Cranial nerves VII - XII 21.02.23

Question 1

What is the brain connection, function and skull foramen of the 7th CN?

Answer 1

Brain connection: pons at the pontomedullary junction
Function: facial movements, salivation, lacrimation, sensation from external ear canal and taste from anterior 2/3 of the tongue
Skull foramen: internal acoustic meatus then stylomastoid foramen

Question 2

What fibre types does the 7th CN have?

Answer 2

Special sensory - anterior 2/3 tongue
Motor - muscles of facial expression
Parasympathetic - lacrimal gland (eye/tear duct), submandibular (salivary) and salivary glands
- Within the parotid the facial nerve divides into 5 branches

Question 3

How do we test the 7th CN?

Answer 3

• Ask about taste
• Is the eye dry
• Is there any asymmetry within the face
• Frown and raise eyebrow
• Screw up eyes tightly
• Puff out cheeks
• Smile

Question 4

How are cell bodies organised in the motor cortex?

Answer 4

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

Question 5

How do the UMNs for the face synapse?

Answer 5

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

With UMN : Lower comes from opposite side and upper comes from both sides

Question 6

What happens if the UMNs on one side are injured?

Answer 6

The lower contralateral face is weak the upper contralateral is not weak as muscles have dual innervation
- If the facial nerve (LMN) on one side is injured, all ipsilateral facial muscles are weak

Question 7

What is the brain connection, function and skull foramen of the 8th CN?

Answer 7

Brain connection: pons
Function: Balance and hearing
Skull foramen: internal acoustic meatus

Question 8

What are the 2 afferents of the 8th CN?

Answer 8

1. Primary auditory cortex
2. Auditory association cortex (Wernicke’s area)

Question 9

How do we test the 8th CN?

Answer 9

• Cover each ear and whisper in the other
• audiometry
• observe patient’s balance, gait

Question 10

What is the brain connection, function and skull foramen of the 9th CN?

Answer 10

9th - Glossopharyngeal
Brain connection: Medulla
Function: taste and sensation from posterior 1/3 of tongue, sensation from pharynx and carotid vessels
Skull foramen: jugular foramen

Question 11

What are the parasympathetic and motor fibres of the 9th CN?

Answer 11

Parasympathetic: parotid gland
Motor: stylopharyngeus muscle in pharynx

Question 12

What is the brain connection, function and skull foramen of the 10th CN?

Answer 12

10th - Vagus
Brain connection: Medulla
Function: parasympathetic to thoracic and abdominal organs, sensation from the ear canal AND motor to soft palate, pharyngeal and laryngeal muscles
Skull Foramen: Jugular foramen

Question 13

How do we test the 10th CN?

Answer 13

Listen for hoarseness and nasal sounds and we can elicit the gag reflex with a light touch to the back of the pharynx
- ask the patient to say ‘ah’ and look for elevation of the palate

Question 14

What is the brain connection, function and skull foramen of the 11th CN?

Answer 14

11th is Accessory
Brain connection: none but it connects to the CNS at C1 - C5
Function: motor function to the trapezium and sternocleidomastoid muscles
Skull foramen: foramen magnum (in) and jugular foramen (out)

Question 15

How can we test the 11th CN?

Answer 15

Patient turns their head against resistance or ask patient to shrug their shoulders (trapezius)

Question 16

What is the brain connection, function and skull foramen of the 12th CN?

Answer 16

12th - hypoglossal
Brain connection : medulla
Function: tongue movements
Skull foramen: hypoglossal canal

Question 17

How do we test the 12th CN?

Answer 17

Ask the patient to stick out their tongue; look for atrophy (look for deviation of the tongue)
- the ipsilateral tongue muscles will be paralysed