cranial nerves. are attached to the brain and pass through foramina magnum of the skull numbered...

Cranial Nerves

Cranial Nerves

Are attached to the brain and pass through foramina magnum of the skull

Numbered from I–XII Cranial nerves I and II attach to the

forebrain CN I is attached to the telencephalon while CN II

is attached to the diencephalon. All others attach to the brain stem

Primarily serve head and neck structures The vagus nerve (X) extends into the abdomen

Mnemonics

Number Name Sensory/Motor/Both I Olfactory On Some II Optic Old Say III Oculomotor Olympus Money IV Trochlear Towering Matters V Trigeminal Tops, But VI Abducens A My VII Facial Finn Brother VIII Auditory And Says IX Glossopharyngeal German Big X Vagus Viewed Brains XI Spinal Accessory Some Matter XII Hypoglossal Hops Most

Cranial Nerve – Synopsis of function

I. Olfactory – Sensory Sense of smell

II. Optic – Sensory Visual information

III. Oculomotor – Motor Involved in eye muscle movement

IV. Trochlear – Motor Involved in eye muscle movement

Cranial Nerve – Synopsis of function

V. Trigeminal – Mixed 3 branches Sensations of the face and chewing

movements VI. Abducens – Motor

Turns the eye side to side (abducts it) VII. Facial – Mixed

Facial expression

Cranial Nerve – Synopsis of function VIII. Vestibulocochlear – Sensory

Hearing and balance IX. Glossopharyngeal – Mixed

Tongue and pharynx movement X. Vagus (“The vagabond”) – Mixed

Extends into abdomen Coordinates abdominal organs

XI. Accessory – Motor Movement of the pharynx, larynx, head, & neck

XII. Hypoglossal – Motor Controls tongue movement

The 12 Pairs of Cranial Nerves

Cranial Nerves & the Autonomic Nervous System (ANS)

Some CNs also serve ANS functions Only parasympathetic functions

CNs involved include the CN III, CN VII, CN IX, and CN X.

CN I: Olfactory Nerves

Sensory nerves of smell

Temporal lobe


Olfactory system – afferent neurons on the nasal mucosal membrane, olfactory bulb, portions of temporal lobe and inferior frontal lobe, and limbic lobe (including the hypothalamus).

CN I nerve endings in the neurosensory cells (that transduce odor molecules) of the olfactory epithelium. Also found here are some sensory endings of the CN

V – which responds to noxious sensations (such as mace spray/mustard oil/onion).

Unmyelinated axons form the CN I nerve, which terminates in the two olfactory bulbs which are found in the inferior surface of the frontal lobe.


Cortical olfactory regions are responsible for olfactory awareness, while the limbic connections are responsible to integrating smell with emotional brain. Connections with the

hypothalamus plays an important role in feeding behavior.

Clinical Conditions – CN I

Clinical testing – Asked to identify various odors (such as

coffee and peppermint) Clinical conditions –

Anosmia/hyposmia – Reduction/loss of the ability to smell

Hyperosmia – Abnormally acute sensation of smell.

CN II: Optic Nerve

Sensory nerve of vision

CN II: Optic Nerve

Photoreceptor cells in the retina transduce light energy into nerve potentials for the optic nerve endings.

Axons of CN II travel till the optic chiasm and then as the optic tract which terminates in the lateral geniculate body (LGB) of the thalamus.

From LGB, the optic radiations travel to the primary visual cortex of the occipital lobe.

Clinical Conditions – CN II

Clinical testing – Asking to close one eye and fix the other

eye on a point straight ahead of him/her. Clinician moves finger from periphery to

midline from all directions and patient is asked to report if he/she can see the finger. To test visual field

Clinical conditions – CN II

Optic nerve lesions - Ipsi blindness

Chiasmatic lesion can result in bitemporal hemianopsia

Post chiasmatic lesions close to LGB can result in unilateral homonymous hemianopsia

Lesions distal to the geniculate ganglion can result in upper (4) or lower (5) homonymous quadrantopsia.

•Injury to any part of the visual pathway results in selected visual field loss.

CN III: Oculomotor Nerve Innervates four of the six extrinsic eye muscles.

Other two extrinsic muscles are lateral rectus muscle (CN VI) and superior oblique muscle (CN IV).

CN III: Oculomotor Nerve

Two functional components – Somatic portion innervates four ocular extrinsic

muscles and the levator superioris (responsible for eye lid movt).

