ANATOMYBY

Dr. THAAER MOHAMMED DAHER ALSAADSPECIALIST IN GENERAL SURGERY

M.B.Ch.B. (MBBS) F.I.B.M.S. (PhD)SENIOR LECTURER

ISM MSU

CRANIAL NERVESCranial nerves are

nerves that emerge directly from the brain,

in contrast to spinal nerves which emerge from segments of the spinal cord.

In humans, there are 12 pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum,

the remaining 10 pairs emerge from the brainstem.

CRANIAL NERVES

• The 12 pairs of cranial nerves are part of the peripheral nervous system (PNS) and pass through foramina or fissures in the cranial cavity.

• All nerves except one, the accessory nerve [XI], originate from the brain.

• In addition to having similar somatic and visceral components as spinal nerves, some cranial nerves also contain special sensory and motor components.

• The special sensory components are associated with hearing, seeing, smelling, balancing, and tasting.

• Special motor components include those that innervate muscles derived embryologically from the pharyngeal arches.

*Special sensory, or special visceral afferent (SVA)-smell, taste; special somatic afferent (SSA)-vision, hearing, balance.

**Special visceral efferent (SVE) or branchial motor.

Cranial nerve functional components

Cranial nerves

*Sensations from head and neck structures derived from embryonic endoderm and/or splanchnopleuric mesoderm are classified in discussions in this text as general visceral afferents

Classification of the cranial nerves.

Motor CN III, IV, XI, XII.SESORY CN I, II, VIII.MIXED CN V, VII, IX, X.

CRANIAL NERVES• In human embryology, six pharyngeal arches are designated, but the fifth

pharyngeal arch never develops. • Each of the pharyngeal arches that does develop is associated with a

developing cranial nerve or one of its branches. • These cranial nerves carry efferent fibers that innervate the musculature

derived from the pharyngeal arch. • Innervation of the musculature derived from the five pharyngeal arches that

do develop is as follows:– first arch-trigeminal nerve [V3]; – second arch-facial nerve [VII]; – third arch-glossopharyngeal nerve [IX]; – fourth arch-superior laryngeal branch of the vagus nerve [X]; – sixth arch-recurrent laryngeal branch of the vagus nerve [X].

Olfactory nerve [I]

• The olfactory nerve [I] carries special afferent (SA) fibers for the sense of smell.

• Its sensory neurons have:– peripheral processes that act as receptors in the nasal mucosa;– central processes that return information to the brain.

The receptors are in the roof and upper parts of the nasal cavity and the central processes, after joining into small bundles, enter the cranial cavity by passing through the cribriform plate of the ethmoid bone.

They terminate by synapsing with secondary neurons in the olfactory bulbs.

Cranial nerves exiting the cranial cavity

Cranial nerves on the base of the brain

Optic nerve [II]

• The optic nerve [II] carries SA fibers for vision. These fibers return information to the brain from photoreceptors in the retina.

• Neuronal processes leave the retinal receptors, join into small bundles, and are carried by the optic nerves to other components of the visual system in the brain.

• The optic nerves enter the cranial cavity through the optic canals.

Oculomotor nerve [III] 1/2

• The oculomotor nerve [III] carries two types of fibers:– general somatic efferent (GSE) fibers

innervate most of the extraocular muscles; – general visceral efferent (GVE) fibers are

part of the parasympathetic part of the autonomic division of the peripheral nervous system (PNS).

Cranial nerves exiting the cranial cavity

Cranial nerves on the base of the brain

Oculomotor nerve [III] 2/2

• The oculomotor nerve [III] leaves the anterior surface of the brainstem between the midbrain and the pons.

• It enters the anterior edge of the tentorium cerebelli, continues in an anterior direction in the lateral wall of the cavernous sinus, and leaves the cranial cavity through the superior orbital fissure.

• In the orbit, the GSE fibers in the oculomotor nerve innervate levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, and inferior oblique muscles.

• The GVE fibers are preganglionic parasympathetic fibers that synapse in the ciliary ganglion and ultimately innervate the sphincter pupillae muscle, responsible for pupillary constriction, and the ciliary muscles, responsible for accommodation of the lens for near vision.

