Download Cranial Nerve X

Cranial Nerve X - Vagus
• "Vagus" is from the
Latin meaning
wandering. This is a
fitting name as the
nerve wanders from
the brainstem to the
splenic flexure of the
colon. The vagus
nerve consists of five
components with
distinct functions
Somatic motor
• Supplies the voluntary
muscles of the
pharynx and most of
the larynx
Visceral motor
• Parasympathetic
innervation of the
smooth muscle and
glands of the pharynx,
larynx, and viscera of
the thorax and
abdomen.
Visceral sensory
• 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. This
component will not be
discussed further.
Overview of SomaticMotor
Component
• The somatic motor
component of CN X
provides voluntary control
of the following:
– Striated muscle of the
pharynx.
– Striated muscle of the
larynx, except for the
stylopharyngeus muscle
(CN IX) and the tensor veli
palatini muscle (CN V).
– Palatoglossus muscle of
the tongue (the rest of the
muscles of the tongue are
innervated by CN XII).
Origin and Central Course
• The somatic motor component originates
from the nucleus ambiguus in the
reticular formation of the medulla.
• Fibers leaving the nucleus ambiguus travel
anteriorly and laterally to exit the medulla
posterior to the olive as a series of 8 - 10
rootlets.
Intracranial Course
•
Upon emerging from the lateral
aspect of the medulla the somatic
motor component travels with the
fibers of the accessory nerve (CN
XI) into the jugular foramen of
the skull. The remaining
components of the vagus nerve
also enter the jugular foramen and
give rise to two ganglia (the
superior and inferior vagal
ganglia) within the jugular
foramen. The somatic motor fibers
join with the rest of the vagus
nerve just below the inferior vagal
ganglion.
Extra-Cranial Course and Final
Innervation
• Upon exiting the skull
the vagus nerve
travels between the
internal jugular vein
and internal carotid
artery within the
carotid sheath.
The somatic motor fibers leave the
vagus nerve as three major branches:
• Pharyngeal branch
• Superior laryngeal nerve
• Recurrent laryngeal nerve
Pharyngeal Nerve
• The pharyngeal nerve is the principle motor nerve of
the pharynx.
It branches from the vagus nerve just below the
inferior ganglion and travels inferiorly and medially to
pass between the internal and external carotid arteries.
• The nerve enters the middle constrictor muscle of
the pharynx where it spreads out to form the pharyngeal
plexus to innervate all muscles of the pharynx and soft
palate (except the stylopharyngeus and tensor veli
palatini muscles which are innervated by CNs IX and V,
respectively).
The muscles innervate by the
pharyngeal nerve include:
• Superior, middle, and inferior constrictor
muscles
• Levator palatini muscle
• Salpingopharyngeus muscle
• Palatopharyngeus muscle
• Palatoglossus muscle of the tongue
Superior Laryngeal Nerve
• The superior laryngeal nerve branches
from the vagus nerve just below the
pharyngeal nerve. The nerve descends in
the neck adjacent to the pharynx and splits
to form the internal and external laryngeal
nerves.
• The external laryngeal
nerve supplies the
inferior constrictor
muscle before piercing it
to supply the
cricothyroid muscle
which is involved in the
controlling the
movements of the vocal
folds.
• The internal
laryngeal nerve
pierces the thyrohyoid
membrane and is a
sensory nerve of the
larynx.
Recurrent Laryngeal Nerve
•
The path of the recurrent laryngeal nerve differs on the right and left
sides of the body.
The left recurrent laryngeal nerve separates from the vagus nerve at the
level of the aortic arch. The nerve loops posteriorly around the aortic
arch and ascends through the superior mediastinum to enter the groove
between the esophagus and trachea.
Recurrent Laryngeal Nerve
•
The right recurrent laryngeal nerve splits from the vagus before entering
the superior mediastinum at the level of the right subclavian artery. The
nerve hooks posteriorly around the subclavian artery and also ascends
in the groove between the esophagus and trachea.
• Both recurrent laryngeal
nerves pass deep to the
lower margin of the
inferior constrictor muscle
to innervate the intrinsic
muscles of the larynx
responsible for controlling
the movements of the
vocal fold
Motor Neuron (MN) Lesion
• Unilateral damage to the vagus nerve is indicated by:
• 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).
• On examination the soft palate droops on the affected
side and the uvula deviates opposite the affected side
due to the unopposed action of the intact levator palatini
muscle.
• Unilateral damage to the recurrent laryngeal
nerve can occur during surgical procedures in
the neck, 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.
