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CRANIAL NERVES • Nerves that emerge directly from the brain (spinal nerves emerge from segments of the spinal cord) • 12 pairs of cranial nerves.

How to remember Cranial Nerves

Cranial Nerve I: Olfactory • It is the first cranial nerve and nerve of smell and form first order neuron of olfactory pathway. • Type → Special Sensory type. • Origin → From olfactory epithelium in the olfactory region of nasal cavity (superior nasal concha and opposed part of nasal septum).

• Course → Fibers run through the olfactory bulb ( mitral cells)olfactory tract and terminate in the primary olfactory cortex

• Innervation → Nasal Mucous Membranes.

• Enter → Cribriform plate of the ethmoid bone.

Peculiarities • 3000 different odours • I sensation to appear in vertebrate evolution • II order neuron ( mitral cells) reaches cortex directly without involvement of thalamus • Ipsilateral - no significant decussation

APPLIED ANATOMY • Anosmia (Olfactory anaesthesia) • Head Injuries -–> CSF Rhinorrhoea. • CVA -> Effusion of blood into base of frontal lobe • Tumours of the Frontal lobe, or those arising near the pituitary gland • Infections –tuberculous meningitis infections like common cold, Viral Hepatitis, syphilis, osteomyelitis of frontal or ethmoidal regions. • Unilateral Anosmia may be of diagnostic significance in localizing brain lessons.

APPLIED ANATOMY • Reduction – hyposmia – local abn of nose • Distortion of smell – parosmia – Head injury or local abnormalities of nose • Increased smell – hyperosmia – In neurotic patients • Olfactory hallucinations & delusions – epilepsy, migraine, psychiatric patients.

Cranial Nerve II - Optic • Part of the CNS as it is derived from an outpouching of the diencephalon during embryonic corrospondence • The fibres are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system and are encased within the meninges • Therefore peripheral neuropathies like GuillainBarré syndrome do not affect the optic N

• ORIGIN: Arises from the retina of the eye. • COURSE: Optic nerves pass thru’ the optic canals and converge at the optic chiasma • They continue as optic tract to the thalamus where they synapse • From there, the optic radiation fibers run to the visual cortex of occipital lobe.

Visual Pathway

APPLIED ANATOMY • • • • • • •

Right-sided circumferential blindness due to retrobulbar neuritis. Total blindness of the right eye due to lesion of right optic nerve. Right nasal hemianopia due to partial lesion of right optic chiasm. Bitemporal hemianopia due to a complete lesion of the optic chiasm. Left temporal and right nasal hemianopias due to a lesion of the right optic tract (homonymous hemianopia) Left temporal and right nasal hemianopia due to a lesion of the right optic radiation. Left temporal and right nasal hemianopia due to a lesion of the right visual cortex.

APPLIED ANATOMY • Damage before the optic chiasm causes loss of vision in the visual field of the same side only. • Damage in the chiasm causes loss of vision laterally in both visual fields (bitemporal hemianopia). It may occur in large pituitary adenoma • Damage after the chiasm causes loss of vision on one side but affecting both visual fields: nasalsame ½ ; temporal – opp ½


VISUAL FIELDS • Ask the patient to cover one eye while the examiner tests the opposite eye • The examiner wiggles the finger in each of the four quadrants and asks the patient to state when the finger is seen in the periphery • The examiner's visual fields should be normal, since it is used as the baseline.

Cranial Nerve III - Occulomotor • ORIGIN: Originates from the oculomotor nucleus located in the rostral midbrain at the level of the superior colliculus.

• COURSE: Fibres leaving the occulomotor nucleus travel ventrally in the tegmentum of the midbrain passing through medial portion of the cerebral peduncle to emerge at the junction of the midbrain and pons. • Upon emerging from the brainstem the oculomotor nerve passes between the posterior cerebral and superior cerebellar arteries and pierces the dura mater to enter the cavernous sinus.

