Term Paper on Cranial Nerves | Brain | Nervous System | Biology

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Here is a term paper on ‘Types of Cranial Nerves’. Find paragraphs, long and short term papers on the ‘Types of Cranial Nerves’ especially written for school and college students.

Term Paper on Cranial Nerves


Term Paper Contents:

  1. Term Paper on the Olfactory Nerve
  2. Term Paper on the Optic Nerve
  3. Term Paper on the Oculomotor Nerve (Motor)
  4. Term Paper on the Trochlear Nerve (Motor)
  5. Term Paper on the Trigeminal Nerve
  6. Term Paper on the Abducent Nerve
  7. Term Paper on the Facial Nerve
  8. Term Paper on the Vestibulo Cochlear Nerve
  9. Term Paper on the Glossopharyngeal Nerve
  10. Term Paper on the Vagus Nerve
  11. Term Paper on the Accessory Nerve
  12. Term Paper on the Hypoglossal Nerve


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1. Term Paper on the Olfactory Nerve:

Nerve of smell (sensory)

Commencement:

Arises from central process of bipolar olfactory receptor nerve cells (neurons) present in the olfactory mucous membrane, situated in the upper part of the nasal cavity above the level of the superior concha.

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About 15 to 20 nerves arise from olfactory plexus of nerves and pass through the openings of cribriform plate of ethmoid bone to enter the olfactory bulb in the anterior cranial fossa.

Olfactory bulb is connected to the olfactory area of cerebral cortex by olfactory tract.

Carry smell sensation from the nose to the brain.

Termination:

ADVERTISEMENTS:

Glomerulus of the olfactory bulb.

Applied Anatomy:

1. During fracture of anterior cranial fossa – olfactory nerves may separate from olfactory bulb and cerebrospinal fluid (C.S.F.) leaks through nose – Rhinorrhoea.

2. Anosmia- Loss of smell sensation, e.g., in Rhinitis.

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3. Parosmia- Perverted sense of smell.

4. Caprosmia- Unpleasant odour due to decom­position of the tissue of the individual – bad smell is felt during expiration.

Clinically, each nostril must be tested separately either from clove oil or rose water.


2. Term Paper on the Optic Nerve:

ADVERTISEMENTS:

Nerve of sight and is second cranial nerve.

It is a tract having more than one million nerve fibres.

Surrounded by three layers of meninges.

Development:

Develops as a diverticulum from the diencephalon – optic stalk.

Commencement:

From central process of the cells present in the ganglionated cell layer of retina.

Course:

Fibres pierce the choroid and sclera, emerges through the lamina cribrosa situated 3 mm medial to central pole of the sclera.

Nerve passes via retrobulbar compartment of the orbit, enters the optic canal via optic foramen and reaches the anterior cranial fossa.

Termination:

Joins the optic nerve of the opposite side to form optic chiasma – where nasal fibres cross and temporal fibres do not cross.

Length – is about 40 mm.

Parts:

1. Intra orbital part – 25 mm long

2. Part of nerve within the optic canal – 5 mm long

3. Intra cranial part – 10 mm long.

Relations in the Orbit:

Nerve is longer than the space, so it is tortuous and surrounded by orbital pad of fat and muscles of eyeball.

Crossed Superiorly:

From lateral to medial side by:

1. Superior ophthalmic vein

2. Ophthalmic artery

3. Nasociliary nerve.

Laterally:

1. Ciliary ganglion

2. Lateral rectus muscle.

Medially:

Central artery of retina – pierces the optic nerve 1 cm behind the eyeball.

Posteriorly:

Nerve is surrounded by origin of recti- muscles.

Inferiorly:

Nerve to medial rectus.

Relations within the optic canal:

5 mm long.

Infero-Laterally:

Ophthalmic artery.

Medially:

Sphenoidal air sinus.

Posterior ethmoidal air sinus.

Relations of Intra Cranial Part:

10 mm long.

Superior:

Anterior cerebral artery.

Posterior:

Hypophysis cerebri.

Lateral:

Internal carotid artery.

Blood Supply:

1. Central artery of retina

2. Superior hypophyseal artery

3. Ophthalmic artery

4. Posterior ciliary artery.

Venous Drainage:

Central vein of retina drains into cavernous sinus.