Trochlear nerve [IV]

• The trochlear nerve [IV] is a cranial nerve that carries GSE fibers to innervate the superior oblique muscle, an extraocular muscle in the orbit.

• It arises in the midbrain and is the only cranial nerve to exit from the posterior surface of the brainstem.

• After curving around the midbrain, it enters the inferior surface of the free edge of the tentorium cerebelli,

• continues in an anterior direction in the lateral wall of the cavernous sinus, and enters the orbit, through the superior orbital fissure.

Cranial nerves exiting the cranial cavity

Cranial nerves on the base of the brain

Trigeminal nerve [V] 1/3

• The trigeminal nerve [V] is the major general sensory nerve of the head, and also innervates muscles that move the lower jaw.

• It carries general somatic afferent (GSA) and branchial efferent (BE) fibers:

• the GSA fibers provide sensory input from the face, anterior one-half of the scalp, mucous membranes of the oral and nasal cavities and the paranasal sinuses, part of the tympanic membrane, the eye and conjunctiva, and the dura mater in the anterior and middle cranial fossae;

• the BE fibers innervate the muscles of mastication, the tensor tympani, the tensor veli palatini, the mylohyoid, and the anterior belly of the digastric.

Trigeminal nerve [V] 2/3

• The trigeminal nerve exits from the anterolateral surface of the pons as a large sensory root and a small motor root.

• These roots continue forward out of the posterior cranial fossa and into the middle cranial fossa by passing over the medial tip of the petrous part of the temporal bone.

• In the middle cranial fossa the sensory root expands into the trigeminal ganglion, which contains cell bodies for the sensory neurons in the trigeminal nerve and is comparable to a spinal ganglion.

• The ganglion is in a depression (the trigeminal depression) on the anterior surface of the petrous part of the temporal bone, in a dural cave (the trigeminal cave).

• The motor root is below and completely separate from the sensory root at this point.

Trigeminal nerve [V] 3/3

• Arising from the anterior border of the trigeminal ganglion are the three terminal divisions of the trigeminal nerve, which in descending order are:

• the ophthalmic nerve (ophthalmic division [V1]);

• the maxillary nerve (maxillary division [V2]);

• the mandibular nerve (mandibular division [V3]).

Cranial nerves exiting the cranial cavity

Cranial nerves on the base of the brain

Cavernous sinus

Ophthalmic nerve [V1]

• The ophthalmic nerve [V1] passes forward in the dura of the lateral wall of the cavernous sinus, leaves the cranial cavity, and enters the orbit through the superior orbital fissure.

• The ophthalmic nerve [V1] carries sensory branches from the eyes, conjunctiva, and orbital contents, including the lacrimal gland.

• It also receives sensory branches from the nasal cavity, frontal and ethmoidal sinuses, upper eyelid, dorsum of the nose, and the anterior part of the scalp.

Maxillary nerve [V2]

• The maxillary nerve [V2] passes forward in the dura mater of the lateral wall of the cavernous sinus just inferior to the ophthalmic nerve [V1],

• leaves the cranial cavity through the foramen rotundum, and enters the pterygopalatine fossa.

• The maxillary nerve [V2] receives sensory branches from the dura in the anterior and middle cranial fossae, the nasopharynx, the palate, the nasal cavity, teeth of the upper jaw, maxillary sinus, and skin covering the side of the nose, the lower eyelid, the cheek, and the upper lip.

Mandibular nerve [V3] 1/2

• The mandibular nerve [V3] leaves the inferior margin of the trigeminal ganglion and leaves the skull through the foramen ovale.

• The motor root of the trigeminal nerve also passes through the foramen ovale and unites with the sensory component of the mandibular nerve [V3] outside the skull.

• Thus, the mandibular nerve [V3] is the only division of the trigeminal nerve that contains a motor component.

Mandibular nerve [V3] 2/2

• Outside the skull the motor fibers innervate the muscles of mastication, including the temporalis, the masseter, and the medial and lateral pterygoid muscles,

• as well as the tensor tympani, the tensor veli palatini, the anterior belly of the digastric, and the mylohyoid muscles.