• The nerve runs along the lateral wall of the cavernous sinus just superior to the trochlear nerve and enters the orbit via the superior orbital fissure. • Within the orbit, CN III fibers pass through the tendinous ring of the extraocular muscles and divide into superior and inferior divisions. • The superior division ascends lateral to the optic nerve to innervate the superior rectus and levator palpebrae superioris muscles on their deep surfaces. • The inferior division of CN III splits into three branches to innervate the medial rectus and inferior rectus muscles on their ocular surfaces and the inferior oblique muscle on its posterior surface.

FUNCTIONS • The somatic motor component of CN III innervates the following four extraocular muscles of the eyes: Ipsilateral inferior rectus muscle Ipsilateral inferior oblique muscle Ipsilateral medial rectus muscle Ipsilateral superior rectus muscle • The remaining extraocular muscles, the superior oblique and lateral rectus muscles, are innervated by the trochlear nerve (CN IV) and abducens nerve (CN VI), respectively • The somatic motor component of CN III also innervates the Bilateral levator palpebrae superioris muscles. These muscles elevate the eyelids.

FUNCTIONS • Viseral motor component: Provides parasympathetic innervation of the constrictor pupillae and ciliary muscles of the eye. The visceral motor component of CN III is involved in the pupillary light and accommodation reflexes.

Pupillary reflex • The reaction of the pupils to light and accommodation • In the direct light reflex, the normal pupil reflexly contracts when a light is shown into the patient's eye • The nervous impulses pass from the retina along the optic nerve to the optic chiasma and then along the optic tract

• Before reaching the lateral geniculate body, the fibers concerned with this reflex leave the tract and pass to the pretectal nuclei • The pretectal nucleus in turn projects bilaterally to the Edinger-Westphal nucleus • Preganglionic parasympathetic fibers from each half of the Edinger-Westphal nucleus then project to the ciliary ganglion of the ipsilateral orbit

• Post-ganglionic parasympathetic fibers exit the ciliary ganglion to innervate the constrictor pupillae muscle of the ipsilateral eye • Due to the bilateral projections from the pretectal nuclei to the Edinger-Westphal nuclei, light shined into one eye produces pupillary constriction in both eyes • Direct pupillary light reflex - response in the stimulated eye • Consensual pupillary light reflex - response in the opposite eye.

Pupillary eye reflex - test • The patient stares into the distance as the examiner shines the penlight obliquely into each pupil • Pupillary constriction should be noted on the eye examined (direct response) and on the opposite eye (consensual response)

Testing the oculomotor nerve • Cranial nerves III, IV and VI are usually tested together • The examiner typically instructs the patient to hold his head still and follow only with the eyes a finger or penlight that circumscribes a large "H" in front of the patient • By observing the eye movement and eyelids, the examiner is able to obtain more information about the extraocular muscles, the levator palpebrae superioris muscle, and cranial nerves III, IV, and VI.

LMN Lesions- Oculomotor Ophthalmoplegia • Due to the close proximity of the oculomotor and EdingerWestphal nuclei and the fact that the fibers of both components travel together all the way to the orbit of the eye, a LMN lesion will most likely affect both components of CN III • Downward, abducted eye on the affected side due to the unopposed actions of the superior oblique and lateral rectus muscles. • Strabismus as a result of extraocular muscle paralysis. This leads to diplopia (double vision).

• Ptosis (eyelid droop) on the affected side due to inactivation of levator palpebrae superioris muscle and the unopposed action of the orbicularis oculi muscle (CN VII) • The patient may compensate for the ptosis by contracting the muscles of the forehead to raise the eyebrow and lid.

• Dilation of the pupil on the affected side due to decreased tone of the constrictor pupillae muscle. • Loss of the accomodation reflex on the affected side.