Structure:

1. Nerve is covered by dura, arachnoid and piamaters.

2. Piamater enters into the nerve as septulae – which divides the nerve into many compartments.

3. In the centre of the nerve – central artery and vein of retina are situated.

Applied Anatomy:

1. Infection from brain and meninges may spread to optic nerve.

2. Injury of one optic nerve results in complete loss of vision of that side.

3. When intra cranial pressure is increased – optic nerve head in the retina is swollen – called papilledema.


3. Term Paper on the Oculomotor Nerve (Motor):

Is the third cranial nerve having motor and parasympathetic fibres.

Nuclear Origin:

Fibres arise from the oculomotor nuclear complex situated in the periaqueductal grey matter of upper part of the midbrain at the level of superior colliculus.

This nuclear complex consists of two components:

i. Somatic Efferent:

Fibres arising from this component supply all the extra ocular muscles except superior oblique and lateral rectus.

ii. Visceral Efferent (Nucleus of Edinger Westphal):

Fibres arising from it relay in the ciliary ganglion. From there postganglionic – parasympathetic fibres arise and supply the sphincter pupillae and ciliaris muscle.

After arising from the nuclear complex, the fibres run forwards through the substance of the midbrain to emerge on the anteromedial side of the cerebral peduncle.

Course:

Nerve emerges as a single trunk from oculomotor sulcus of midbrain runs infront of crus cerebri between posterior cerebral and superior cere­bellar arteries, lies in interpeduncular cistern.

It pierces the arachnoid and runs forwards and laterally to the oculomotor triangle between the free and attached margins of the tentorium cerebelli.

Passes lateral to posterior clinoid process and pierces the duramater to enter the roof of the cavernous sinus. Here it runs forwards in the lateral wall of the sinus.

In the anterior part of the cavernous sinus, nerve divides into upper and lower divisions, which enter the orbit by passing through the superior orbital fissure within the common tendinous ring.

Distribution:

i. Smaller superior division passes upwards on the lateral side of the optic nerve to supply superior rectus, it pierces the muscle and reaches the levator palpebra superiors to supply it on its inner aspect.

ii. Large inferior division divides into three branches:

(a) One branch passes below the optic nerve and supplies medial rectus.

(b) Second branch supplies inferior rectus muscle.

(c) Third branch passes between inferior rectus and lateral rectus to supply inferior oblique muscle.

Nerve to inferior oblique gives a motor root to the ciliary ganglion. From ganglion short ciliary nerves arise and supply the ciliary muscle and sphincter pupillae. These are parasympathetic fibres coming from Edinger Westphal nucleus.


4. Term Paper on the Trochlear Nerve (Motor):

Is the fourth cranial nerve.

It is most slender nerve and the only one, which arises from the dorsal aspect of the midbrain.

Nuclear Origin:

Trochlear nucleus lies in the ventro medial part of the central grey matter around the cerebral aqueduct, situated in the lower part of midbrain at the level of inferior colliculus.

Fibres arise, wind backwards around the central grey matter and decussate with the nerve fibres of the opposite side in the superior medullary velum.

It emerges on the dorsal surface of brain as a single trunk one on either side of the frenulum.

Course:

Each trochlear nerve passes laterally crossing the superior cerebellar peduncle.

It winds forward between the temporal lobe and cerebral peduncle.

Now it passes between posterior cerebral and superior cerebellar arteries and appears in the triangular area of duramater in front of the crossing of the attached and free margins of the tentorium cerebelli.

It pierces the duramater lateral to the posterior clinoid process and passes forward in the lateral wall of cavernous sinus below the oculomotor nerve.

The nerve enters the orbit through the lateral part of superior orbital fissure.

In the orbit nerve passes forwards and medially above the levator palpebrae superiors and supplies the superior oblique muscle from its orbital surface.

Distribution:

It supplies the superior oblique muscle only.

Peculiarity of the Trochlear Nerve:

1. Only cranial nerve emerges from the dorsal aspect of brain stem.

2. It is the only nerve that undergoes complete decussation with the nerve of opposite side before emerging.

Applied Anatomy:

1. Injury to 4th nerve causes paralysis of superior oblique muscle – person cannot look downward and laterally. Hence, during descending a stair – difficulties are noted, and head is tilted as a compensatory adjustment.

2. During cavernous sinus thrombosis 3rd, 4th and 6th cranial nerves may be paralysed.

3. Brain tumour, syphilis, meningitis, encephalitis and cavernous sinus thrombosis involves IIIrd, IVth and VIth cranial nerves.

