part of the solitary nucleus, which is also
referred as gustatory nucleus.
Gustatory fibers
• Fibers from gustatory nucleus becomes
central tegmental tract and runs
ipsilaterally and projects to the medial part
of the ventral posterior nucleus of the
thalamus. From there, fibers project to the
cortical area for taste, which is adjacent to
the general sensory area for the tongue
and extends onto the insula and forward to
frontal operculum.
Cutaneous fibers
• Distributed to auricle, external area of
external acoustic meatus and external
surface of tympanic membrane. Axons
from geniculate ganglion for cutaneous
sensation continue into nervus intermedius
and then get into spinal tract and terminate
into spinal trigeminal nucleus.
Parasympathetic nuclei
• Superior salivatory:
– Leave facial nerve in the chorda tympani branch and
join the lingual branch of the mandibular nerve to the
floor of oral cavity. Terminates in submandibular
ganglion. Postganglionic fibers innervate salivary
secretion of submandibular and sublingual glands.
• Lacrimal nuclei:
– Fibers leave facial nerve in the greater petrosal nerve
and terminate the ptergopalatine ganglion located in
pterygopalatine fossa. Postganglionic fibers innervate
secretion and vasodilation of lacrimal secretion.
Bell's palsy
• Caused by the edema compressing facial nerve (viral
infection?). Affected side: paralysis of facial muscles,
loss of taste (ageusia) in the anterior two thirds of the
tongue, impaired secretion of sublingual and
submandibular glands, and hyperacusis (paralysis of
stapedius muscle).
• Most Bell's Palsy can be recovered fully without any
complications. Recovery of severe case may rely on
axonal regeneration. Sometimes the regeneration of the
salivary fibers may tap into greater petrosal nerve and
reach the pterygopalatine ganglion, which result in
lacrimation (crocodile tears) instead of salivation when
stimulated by aroma and taste onto superior salivatory
nucleus.
Cranial Nerve VIII: Vestibulocochlear Nerve
• CN-VIII is a purely sensory nerve. Some
refer to it as the acoustic or auditory nerve.
The vestibulocochlear nerve carries two
kinds of sensations: vestibular (balance)
and audition (hearing) from receptors in
the inner ear. Auditory information travels
to the auditory cortex in the temporal
lobes.
Vestibulocochlear Nerve
• Cochlear nerve originates from spiral ganglion. Once it
gets inside the skull, it bifurcates. One branch ends in
dorsal cochlear nucleus and the other ends in ventral
cochlear nucleus. Fibers from ventral cochelear partly
cross and terminate to the superior olivary nucleus. Axons
from superior olivary nucleus then terminate to inferior
colliculus via lateral lemniscus. Uncrossed fibers from
ventral cochelear nucleus run ipsilaterally. Fibers from
dorsal cochelear nucleus cross over and relay at superior
olivary nucleus, joins the lateral lemniscus and to inferior
colliculus. Auditory fibers that cross pons are referred as
trapezoid body. Lateral lemniscus are the ascending
auditory tract ending at inferior colliculus. Fibers from
inferior colliculus project into medial geniculate body via
inferior brachium and then project ipslaterally to the
primary auditory cortex in the temporal lobe. Posterior to
the primary auditory cortex lies the auditory association
cortex (Wernicke’s area), essential for understanding
spoken language.
Vestibulocochlear Nerve
• Above the cochlear level, the auditory pathway is both
crossed and uncrossed. Not only nucleus projects fibers to
both sides, there are also commissural fibers in between
the nuclei of lateral lemniscus and inferior colliculi.
• The ability to detect the direction and sources of sound are
determined from the discrepancy in times of arrival of the
stimulus in left and right ears. Deafness in one-ear can
lose such abilities.
• Along with ascending fibers, fibers from auditory and
cortical area terminate in medial geniculate body
(corticogeniclate fibers). Cortico-collicular fibers to inferior
colliculi. Colliculo-olivary fibers, from inferior colliculi to
olivary nucleus. Colliculo-cocheleonuclear, from inferior
colliculus to dorsal and ventral cochlear nuclei. All above
fibers run ipsilaetrally except cortico-collicular runs on both
sides. Their functions involve with auditory reflexes.
Vestibular portion
• Vestibular nuclei: four groups have been
found. Including lateral vestibular nucleus
(Deiters' nucleus), superior. medial, and
inferior vestibular nuclei.
Connection to the cerebellum
• The vestibulocerebellum, consisting the
flocculonodular lobes, inferior vermis, and
etc., receiving info from superior, medial
and inferior vestibular nuclei, entering the
cerebellum by inferior cerebellar peduncle.
Connection to the spinal cord
• Vestibulospinal tract, originate from lateral
vestibular nucleus, uncrossed, terminates in the
medial part of the ventral horn. Its major function
is to maintain and regulate the tone of muscles
involved with posture to maintain the balance.