Cranial Nerve IV: Trochlear • ORIGIN: Fibres emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures. • The fibers of the trochlear nerve originate from the trochlear nucleus located in the tegmentum of the midbrain at the level of the inferior colliculus. • The nucleus is located just ventral to the cerebral aqueduct

COURSE • Fibers leaving the trochlear nucleus travel dorsally to wrap around the cerebral aqueduct • All fibers of the two trochlear nerves decussate and exit the dorsal surface of the brainstem just below the contralateral inferior colliculus. • Then trochlear nerve curves around the brainstem in the subarachnoid space and emerges between the posterior cerebral and superior cerebellar arteries (along with CN III fibers) • • The trochlear nerve then enters and runs along the lateral wall of the cavernous sinus with CN III, V, and VI.

• From the cavernous sinus the trochlear nerve enters the orbit through the superior orbital fissure • Innervate the superior oblique muscle along its proximal one-third • The only nerve to exit from the dorsal surface of the brain. • Is the only nerve in which all the lower motor neuron fibers decussate. • Has the longest intracranial course. • Has the smallest number of axons.

ACTIONS • The superior oblique muscle normally depresses,intorts, and abducts the eye • Damage to the trochlear nerve will present as Extorsion (outward rotation) of the affected eye due to the unopposed action of the inferior oblique muscle. • Vertical diplopia (double vision) due to the extorted eye • Weakness of downward gaze most noticeable on mediallydirected eye. This is often reported as difficulty in descending stairs.

• Head tilt: patient will often tilt his head opposite the side of the affected eye in an attempt to compensate for the outwardly rotated eye • Due to its long peripheral course around the midbrain CN IV is particularly susceptible to head trauma.

Applied anatomy ďƒ˜ If the nerve is injured, downward and lateral movement of eyeball will not be possible and no difficulty so long the patient looks above the horizontal level. ďƒ˜ Double vision will occur if he looks downward and the patient has a pathetic look and so this nerve is known as pathetic nerve.

Cranial nerve V Trigeminal nerve • It is the fifth cranial nerve and largest of all cranial nerves. • Type → Mixed so both Motor & Sensory.

• ORIGIN AND COURSE: Superficial origin: Two roots: Motor

and sensory emerge from the ventral aspect of the pons. Sensory root larger and motor root smaller and motor root lies ventrimedial to sensory root. • The sensory root passes forward from the posterior cranial fossa and joins the concave posterior margin of trigeminal ganglion. • The motor root passes forward and then passes below the sensory root and trigeminal ganglion in the trigeminal cave and finally joins with the sensory part of mandibular nerve in the foramen ovale and from trunk of mandibular nerve.

• Branches • Ophthalmic Nerve (V1) → Purely Sensory Nerve. • Maxillary Nerve (V2) → Sensory. • Mandibular Nerve (V3) → Mixed and consisting of two roots

OPHTHALMIC It is one of the divisions of trigeminal nerve. - It is purely a sensory nerve. - Arises from the convex anterior margin of trigeminal ganglion. - After origin it lies on the lateral wall of cavernous sinus below 4th cranial nerve and above maxillary division. - In the anterior part of cavernous sinus it terminates by dividing into a) Frontal, b) Lacrimal, c) Nasociliary.

MAXILLARY • It is the intermediate division of trigeminal nerve. • Origin: from the convex aspect of trigeminal ganglion. • Course: After origin it runs forwards along the lower part of lateral wall of cavernous sinus below the ophthalmic nerve. • Then it leaves the skull by passing through foramen rotundum and enters into the pterygopalatine fossa. From there it inclines to the posterior surface of maxilla and enters the orbit through inferior orbital fissure. It is then named infraorbital nerve It passes through infraorbital groove and canal on the floor of the orbit.

• Branches: 1) Within cranium: Meningeal. It supplies duramater of middle and partly in the anterior cranial fossa. 2) In the pterygopalatine fossa: 1) Ganglionic: 2) Zygomatic: a. zygomaticotemporal b. zygomaticofacial. 3) Posterior superior alveolar. 3) In the infraorbital canal: i. Middle superior alveolar. ii. Anterior superior alveolar. 4) In the face: 1. Palpebral. 2. Nasal. 3. Superior labial.