Fracture of superior orbital fissure may involve these nerves in cases of head injuries.


5. Term Paper on the Trigeminal Nerve:

It is the fifth cranial nerve, containing both sensory and motor roots, i.e., mixed nerve.

Nuclei:

Motor and sensory both nuclei are situated in the pons.

(i) Motor nucleus of trigeminal – lies medial to sensory nucleus in the pons. It supplies muscles of mastication, anterior belly of digastric, mylohyoid, tensor tympani and tensor palati muscles.

(ii) Superior sensory nucleus of trigeminal – lies lateral to motor nucleus in the pons. Inferior to this nucleus lies the nucleus of the spinal tract of the trigeminal nerve. It receives sensory impulses from the face, conjunctiva, nose and mouth etc.

(iii) Mesencephalic nucleus – is situated in between the sensory and motor nuclei present in the pons. It superiorly extends into the mid-brain. It receives proprioceptive impulses from muscles of mastication, face and eye.

Course:

The nerve leaves anterior aspect of the pons as a small motor root and a large sensory root.

Passes forwards from the posterior cranial fossa to the apex of the petrous temporal in middle cranial fossa.

Large sensory root expands to form trigeminal ganglion (crescentric shaped).

From the convex anterior border of the ganglion three divisions arise:

(1) Ophthalmic nerve – purely sensory – divides into – Lacrimal, frontal, and nasociliary branches.

(2) Maxillary nerve – sensory.

(3) Mandibular nerve – mixed.

Ophthalmic Nerve:

Purely sensory, runs in lateral wall of cavernous sinus below the trochlear nerve.

Reaching the anterior part of the sinus nerve divides into three branches:

a. Lacrimal,

b. Frontal, and

c. Nasociliary nerves.

They enter into the orbit through superior orbital fissure.

Ophthalmic nerve via its branches may supply:

(i) Anterior quadrant of scalp

(ii) Cornea

(iii) Conjunctiva

(iv) Eye ball

(v) Eye lids

(vi) Nose

(vii) Frontal and ethmoidal air sinuses

(viii) Lacrimal gland.

a. Lacrimal Nerve:

It passes through the lateral most aspect of the superior orbital fissure and enters the orbit.

It runs forwards and laterally to supply:

(i) Lateral portion of eyelids

(ii) Palpebral conjunctiva

(iii) Lacrimal gland

b. Frontal Nerve:

Largest branch of ophthalmic nerve.

Enters the orbit through the lateral part of the superior orbital fissure.

It passes above the levator palpebrae superioris muscle.

Trigeminal Nerve and its Distribution (Diagrammatic Representation):

Terminates by dividing into:

(A) Supra trochlear nerve and

(B) Supra orbital nerve.

(A) Supra Trochlear Nerve:

Supra trochlear is the smaller branch, passes round the trochlea of the superior oblique muscle, curves round the upper border of the orbit and enters the forehead.

It gives branches to supply:

(i) Medial part of eyelids

(ii) Skin of central portion of the forehead.

(B) Supra Orbital Nerve:

Passes through supra orbital foramen or notch, runs in the forehead and scalp to supply:

(i) Conjunctiva

(ii) Upper eyelid

(iii) Skin of forehead

(iv) Skin of scalp upto vertex

(v) Frontal air sinus.

Lacrimal nerve communicates with the pterygo palatine ganglion through zygomatico temporal nerve and receives secretomotor parasympathetic fibres for the lacrimal gland.

(iii) Nasociliary Nerve:

It passes through the superior orbital fissure within the common tendinous ring and enters the orbit.

It crosses the optic nerve superiorly from lateral to medial side.

Terminates by becoming the anterior ethmoidal nerve.

Branches:

(a) Sensory root to ciliary ganglion.

(b) Two or three long ciliary nerves – supply eyeball.

(c) Posterior ethmoidal nerve – supplies ethmoidal and sphenoidal air sinuses and nose.

(d) Infra trochlear nerve – supplies medial portion of eyelids and conjunctiva.

(e) Anterior ethmoidal nerve – supplies meninges of anterior cranial fossa, ethmoidal air sinuses, frontal sinus and nasal mucosa. Skin of the tip and around the anterior nasal opening.

Maxillary Nerve (Sensory):

It runs in the lateral wall of cavernous sinus for a short distance below the opthalmic nerve, pierces the duramater and passes through the foramen rotundum.

