L17 Cranial Nerves 1

Question 1

Which cranial nerves aren’t true cranial nerves?

Answer 1

CN I and II, olfactory and optic.

They have no peripheral projections and are just brain tracts.

Question 2

What is meant by the term afferent?

Answer 2

Axons carrying nerve impulses towards the CNS, sensory.

Question 3

What is meant by the term efferent?

Answer 3

Axons carrying nerve impulses away from the CNS, motor.

Question 4

What is meant by the term somatic?

Answer 4

Either sensory (afferent) innervation to skin or muscle and/or motor (efferent) innervation to striated muscles

Question 5

What is meant by the term visceral?

Answer 5

Sensory (afferent) or motor (efferent) innervation to visceral organs, glands and smooth muscle.

Question 6

What is meant by the term general?

Answer 6

Components of spinal nerves.

Question 7

What is meant by the term special?

Answer 7

Components only found in cranial nerves e.g. special visceral afferent axons for taste. E.g. special visceral motor, inneravtion of striated muscles derived from pharyngeal arches (i.e. mouth, pharynx, larynx).

Question 8

Which muscles develop from each pharyngeal arch?

Answer 8

• Arch 1: Muscles of mastication
• Arch 2: muscles of facial expression, stylohyoid, posterior belly of digastric
• Arch 3: stylopharyngeus
• Arch 4: soft palate muscles
• Arch 5: muscles of larynx

Question 9

What do the afferent neuron columns contain?

Answer 9

• GVA and GSA neuron columns are nuclei that contain second order sensory interneurons innervated by DRG primary afferents.

Question 10

What do the efferent neuron columns contain?

Answer 10

• Efferent neuron columns contain lower motor neuron cell bodies that project axons which innervate skeletal muscle (GSE) or autonomic nuclei (GVE) that contain preganglionic neuron cell bodies

Question 11

Where are cranial nerve components found?

Answer 11

Within columns of neurons found in the midbrain and hindbrain (rather than the spinal column).

• SSA in hindbrain where vestibulocochlear nerve projects
• SVA in between GSA and GVA
• SVE in betwee GVE and GSE

Question 12

Which anatomical boundary seperates afferent neurons from efferent neurons in the medulla?

Answer 12

The sulcus limitans.

Question 13

Describe the structure of the general somatic efferent cranial nerve nuclei.

Answer 13

Cranial nerves III, IV, VI and XII carry GSE fibres.

• III and IV in the midbrain innervate extrinsic ocular mucles
• VI in the pons innervates the extrinsic ocular muscles
• XII in the medulla innervate the muscles of the tongue

Question 14

Describe the structure of the special visceral efferent cranial nerve nuclei.

Answer 14

Cranial nerves V, VII, IX, X and XI carry SVE fibres.

• V in pons innervates muscles of mastication and swallowing
• VII in pons innervates muscles of facial expression
• IX, X and XI in the medulla innervate the pharynx, larynx and some muscles of the neck and shoulders

Question 15

Describe the structure of the general visceral efferent cranial nerve nuclei.

Answer 15

Cranial nerves III, VII, IX and X carry GVE fibres.

• III in midbrain controls radial iris sphincter muscle
• VII in pons targets submandibular and sublingual salivary glands, and lacrimal glands
• IX in pons targets parotid gland
• X in medulla targets smooth muscle, cardiac muscle and glands

Question 16

Describe the structure of the general visceral afferent and special visceral afferent cranial nerve nuclei.

Answer 16

• NTS (nucleus of the solitary tract) in the medulla recieves taste info, visceral sensory info (e.g. stretch, blood pressure and gases) and receives sensory afferents from petrosal ganglia (IX) and nodose ganglia (X)

Question 17

Describe the structure of the general somatic afferent cranial nerve nuclei.

Answer 17

GSA cranial nerve nuclei (trigeminal nerve nuclei) recieve innervation from primary afferent sensory neurons and contain cell bodies of second order sensory neurons.

Question 18

Describe the structure of the special somatic afferent cranial nerve nuclei.

Answer 18

Cranial nerves VIII and VIIII carry SSA fibres.

• VIII in pons and medulla recieves info on balance
• VIIII in medulla recieves info on hearing