• Fibers from medial vestibular nucleus form the
medial longitudinal fasciculus, mediate reflexes
like vestibulo-ocular reflex (turning the head and
the turning of eyes in opposite direction).
Cranial Nerve IX: Glossopharyngeal Nerve
• CN-IX is a mixed nerve. The sensory
component provides general sensation
and taste from the posterior one-third of
the tongue, and part of the skin of the
external ear. The motor component serves
to control the stylopharyngeas muscle,
which elevates the pharynx during
swallowing and speech. Also, part of the
motor component serves to innervate the
parotid gland, an important salivary gland.
Afferent fibers
• Taste information collected from posterior one
third of the tongue joins the solitary tract along
with the few taste buds on the epiglottis
collected by vagus nerve.
• Carotid sinus functions as baroreceptors which
monitor arterial blood pressure and the carotid
body, located in the bifurcation of internal and
external carotid artery, contains chemoreceptors
which monitor the level of oxygen in the blood.
Similar structures like aortic bodies
(chemoreceptors) and aortic arch (barorecetors)
are innervated by vagus nerve.
Somatic afferent fibers
• General sensations of pain, temperature,
touch from posterior one third of the
tongue
Efferent fibers
• Innervate stylopharyngeus muscle
Parasympathetic fibers
• Parasympathetic innervation of the smooth
muscle and glands of the pharynx, larynx,
parotid gland
Brancial motor
(special visceral efferent)
Supplies the stylopharyngeus
muscle.
Visceral motor
(general visceral efferent)
Parasympathetic innervation of
the smooth muscle and glands of
the pharynx, larynx, parotid
gland, and viscera of the thorax
and abdomen.
Visceral sensory
(general visceral afferent)
Carries visceral sensory
information from the carotid
sinus and body.
General sensory
(general somatic afferent)
Provides general sensory
information from the skin of the
external ear, internal surface of
the tympanic membrane, upper
pharynx, and the posterior onethird of the tongue.
Special sensory
(special afferent)
Provides taste sensation from
the posterior one-third of the
tongue.
Cranial Nerve X: Vagus Nerve
• The vagus nerve is a mixed nerve and is the
only cranial nerve that regulates the functions of
organs in the thoracic and abdominal cavities. It
is called the vagus ("wandering") nerve because
its branches wander throughout the body. Its
sensory component includes sensory fibers from
the larynx, pharynx, esophagus, and parts of the
external ear. Its motor component serves
muscles in the larynx and pharynx, and
parasympathetic innervation of the smooth
muscles and glands of the same areas, and
thoracic and abdominal areas.
Brancial motor
(special visceral
efferent)
Supplies the voluntary muscles of the
pharynx and most of the larynx, as well as
one extrinsic muscle of the tongue.
Visceral motor
(general visceral
efferent)
Parasympathetic innervation of the smooth
muscle and glands of the pharynx, larynx,
and viscera of the thorax and abdomen.
Visceral sensory
(general visceral
afferent)
Provides visceral sensory information from
the larynx, esophagus, trachea, and
abdominal and thoracic viscera, as well as
the stretch receptors of the aortic arch and
chemoreceptors of the aortic bodies .
General sensory
(general somatic
afferent)
Provides general sensory information from
the skin of the back of the ear and external
auditory meatus, parts of the external
surface of the tympanic membrane, and
the pharynx.
Special sensory
(special afferent)
A very minor component of CN X. Provides
taste sensation from the epiglottic region.
Lower Motor Neuron (LMN) Lesion
• Hoarseness (due to paralysis of the
intrinsic muscles of the larynx on the
affected side).
• Difficulty in swallowing due to the inability
to elevate the soft palate on the affected
side (due to paralysis of the levator palatini
muscle).
Lower Motor Neuron (LMN) Lesion
• Unilateral damage to the recurrent laryngeal
nerve can occur during surgical procedures in
the neck (Grave’s Disease), resulting in
hoarseness due to unilateral weakness or
paralysis of the muscles controlling the vocal
fold on the affected side.
• Enlargement of the paratrachial lymph nodes, as
can be seen in metastatic lung cancer, can lead
to compression of one of the recurrent laryngeal
nerves with similar results.
Cranial Nerve XI: Accessory Nerve
• CN-XI is a purely motor nerve serving the
sternomastoid and trapezius muscles in
the neck and back
• The accessory nerve has a cranial root
and a spinal root, both of which consist of
branchial motor fibers.
Branchial motor cranial root
(special visceral
efferent)
Innervates muscles of
larynx and pharynx.
Branchial motor spinal root
(special visceral
efferent)
Innervates the
trapezius and
sternocleidomastoid
muscles.
Cranial Nerve XII: Hypoglossal Nerve
• CN-XII is a purely motor nerve supplying
most of the muscles of the tongue (three
of the four extrinsic muscles of the tongue
including genioglossus, styloglossus, and
hyoglossus except Palatoglossus by
Vagus nerve)