Vagus nerve DR MASOOMA SYED - PowerPoint Presentation

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Vagus nerve

DR MASOOMA SYED

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Vagus nerveMixed nerve.l

ongest

and most

widely distributed

cranial nerve.

It

is so called because of

its extensive

vague course and distribution.

It conveys most

of the efferent fibres of the cranial part of

the parasympathetic

outflow and distributes the fibres of

an cranial

part of the accessory nerve.

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Functional Components and Nuclei GENERAL SOMATIC AFFERENT FIBRES: carry general sensations from skin of the

auricle and

terminate in the nucleus of the spinal tract of the trigeminal

nerve

SPECIAL

VISCERAL AFFERENT FIBRES:

carry taste sensations from the posteriormost part of the tongue and epiglottis and terminate in the nucleus tractus

solitarius

GENERAL VISCERAL AFFERENT FIBRES:

carry general sensations from the mucous membrane of pharynx, larynx, trachea,

oesophagus, and thoracic and abdominal viscera

terminate in the nucleus tractus solitarius and some in the dorsal nucleus of the vagus.

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SPECIAL VISCERAL EFFERENT FIBRES: supply the muscles of palate, pharynx, and

larynx.

They arise from

nucleus ambigus

.

GENERAL VISCERAL EFFERENT FIBRES:

arise from the

dorsal

nucleus of vagus

parasympathetic

innervation to heart, bronchial tree, and most of the GIT.

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Course and Relations Arises from the lateral aspect of the medulla between the olive and inferior cerebellar peduncle by

about 10

rootlets below and in line of the rootlets of

the glossopharyngeal nerve.

These

nerve rootlets unite to

form the

nerve trunk

which leaves

the cranial cavity by passing through

the middle

part of the jugular foramen enclosed in the

common dural

sheath with the 11th nerve.

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The superior and inferior sensory ganglia are located on the nerve as it passes through the jugular foramen:1. A smaller superior ganglion (juglar )lies

within the

jugular foramen

.

2. The larger inferior (nodose) ganglion lies just below

the jugular

foramen.

Both

the ganglia contain the cell

bodies of

the sensory fibres of the vagus nerve.

The superior ganglion

contains the cell bodies of GSA fibres,

whereas the

inferior ganglion contains the cell bodies of

visceral afferent

fibres.

The

cranial root of the accessory (

11th) nerve

unites with the vagus nerve just below its

inferior ganglion

and thus transfers all its fibres to the

vagus nerve

for distribution.

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After coming out of the cranial cavity through the jugular foramen, the nerve runs vertically downward within the carotid sheath in the neck first between the internal

jugular vein

laterally and the internal carotid artery medially

and then

between the internal jugular vein (laterally) and

the common

carotid artery (medially).

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At the root of the neck, the nerve enters the thorax. The right vagus nerve enters the thorax by crossing in front of the

right subclavian artery, whereas the

left vagus

nerve

enters

the thorax by passing between the left common

carotid and

left subclavian arteries.

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Branches and Distribution NECK

SUPERIOR GANGLION

1

.

Meningeal branch:

Takes

a recurrent course, and enters the cranial

cavity through

the jugular foramen to supply the dura mater

of the

posterior cranial fossa.

2.

Auricular branch (Arnold’s nerve or Alderman’s nerve

):

Passes upwards and backwards through mastoid canaliculi and tympano-mastoid fissure

It is distributed to the skin of cranial surface of auricle, floor and posterior wall of external acoustic meatus and adjoining part of tympanic membrane.

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INFERIOR GANGLION3. Pharyngeal branch:

passes

forward between the internal and external

carotid arteries

, and takes part in the formation of

pharyngeal plexus

. It supplies:

(a) all the muscles of pharynx

except

the stylopharyngeus, which

is supplied by the

glossopharyngeal nerve

, and

(b) all the muscles of soft palate

except

the tensor

palati

which

is supplied by the mandibular nerve (

through the

nerve to medial pterygoid).

4.

Branches to carotid body:

join with the glossopharyngeal nerve and acts as baro –receptors and chemo –receptore.

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5. Superior laryngeal nerve :Passes downward and forward medial to internal carotid artery and divides into (a

) The

external laryngeal nerve (motor)

accompany

with

superior

thyroid

vessels

supplies

cricothyroid muscle

.

It also gives twigs

to the

inferior constrictor and

pharyngeal

plexus.

(b) The

internal laryngeal nerve (sensory)

passes downward

and forward toward the gap between

the middle

and inferior constrictors

.

It pierces

the thyrohyoid

membrane to enter the larynx.

It supplies the(i

) mucous membrane of larynx above the

vocal cords

, and

(ii) mucous membrane of the pharynx,

epiglottis, vallecula

, and the posteriormost part of

the tongue

.

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TRUNK6. cardiac branches:Consists of superior and inferior branches

Cardiac branches join with the deep cardiac plexus except the inferior cervical cardiac branch of left vagus which forms superficial cardiac branch.

Concerned with reflex inhibition of cardiac activity.

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Right recurrent laryngeal nerve:Arises from the root of the neck from right vagus and winds around the under surface of 1st part of right subclavian artery .Runs obliquely upward behind common carotid

a

rtery and lodges in the tracheo-oesophageal groove.

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THORAXLeft recurrent laryngeal nerve: It nerve winds around the under surface of the arch of aorta, behind and to the left side of ligamentum arteriosum and passes upwards at first between the bifurcation of trachea and the aortic arch.

As it ascends it lodges in the right tracheo-oesophageal groove and appears in the neck.

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The recurrent laryngeal nerve provides: motor innervation to all the intrinsic muscles of the larynx (exce

pt

the cricothyroid which is supplied by

the external

laryngeal nerve)

sensory

innervation to

the mucous membrane of laryngeal cavity up

to the

vocal cord.

Each recurrent laryngeal nerve passes deep to the

inferior constrictor

muscle to enter the laryngeal cavity deep to

the cricothyroid

joint. Now it is called the inferior laryngeal nerve.

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Clinical correlation Alderman’s nerve phenomenon:

The

tickling of

the cutaneous

distribution of the vagus nerve stimulates

jaded appetite

. The Alderman in ancient Roman days used

to stimulate

their appetite by dropping cold water behind

the ear

supplied by the auricular branch of the vagus

nerve.

For

this reason, the auricular branch of the vagus nerve

is also

called

Alderman’s

nerve.

Apparently, this occurs by

a reflex

increase in gastric motility supplied by the

vagus nerve

(to the stomach).

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Lesions of vagus nerve:The bilateral lesions of vagus nerve

cause:

(a) nasal regurgitation of the swallowed liquids,

(b) nasal twang of

voice

(c) hoarseness of

voice

(d) flattering of palatal

arches

(e) cadaveric position of vocal

cards

(f)

dysphagia

(g) loss of cough

reflex

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Clinical testing of vagus nerve: The vagus nerve can be tested

clinically by asking the patient to open his

mouth and

say ‘ah’, and then comparing the palatal arches of

the two

sides.

vagus is intact, the soft palate rises

in the midline

.

In bilateral lesions, the soft

palate drops.

In the unilateral lesion, there is flattening (

drooping) of

palate arch on the side of paralysis and uvula pulled

to the

normal side.

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