Visceral portion (controlled by the Edinger-Westphal nuclei) innervates the intrinsic ocular muscles (such as the constrictor muscles of the iris). Controls parasympathetic functions such as pupillary

constriction in response to light (light reflex) and lens modifications for near vision (accommodation-convergence reflex).

Clinical testing of CNs III, IV & VI

Cranial nerves III, IV and VI are usually tested together.

Instruct 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. Observe the eye movements and eyelids for

information about the extrinsic eye muscles and levator superiorsis (eye lid muscle).

In addition, the CN III controls the intrinsic eye muscles, so test for light reflex & accommodation-convergence reflex.

Clinical conditions – CN III

Can result in external and internal opthalamoplegia. External Opthalamoplegia – paralysis of the

extrinsic muscles & levator superiorsis leads to deviation of the ipsi eye to the lateral side (lateral striabismus) and eyelid drooping (ptosis). Lateral striabismus can inturn result in diplopia (double

vision)

Internal Opthalomoplegia – paralysis of intrinsic muscles results in permanent dilation of the pupil (mydriasis)

CN IV: Trochlear Nerve Innervates an extrinsic eye muscle (superior oblique

muscle) – action results in abduction (laterally rotate) and depressing the eyeball (i.e. it makes the eye move outward and downward).

Is the only CN that exits the "posterior" side of the brainstem

Clinical conditions – CN IV

Damage results in difficulty in looking downward and outward. Also results with the eye being fixated

with an upward medial gaze because of the uncontrolled activity of the other extrinsic ocular muscles (which are controlled by CN III).

CN VI: Abducens Nerve Innervates an extrinsic eye muscle (lateral

rectus muscle which abducts the eyeball)

Clinical conditions – CN VI

Is more susceptible to damage because it runs a long intracranial course.

Damage results in medial strisbismus (since the medial rectus innervated by the CN III is unopposed) which in turn causes diplopia.

Medial longitudinal Fasciculus - important brainstem tract that helps communication between CNs III, IV, & VI, and with vestibular system and neck muscles. Coordinates eye muscles for gaze control and

coordinates head position with eye movements.

CN V: Trigeminal Nerve Is a mixed nerve. Sensory innervations from the face & motor

innervations to chewing muscles. Sensory and motor components for the reflex arc of

the Jaw Jerk Reflex. It is the largest of the cranial nerves. Its name derives from the fact that it has three

major branches: the ophthalmic nerve (V1), the maxillary nerve (V2) and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has both sensory and motor functions.

Trigeminal Nerve

Trigeminal Nerve CN V is responsible for cutaneous (touch, pain, temperature)

and proprioceptive (awareness of posture and relative muscle movt) sensations from the - face, head, oral and nasal cavities, Sinuses & teeth Anterior 1/3rds of the tongue Anterior half of the pinna, external auditory meatus & external

surface of the tympanic membrane. Motor part controls muscles of mastication (including lateral

and medial pterygoid, masseter, temporalis) and speech production, tensor veli palatani (soft palate) and tensor tympani (middle ear muscle). CN V controls muscles involved in chewing but not facial expression

Trigeminal Nerve The mandibular nerve carries only general (touch/

position and pain/temperature) sensory sensation from the mouth. It does not carry taste sensation.

Taste is a “special sense”, like sight, smell, hearing and balance. Taste fibers from the anterior 2/3 of the tongue are initially

carried in the lingual nerve (which is anatomically a branch of the mandibular nerve) but then enters the chorda tympani, which is a branch of cranial nerve VII.

Taste fibers from the posterior 1/3 of the tongue and the pharynx are carried in branches of cranial nerves VII, IX and X.

Clinical Testing –CN V

To test the sensory part of the trigeminal nerve, lightly touch various parts of the patients face with piece of cotton or a blunt object. Also check for corneal reflex (blinking in

response to touching of cornea) and sneezing reflex.

To test the motor part of the nerve, tell the patient to bite down hard and check the masseter muscle. Next, ask the patient to open their mouth against

resistance at the base of the patient's chin.

Clinical conditions – CN V

Damage to the sensory portion results in – Ipsilateral loss of sensation in areas of

distribution. Sneezing and blinking reflexes are lost Trigeminal neuralgia

Paroxysmal episodes of intense (stabbing) pain in the eyes, lips, nose, scalp, forehead, and jaw.

Not easy to treat – In severe cases, severing of the nerve branch might be the last option.