Enters into pterygopalatine fossa and divides into these branches:

1. Meningeal branch arise before entering to foramen rotundum it supplies duramater of middle and anterior cranial fossa.

2. Ganglionic branches two or three suspends pterygo palatine ganglion in the fossa and distributed through its branches.

3. Zygomatic branch is divides into zytomatico temporal and zygomatico facial branch.

4. Posterior superior alveolar nerve.

5. Infra orbital nerve is the continuation of the maxillary nerve gives following branches:

(a) Anterior and middle superior alveolar nerves.

(b) Palpebral branch to lower eyelid.

(c) Nasal branches.

(d) Labial branches to upper lip.

Distribution of maxillary nerve to skin of face over maxilla.

Teeth of upper jaw and gums.

Mucous membrane of nose, maxillary air sinus and palate.

Mandibular Nerve (Mixed):

It passes through foramen ovale and enters into infra temporal fossa.

Initially both sensory and motor roots are separate.

Just below the foramen ovale both roots unite and form the main trunk, after a short course it divides into anterior and a posterior divisions which gives branches to supply.

Sensory fibres are distributed to – skin of cheek, meninges of middle cranial fossa.

Skin over mandible, lower lip, side of head, external ear and tympanic membrane, mastoid antrum.

Temporo-mandibular joint.

Teeth and gums of lower jaw.

Mucous membrane of cheek, floor of mouth and anterior 2/3 of tongue.

Motor fibres are distributed to muscles of mastication, mylohyoid muscle and anterior belly of digastric muscle, tensor tympani and tensor palatini muscle.


6. Term Paper on the Abducent Nerve:

It is the sixth cranial nerve containing motor nerve fibres to supply lateral rectus muscle of eyeball.

Nucleus is found in the dorsal part of the pons in the floor of the fourth ventricle, deep to the facial colliculus – facial nerve winds round the abducent nerve nucleus and forms colliculus. VIth nerve passes forwards within the tegmentum of the pons.

Emergence from the Pons:

It leaves between upper border of pyramid and lower border of pons.

Course:

Passes forwards and laterally pierces the duramater lateral to dorsum sellae, passes via canal of Dorallo and enters the cavernous sinus. Here it lies infero lateral to internal carotid artery and passes through the superior orbital fissure within the common tendinous ring and enters the orbit.

Termination:

It terminates by supplying the proximal part of medial surface of the lateral rectus muscle.

Applied Anatomy:

1. Fracture of base of skull involves VIth nerve.

2. Carvernous sinus thrombosis – VIth nerve is affected compressed and paralysed.

3. Brain tumours.

4. Meningitis, encephalitis may involve VIth nerve.


7. Term Paper on the Facial Nerve:

It is a mixed cranial nerve.

Nerve of IInd pharyngeal arch.

Nuclei of Facial Nerve:

They are situated in the dorsal part of pons.

1. Motor nucleus – for muscles of face, ear and scalp, posterior belly of digastric and stylohyoid.

2. Sensory nucleus (for taste) – nucleus of tractus solitaries.

Sensory root is also called nervous intermedius.

3. Parasympathetic nucleus:

(a) Superior salivatory nucleus – for supply of submandibular and sublingual glands.

(b) Lacrimatory nucleus – for lacrimal gland.

4. Upper part of nucleus of spinal tract of trigeminal (for general sensation).

Course within the Pons:

Motor and sensory roots winds round the abducent nerve nucleus to form facial colliculus. They pass forwards and leave the pons – between lower border of pons and upper border of olive of medulla oblongata.

Course Outside the Pons (VIIth N.):

Intra petrous course.

Two roots of VIIth nerve pass laterally and enter the internal auditory meatus – accompanied by VIIIth nerve.

Two roots unite to form geniculate ganglion and from the ganglion-trunk of facial nerve is formed.

Now the nerve is passing through facial canal or canal of fallopei.

On reaching the medial wall of middle ear it runs posteriorly – situated superior to the promontory of middle ear.

Passes behind the posterior wall and runs vertically downwards to the stylomastoid foramen.

Extra Cranial Course of Facial Nerve:

After emerging through stylomastoid foramen it runs forwards and crosses the styloid process of temporal bone and enters the postero-medial surface of parotid gland. Within the gland it crosses laterally to retromandibular vein and external carotid artery.

Termination:

It terminates by dividing into temporo facial and cervico facial branches.

Temporo facial divides into temporal and zygo­matic branch.

