Download Lower 4 Cranial Nerves2009-02-12 01:573.6 MB

The Cranial Nerves
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Olfactory (I)
Optic (II)
Occulomotor (III)
Trochlear (IV)
Trigeminal (V)
Abducent (VI)
Facial (VII)
Vestibulocochlear (VIII)
Glossopharyngeal (IX)
Vagus (X)
Accessory (XI)
Hypoglossal (XII)
Glossopharyngeal Nerve
• A mixed nerve (sensory,
motor, parasympathetic)
• Emerges from the ventral
surface of the medulla
oblongata
• Runs laterally in the
posterior cranial fossa
• Leaves the skull by
passing through the
central part of the jugular
foramen
• Has superior and inferior
ganglia, that are located
within the jugular foramen.
• At its exit from the skull, it
passes forward between
the internal jugular vein
and internal carotid artery,
within the carotid sheath
• Descends to the lower
border of the
stylopharyngeus muscle.
• Then curves forward
around the
stylopharyngeus and
• Passes through the gap
between the superior and
middle constrictor
muscles of the pharynx
• Passes under cover of
the hyoglossus muscle
• Distributed to the:
 Palatine tonsil
 Mucous membrane
of the fauces and
base of the tongue,
 Mucous glands of
the mouth
P
FPT
T
Functions
• Receives general sensory fibers from the
posterior ⅓ of the tongue, tonsil, pharynx,
middle ear and carotid sinus.
• Receives special sensory (taste) fibers from the
posterior ⅓ of the tongue and the circumvellate
papillae
• Supplies parasympathetic fibres to the parotid
gland via the otic ganglion
• Supplies motor fibers to stylopharygeus muscle
• Contributes sensory fibers to the pharyngeal
plexus
Branches
• Tympanic branch: Passes to
the tympanic plexus in the
middle ear and:
 Supplies sensory fibers to
the plexus
 Carries preganglionic
parasympathetic fibers, that
leave the plexus as lesser
petrosal nerve and synapse
in the otic ganglion
• Carotid branch: carries
sensory fibers from the carotid
sinus & carotid body
• Muscular branch to the
stylopharyngeus muscle
Branches cont’d
• Lingual branch: passes to
the posterior third of the
tongue and the
circumvellate papillae
• Pharyngeal branches:
carry sensory fibers to the
pharyngeal plexus, which
supplies the mucous
membrane of the pharynx,
tonsil and soft palate
• Communicates with the:
• Vagus & facial nerves
• Superior cervical
ganglion of the
sympathetic chain
Glossopharyngeal Nerve Lesions
• Glossopharyngeal nerve lesions
produce:
 Difficulty in swallowing
 Loss of general sensation over
the posterior one-third of the
tongue, palate, and pharynx
 Loss of taste sensation over
the posterior one-third of the
tongue and palate
 Dysfunction of the parotid
gland
 Loss of the gag reflex
Vagus Nerve
• A mixed nerve (sensory, motor,
parasympathetic)
• Emerges from the ventral surface
of the medulla oblongata
• Runs laterally in the posterior
cranial fossa
• Leaves the skull by passing
through the central part of the
jugular foramen
• Has superior and inferior ganglia,
that are located within the jugular
foramen
• Below the inferior ganglion, it is
joined by the cranial part of
accessory nerve
• Both right and left vagus nerves
descend in the carotid sheath,
lateral to the carotid artery
• The right vagus nerve
gives right recurrent
laryngeal nerve which
hooks around the right
subclavian artery
• Then crosses anterior to
the right subclavian artery
• Runs posterior to the
superior vena cava
• Descends posterior to the
right main bronchus
• Contributes to cardiac,
pulmonary and esophageal
plexuses
• Enters the abdomen as the
posterior vagal trunk
through the esophageal
hiatus of the diaphragm
• The left vagus nerve enters
the thorax between left
common carotid artery and
left subclavian artery
• Descends on the aortic arch.
• Gives rise to the left
recurrent laryngeal nerve
which hooks around the
aortic arch
• Descends posterior to the
left main bronchus
• Gives off thoracic cardiac
branches
• Contributes to cardiac,
pulmonary and esophageal
plexuses
• Enters the abdomen as the
anterior vagal trunk through
the esophageal hiatus of the
diaphragm.
Functions
• Supplies
parasympathetic fibers to
all the organs except the
suprarenal glands, from
the neck down to the
proximal ⅔ of the
transverse colon
• Supplies motor fibers to
the pharyngeal plexus
that supplies the muscles
of the palate, pharynx
and larynx
• Receives general
sensation from the
auricle of the ear and
part of the meninges
Branches
• Meningeal branch
• Auricular branch
• Pharyngeal branch to the
pharyngeal plexus. It contains nerve
fibers from the cranial part of the
accessory nerve
• Superior laryngeal nerve divides
into the:
 Internal laryngeal nerve:
sensory to the mucous
membrane of the piriform fossa
and the larynx down as far as
the vocal cords.
