Lecture 20 - Non-parasympathetic Cranial Nerves

Question 1

What are the different special modalities? (3)

L20 S3

Answer 1

Special somatic sensory (SSS):

• ectoderm derived
• sight
• sound
• balance

Special visceral sensory (SVS):

• endoderm derived
• taste

Special visceral motor (SVM):
-muscles from pharyngeal arches

Question 2

What are the different general modalities? (4)

L20 S3

Answer 2

General visceral sensory (GVS):
-sensation from viscera

General visceral motor (GVM):

• to smooth muscles of gut tract
• autonomic

General somatic sensory (GSS):
-sense from ectoderm (skin)

General somatic motor (GSM):
-skeletal muscles

Question 3

What generalizations can be made about the cranial nerves (special sensory, motor, and mixed)?

L20 S5

Answer 3

Special sensory cranial nerves:

• no motor nuclei
• no sensory ganglia (analogous to dorsal root ganglia)

Motor cranial nerves:

• begin in motor nuclei (analogous to anterior horn)
• no sensory root or sensory root ganglia

Mixed cranial nerves:
-have both motor nuclei and sensory ganglia

Question 4

What are the names of each of the CNS?

L20 S7

Answer 4

CN I - Olfactory
CN II - Optic
CN III - Oculomotor
CN IV - Trochlear
CN V - Trigeminal
CN VI - Abducens
CN VII - Facial
CN VIII - Vestibulocochlear
CN IX - Glossopharyngeal
CN X - Vagus
CN XI - Accessory
CN XII - Hypoglossal

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Question 5

What is the modality, function, and path of CN I?

L20 S9;15

Answer 5

Olfactory nerve

Modality:
-special visceral sensory (SVS)

Function:
-smell

Path:

• upper third of nasal mucosa
• through cribiform plate
• to olfactory bulbs
• to olfactory tracts (extensions of forebrain)

Question 6

Describe the olfactory epithelium and the cell types it contains.

L20 S11-12

Answer 6

Located in roof of nasal cavity

Basal cells:
-replenish olfactory cells

Olfactory cells:

• bipolar neurons
• cilia with GPCR specific to odor molecules
• umyelinated axons

Glands of Bowman:
-secrete odorant binding protein

Question 7

What is the modality, function, and path of CN II?

L20 S16

Answer 7

Optic nerve

Modality:
-special somatic sensory (SSS)

Function:
-sight

Path:

• begins in ganglionic layer of retina
• exits eye through optic canal
• 50% decussate in optic chiasma

Question 8

What is the modality, function, and path of CN III?

L20 S20

Answer 8

Oculomotor nerve

Modality:

• general somatic motor (GSM), primary
• general visceral motor (GVM)

Function:

• supplies 4/6 extrinsic muscles of the eye
• supplies iris and ciliary muscles

Path:
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Question 9

What is the modality, function, and path of CN IV?

What are the two unique features of this nerve?

L20 S21

Answer 9

Trochlear nerve

Modality:
-general sensory motor (GSM)

Function:
-eye movement

Path:

• enters orbit through superior orbital fissure
• innervates superior oblique
• *only crossed cranial nerve
• *only nerve that emerges dorsally from brain stem

Question 10

What is the modality, function, and path of CN VI?

L20 S22

Answer 10

Abducens nerve

Modality:
-general somatic motor (GSM)

Function:
-eye movement

Path:

• enters orbit through superior orbital fissure
• lies on lateral rectus muscle
• innervates lateral rectus muscle

Question 11

What is the modality, function, and path of CN VIII?

L20 S23

Answer 11

Vestibulocochlear nerve

Modality:
-special somatic sensory (SSS)

Function:

• hearing (cochlear component)
• balance (vestibular component)

Path:
-leaves cranium via internal acoustic meatus

Question 12

What is the modality, function, and path of CN XI?

L20 S24

Answer 12

Spinal accessory nerve

Modality:
-special visceral motor (SVM)

Function:

• innervation of sternocleidomastoid and trapezius muscle (spinal roots)
• innervation of larynx (cranial roots)

Path:

• originates from lateral roots of C1-3
• enters cranium through foramen magnum
• passes through nucleus ambiguus in medulla
• travels temporarily with vagus nerve
• exits through jugular foramen

Question 13

What is the modality, function, and path of CN XII?

L20 S26

Answer 13

Hypoglossal nerve

Modality:
-general somatic motor (GSM)

Function:
-innervates intrinsic and extrinsic muscles of the tongue (genioglossus, hyoglossus, and styloglossus)

Path:

• originates in hypoglossal nucleus of 4th ventricle
• exits cranium through hypoglossal foramen
• descends in neck with internal carotid and internal jugular
• spilts into ansa cervicallis and to thyrohyoid muscle