3rd, 4th and 6th Cranial Nerves

Question 1

Name the 3rd, 4th and 6th cranial nerves.

Answer 1

• CNIII – Oculomotor nerve
• CNIV – Trochlear nerve
• CNVI – Abducens nerve

Question 2

What do the oculomotor, trochlear, and abducens nerves supply?

Answer 2

Together the oculomotor, trochlear and abducens nerves supply all the extraocular eye
muscles.

Question 3

What does the 3rd cranial nerve, oculomotor nerve also supply?

Answer 3

CNIII also supplies 2 intrinsic eye muscles with sympathetic fibres
•dilator pupillae and the smooth muscle component of LPS (levator palpebrae superioris)

Question 4

List the functional components of oculomotor nerve.

Answer 4

▪ General somatic efferent – movements of the eyeball
▪ Parasympathetic – contraction of pupil & accommodation
▪ General somatic afferent – proprioception

Question 5

Nucleus of the oculomotor nerve :

Location and function

Answer 5

• Somatic Motor:
Ventromedial part of central grey matter of midbrain – level of SUPERIOR COLLICULUS
• Visceral Motor: (Parasympth)
Edinger-Westphal Nucleus – dorsal to the anterior two thirds of somatic motor nucleus
❖gives fibres for constrictor pupillae and ciliaris muscles

Question 6

The Edinger - Westphal nucleus is the…

Answer 6

Source of the parasympathetics to the eye

Question 7

What does the Edinger - Westphal do?

Answer 7

Constrict the pupil and accommodate the lens.

Question 8

Where is the Edinger - Westphal nucleus located?

Answer 8

It is located just inside the oculomotor nuclei, like nested “V”s.

Question 9

Where do the fibres of the Edinger - Westphal nucleus travel?

Answer 9

The fibres travel in the CNIII, so damage to that nerve will also
produce a dilated pupil.

Question 10

State the series of activities that take place when eye drops are applied to the eye.

Answer 10

Eye drops given at the ophthomologist’s office are an acetylcholine
antagonist (blocker) inhibiting actions of the parasympathetic system.
As a result your eyes are dilated, so the physician can look inside clearly.
As a side effect, you cannot accommodate your lens (focus on close
objects) which is why you can’t read while you are sitting in the waiting
room.

Question 11

State the course and distribution of the oculomotor nerve.

Answer 11

1. Attached to oculomotor sulcus in medial aspect of CRUS CEREBRI
2. Emerges from MIDBRAIN
3. Pierces dura mater to enter CAVERNOUS SINUS
4. Lies ABOVE CNIV in cavernous sinus
5. Leaves cranial cavity to enter orbit via SUPERIOR ORBITAL FISSURE
6. In fissure DIVIDES into Upper and Lower Divisions

Question 12

What does the upper division supply?

Answer 12

UPPER DIVISION: supplies Superior rectus and Levator palpebrae superioris

Question 13

The lower division has 3 branches supplying the :

Answer 13

Medial rectus
Inferior rectus
Inferior oblique (fibres from this branch enter ciliary ganglion – parasympth)

Question 14

List the functional components of the trochlear nerve.

Answer 14

▪ General somatic efferent – lateral movement of the eyeball

▪ General somatic afferent – proprioception

Question 15

Unique features of the trochlear nerve :

Answer 15

o Exits brainstem dorsally

o Crosses – fibres cross over each other in the roof of the fourth ventricle

Question 16

Nucleus of the trochlear nerve : Location

Answer 16

• Ventromedial part of central grey matter of midbrain – level of INFERIOR COLLICULUS
• Immediately below oculomotor nucleus

Question 17

Course and distribution of the trochlear nerve :

Answer 17

1. Emerges from posterior surface of MIDBRAIN
2. Winds around superior cerebellar peduncle just above PONS
3. Passing anteriorly around BRAINSTEM
4. Pierces dura mater to enter CAVERNOUS SINUS
5. Enters orbit through lateral aspect of SUPERIOR ORBITAL FISSURE
6. Passes ABOVE origin of Levator palpebrae superioris
7. Supplies Superior oblique

Question 18

List the functional components of the abducens nerve.

Answer 18

▪ General somatic efferent – lateral movement of the eyeball

▪ General somatic afferent – proprioception

Question 19

Nucleus of the abducens nerve : Location

Answer 19

• Situated in upper aspect of the floor of the 4th ventricle
• Inferior to the FACIAL COLLICULUS

Question 20

Course and distribution of the abducens nerve :

Answer 20

1. Emerges from brainstem BETWEEN pons and medulla – PONTOMEDULLARY JUNCTION
2. Traverses PONTINE CISTERN of Subarachnoid space
3. Pierces posterior wall of CAVERNOUS SINUS
4. Enters orbit through middle part of SUPERIOR ORBITAL FISSURE
5. Lies inferolateral to nasociliary and oculomotor nerves
6. Supplies Lateral rectus