MANDIBULAR It is the largest division of trigeminal nerve. • Origin: Larger sensory root arises from convex aspect of trigeminal ganglion and smaller motor root from motor nucleus of trigeminal nerve in the pons. • Course: The united trunk enters the infratemporal fossa by passing through foramen ovale and lies in between tensor veli palate-medially and lateral pterygoid laterally.

Branches 1) From the trunk, i.e. before division: i) Nervous spinous or meningeal branch ii) Nerve to medial pterygoid. 2) From anterior divisions: Motor branches: i) Deep temporal ii) Nerve to lateral pterygoid iii) Massetric Sensory branch: Buccal nerve and skin 3) From posterior division: i) auriculo temporal ii) lingual

• Inferior alveolar nerve: It is the branch of posterior trunk of mandibular nerve. • Course: it runs downward deep to lateral pterygoid and passes between sphenomandibular ligament and ramus of mandible upto mandibular foramen and enters the mandibular canal and runs below the teeth as far as mental foramen and terminates by dividing into mental and incisive branch. • Branches: 1) Nerve to myolohyoid 2) Mental 3) Incisive branch 4) Dental branch

Applied anatomy ďƒ˜ The sensory root of this nerve is divided into three divisions, each division may be tested by light touch or pinprick on the skin overlying its respective area of distribution. ďƒ˜ The motor root of trigeminal supplies the muscles of mastication and can be tested by palpating the temporalis and masseter during clenching movements.

Applied anatomy 

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Lesion of whole of trigeminal nerve, 1) Anesthesia of the corresponding anterior half of scalp, face(except the area at the angle of mouth, because of supply by great auricular), cornea, conjunctiva, mucous membrane of nose, mouth, anterior 2/3rd of tongue. 2) Paralysis and atrophy of muscles supplied by the nerve and so when patient tries to open the mouth the mandible will thrust to the paralysed side. Lesions of any divisions of nerve. Lesion of lingual nerve below the point of joining of chorda tympani Pain or neuralgia is of very common. In case of frontal or ethmoidal sinusitis or glaucoma severe supraorbital pain occurs. It is also a case of referred pain.

Trigeminal neuralgia ďƒ˜ It is a disorder of unilateral (usually right-sided) facial pain. While the exact cause is unknown, it is thought that TN results from irritation of the trigeminal nerve. This irritation results from damage due either to changes in the blood vessels or the presence of a tumor or other lesions that cause compression of the nerve. ďƒ˜ The pain quality is usually sharp, stabbing, lancinating (cutting or tearing), and burning. It may have an "electric shock"-like character. ďƒ˜ In some individuals the attacks may be initiated by non-painful physical stimulation of specific areas (trigger points or zones) that are located on the same side of the face as the pain.

Cranial nerve VI-Abducens nerve • It is the sixth cranial nerve which supplies lateral rectus muscle. • Type → Motor nerve. • Origin → The fibres arise from a small nucleus situated in the dorsal aspect of the pons in the floor of the fourth ventricle close to the median plane and beneath the facial colliculus.

• Course → The abducent nerve after leaving the brain stem runs upwards laterally and forwards through cisterna pontis. As it proceeds forwards it will be crossed by anterior inferior cerebellar artery ventrally and then loses its dural sheath at the lateral side of dorsal sellae. Then it bends sharply forwards at the apex of petrous part of temporal bone to the lateral margin of dorsum sellae. After that enters into orbital cavity through middle part of superior orbital fissure within annulous tendinous communis. Finally it terminates in the orbit. • Enter → Superior Orbital Fissure.

Applied anatomy  It is liable to be damaged during fracture of skull. When intracranial pressure increases, pons is pushed backwards and downwards and this nerve may get stretched and may lose its function.  Effects of paralysis: – Convergent squint due to unopposed action of medial rectus. – Often diplopia with convergent squint will be present.