Cervico facial divides into buccal, marginal mandibular and cervical branches.

Branches of Facial Nerve:

I. Branches in the facial nerve canal:

1. Nerve to stapedius

2. Chorda tympani nerve.

II. Branches immediately below the stylomastoid foramen:

1. Posterior auricular nerve

2. Nerve to posterior belly of digastric gives a branch to stylohoid.

III. Branches on the face:

Supplies all the muscles of facial expression except levator palpebrae superioris which is supplied by oculomotor nerve.

1. Temporo-Facial or Zygomatico Temporal Division:

(i) Temporal branch

(ii) Zygomatic branch.

2. Cervico Facial Division:

(i) Buccal – upper and lower

(ii) Marginal mandibular

(iii) Cervical branch.

Communications of VIIth Nerve:

1. Communicating branch to VIIIth nerve within internal acoustic meatus.

2. Communicating branch at geniculate ganglion:

(a) External petrosal to middle meningeal plexus,

(b) Lesser superficial petrosal nerve – otic ganglion,

(c) Greater superficial petrosal nerve – pterygo palatine ganglion.

3. At facial nerve canal – communicates with auricular branch of vagus.

4. Just below stylomastoid foramen – communi­cates with IXth, Xth, auriculo temporal and great auricular nerves.

5. In face – it communicates with branches of trigeminal nerve (Vth).


8. Term Paper on the Vestibulo Cochlear Nerve:

It is the eighth cranial nerve – purely sensory.

Also called as stato acoustic nerve.

It performs the functions of hearing and balancing of the body.

Cochlear Nerve- (The Nerve of Hearing):

The spiral ganglion of the spiral organ has bipolar cells.

The peripheral processes of these cells end in the organ of corti.

The central processes of these cells form the cochlear nerve.

Vestibular Nerve- (The Nerve of Balance):

Vestibular ganglion of the vestibule of internal ear is made up of bipolar cells.

The peripheral processes of these cells pass to the neuro-epithelium of the semicircular canals (crista ampularis), utricle and saccule (Maculae).

The central processes of these bipolar cells collect to form the vestibular nerve.

Course of Vestibulo Cochlear Nerve:

The cochlear nerve and vestibular nerve are passing through the internal acoustic meatus. They run along with the facial nerve and enter the posterior cranial fossa reaching at ponto-medullary junction.

Termination:

A. The Cochlear Nerve:

End in the dorsal and ventral cochlear nuclei. From cochlear nuclei fresh fibres originate and go to the trapezoid body and lateral lemniscus. From the lateral lemniscus these fibres enter the medial geniculate body. From the medial geniculate body via auditory radiation they ultimately end in the auditory cortex.

B. The Vestibular Nerve:

Terminates within the superior, inferior, medial and lateral vestibular nuclei, these fibres go to the cerebellum.

From the lateral vestibular nucleus fibres go to the spinal cord via vestibulo-spinal tract.

From superior and medial nuclei fibres go to those nuclei innervating eye muscles.

Medial longitudinal bundle connects this nucleus with other motor cranial nerve nuclei.

Applied Anatomy:

1. Certain drugs like streptomycin, quinine may affect the cochlear nerve.

2. Vestibular nerve involvement has the following features:

(a) Vertigo

(b) Nystagmus

(c) Nausea and vomiting

(d) Tachycardia.

3. Cochlear nerve involvement has the following features:

(a) Tinnitus

(b) Deafness

(c) Hearing scotoma (deafness for certain pitches)

(d) Word deafness (sensory aphasia).

4. Fractures of petrous part of temporal bone may involve facial and vestibulo cochlear nerve.


9. Term Paper on the Glossopharyngeal Nerve:

IXth cranial nerve.

It is a mixed cranial nerve.

Embroylogically, it is the nerve of the third pharyngeal arch.

Nuclei are situated within the medulla oblongata.

(a) Motor nucleus is a part of nucleus ambiguuas.

(b) Sensory nucleus is a part of nucleus of the tractus solitarius.

(c) Para Sympathetic nucleus is the inferior salivatory nucleus.

Emergence from the medulla oblongata – about 8 to 10 rootlets emerge through the postero lateral sulcus of medulla oblongata superior to the vagus and accessory nerves.

Course:

All roots unite to form the nerve trunk. It passes through middle part of jugular foramen and leaves the cranial cavity.

At jugular foramen it has a pair of ganglia, i.e., superior and inferior ganglia.