• The mandibular nerve [V3] also receives sensory branches from the skin of the lower face, cheek, lower lip, the ear, the external acoustic meatus and the temporal region, the anterior two-thirds of the tongue, the teeth of the lower jaw, the mastoid air cells, the mucous membranes of the cheek, the mandible, and dura in the middle cranial fossa.

Abducent nerve [VI]

• The abducent nerve [VI] carries GSE fibers to innervate the lateral rectus muscle in the orbit.

• It arises from the brainstem between the pons and medulla and passes forward, piercing the dura covering the clivus.

• Continuing upward in a dural canal, it crosses the superior edge of the petrous temporal bone, enters and crosses the cavernous sinus just inferolateral to the internal carotid artery,

• and enters the orbit through the superior orbital fissure.

Cranial nerves exiting the cranial cavity

Cranial nerves on the base of the brain

Parasympathetic ganglia of the head

Facial nerve [VII] 1/2 • The facial nerve [VII] carries GSA, SA, GVE, and BE fibers:• The GSA fibers provide sensory input from the external acoustic

meatus and a small amount of skin posterior to the ear; • The SA fibers are for taste from the anterior two-thirds of the

tongue; • The GVE fibers are part of the parasympathetic part of the

autonomic division of the PNS and stimulate secretomotor activity in the lacrimal gland, submandibular and sublingual salivary glands, and mucous membranes of the nasal cavity, and hard and soft palates;

• The BE fibers innervate the muscles of the face (muscles of facial expression) and scalp derived from the second pharyngeal arch, and the stapedius, the posterior belly of the digastric, and the stylohyoid muscles

Facial nerve [VII] 2/2 • The facial nerve [VII] attaches to the lateral surface of the

brainstem, between the pons and medulla oblongata. • It consists of a large motor root and a smaller sensory root (the

intermediate nerve):• the intermediate nerve contains the SA fibers for taste, the

parasympathetic GVE fibers and the GSA fibers; • the larger motor root contains the BE fibers. The motor and sensory roots cross the posterior cranial fossa and

leave the cranial cavity through the internal acoustic meatus. After entering the facial canal in the petrous part of the temporal

bone, the two roots fuse and form the facial nerve [VII]. Near this point the nerve enlarges as the geniculate ganglion, which

is similar to a spinal ganglion containing cell bodies for sensory neurons.

Cranial nerves exiting the cranial cavity

Cranial nerves on the base of the brain

Facial nerve [VII] 2/2

• At the geniculate ganglion the facial nerve [VII] turns and gives off the greater petrosal nerve, which carries preganglionic parasympathetic (GVE) fibers.

• The facial nerve [VII] continues along the bony canal, giving off the nerve to stapedius and the chorda tympani, before exiting the skull through the stylomastoid foramen.

• The chorda tympani carries taste (SA) fibers from the anterior two-thirds of the tongue and preganglionic parasympathetic (GVE) fibers destined for the submandibular ganglion.

Vestibulocochlear nerve [VIII]

• The vestibulocochlear nerve [VIII] carries SA fibers for hearing and balance, and consists of two divisions: – a vestibular component for balance; – a cochlear component for hearing

The vestibulocochlear nerve [VIII] attaches to the lateral surface of the brainstem, between the pons and medulla, after emerging from the internal acoustic meatus and crossing the posterior cranial fossa.

The two divisions combine into the single nerve seen in the posterior cranial fossa within the substance of the petrous part of the temporal bone.

Cranial nerves exiting the cranial cavity

Cranial nerves on the base of the brain

Glossopharyngeal nerve [IX] 1/2

• The glossopharyngeal nerve [IX] carries GVA, SA, GVE, and BE fibers:• The GVA fibers provide sensory input from• The carotid body and sinus, posterior one-third of the tongue,

palatine tonsils, upper pharynx, and mucosa of the middle ear and pharyngotympanic tube;

• The SA fibers are for taste from the posterior one-third of the tongue;

• The GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate secretomotor activity in the parotid salivary gland;

• The BE fibers innervate the muscle derived from the third pharyngeal arch (the stylopharyngeus muscle).

Glossopharyngeal nerve [IX] 2/2

• The glossopharyngeal nerve [IX] arises as several rootlets on the anterolateral surface of the upper medulla oblongata.

• The rootlets cross the posterior cranial fossa and enter the jugular foramen.

