Cranial Nerves VII-XII

Question 1

CN VII: Facial

Answer 1

Sensory, motor and parasympathetic fibres

Attached to the brainstem at the pontomedullary junction

Has two ‘roots’
-Medial- motor fibres
-Lateral- sensory and parasympathetic fibres (the nervous intermedius)

Complex course through the temporal bone

Question 2

CN VII: Fibre types

Answer 2

Special sensory- taste anterior 2/3 tongue

Motor- muscles of facial expression

Parasympathetic- lacrimal gland, submandibular and sublingual salivary glands

Within the parotid, the terminal part of the facial nerve divides into 5 branches

Question 3

The motor cortex

Answer 3

Stroke (cerebral infarction) affecting the primary motor cortex can cause facial weakness

Part of the motor cortex is dedicated to the upper face, part to the lower face

The cell bodies of UMNs reside in the motor cortex Their axons travel to the facial motor nuclei in the pons

Question 4

CN VII- Upper and lower motor neurons

Answer 4

The UMN axons synapse with cell bodies of the LMNs in the facial motor nuclei (pons)

Axons of the UMNs for the upper and lower face cross the midline and synapse with the contralateral (opposite) facial motor nucleus

The facial motor nucleus also receives input from the ipsilateral motor cortex which controls the upper face

upper part of the face is innervated by fibres from
both sides of the brain, from both motor cortices.
But the lower part of the face is only innervated
by the contralateral Side of the brain.

Question 5

If the UMNs on one side are injured (e.g. in the motor cortex) we see:

Answer 5

Lower contralateral face is weak
Upper contralateral face is not weak as the muscles have dual innervation from both sides of the motor cortex (forehead is spared)

If the facial nerve (i.e. LMN) on one side is injured, all the ipsilateral facial muscles are weak

Question 6

CN VIII: Vestibulocochlear

Answer 6

Sensory nerve

Vestibular afferents > vestibular nuclei
Connections to spinal cord, cerebellum, nuclei of CNs III, IV and VI, cerebral cortex for posture, balance, eye movements, conscious perception of position of the head.

Cochlear afferents > 2 cochlear nuclei
Primary auditory cortex (superior temporal gyrus) - conscious perception of sound
Auditory association cortex (Wernicke’s area) – interpretation.

Question 7

CN IX: Glossopharyngeal

Answer 7

Sensory, motor and parasympathetic fibres
Attached to the medulla via several small rootlets

Taste - posterior 1/3 of the tongue
General sensation: (touch, temp, pain)
pharynx, Eustachian tube, posterior 1/3 of the tongue
Afferents from the carotid sinus (baroreceptors) and carotid body (chemoreceptors)

Parasympathetic fibres > parotid gland

Typically tested with X

Question 8

CN X: Vagus

Answer 8

Sensory, motor and parasympathetic fibres
Attached to the medulla via several small rootlets

General sensation: > pharynx, larynx, oesophagus, EAM, tympanic membrane
Visceral afferents - thoracic and abdo viscera.
Afferents from the aortic bodies (chemoreceptors) and the aortic arch (baroreceptors)

Motor fibres > soft palate, pharynx and larynx – vital for swallowing and speech

Parasympathetic fibres:
Thoracic and abdo viscera

Question 9

CN XI: Accessory

Answer 9

Motor nerve

Cranial part: rootless arise from the medulla
leaves via the jugular foramen by joining the vagus

Spinal part: from ventral horn spinal cord, C1-C5
Travels up through the foramen magnum
Leaves again through the jugular foramen
Innervates sternocleidomastoid and trapezius

Test SCM - patient turns their head against resistance

Test trapezius - look for symmetry – atrophy?
Ask patient to shrug their shoulders

Question 10

CN XII: Hypoglossal

Answer 10

Motor nerve > muscles of the tongue

Arises from the medulla, leaves through the hypoglossal canal