 External laryngeal nerve: motor,
accompany the superior thyroid
artery; supplies the cricothyroid
muscle.
• Superior & Inferior
cervical cardiac branches
• Recurrent laryngeal
nerve:
 Ascends in the groove
between the trachea and
the esophagus
 Is closely related to the
inferior thyroid artery.
 Mixed nerve: Sensory to
mucous membrane of
the larynx below the
vocal cords. Motor to all
the intrinsic muscles of
the larynx except the
cricothyroid muscles
Vagus Nerve Lesions
• Clinical manifestations range from mild symptoms of
hoarseness of voice, loss of gag reflex and loss of
effective cough mechanism, to dysphagia and choking
when drinking fluids, to life-threatening airway
obstruction from bilateral
recurrent laryngeal nerve injury
• Failure of soft palate elevation
• Deviation of uvula away from
the
side of lesion
• Abnormalities of esophageal motility, gastric acid
secretion, gallbladder emptying, and heart rate; and
other autonomic dysfunction.
Pharyngeal Plexus
• Located on the middle
constrictor muscle of the
pharynx
• Contains:
• Sensory fibers (from
glossopharyngeal nerve)
• Motor fibers (from cranial
root of accessory nerve via
vagus nerve)
• Postganglionic sympathetic
fibers (from superior cervical
ganglion)
• Supplies:
• The mucous membrane of
the pharynx, tonsil and soft
palate
• The muscles of the pharynx
& larynx
Accessory Nerve
• A motor nerve
• Has two parts:
 Cranial
 Spinal
• Cranial Part:
 Emerges from the
anterior surface of the
medulla oblongata .
 Runs laterally in the
posterior cranial fossa
 Joins the spinal root.
• Spinal Part:
• Arises from nerve cells in
the ventral horn of the C1C5 segments of the spinal
cord
• Ascends alongside the
spinal cord
• Enters the skull through the
foramen magnum
• It then turns laterally & joins
the cranial root.
• The two roots unite and
leave the skull through the
jugular foramen
• The roots then separate:
 The cranial root : joins the
vagus nerve and is distributed
in its branches (via the
pharyngeal plexus) to the:
muscles of the soft palate and
pharynx and to the muscles of
the larynx (except the
cricothyroid muscle).
 The spinal root: runs
downward and laterally and
enters the deep surface of the
sternocleidomastoid muscle,
which it supplies, and then
crosses the posterior triangle of
the neck to supply the
trapezius muscle
Lesion of the Spinal Part
• Injury to the spinal accessory
nerve results in paralysis of the
sternocleidomastoid and the
trapezius muscles.
• Patients exhibit signs of lower
motor neuron disease, such as
paralysis, fasciculation, and
wasting of the affected muscles.
• Because of its superficial
position in the posterior triangle
of the neck, it can be injured in
penetrating wounds. The
trapezius muscle gets paralyzed,
and shows wasting.
• Paralysis of the
sternocleidomastoid
muscle results in an
asymmetric neckline
• Paralysis of the trapezius
muscle results in:
 Drooping of shoulder
 Winging of scapula
 Difficulty in elevating the arm
above the head, having
abducted it to a right angle
by using the deltoid muscle.
 The patient is unable to
shrug the shoulders.
Hypoglossal Nerve
• A motor nerve
• Emerges from the ventral
surface of the medulla
oblongata
• Runs laterally in the
posterior cranial fossa
• Leaves the skull by
passing through the
hypoglossal canal
• Descends in the neck
within the carotid sheath
• Reaches lower border of
digastric muscle
• Curves forward by crossing
the loop of lingual artery
just above the tip of greater
cornu of hyoid bone
• Ascends deep to mylohyoid
and superficial to
hyoglossus muscle to
reach the tongue
• In the upper part of its
course, it is joined by C1
fibers from the cervical
plexus
Functions
• The hypoglossal nerve innervates:
 All the intrinsic muscles of the tongue
 All the extrinsic muscles of the tongue (except
the palatoglossus, which is supplied by the
pharyngeal plexus)
and therefore controls the shape and
movements of the tongue
Branches
• Meningeal branch
• Descending branch: carries
C1 fibers, passes downward
and joins the descending
cervical nerve (C2 and 3) to
form the ansa cervicalis
• Nerve to the thyrohyoid
muscle (C1)
• Nerve to the geniohyoid
muscle (C1)
• Muscular branches to all the
muscles of the tongue except
the palatoglossus
Hypoglossal Nerve Lesion
• If the patient is asked to protrude
the tongue, it will deviate toward
the paralyzed side .
• As the genioglossus muscle is
paralyzed on the affected side,
the normal genioglossus muscle
pulls the unaffected side of the
tongue forward, leaving the
paralyzed side of the tongue
stationary. The result is the tip of
the tongue deviates toward the
paralyzed side.
• The paralyzed muscles show
wasting, and the tongue
becomes wrinkled on that side.