• Within the jugular foramen, and before exiting from it, the rootlets merge to form the glossopharyngeal nerve.

• Within or immediately outside the jugular foramen are two ganglia (the superior and inferior ganglia), which contain the cell bodies of the sensory neurons in the glossopharyngeal nerve [IX].

Tympanic nerve• Branching from the glossopharyngeal nerve [IX] either within or

immediately outside the jugular foramen is the tympanic nerve. • This branch re-enters the temporal bone, enters the middle ear

cavity, and participates in the formation of the tympanic plexus. • Within the middle ear cavity it provides sensory innervation to the

mucosa of the cavity, pharyngotympanic tube, and mastoid air cells. • The tympanic nerve also contributes GVE fibers, which leave

the tympanic plexus in the lesser petrosal nerve-a small nerve that exits the temporal bone,

The lesser petrosal nerve• enters the middle cranial fossa, and descends through the

foramen ovale to exit the cranial cavity carrying preganglionic parasympathetic fibers to the otic ganglion.

Vagus nerve [X] 1/2

• The vagus nerve [X] carries GSA, GVA, SA, GVE, and BE fibers:• The GSA fibers provide sensory input from the skin posterior to the ear and

the external acoustic meatus, and the dura mater in the posterior cranial fossa;

• The GVA fibers provide sensory input from the aortic body chemoreceptors and aortic arch baroreceptors, and the mucous membranes of the pharynx, larynx, esophagus, bronchi, lungs, heart, and abdominal viscera in the foregut and midgut;

• The SA fibers are for taste around the epiglottis; • The GVE fibers are part of the parasympathetic part of the autonomic

division of the PNS and stimulate smooth muscle and glands in the pharynx, larynx, thoracic viscera, and abdominal viscera of the foregut and midgut;

• The BE fibers innervate one muscle of the tongue (palatoglossus), the muscles of the soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), and larynx.

Vagus nerve [X] 1/2

• The vagus nerve arises as a group of rootlets on the anterolateral surface of the medulla oblongata just inferior to the rootlets arising to form the glossopharyngeal nerve [IX].

• The rootlets cross the posterior cranial fossa and enter the jugular foramen.

• Within this foramen, and before exiting from it, the rootlets merge to form the vagus nerve [X].

• Within or immediately outside the jugular foramen are two ganglia, the superior (jugular) and inferior (nodose) ganglia, which contain the cell bodies of the sensory neurons in the vagus nerve [X].

Cranial nerves exiting the cranial cavity

Cranial nerves on the base of the brain

Accessory nerve [XI] 1/2

• The accessory nerve [XI] is a cranial nerve that carries BE fibers to innervate the sternocleidomastoid and trapezius muscles.

• It is a unique cranial nerve because its roots arise from motor neurons in the upper five segments of the cervical spinal cord.

• These fibers leave the lateral surface of the spinal cord and, joining together as they ascend, enter the cranial cavity through the foramen magnum.

• The accessory nerve [XI] continues through the posterior cranial fossa and exits through the jugular foramen.

• It then descends in the neck to innervate the sternocleidomastoid and trapezius muscles from their deep surfaces.

Lesion of the long thoracic nerve. Lesion of the spinal accessory nerve

Course of the spinal accessory nerve

Cranial root of the accessory nerve 2/2

• Some descriptions of the accessory nerve [XI] refer to a few rootlets arising from the caudal part of the medulla oblongata on the anterolateral surface just inferior to the rootlets arising to form the vagus nerve [X] as the 'cranial' root of the accessory nerve.

• Leaving the medulla, the 'cranial' roots course with the 'spinal' roots of the accessory nerve [XI] into the jugular foramen, at which point the 'cranial' roots join the vagus nerve [X].

• As part of the vagus nerve [X], they are distributed to the pharyngeal musculature innervated by the vagus nerve [X] and are therefore described as being part of the vagus nerve [X].

Hypoglossal nerve [XII]

• The hypoglossal nerve [XII] carries GSE fibers to innervate all intrinsic and most of the extrinsic muscles of the tongue.

• It arises as several rootlets from the anterior surface of the medulla, passes laterally across the posterior cranial fossa and exits through the hypoglossal canal.

