Week 15 - Skull

Question 1

Where does the facial nerve (CN VII) divide into its five terminal motor branches?

• a) Within the facial canal
• b) Within the parotid gland
• c) Within the stylomastoid foramen
• d) Immediately after its emergence from the pons
• e) Within the internal acoustic meatus

Answer 1

= b) within the Parotid gland

Question 2

The cranial nerves that pass through the internal acoustic meatus are:

• a) Facial (VII) & hypoglossal (XII)
• b) Vestibulocochlear (VIII) & glossopharyngeal (IX)
• c) Vestibulocochlear (VIII) & vagus (X)
• d) Facial (VII) & vestibulocochlear (VIII)
• e) Accessory (XI) & hypoglossal (XII)

Answer 2

Internal Acoustic Meatus = d) Facial (VII) & vestibulocochlear (VIII)

Question 3

Which cranial nerve provides parasympathetic innervation to the parotid gland?

• a) Facial (VII)
• b) Vagus (X)
• c) Glossopharyngeal (IX)
• d) Accessory (XI)
• e) Mandibular branch of trigeminal (V3)

Answer 3

Parotid Gland = glossopharyngeal nerve (CN IX) via the otic ganglion, while the submandibular and sublingual glands receive their parasympathetic input from the facial nerve (CN VII) via the submandibular ganglion.

Question 3

Which nerve is responsible for the afferent limb of the corneal reflex?

Answer 3

The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body).

Sensory (afferent) limb = Opthalmic division of Trigeminal nerve (CNV1)

Motor (efferent) limb = Facial nerve to obicularis oculi muscle

Question 4

Damage to the spinal accessory nerve within the posterior triangle of the neck may cause paralysis of which two muscles?

Answer 4

sternocleidomastoid and trapezius muscles

The spinal portion arises from neurones of the upper spinal cord, specifically C1-C5/C6 spinal nerve roots. These fibres coalesce to form the spinal part of the accessory nerve, which then runs superiorly to enter the cranial cavity via the foramen magnum.

The nerve traverses the posterior cranial fossa to reach the jugular foramen. It briefly meets the cranial portion of the accessory nerve, before exiting the skull (along with the glossopharyngeal and vagus nerves).

Outside the cranium, the spinal part descends along the internal carotid artery to reach the sternocleidomastoid muscle, which it innervates. It then moves across the posterior triangle of the neck to supply motor fibres to the trapezius.

Note: The extracranial course of the accessory nerve is relatively superficial (it runs between the investing and prevertebral layers of fascia), and thus leaves it vulnerable to damage.