Damage to the motor portion – Paralysis of ipsilateral muscles of mastication.

Jaw is deviated towards side of lesion which is pronounced during extension.

Muscle tics/twitching & Jaw Jerk reflex is absent. Dysarthria - Misarticulations due to paralyzed

mandible and soft palate.


Wallenberg Syndrome or Lateral Medullary (or Posterior Inferior Cerebellar Artery [PICA]) syndrome- loss of pain/temperature sensation from side of the face ipsilateral to the lesion along with loss of pain/temperature from side of body contralateral to the side of the lesion. Believed to be a stroke involving the

posterior inferior Cerebellar artery (PICA).

Wallenberg Syndrome

Reason is because in the medulla, the ascending spinothalmic tract (which carries pain/temperature information from the contralateral side of the body) is adjacent to the descending tract of the CN V (which carries pain/temperature information from the ipsilateral side of the face).

A stroke that cuts off the blood supply to this area (e.g., a clot in the Posterior Inferior Cerebellar Artery [PICA]) destroys both tracts simultaneously.

CN VII: Facial Nerve Is a mixed nerve. Primarily controls the muscles of facial expression, carries

special visceral sensory taste information from the anterior 2/3rd of the tongue and hard and soft palate, and parasympathetic efferents to the secretor glands in the mouth and nasal cavities.

Muscles of facial expression

The masseter & temporalis shown in the figure are muscles of mastication that are innervated by the CN V (trigeminal).

CN VII: Facial Nerve

In addition, it also carries general sensory information from the epidermis of the external ear, and motor fibers to the stapedius muscle (middle ear muscle) It emerges from the brainstem

between the pons and the medulla and along its path commutes through the middle ear, and travels along with CN VIII within the internal auditory meatus.

Clinical testing – CN VII

Voluntary facial movements, such as wrinkling the brow, showing teeth, frowning, closing the eyes tightly, pursing the lips and puffing out the cheeks. There should be no noticeable asymmetry.

Check taste of anterior 2/3rd of tongue with sugar, salt, or lemon juice on cotton swabs.

Also check if there is an excessive secretion of saliva glands due to impairment of parasympathetic efferents.

Also check for acoustic stepedial reflexes.

Acoustical Stapedial Reflex

Clinical conditions – CN VII

The facial nerve fibers take different routes to serve different functions. Hence, depending upon the site of the lesion,

different clinical signs will result. However, if the damage is at the level of the

Pons, all three main functions will be affected resulting in paralysis of the ipsilateral facial muscles, excessive secretion from salivary glands, and loss of taste from the anterior 2/3rd of the tongue.


The schema of cortical control (through corticobulbar fibers) over the facial nerve results in a differential innervation pattern of the lower and upper facial muscles.

The motor nucleus that controls the lower half of the face receives projections from the contralateral motor cortex alone. (Right moter Cortex)

However the facial nucleus supplying upper facial muscles (such as frontalis and orbicularis oris) receives corticobulbar projections from both motor cortices.

Distribution of Facial nerve fibers and UMN/LMN lesions

Clinical Video

Basics about the Motor System

The Pyramidal Motor System or Tract controls all of our voluntary movements.

The pyramidal system has two main neuron systems: Upper Motor Neuron

system (UMN) Lower Motor Neuron

system (LMN)


The extra-pyramidal motor system Main purpose - Dampen erratic motions, maintain

muscle tone and truncal stability Responsible for maintaining rhythmic, phasic

behavior (such as walking) but does not initiate movement

The major parts of the extrapyramidal system are the "subcortical nuclei". Such as caudate, putamen, and globus pallidus of the

Basal ganglia, substantia nigra and red nucleus of the pons, parts of the thalamus, and sub-thalamic nuclei.

Basics about the Motor System – Pyramidal system

UMN – motor neurons that originate in the cerebral cortex (motor strip), terminating in the brainstem (known as corticobulbar tract or fibers) or spinal cord (corticospinal tract or fibers).

Remember the motor homunculus - face and mouth located near the lateral fissure, arms/thighs/legs are progressively located near the longitudinal fissure and within the central sulcus.

Basics about the Motor System – Pyramidal system

The muscles of the face, head and neck are controlled by the corticobulbar system, which terminates on different Cranial Nerve nuclei within brainstem.

The corticospinal tract connects the cerebral cortex to motor neurons of the Spinal nerves and controls movement of the torso, upper and lower limbs.