Cranial nerve VII- Facial nerve • Type of nerve: It is a mixed nerve consisting of two roots – sensory and motor roots. The sensory root is known as Nervus intermedius. • Developmental representation: It is the nerve of second branchial arch.

• Branches of distribution: – Within facial canal – Nerve to stapedius muscle. – Chorda tympani nerve. – Just at its exit from stylomastoid foramen. – Posterior auricular. – Nerve to stylohyoid. – Nerve to posterior belly of diagastric. – In the face: – Temporal. – Zygomatic. – Buccal. – Marginal mandibular. – Cervical.

Applied anatomy • Supra nuclear lesions- Hemiplegia. • Infra nuclear lesions- Bells palsy.

VIII Nerve- Vestibulocochlear • Type: Special sensory nerve and nerve of hearing and equilibrium. • Have two components vestibular component and cochlear component. • ORIGIN: Cochlear nerve ( two nuclei) ventral cochlear and dorsal cochlear nuclei. • Vestibular nerve (four nuclei) superior, inferior, medial, lateral.

• COURSE: The vestibulocochlear nerve along with two roots of facial nerve after emergence from the brain stem runs laterally to internal acoustic meatus accompanied by internal acoustic branch of basilar artery and corresponding veins. • In the meatus the motor root of facial nerve lies on upper and anterior surface of vestibulocochlear and the sensory root lies between them. • Then the vestibulocochlear nerve divides into two components- (a) Vestibular and (b) Cochlear nerves.

actions • The vestibular nerve is sensory from receptors in the inner ear that provide information concerning movement of the body, balance, and body position in relation to gravitational force. • The cochlear nerve is sensory from auditory (hearing) receptors in the cochlea of the inner ear.

Applied anatomy • Vestibulocochlear nerve is frequently injured along with facial nerve in fracture of middle cranial fossa involving internal acoustic meatus. • Nerve may be injured by violent blows of the head or by loud explosions and deafness may occur. • Tumors at cerebello-pontine angle may involve both the facial and vestibulocochlear nerve.

Applied anatomy • Disturbances in the vestibular nerve function include giddiness(VERTIGO) and NYSTAGMUS. Vestibular nystagmus is uncontrollable rhythmic oscillations of the eyes. This form of nystagmus is essentially a disturbance in reflex control of the extraocular muscles, which is one of the function of the semicircular canals. The causes of vertigo include diseases of the labrynth, lesions of the vestibular nerve and cerebellum, multiple sclerosis, tumors and vascular lesions of brainstem. • Disturbances in the cochlear nerve include deafness and tinnitus. Loss of hearing may be due to defect in the auditory conducting mechanism in the middle ear, damage to receptor cells in spinal organ of corti in cochlea, lesions of the cochlear nerve due to acoustic neuroma and trauma, or lesion of the cerebral cortex of temporal lobe due to multiple sclerosis.

TESTS • Rinne’s test: vibrating tuning fork is held in the ear and then placed on the mastoid process patient is asked to compare the relative loudness of the two. • Weber’s test: vibrating tuning fork is placed in middle of forehead – the sound will be heard better in the middle ear diseased side than on the normal side.

IX Nerve- Glossopharyngeal • Mixed nerve • Deep origin: The nuclei are: 1. Upper part of nucleus ambigus: It gives branchiomotor fibres. 2. Inferior salivatory nucleus: origin of parasympathetic secretomotor fibres to parotid gland. • Upper part of nucleus of spinal tract of trigeminal nerve: for general somatic afferent. • Upper part of tractus solitarius: for special sense taste (special Visceral afferent) and other general visceral sensations from posterior one third of tongue, tonsil, palate, oral part of pharynx. • Superficial origin: The nerve emerges out as two or three rootlets from the posterolateral sulcus of medulla oblongata above the rootlets of vagus nerve.

