Cranial Nerves Part I

Question 1

Describe the site of entry/exit for the CN.

Answer 1

The brainstem is the site of emergence and entry of the 10 pairs of true cranial nerves (CN III-XII).

2 from midbrain (III and IV)
4 from pons (V, VI, VII, VIII)
4 from medulla (IX X XI XII)

Question 2

How can you tell the difference between a CT and MRI?

Answer 2

On CT bone is white

MRI (fluid/H2O is white)

Question 3

Describe the CN nucleus for VIII.

Answer 3

The cranial nerve nucleus for VIII is really made up of 4 vestibular and 2 cochlear nuclei..

Question 4

How are nuclei arranged in columns?

Answer 4

nuclei are arranged in columns according to their functional components—motor nuclei are near the midline, sensory more lateral

Question 5

Describe how CN can take origin from, or synapse on one or more nuclei depending on their functional components.

Answer 5

12 has one nucleus (hypoglossal motor nucleus) and only 1 functional component (GSE)—

While the Vagus uses 4—dorsal motor X for GVE, N. Solitarius for SVA and GVA, nucleus ambiguous for SVE, and spinal V for GSA.

Question 6

Describe the attachment, foramen, components, nucleus of origin (efferent) or termination (afferent) and main structures innervated from CN I.

Answer 6

CN I: Olfactory
Attachment: Olfactory bulb
Foramen: cribriform plate (of ethmoid)
Components: SVA
Nucleus of origin or termination: Olfactory mucosa
Main structures innervated: olfactory nasal mucosa

Question 7

What is CN I in close proximity to?

Answer 7

I is in close proximity to entorhinal cortex/hippocampus

Question 8

Describe the attachment, foramen, components, nucleus of origin (efferent) or termination (afferent) and main structures innervated from CN II.

Answer 8

CN I: Optic
Attachment: optic chiasma
Foramen: optic foramen (canal)
Components: SSA
Nucleus of origin or termination: lateral geniculate body (diencephalon) (relayed to calcarine fissure)
Main structures innervated: retina

Question 9

Describe what the optic nerve communicates with. Where does it end up synapsing?

Answer 9

The optic nerve communicates with the lateral geniculate and superior colliculus—and ends up synapsing in the occipital cortex (area 17 surrounding the calcarine fissure)

Question 10

Where are the location of specific visual fields in regards to the retina?

Answer 10

Remember that the location of specific visual fields are directly opposite the physical location of the retina that records that field—think about it. Recall that nasal fibers cross while temporal optic nerve fibers don’t.

Question 11

What are optic radiations?

Answer 11

Fibers running from lateral geniculate to area 17 are called optic radiations

Question 12

What is the lateral geniculate attached to?

Answer 12

The lateral geniculate is attached to the back of the thalamus

Question 13

Describe the attachment, foramen, components, nucleus of origin (efferent) or termination (afferent) and main structures innervated from CN III.

Answer 13

CN III- Oculomotor
Attachment- sulcus on walls of interpeduncular fossa
Foramen- sup. orbital fissure
Components: GVE (parasympathetic) and GSE

Nucleus of origin or Termination: 1) Edinger-Westphal (mid brain) 2) Oculomotor nucleus (midbrain)

Main structures innervated: 1) (via ciliary ganglion) to sphincter pupillae and ciliary muscles 2) sup. med. and inf. recti and inf. oblique eyeball muscles and levator palebrae superioris

Question 14

What 2 nuclei does III use?

Answer 14

The Edinger Westphal nucleus is responsible for parasympathetic (GVE) innervation of the pupil and lens—it shrinks the pupil and fattens up the lens.

The oculomotor nucleus sends out motor axons to all eye muscles except LR6SO4 (GSE)

Question 15

Describe the attachment, foramen, components, nucleus of origin (efferent) or termination (afferent) and main structures innervated from CN IV.

Answer 15

CN IV: Trochlear
Attachment: superior medullary velum
Foramen: superior orbital fissure
Components: GSE
Nucleus of Origin or Termination: 1) trochlear nucleus (midbrain)
Main structures innervated: 1) superior oblique eyeball muscles

Question 16

Describe unique things about CN IV.