LMN - are the motor neurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the UMNs out to the muscles. Cranial nerves and Spinal nerves

Animation


Unilateral lesions in the motor cortex corresponding to areas of face (i.e., UMN lesion or Pseudo-bulbar lesions or supranuclear lesion) will only affect the muscles in the contralateral lower half of the face. The upper facial muscles are spared

because of the bilateral innervation.


However bilateral cortical lesions or complete destruction of the facial nucleus (at the brainstem level) will cause paralysis of all the upper and lower muscles of the face. Affects articulation of labial and labiodental sounds

Interesting clinical observation in facial paralysis as a result of a UMN lesion – although facial muscles are paralyzed for voluntary control, they may still respond to emotional stimuli/states. Emotions are not controlled by the Pyramidal system

but by the extrapyramidal system, limbic system, and hypothalamus.


Lesions below the facial nerve nucleus at the level of the brainstem are LMN lesions.

A common condition – Bell’s Palsy. Characterized by a sudden onset of paralysis of all

ipsilateral upper and lower facial muscles. May be a result of a degenerative inflammatory

injury or from an infection of the facial nerve after its exit from the brainstem.

Animation

Bells Palsy Bells Palsy signs

Ipsilateral muscles of the lower face sag; Nasolabial folds flatten out; Unable to wrinkle forehead, close eyes, or show teeth; Corner of the mouth droops and saliva/food accumulates in the

affected side; When smiling, lower portion of face is pulled towards unaffected

side and motor part of corneal reflex is absent (although vision is not

affected) and Additional LMN signs seen in Bell’s Palsy include –

saliva secretion is affected, abnormal stapedial reflexes, absent corneal reflex and loss of taste of anterior 2/3rd of tongue. Patient might complain of hyperacusis (increased auditory

volume in an affected ear)

CN VIII: Vestibulocochlear Nerve Sensory nerve of hearing and balance Two branches – Auditory and vestibular nerve Both nerves are attached to the brainstem at the

junction of the medulla and pons

CN VIII: Vestibulocochlear Nerve

Vestibular system - Controls equilibrium including regulation of neck

position Coordinate head and body movements Retain a stable visual fixation point in space during

head/body movts (oculocephalic reflex or “doll’s eye reflex”).

Distal fibers of the vestibular nerve innervate the hair cells in the cristae of the semicircular canals, utricle and saccule.

The vestibular nuclei has projections to the flocculonodular lobe of the cerebellum, reticular formation, medial longitudinal fasciculus and motor nuclei of other CN and spinal nerves.

Clinical conditions – Vestibular Nerve

Lesions result in impaired equilibrium, vertigo (or dizziness) and nystagmus (rhythmic movement of the eye).

Vestibular System

CN VIII - Auditory Nerve

Distal nerve fibers of the auditory nerve innervate the hair cells in the Organ of Corti in the Inner ear.

The auditory nerve terminates at the Cochlear Nuclei in the Medulla.

Lesions affecting the auditory nerve will result in a neural hearing loss (also called as a retrocochlear hearing loss) and Tinnitus.

CN IX: Glossopharyngeal Nerve

Sensory and motor innervations of structures of the tongue and pharynx

CN IX: Glossopharyngeal Nerve

Specifically, the functions of CN IX include: Receives general sensory fibers from the posterior

1/3rd of the tongue, the tonsils, soft palate, the pharynx, and the middle ear (through the tympanic nerve) and Eustachian tube.

Special sensory fibers mediating taste from the posterior 1/3rd of the tongue and oral pharynx

Supplies parasympathetic fibers to the parotid gland Which is the largest of the salivary glands found in the

subcutaneous tissue of the face which empties its secretion within the buccal cavity.

Supplies motor fibers to stylopharyngeus muscle and the upper pharyngeal muscles. Action – Facilitates swallowing by elevating the larynx and pharynx.

Clinical testing – CNs IX and X Ask the patient if they have difficulty swallowing. Ask the patient to swallow and note any difficulty doing

so. Also test the gag reflex and cough by stimulating with a tongue

depressor or a long Q-tip. Note the quality and sound of the patient's voice.

Is it hoarse or nasal? Ask the patient to open their mouth wide, protrude their

tongue, and say "AHH“ or yawn. Flash your penlight into the patient's mouth and observe the

soft palate, uvula and pharynx. The soft palate should rise symmetrically, the uvula should

remain midline and the pharynx should constrict medially like a curtain.