Overview of Visceral Motor
Component
• The parasympathetic
(secretomotor)
component of the vagus
nerve consists of efferent
fibers which innervate the
smooth muscle and
glands of the pharynx,
larynx, and thoracic and
abdominal viscera down
to the splenic flexure.
• In general, parasympathetic stimulation
leads to increased secretion from glands
and smooth muscle contraction.
Specifically, CN X parasympathetic
stimulation has the following effects (think
"rest and digest")
rest and digest
• Cardiac - Slows heart rate
• Lungs - Stimulates increased bronchiolar
secretions and bronchoconstriction
• GI tract- Stimulates increased secretions
and motility
Visceral Motor Component Origin and Central Course
• The visceral motor component fibers
originate from the dorsal motor nucleus
of the vagus located in the floor of the
fourth ventricle (vagal trigone) in the
rostral medulla and in the central grey
matter of the closed (caudal) medulla.
Preganglionic fibers course through the
spinal trigeminal tract and nucleus to exit
the lateral medulla.
Intracranial Course - Visceral
Motor Component
• Upon emerging from
the lateral aspect of
the medulla, the
visceral motor fibers
join the other
components of CN X
to exit the skull via the
jugular foramen.
Extra-Cranial Course and Final
Innervations
• Upon exiting the skull the
vagus nerve travels between
the internal jugular vein and
internal carotid artery within
the carotid sheath.
Preganglionic fibers to the
secretomotor glands of the
pharyngeal and laryngeal
mucosa travel with the
pharyngeal and internal
laryngeal nerves discussed
above.
• Within the thorax the left and
right vagus nerves break up
into many branches to form
plexuses around the
esophagus and major blood
vessels to the heart and
lungs.
From the esophageal plexus,
the left and right gastric nerves
emerge and provide
preganglionic parasympathetic
innervation to the stomach.
Innervation to the intestines
and visceral organs
generally follow the arterial
blood supply to that organ.
Overview of visceral sensory
component
• The visceral sensory
component of CN X
provides 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
Peripheral Course
• Sensory fibers from the plexuses surrounding the
abdominal viscera converge and join the gastric nerves
which ascend through the esophageal hiatus of the
diaphragm and merge with the esophageal plexus.
In the thorax, visceral sensory fibers from the heart and
lungs also join the ascending fibers in the esophageal
plexus which converge to form the left and right vagus
nerves which ascend within the carotid sheath between
the internal jugular vein and internal carotid artery.
•
Visceral sensory fibers
from the larynx and
pharynx join the
ascending vagal fibers via
the internal laryngeal and
recurrent laryngeal
nerves.
The cell bodies of these
afferent neurons reside in
the inferior vagal
ganglion in the jugular
foramen
Central Course - Visceral
Sensory Component
• The central processes of the visceral sensory neurons pass from the
inferior vagal ganglion through the jugular foramen and enter the
medulla. These fibers descend in the tractus solitarius to synapse
in the caudal nucleus solitarius.
From the nucleus solitarius, bilateral projections to several areas in
the reticular formation and hypothalamus allow reflex control of
cardiovascular, respiratory, and gastrointestinal functions.
Connections between the reticular formation and the dorsal motor
vagus nuclei (via the reticulobulbar pathway) allow most of these
reflexes to be mediated by the visceral motor component of CN X
Overview of general sensory
component
• This component of CN X carries general
sensory information (pain, temperature,
and touch) from the skin of the back of the
ear and external auditory meatus, parts of
the external surface of the tympanic
membrane, and the from the larynx and
pharynx.
Peripheral Course
• Sensory fibers from the external ear, external auditory
canal, and external surface of the tympanic membrane
are carried via the auricular branch of CN X. These
fibers pass into the jugular foramen and enter the
superior vagal ganglion where their cell bodies reside.
General sensory information from the larynx and
pharynx travels in the recurrent laryngeal and internal
laryngeal nerves which join and ascend into the jugular
foramen with the vagus nerve. The cell bodies of these
neurons reside in the inferior vagal ganglion.
Central course - general sensory
component
• The central processes of the general
sensory neurons exit the vagal ganglia
and pass through the jugular foramen to
enter the brainstem at the level of the
medulla.
Upon entering the medulla these fibers
descend in the spinal trigeminal tract and
synapse in the spinal nucleus of the
trigeminal
Clinical Correlation
• Stimulation of the fibers of the auricular
nerve in the external auditory meatus can
cause coughing and/or vomiting by reflex
activation of the visceral motor component
of the vagus nerve via the reticulobulbar
pathway.