It descends between internal carotid artery and internal jugular vein, passes forwards between internal and external carotid arteries, and lies deep to the styloid process. It hooks round the stylopharyngeus muscle and passes in the interval between the superior and middle constrictors of the pharynx.

Termination:

It terminates by supplying the posterior 1/3 of the tongue, tonsil, pharynx and glands of the mouth.

Branches:

1. Tympanic branch (Jacobson’s nerve) is carrying para-sympathetic fibres to supply the parotid gland.

2. Carotid sinus nerve (nerve of herring) to supply the carotid sinus and carotid body.

3. Pharyngeal branches to join pharyngeal plexus of nerves.

4. Muscular branch to supply stylopharyngeus.

5. Tonsillar branch for palatine tonsil and soft palate.

6. Lingual branches to supply posterior 1/3 to tongue. It carries general sensation and taste sensation from posterior 1/3 of tongue.

Parasympathetic Component:

Inferior salivary nucleus → glossopharyngeal nerve → tympanic branch → tympanic plexus → lesser superficial petrosal nerve → otic ganglion → auricuotemporal nerve → parotid gland.

Applied Anatomy:

1. Glossopharyngeal neuralgia.

2. Lesions of IXth nerve cause loss of gag reflex.


10. Term Paper on the Vagus Nerve:

It is a mixed nerve having both motor and sensory fibres.

Nuclei:

1. Dorsal nucleus

2. Nucleus ambigus

3. Nucleus of the tractus solitarius

4. Spinal tract of trigeminal nerve.

All nuclei of vagus nerve lies in medulla oblongata.

1. Dorsal Nuclei:

Dorsal nuclei is situated in the floor of 4th ventricle, supplies motor muscles of the thoracic and abdominal viscera.

2. Nucleus Ambiguus:

Fibres supply muscles of larynx and constrictor muscles of pharynx.

3. Nucleus of Tractus Solitarius:

It receives taste sensation from the epiglottis and root of tongue (vallecula).

4. Spinal Tract of Trigeminal:

It receives sensory fibres from the external ear and tympanic membrane.

Emergence from medulla oblongata 8 to 10 rootlets emerge from postero lateral sulcus of medulla oblongata between glossopharyngeal and cranial part of accessory nerve.

Course:

It leaves the cranial cavity through the intermediate compartment of jugular foramen.

Ganglia of Vagus:

Within the jugular foramen – superior ganglion and below the jugular foramen inferior ganglion are situated. The cranial root of accessory nerve fuses with the vagus just below the inferior ganglion.

The nerve enters the carotid sheath and passes vertically downwards, at the root of neck it crosses anterior to the first part of subclavian artery and enters the thorax.

Right Vagus Nerve:

In the superior mediastinum it lies on the right side of trachea but postero medial to the right brachiocephalic vein and superior vena cava. It is crossed by the arch of azygos vein and descends behind the root of right lung. After giving pulmonary branches, it passes behind the oesophagus, joins the oesophageal plexus and passes through the oesophageal opening of the diaphragm as posterior vagal trunk and ends by supplying the pyloric end of the stomach.

Left Vagus Nerve:

From the neck it enters the superior mediasti­num, passes deep to left brachiocephalic vein between the left common carotid and left subclavian arteries.

It crosses the left side of the arch of aorta, passes posterior to the root of left lung, gives branches to left pulmonary plexus and passes anterior to oesophagus.

Enters the abdomen through oesophageal opening in the diaphragm as anterior vagal trunk.

Branches:

(a) From the Jugular Ganglion (Superior Ganglion):

1. Meningeal nerve.

2. Auricular nerve (Alderman’s nerve or Arnold’s nerve).

(b) From Ganglion Nodosum (Inferior Ganglion):

1. Communicating branches to –

(i) Cervical plexus

(ii) Superior cervical sympathetic ganglion

(iii) Hypoglossal nerve.

2. Pharyngeal branches.

3. Superior laryngeal nerve.

(c) From Trunk of Vagus Nerve in the Neck:

1. Right recurrent laryngeal nerve.

2. Superior cervical cardiac nerve.

(d) Branches in Thorax:

1. Cardiac nerves

2. Left recurrent laryngeal nerve

3. Pulmonary branches

4. Oesophageal branches.

(e) Branches in the Abdomen:

1. Gastric branch

2. Coeliac branch

3. Hepatic branch.


11. Term Paper on the Accessory Nerve:

It is a motor nerve and XIth cranial nerve, having cranial part and spinal part.