Applied anatomy • Glossopharyngeal nerve is not involved separately usually. It may be injured along with tenth nerve. • Acute pharyngitis may cause referred pain in the ear but inflammation of pharyngotympanic tube must be excluded. • Reflex contraction of muscles of throat if posterior wall of pharynx is stimulated and 9th nerve can be tested in this way. • Taste sensation of posterior one-third of tongue will be lost in case of involvement of 9th nerve. • After a series of coughing carotid sinus may be subjected to pressure and results in syncope or cardiac arrest. This is due to stimulation of cardioinhibitory centre reflexly by sinus nerve.

X Nerve- Vagus • The vagus nerve supplies motor fibers to constrictor muscles of the pharynx, intrinsic muscles of the larynx, and involuntary muscles of the bronchi, heart, esophagus, stomach, small intestine, and part of the large intestine. Secretory motor fibers of the vagus supply the pancreas and secretory glands of most of the alimentary canal. The vagus is sensory from the laryngeal mucosa, heart, lungs, esophagus, stomach, small intestine, and part of the large intestine. In addition, vagal sensory fibers convey taste from the epiglottis and blood pressure and chemistry information from the aorta. The ninth and tenth cranial nerves are tested together because their functions overlap.

Applied anatomy • Auricular branch of vagus is irritated by scratching, or by earwax or syringing the ear with warm water. This irritation may cause reflex vomiting and also stoppage of heart by reflex irritation of vagus. • Recurrent laryngeal nerve may be injured during operation on thyroid and application of ligature of inferior thyroid artery. It may also be compressed during enlargement of thyroid, specially a growth. Its affection causes hoarseness of voice. • Vagotomy i.e. section of anterior and posterior or vagal trunks are sometimes done in treatment of peptic ulcer.

XI Nerve- Spinal accessory • The spinal accessory nerve, cranial nerve XI, innervates the sternocleidomastoid and trapezius muscles. It is composed of spinal fibers originating in the anterior horn cells of the first five cervical cord segments and an accessory component, which travels briefly alongside the vagus nerve. The dorsal and ventral roots from the first five cervical cord segments unite to enter the skull through the foramen magnum and exit through the jugular foramen.

Actions • The eleventh cranial nerve supplies some motor fibers to the muscles of the larynx and pharynx via the pharyngeal plexus (C.N. IX-X-XI), but its principal distribution is motor to the sternocleidomastoid and trapezius muscles. The sternocleidomastoid turns the head to the opposite side, and the trapezius muscle elevates the shoulder on the same side.

Applied anatomy • When the sternocleidomastoid and trapezius are weak on the same side, an ipsilateral peripheral accessory palsy, involving cranial nerves X and XI, is implied as may be seen with a jugular foramen tumor, ie, glomus tumor or neurofibroma. Because the cerebral hemisphere innervates the contralateral trapezius and ipsilateral sternocleidomastoid, a large right hemisphere stroke will result in weakness of the left trapezius and right sternocleidomastoid. Bilateral wasting of the sternocleidomastoid may be seen with myopathic conditions such as myotonic dystrophy and polymyositis or motor neuron disease, the latter usually associated with


XII Nerve- Hypoglossal • The hypoglossal nerve is a pure motor nerve, innervating the muscles of the tongue. It obtains supranuclear innervation from the contralateral motor cortex. The nucleus of the hypoglossal nerve sits in the medial aspect of the medulla, near the floor of the fourth ventricle and exits the skull through the hypoglossal canal.

Applied anatomy • Tongue deviation, combined with wasting on the side to which it is deviated, implies a unilateral, lower motor neuron, hypoglossal nucleus or nerve lesion as may be seen with syringobulbia (a degenerative cavity within the brainstem), with basilar meningitis, or foramen magnum tumor. If the tongue deviates and is of normal bulk, one should consider an upper motor neuron lesion, such as stroke or tumor in the hemisphere contralateral to the side of deviation, and look for associated hemiparesis on the side of tongue deviation.



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