16. CN - I-IV, VI

Question 1

What is unique about CN I and II compared to other CNs?

Answer 1

They are extensions of the brain! (Meninges are continuous)

Question 2

CN I

Name, Exit location of skull, primordium

Answer 2

Olfactory Nerve
Cribiform Plate of Ethmoid
Olfactory Placode (epidermal cells become sensory olfactory neurons)

Question 3

Nasal Anatomy:
Crista galli
Olfactory tract vs. bulb vs. nerves vs. mucosa (what coats the nasal mucosa??)

Answer 3

Crista galli: ethmoid b/w both olfactory bulbs
Tract: extension of brain surrounded by meninges
Bulb: swelling of tract on cribiform plate
Nerves: in olfactory epithelium below cribiform plate - these neurons send axons to olfactory bulb
Mucosa: epithelium is pseudostratified columnar with bipolar neurons (350 receptors for scents with integrative response)

Bowmans serous glands: coats epithelium, not mucous

Question 4

CN II

Name, Skull Exit, Function, Primordium

Answer 4

Optic Nerve
Exits Optic Canal (of Lesser wing of sphenoid with opthalmic artery)
Fx: Special sensory for vision
Primordium: Optic Cup - ectodermal expansion of brain, surrounded by meninges
Inner layer = visual retina; outer layer = pigmented retina

Question 5

Optic Anatomy:
Optic Nerve vs. Chiasma vs. Tract
What parts of the eye perceive the left visual field?
How do the eyes see if damage to the R Optic Nerve vs. Optic Chiasma vs. R Optic Tract?

Answer 5

O Nerve: vision for each eye
O Chiasma: crossing over of Medial Retinal Fibers
O Tract: vision from each visual field (right tract is left visual field)

Left Visual Field: Medial Left Eye and Lateral Right Eye perceive it (Medial Left Eye fibers cross over at chiasma to join right optic tract)

Disrupt R. Optic Nerve: lose vision out of right eye
Disrupt Optic Chiasma: lose medial vision of both eyes (narrow vision)
Disrupt R. Optic Tract: lose entire vision field - lose lateral right eye and medial left eye

Question 6

CN III

Name, Skull Exit, Function, what happens when damaged, Primordium

Answer 6

Oculomotor Nerve
Exits Superior Orbital Fissure
Fx: Somatomotor to most extraocular eye muscles and levator palpebrae superioris; Presynaptic PARASYMPs to ciliary ganglion (to ciliary muscle - contract lens for close up vision, and pupil constrictor m via CN V)

Damage: ptosis (no levator palpebrae sup.), dilated pupil (no parasymp), pupil is down and out (only lateral rectus and superior oblique active)

Question 7

CN IV

Name, Skull Exit, Function, Primordium

Answer 7

Trochlear Nerve
Exits Superior Orbital Fissure
Fx: motor to superior oblique (moves pupil down and out)

P: Pre-otic head somites

Question 8

CN VI

Name, Skull Exit, Function, Damage, Primordium

Answer 8

Abducens Nerve
Exits Superior Orbital Fissure
Fx: motor to lateral rectus (abducts pupil)

Abduces Palsy: inability to abduct pupil (most often CN damaged due to long intracranial course that is over petrous part of temporal bone)

P: Pre-otic head somites