• This nerve innervates the hyoglossus, styloglossus, and genioglossus muscles and all intrinsic muscles of the tongue.

• Cribiform plate (Olfactory), • Optic canal (Optic), • Superior Orbital Fissure (Oculomotor),• Superior Orbital Fissure (Pathetic/Trochlear),• Superior Orbital Fissure (Trigeminal - Ophthalmic),• Foramen Rotundum (Trigeminal - Maxillary),• Foramen Ovale (Trigeminal - Mandibular),• Superior Orbital Fissure (Abducens), • Internal Acoustic Meatus (Facial),• Internal Acoustic Meatus (Auditory/Vestibulocochlear),• Jugular Foramen (Glossopharyngeal),• Jugular Foramen (Vagus),• Jugular Foramen ( Spinal Accessory),• Hypoglossal Canal (Hypoglossal Nerve)

Cranial Nerves Examination

CN I: Olfactory

• Usually not tested.• Rash, deformity of nose.• Test each nostril with essence bottles of

coffee, vanilla, peppermint.• Lesion – Reduced taste and smell, but not to ammonia

which stimulates the pain fibres carried in the trigeminal nerve.

CN II: Optic

• With patient wearing glasses, test each eye separately on eye chart/ card using an eye cover. Examine visual fields by confrontation by wiggling fingers 1 foot from pt's ears, asking which they see move.• Keep examiner's head level with patient's head. If poor visual acuity, map fields using fingers and a quadrant-covering card. Look into fundi.

• Visual field defects:– Field defects start as small areas of visual loss (scotomas).– Monocular blindness: Lesions of one eye or optic nerve eg MS, giant cell arteritis.– Bilateral blindness: Methyl alcohol, tobacco amblyopia; neurosyphilis.– Bitemporal hemianopia: Optic chiasm compression eg internal carotid artery aneurysm,

pituitary adenoma or craniopharyngioma– Homonymous hemianopia: Affects half the visual field contralateral to the lesion in each

eye.Lesions lie beyond the optic chiasm in the tracts, radiation or occipital cortex eg stroke, abscess, tumour.

• Pupillary Abnormalities

CN III, IV, VI: Oculomotor, Trochlear, Abducens

• Look at pupils: shape, relative size, ptosis. Shine light in from the side to gauge pupil's light reaction.– Assess both direct and consensual responses.– Assess afferent pupillary defect by moving light in arc from pupil to pupil.

unne). Optionally: as do arc test, have pt place a flat hand extending vertically from his face, between his eyes, to act as a blinder so light can only go into one eye at a time

• Follow finger with eyes without moving head": test the 6 cardinal points in an H pattern.– • Look for failure of movement, nystagmus [pause to check it during upward/

lateral gaze].• Convergence by moving finger towards bridge of pt's nose. Test

accommodation by pt looking into distance, then a hat pin 30cm from nose. If MG suspected: pt. gazes upward at Dr's finger to show worsening ptosis.

• CN III lesion• The initial sign is often a fixed dilated pupil which doesn't

accommodate; then ptosis develops and then a complete internal ophthalmoplegia (masked by ptosis). Unopposed lateral rectus causes outward deviation of the eye. If the ocular sympathetic fibres are also affected behind the orbit, the pupil will be fixed but not dilated.

• CN IV lesion• Diplopia due to weakness of downward and inward eye movement.

Commonest cause of a pure vertical diplopia. Patient tends to compensate by tilting head towards the affected side.

• CN VI lesion• Inability to look laterally. Eye is deviated medially because of

unopposed action of medial rectus.

CN V: Trigeminal

• Corneal reflex: patient looks up and away.• Touch cotton wool to other side.• Look for blink in both eyes, ask if can sense it• Repeat other side [tests V sensory, VII motor].

• Facial sensation: sterile sharp item on forehead, cheek, jaw.– Repeat with dull object. Ask to report sharp or dull.– If abnormal, then temperature [heated/ water-cooled tuning fork], light touch [cotton].

• Motor: pt opens mouth, clenches teeth (pterygoids).– Palpate temporal, masseter muscles as they clench.