Answer 16

4—Only nerve to cross and originate from dorsum of brainstem—important point—just like anterior horn cells, cranial motor nuclei have upper motor neurons synapsing on them—We call these “corticobulbar fibers”—-the bulb is an old name for the brainstem.

also 4 has the longest intracranial exposure

Question 17

What does the superior oblique muscle do?

Answer 17

down and out

IO UO SO DO

Question 18

What is the trochlear nucleus and where is it found?

Answer 18

The trochlear nucleus (GSE to the superior oblique) is very small and found at the level of the inferior colliculus

4 lies under the inferior colliculus in the caudal midbrain

Question 19

What is the trochlear nucleus on top of? What is the function of that thing?

Answer 19

High power showing trochlear nucleus on top of MLF—the medial longitudunal fasciculus which coordinates conjugate eye movements and head and neck movements with the vestibular and auditory systems.

Question 20

Describe the attachment, foramen, components, nucleus of origin (efferent) or termination (afferent) and main structures innervated from CN V.

Answer 20

Trigeminal

1) Opthalmic
2) Maxillary
3) Mandibulary

Attachment: lateral part of pons

Foramen: superior orbital fissure, foramen rotundum, foramen ovale

Components: 1) GSA 2) SVE

Nucleus of Origin:
1) pain and temp from face to spinal tigeminal N. conscious proprioception to chief sensory nucleus
Unconscious proprioception from jaw (V3) to mesencephalic N.
2) motor nucleus of Nerve V (pons)

Main structures innervated:
VI) skin of upper part of face (upper orbit and above)
V2) skin of mid face, upper teeth, nasal and palatal mucosa
V3) skin of lower face and jaw, floor of mouth, mucosa of ant 2/3 tongue, lower teeth and gums, ear pinna and canal

2) motor to muscles of mastication, ant. belly of digastric, tensor tympani, mylohyoid, tensor palatini (first arch muscles)

Question 21

Describe where the cell bodies are for GSA function of V. How is pain and temperature relayed?

Answer 21

Cell bodies for GSA function are in the trigeminal(semilunar) ganglion. Pain and temperature are relayed via the spinal tract and nucleus of V (a nucleus proprius analog (STT)) Position sense travels to the main or chief sensory nucleus of V. This nucleus is like the dorsal column pathway nuclei. The mesencephalic nucleus of V is histologically like a dorsal root ganglion sucked into the brainstem. It has pseudopolar neurons in it and relays the afferent limb of the “jaw-jerk” reflex

Question 22

Describe sensory components for V.

Answer 22

Note spinal V (GSA for ear pinna carried by 7,9, and 10)—-note the solitary tract and nucleus—SVA/GVA for 7, 9, and 10

Question 23

The trigeminal nerve (V) is the GSA nerve for the head; describe the following:

Trigeminal ganglion

Mesencephalic nucleus

Main or principal nucleus of V

Spinal trigeminal nucleus

Trigeminal motor nucleus

Answer 23

Trigeminal ganglion—semilunar or Gassarian (pseudounipolar cells conveying sensory info from head)

Mesencephalic nucleus—more pseudouniplolar cells sucked into the brainstem “jaw jerk reflex” (in on V3 spindle afferents to Motor N of V out on V3 to masseter) Similar to DRG sucked into brainstem

Main or principal nucleus of V—like nuc. cuneatus, relays position and touch (like DCP - touch and proprioception)

Spinal trigeminal nucleus—like n. proprius and the STT relays pain and temp info

Trigeminal motor nucleus—SVE to muscles of mastigation, tensor tympani, ant belly digastric, and tensor veli palatini

Question 24

Where do the trigeminal proprioceptive or pain fibers synapse? How does this differ from other tracts?

Answer 24

Unlike the DCP or the STT, trigeminal proprioceptive or pain fibers synapse in the VPM of the thalamus (not the VPL)

Question 25

How are pain and temp from ear pinna relayed?

Answer 25

Pain and temp from ear pinna are relayed from 7,9,10 thru the spinal tract and nucleus of V (GSA)