Clinical conditions – CN IX

Ipsilateral lesions will result in – Partial paresis (weakening) of the unilateral

stylopharyngeal muscle. Affects elevation of pharynx during swallowing

Impaired cutaneous sensation from the posterior tongue. Loss of gag reflex

Poor control of parotid gland Excessive saliva secretion

CN X: Vagus Nerve Is the longest CN Mixed nerve

although mostly sensory (90%).

CNs IX and X are important for phonation and swallowing.

Also innervates cardiac and smooth muscles of esophagus, stomach and intestine

CN X: Vagus Nerve Specifically, CN X functions include –

general sensory information From the external ear, parts of the external surface of the

tympanic membrane, Pharynx , Larynx, esophagus, trachea, heart and abdominal and

thoracic viscera Motor fibers from

voluntary muscles of the pharynx and most of the larynx, and soft palate muscles such as Palatoglossus and Levator Palatani But not Tensor Veli Palatani which is innervated by CN V.

Parasympathetic innervation of smooth muscles/glands of the above structures

Afferent and efferent projections of CN X along with CN IX form the reticular neural circuits of reflexes such as gagging, coughing, vomiting, sneezing and swallowing.

Clinical conditions – CN X Unilateral LMN damage to the vagus nerve is

indicated by: Breathy voice, hoarseness and diplophonia (due to

paralysis of the intrinsic muscles of the larynx on the affected side). Vocal fold paralysis in turn can cause choking and pulmonary

aspiration. 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 towards the unaffected side due to the unopposed action of the intact contralateral levator palatini muscle.

Clinical conditions – CN X

Damage to the CN X also impairs parasympathetic functions such as heart-rate, function of smooth muscles of trachea and bronchus, reflexes such as vomiting, coughing, sneezing, sucking, and yawning.

CN XI: Accessory Nerve Controls head movement Innervates the sternocleidomastoid muscle

and trapezius muscle on the ipsilateral side.

CN XI: Accessory Nerve

Contraction of the sternocleidomastoid muscle results in tilting the head forward and rotating it to the opposite side.

Contraction of the trapezius muscle tilts the head back and to the side.

Clinical Testing – Getting a person to shrug their shoulders while you

push down tests the trapezius. Asking him to turn their head with resistance will

test the sternocleidomastoid. Clinical condition –

Damage to CN XI will affect head movements.

CN XII: Hypoglossal Nerve Is a motor nerve

Innervates all of the intrinsic (ie, Inferior and Superior Longitudinal Muscles, Transverse Muscle & Vertical Muscle) and three of the four major extrinsic muscles of the tongue (genioglossus, styloglossus, and hyoglossus) The palatoglossus muscle is supplied by CN X (vagus nerve).

CN XII: Hypoglossal Nerve

Clinical testing – Ask to the patient to stick out their tongue.

If there is a loss of function on one side (unilateral paralysis) the tongue will point towards the affected side.

The strength of the tongue can be tested by getting the person to stick out their tongue at the inside of their cheek, and feeling how strongly they can push a finger pushed against their cheek.

The tongue can also be looked at for signs fasciculation (Involuntary contractions and twitching of muscle) and muscular atrophy.

CN XII: Hypoglossal Nerve

Clinical condition – Paralysis of tongue and if condition is for

a prolonged period, may result in atrophy and fasciculation (involuntary muscle twitching).

Results in dysarthria and chewing difficulties

Different peripheral speech production structures

http://w3.ling.su.se/STAFF/ericsdotter/projects/pion_01.htm

http://w3.ling.su.se/STAFF/ericsdotter/projects/xray_info.htm

Different peripheral speech production structures

Primary Cortical areas important for Speech

1. Primary Auditory Cortex

2. Primary Visual Cortex

3. Wernicke’s Area

4. Broca’s Area 5. Primary

Motor Cortex

Cranial nerves for speech

Trigeminal (V): mixed Facial (VII): motor / mixed Auditory/vestibular (VIII): sensory Glossopharyngeal (IX): mixed Vagus (X): mixed (mainly

sensory) Spinal accessory (XI): motor Hypoglossal (XII): motor

Nuclei in pons

Nuclei in medulla

Cranial Nerves & Speech Motor Control

Speech feed-back system

Cranial Nerves

Take some time to look at the interesting case studies at the end of the chapter on Cranial Nerves in Bhatnagar’s book.

cranial nerves. are attached to the brain and pass through foramina magnum of the skull numbered...

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