Cranial Nerves - 20

Question 1

SSS: Special Somatic Sensory:

Answer 1

Special senses derived from ectoderm: •Sight, sound, balance

Question 2

SVS: Special Visceral Sensory:

Answer 2

Special senses derived from endoderm: •Taste

Question 3

SVM: Special Visceral Motor:

Answer 3

Muscles derived from pharyngeal arches

Question 4

GVS: General Visceral Sensory

Answer 4

General sensation from viscera

Question 5

GVM: General Visceral Motor:

Answer 5

• To smooth muscles of gut tract

* Autonomic motor

Question 6

GSS: General Somatic Sensory

Answer 6

General senses from ectoderm (skin)

Question 7

GSM: General Somatic Motor:

Answer 7

Skeletal muscles

Question 8

Cranial nerves typically have same basic structure

Answer 8

Dorsal root and ventral root. Dorsal root ganglion.

Question 9

Motor components of cranial nerves begin

Answer 9

within the brain within motor nuclei.

Comparable to spinal cord anterior horns.

Question 10

Cell bodies of sensory fibers are located in

Answer 10

dorsal root (cranial) ganglia

Question 11

Most cranial nerves, however, are not typical:

Answer 11

Cranial nerves I and II are sensory tracts/nerves but have no dorsal ganglia or roots. Some cranial nerves are strictly motor and have no dorsal ganglia or roots.

Question 12

Special sensory cranial nerves:

Answer 12

Are actually tracts

No motor nuclei and no sensory ganglia.

Question 13

Motor cranial nerves:

Answer 13

Begin in cranial motor nuclei

Have no sensory roots and no sensory root ganglia

Question 14

Mixed cranial nerves

Answer 14

Have both cranial motor nuclei and sensory ganglia

Sensory ganglia are usually given specific names.

Question 15

Olfactory Nerve (CN I)

Answer 15

made up of many fibers that pass from the upper third of the olfactory (nasal) mucosa:

Olfactory receptor cells
Pass through: •Cribriform plate
To: •Olfactory bulbs
Modality: •SVS

Question 16

Olfactory Epithelium

Answer 16

• Located in nasal cavity roof:
• Pseudostratified columnar epithelium without goblet cells
• Sustentacular cells (support cells) with pigment granules

Question 17

Basal cells with pigment granules:

Answer 17

Stem cells –give rise to immature olfactory cells

Question 18

Olfactory cells:

Answer 18

• Bipolar neurons
• Apical end projects into nasal cavity as a knoblike ending with nonmotilecilia.
• Cilia possess G-protein-linked odor-specific receptors
• Basal end of the cell extends as an unmyelinated axon, bundled with other similar axons, through the ethmoid plate to mitral cells located in the olfactory bulb
• Olfactory cells senesce and are replaced from basal cells.

Question 19

Olfactory glands of Bowman:

Answer 19

• Located in the lamina propria
• Secrete odorant-binding protein
• Odorant-binding protein binds to odorant molecule in nasal cavity.

Question 20

Olfactory tracts:

Answer 20

Slender extensions of forebrain

Question 21

Olfactory bulbs:

Answer 21

• Expanded endings of the olfactory tracts that lie on either side of the crista galli within the cribriform fossa
• Sites where axons of olfactory neurons synapse with dendrites of mitral cells
• Axons of mitral cells form the major connecting tracts with the olfactory centers within the brain

Question 22

Olfactory Nerve (CN I)

Answer 22

Olfactory nerve fibers pass from: •Olfactory receptor cells 
Through: •Cribriform plate 
To: •Olfactory bulbs 
Function: •Smell 
Modality: •SVS

Question 23

Optic Nerve (CN II)

Answer 23

Begins in ganglionic layer of retina (not rods and cones) 
Exits orbit through optic canal 
50% decussation in optic chiasma: 
•Near pituitary gland 
•Near internal carotid 

Function: •Sight
Modality: •SSS

Question 24

Oculomotor Nerve (CN III)

Answer 24

• Supplies four of the six extrinsic muscles of the eye.
• Has a parasympathetic component.
• Will be discussed in a group with other parasympathetic nerves.

Question 25

Trochlear Nerve (CN IV)

Answer 25

•Enters orbit through superior orbital fissure
•Innervates superior oblique muscle of the eye
Function: •Eye movement
Modality: •GSM
•Only crossed cranial nerve
•Only cranial nerve that emerges dorsally

Question 26

Abducens Nerve (CN VI)

Answer 26

•Originates from abducens nucleus
•Enters orbit through superior orbital fissure
•Lies on medial aspect of lateral rectus muscle
•Innervates lateral rectus muscle of the eye
Function: •Eye movement
Modality: •GSM

Question 27

Vestibulocochlear Nerve (CN VIII)

Answer 27

Leaves cranial cavity via internal acoustic meatus:
•Accompanied by facial nerve.
Modality: •SSS
Auditory (cochlear) component:
•Cell bodies in spiral ganglion of cochlea.
•Function: Hearing.
Vestibular component:
•Cell bodies in vestibular ganglion.
•From receptors for balance and equilibrium.
•Function: Balance.

Question 28

Spinal Accessory Nerve (CN XI)

Answer 28

• Arises from C1-3 (4) lateral rootlets (combination of dorsal and ventral roots of cervical nerves)
• Single trunk enters cranial cavity through foramen magnum.
• Temporarily joins cranial root
• Cranial roots leave with vagus nerve, which they are considered part of anyway.
• Spinal accessory trunk exits cranial cavity via jugular foramen.

Function: •Motor innervation to the sternocleidomastoid and trapezius muscles
Modality: •SVM
Cranial roots:
•Originate from nucleus ambiguus in the medulla
•Join fibers of the vagus nerve
•Supply muscles of the larynx via the recurrent laryngeal nerve

Question 29

Hypoglossal Nerve (CN XII)

Answer 29

•From hypoglossal nucleus in floor of fourth ventricle
•Exits cranial cavity via hypoglossal foramen
•Descends anteriorly in neck between internal carotid and internal jugular
•In neck gives rise to superior root of ansacervicalis and a nerve to thyrohyoid muscle
•Supplies extrinsic and intrinsic muscles of tongue: •Incl. genioglossus, hyoglossus, styloglossus
Modality: •GSM