Cranial Nerve 6

Abducens Nerve

Abducens Nerve Physiology

• “somatic efferent” nerve that controls the movement of a single muscle, the lateral rectus muscle of the eye

Abducens Anatomy and CourseSource

Abducens Nucleus located in the caudal ponsPeripheral Anatomy

From pons to petrous portionPeripheral Anatomy

From cavernous sinus to supraorbital fissure

CN 6 Test and Impairment

Normal Lateral Rectus Movement

Impaired Lateral Rectus Muscle

Ipsilateral Rectus Muscle Paralysis

Diseases and Disorders

• Diplopia – medially pulled eye due to unopposed action of medial rectus muscle.

• Tumors, Aneurysms and Fractures – damage of peripheral 6th nerve due to nerve compression

• Diabetic Neuropathy – injury involving the small blood vessels which supply blood to the CN 6.

• Wernicke-Korsakoff Syndrome - isolated CN 6 damage, abnormalities are nystagmus and lateral rectus weakness.

• Tolosa- Hunt Syndrome – idiopathic granulomatous disease that causes oculomotor palsies

Cranial Nerve 7

Facial Nerve

Facial Nerve

• Four Divisions

1) Brancial Motor (Special Visceral Efferent)

2) Visceral Motor (General Visceral Efferent)

3) Special Sensory (Special Afferent)

4) General Sensory (General Somatic Efferent)

*General Anatomy

Brancial Motor

Physiology - Supplies the muscles of facial expression; posterior belly of digastric muscle; stylohyoid, and stapedius.

Anatomy

1) Originates at pons at facial nucleus

2) Circles centrally around 6th Cranial nerve nucleus

*Facial Nerve

Visceral Motor

Physiology - Parasympathetic innervation of the lcrimal, submandibular, and sublingual glands, as well as mucous membranes of nasopharynx, hard and soft palate.

Anatomy

1) Originates in medulla at superior Salivatory nucleus.

*Facial Nerve

Special Sensory

Physiology - Taste sensation from the anterior 2/3 of tongue; hard and soft palates.

Anatomy

1) Originates in medulla at spinal nucleus of Cranial Nerve 5

2) Peripheral Course along the taste bud chemoreceptors on anterior 2/3 of tongue.

*Facial Nerve

General Sensory

Physiology - General sensation from the skin of the concha of the auricle and from a small area behind the ear.

Anatomy

1) Originates in medulla at solitary tract nucleus.

*General Anatomy

General Anatomy

Geniculate Ganglion to Motor Branches1. Ganglion within facial canal between labyrinthine and

tympanic segments

2. Facial nerve turns 90 degrees to travel inferiorly through stylomastoid foramen

3. Facial nerve branches (motor innervation) • Temporal branch (forehead and eye) • Zygomatic branch (vicinity of zygomatic arch) • Buccal branch (cheek) • Marginal mandibular branch (jaw line) • Cervical branch (neck)

General Anatomy

Innervation

1. Motor fibers • Scalp, Face, and Auricula • Buccinator, Platysma, Stapedius, Stapedius, and Posterior

Belly of Digastric Muscle

2. Autonomic motor fibers • Vasodilatation and secretion of Salivary Glands

– Submaxillary gland – Sublingual Gland

3. Sensory fibers • Taste for anterior two thirds of Tongue • Sensation to ear canal and behind ear

CN 7 Test

Facial Motor Exam • Forehead and Upper lid Innervation

– Eyebrow elevation – Forehead wrinkling – Frowning – Tight Closing of the eyes

• Lower Face innervation – Showing teeth – Whistling – Puffing cheeks – Natural smile – Test or inquire about Taste Sensation

CN 7 Lesions

1. Upper Motor Neuron (UMN) – Unless bilateral lesion, does not affect forehead – Mouth paralysis is overcome by emotional

expression

2. Lower Motor Neuron (LMN) – Ipsilateral forehead and lower face paralysis

CN 7 Diseases and Disorders

• Bell’s Palsy - idiopathic acute facial nerve paralysis described as a multiple cranial nerve ganglionitis that involves the facial nerve

• Melkersson–Rosenthal Syndrome - characterized by recurring facial paralysis, swelling of the face and lips (usually the upper lip), and the development of folds and furrows in the tongue.

• Bulbar Polio - weakness of muscles innervated by cranial nerves.

• Amyotrophic Lateral Sclerosis – progressive, fatal, neurodegenerative disease caused by the degeneration of motor neurons, the nerve cells in the central nervous system that control voluntary muscle movement.

Cranial Nerve 8

Vestibulocochlear Nerve

Vestibulocochlear Nerve

General Physiology - responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain.

General Anatomy - emerges from the medulla oblongata and enters the inner skull via the internal acoustic meatus in the temporal bone, along with the facial nerve.

2 Parts

a) Cochlear Nerve

b) Vestibular Nerve

Cochlear Nerve

Physiology – concerned with the hearing process through inner hair cells of the organ of Corti.

Anatomy

1) Originates from neurons of the spiral ganglion

2) Processes from the spiral ganglia and ends at the organ of Corti.

*CN 7

Vestibulocochlear Nerve

Vestibulocochlear Nerve

Vestibular Nerve

Physiology – mediates the sense of balance and head position.

Anatomy

1) Originates from the neurons of Scarpa’s ganglion.

2) Travels through the Vestibular System and extends processes to 5 sensory organs; 3 are cristaes located in the ampullae of the semicircular canals, 2 are in the maculae of the saccule and utircle.

CN 8 Test

Cochlear Nerve• Audiometer – use of headphones tuned with varying

frequencies (20dBSPL = normal hearing)• Rinne and Weber Test – done by placing a vibrating tuning

fork behind the ear, on the mastoid process and afterwards on the forehead.

Vestibular Nerve

a) Vestibular (Labyrinth) Testing - involves irrigating cold or warm water or air into the external auditory canal. (FAST horizontal nystagmus: COWS)

b) Spontaneous Nystagmus - presence indicates balance disorder

CN 8 Diseases and Disorders

Vestibular/Cochlear Neuronitis - can be a paroxysmal, single attack of vertigo, a series of attacks, or a persistent condition which diminishes over two weeks.

Acoustic Neuroma - a benign primary intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve.

Measles, Meningitis and Autoimmune Diseases - results in cochlear nerve damage which results to deafness.