Cranial Nerves V11-X11

Question 1

Where do all the cranial nerves arise from?

Answer 1

part of Peripheral Ns

relate to brain stem bar 2 which arise from forebrain (olfactory and optic CN1&2)

Midbrain - occulomotor and trochlear CN3&4

Pons - trigeminal, abducens, facial, vestibulocochlear CN5-8

Medulla-> carotid sheath - glossopharyngeal, vagus (runs length CS), spinal accessory, hypoglossal CN9-12
but hypoglossal not through carotid sheath instead hypoglossal canal

Question 2

Route of the facial CN7

Answer 2

Lower pons -> interna, acoustic meatus -> petrous bone-> three branches -> exits through stylomastoid formamen

Question 3

Function of CN7

Answer 3

MIxEd

Specially sensory- anterior 2/3 tongue taste
Generally sensory- small area external ear

Autonomic - lacrimal glands, mucosal glands (nose/ roof mouth), salivary glands (bar parotid so submandibular and sublingual)

Motor- muscles of facial expression/ scalp nerve to stapedius (in middle ear prevents damage loud sounds)

Question 4

What are the two roots of the facial nerve, where does this occur?

Answer 4

Motor root (larger) and nervus intermedius (sensory and parasympathetic axons) at cerebellopontine angle

Question 5

How is testing of the facial nerve done? What are some symptoms of facial nerve pathology?

Answer 5

Mostly by teasing the muscles of facial expression and the corneal reflex (trigeminal ophthalmic afferent limb) palpebral orbicularis

Can present with a range of symptoms depending on where along the nerve route the pathology is e.g. hyperacusis, dry eyes, altered taste, facial nerve palsy (Bell’s palsy - absence of muscles of facial expression one side)

Middle ear pathology

Parotid malignancy -> problems as runs through this gland

Question 6

5 main branches of the facial nerve

Answer 6

Temporal, zygomatic, buccal, marginal mandibular, cervical

Question 7

Route of vestibulocochlear CN8 and function

Answer 7

Cochlea N + semicircular canals (vestibular N) = vestibulocochlear N

-> internal acoustic meatus -> lower pons

Special sensory - hearing and balance

Question 8

How to test CN8? What pathology could cause problems with this nerve and it’s function?

Answer 8

Crude hearing test (whispering 99 in each ear) & enquiring about balance Or more formal test if investigating hearing loss e.g. pure tone audiometry

Damage involving cochlear or brainstem nucleus causes hearing loss (sensorineural). Presbyacusis - old age related hearing loss

Damage involving semicircular canals or brain nucleus causes disturbance of balance (vertigo)

Acoustic neuroma - benign tumour involving vestibulocochlear Nerve of Schwann cells which surround vestibular component -> compression. Acute sensorineural unilateral hearing loss, tinnitus, vertigo, numbness/ pain one half face (close to facial nerve)

Question 9

Route of last 4 cranial nerves?

Answer 9

Arise in medulla

->Exit via jugular foramen with IJV in carotid sheath-> most exit quickly but vagus runs length

Question 10

Functions of cranial nerve 9?

Answer 10

Glossopharyngeal nerve

General sensation- palatine tonsils and oropharynx (soft palette/ base of tongue/ posterior pharyngeal wall), middle ear, tympanic membrane, carotid body, carotid sinus
Special sensory- taste & general sensation posterior 1/3 tongue

Autonomic- parasympathetic innervation parotid gland

Motor- one muscle (stylopharyngeus) assists in swallowing

Question 11

How to test the glossopharyngeal N

Answer 11

Gag reflex sensory limb only if concerns around swallowing and integrity of nerves involved (+ vagus N)

Taste informally tested

Isolated lesions of CN9 are rare

Question 12

Functions of the CNX 10?

Answer 12

MIXED

General sensory- sensory to lower pharynx and whole larynx & small part external ear and tympanic membrane

Motor - muscles soft palate/ pharynx/ larynx

Autonomic- Parasympathetic to thoracic (heart/ tracheobronchial tree) and abdominal (oesophagus, stomach, most intestinal tract up to splenic flexure/ start descending large colon) viscera

Branches into inferior and recurrent laryngeal nerves

Left recurrent turns under arch aorta

Right recurrent turns under right subclavian artery

Question 13

Testing the vagus Nerve

Answer 13

Speech/ cough/ swallowing

Movement of uvula and soft palate when sharing ‘ahh’ should rise On both sides

Gag reflex (efferent limb)

Isolated lesions rare

Injury to recurrent laryngeal e..g following thoracic surgery -> hoarseness and dysphonia

Question 14

Function of the spinal accessory nerve and route

Answer 14

CN 11

Motor- to sternocleidomastoid and trapezius

Medulla-> Rootlets from cervical spine and brainstem -> jugular foramen -> deep to SCM -> posterolaterally across posterior triangle -> deep to trapezius

Question 15

Testing the spinal accessory nerve

Answer 15

Shrug shoulders against resistance - trapezius

Turn head Agassi t resistance- sternocleidomastoid (susceptible to injury e.g. LN biopsies, surgery, stab wound)

Question 16

Function of cranial nerve 12 and route

Answer 16

Hypoglossal

Motor- muscles of the tongue (all bar one)

Medulla rootlets-> hypoglossal canal -> medial to angle of mandible and crosses internal and external carotid arteries in neck

Question 17

Testing the hypoglossal nerve

Answer 17

Inspection of tongue and movement

Rare

Damage to cranial nerve 12 causes weakness and atrophy of tongue muscles ipsilateral side (same side)