Nuclei:

1. Nucleus of Cranial Part:

Nucleus ambiguus lies in medulla oblongata.

2. Nucleus of Spinal Part:

Lateral part of anterior grey column of the upper five segments of the spinal cord.

Emergence:

Cranial part emerges from postero­-lateral sulcus of medulla below IXth and Xth nerve.

Spinal part emerges from the lateral surface of the upper five cervical segments of the spinal cord.

Course:

Cranial part passes forwards and laterally to the jugular foramen.

Within the jugular foramen both cranial and spinal roots unite to form main trunk of accessory nerve.

In the lower part of the foramen, both roots separate.

The cranial part joins the inferior ganglion of vagus and fibres are distributed with vagus nerve branches, e.g., pharyngeal, laryngeal and cardiac branches.

Spinal Part:

Spinal part has five roots.

Unite to form spinal accessory passes upwards through foramen magnum and enters the posterior cranial fossa.

Passes laterally towards jugular foramen and unites with cranial part.

At lower part of foramen it separates and leaves the foramen.

It passes backwards and laterally deep to internal jugular vein passes deep to posterior belly of digastric and sterno cleidomastoid and enters the posterior triangle of the neck.

Here it lies on the levator scapulae and pre­vertebral fascia passes deep to trapezius muscle upto 12th thoracic vertebra.

Termination:

It terminates by forming sub-trapezoid plexus by uniting with C3 and C4 nerves and supply trapezius.

Branches:

1. Muscular branches to sternocleido mastoid and trapezius muscle.

2. Communicating branches to C3, C4 and C5 nerves.

Applied Anatomy:

1. Spinal accessory may be irritated by enlarged lymph nodes of posterior triangle of neck and causes spasmodic torticollis.

2. During bilateral paralysis of accessory nerve, there is difficulty in rotating the neck on raising the chin, head drops forwards, trapezius atrophy and results in flat shoulder.

3. Cervical lymph glands are enlarged and compress the accessory nerve.


12. Term Paper on the Hypoglossal Nerve (Motor Cranial Nerve):

It is the XIIth cranial nerve.

Emerging from anterior part of medulla oblongata just like ventral root of a spinal nerve emerges from the spinal cord (i.e., Antero-lateral sulcus of medulla).

Nucleus:

2 cm long nucleus present in medulla oblongata in the floor of the 4th ventricle.

Emergence from brain stem – about 10 rootlets emerge from lateral sulcus of medulla in between pyramid and olive.

Course:

Passes forwards and laterally towards hypo­glossal canal. Here fibres unite to form two nerve bundles.

Pierce the duramater and two bundles unite to form a single nerve and leave the cranial cavity.

It winds round the inferior ganglion of vagus nerve.

It runs vertically downwards between internal jugular vein and internal carotid artery.

Passes deep to posterior belly of digastric and reaches the carotid triangle.

At the level of the angle of the mandible it passes forwards and crosses superficial to – a. Internal carotid artery, b. External carotid artery, c. Loop of lingual artery.

It is superficially crossed by common facial vein.

It runs on the outer surface of hyoglossus muscle and accompanied by vene commitence hypoglossi.

The nerve is related superiorly to deep part of submandibular gland, submandibular ganglion, submandibular duct and lingual nerve.

Termination:

It passes deep to mylohyoid muscle and ends by supplying all the muscles of the tongue except palato glossus muscle – supplied by pharyngeal plexus.

Communications:

1. Superior cervical sympathetic ganglion.

2. C1 fibres join the hypoglossal nerve and leave it as the superior limb of ansa cervicalis.

3. Pharyngeal plexus.

4. Lingual nerve.

Branches:

1. Meningeal branch – nervi spinosus

2. Superior limb of ansa carvicalis

3. Nerve to thyrohyoid and geniohyoid

4. Muscular branches to supply muscles of tongue – (a) Styloglossus, (b) Hyoglossus, (c) Genioglossus and (d) All the intrinsic muscles of the tongue.

Applied Anatomy:

1. When hypoglossal nerve is injured unilaterally the affected side of the tongue is swollen. When protruded it deviates towards the affected side.

2. Bilateral injury of XIIth nerve causes – (a) Immobile tongue, (b) Sticky speech and (c) Difficulty in swallowing.

The tongue may fall back and closes the glottis, this produces suffocation.


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