• Test jaw jerk:• Dr's finger on tip of jaw.• Grip patellar hammer halfway up shaft and tap Dr's finger lightly.• Usually nothing happens, or just a slight closure. • If increased closure, think UMNL, esp. pseudobulbar palsy.• CN V lesion • Reduced sensation or dysasthesia over affected area. Weakness of jaw clenching and side to side

movement. If there is a LMN lesion, the jaw deviates to the weak side when the mouth is opened. There may be fasiculation of temporalis and masseter.

CN VII: Facial

• Inspect facial droop or asymmetry. • Facial expression muscles: pt looks up and wrinkles forehead.

– Examine wrinkling loss.– Feel muscle strength by pushing down on each side [UMNL preserved because of bilateral

innervation].• Pt shuts eyes tightly: compare each side. • Pt grins: compare nasolabial grooves.• Also: frown, show teeth, puff out cheeks.• Corneal reflex already done.• CN VII lesion• Facial weakness. In a LMN lesion the forehead is paralysed - the final common pathway to

the muscles is destroyed; whereas the upper facial muscles are partially spared in an UMN lesion because of alternative pathways in the brainstem. There appear to be different pathways for voluntary and emotional movement. CVA's usually weaken voluntary movement often sparing involuntary movements (eg spontaneous smiling). The much rarer selective loss of emotional movement is called mimic paralysis and is usually due to a frontal or thalamic lesion.

CN VIII: Vestibulocochlear (Hearing, Vestibular rarely)

• Dr's hands arms length by each ear of pt.• Rub one hand's fingers with noise on one side, other hand noiselessly.• Ask pt. which ear they hear you rubbing.• Repeat with louder intensity, watching for abnormality.

• Weber's test: Lateralization• 512/ 1024 Hz [256 if deaf] vibrating fork on top of patients head/ forehead.• "Where do you hear sound coming from?"• Normal reply is midline.

• Rinne's test: Air vs. Bone Conduction• 512/ 1024 Hz [256 if deaf] vibrating fork on mastoid behind ear. Ask when stop hearing it.• When stop hearing it, move to the patients ear so can hear it.• Normal: air conduction [ear] better than bone conduction [mastoid].

• If indicated, look at external auditory canals, eardrums.• CN VIII lesion• Unilateral sensorineural deafness, tinnitus. Slow growing lesions seldom present with vestibular

symptoms as compensation has time to occur.• CN X lesion• Palatal weakness can cause "nasal speech" and nasal regurgitation of food. The palate moves

asymmetrically when the patient says "ah". Recurrent nerve palsy results in hoarseness, loss of volume and "bovine cough"

CN IX, X: Glossopharyngeal, Vagus

• Voice: hoarse or nasal.• Pt. swallows, coughs (bovine cough: recurrent laryngeal).• Examine palate for uvular displacement. (unilateral lesion: uvula

drawn to normal side).• Pt says "Ah": symmetrical soft palate movement.• Gag reflex [sensory IX, motor X]:

• Stimulate back of throat each side.• Normal to gag each time.

• CN IX lesion• Unilateral lesions do not cause any deficit because of bilateral

cortico-bulbar connections. Bilateral lesions result in pseudo-bulbar palsy. These nerves are closely interlinked.

CN XI: Accessory

• From behind, examine for trapezius atrophy, asymmetry.

• Pt. shrugs shoulders (trapezius).• Pt. turns head against resistance: watch,

palpate SCM on opposite side.• CN XI lesion• weakness and wasting of these muscles.• Winging of the scapula

CN XII: Hypoglossal

• Listen to articulation.• Inspect tongue in mouth for wasting, fasciculations.• Protrude tongue: unilateral deviates to affected side.• CN XII lesion • A LMN lesion produces wasting of the ipsilateral side

of the tongue, with fasiculation; and on attempted protrusion tongue deviates towards affected side, but the tongue deviates away from the side of a central lesion.

CN VI PALSY

paralysis of the seventh cranial nerve; affects one side of the face.

nasociliary, and maxillary branches of the trigeminal nerve

Trigeminal neuralgia is a disorder of the trigeminal nerve

Patient with traumatic bilateral superior oblique palsy; note right hypertropia on right head tilt and left hypertropia on left head tilt

A 2-year-old girl with compensatory left head tilt due to congenital right superior oblique palsy.