Cranial nerves III, IV, VI (eye movements) Flashcards
Name CN III, IV, VI
What is the characteristic that is common to IV and VI but not III
III, oculomotor MOTOR + PNS
IV, trochlear MOTOR
VI, abducens MOTOR
Where are these nerves found on the brainstem
III, between crus cerebri
IV, dorsally under inf colliculus
VI, between pons and medulla oblongata
What nuclei are associated with the oculomotor, trochlear and abducens nerve and where are they found
III, Edinger Westphal, Oculomotor
-At level of superior colliculi, ventrally in midbrain
IV, Trochlear
-At level of inferior colliculi, dorsally in midbrain
VI, Abducens
-At level of floor of 4th ventricle in pons
What exit foramen is associated with all 3 CN
Superior orbital fissure
Describe the route of the oculomotor nerve at the level of the superior colliculli
Fibres from EW and O nuclei radiate ventrally
Oculomotor nerve emerges ventrally
Describe the route of the trochlear nerve at the level of the inferior colliculli
Fibres from T nucleus wrap around grey matter around cerebral aqueduct
Emerge contralaterally and dorsally
Describe the route of the abducens nerve at the level of the pons
Fibres from A nucleus that are ventral to the 4th ventricle
Emerge ipsilaterally ventrally between pons and medulla
What eye muscles does the oculomotor nerve innervate
Levator pelpebrae (eyelids) Sup rectus Med rectus Inf rectus Inf oblique
What eye muscles does the trochlear nerve innervate
Sup oblique
What eye muscles does the abducens nerve innervate
Lateral rectus
Describe the pathway of the trochlear and abducens and the motor nerve of the oculomotor taken to move the eye
Exit neurocranium
Enter eye orbit via superior orbital fissure
Innervate motor eye muscles
Describe the parasympathetic pathway of the oculomotor nerve
Light shines on eye
Impulse sent down optic nerve
Synapses in pretectal area
Synapse in EW nuclei
Preganglionic nerve synapses => ciliary ganglion
Postganglionic nerve acts on sphincter pupillary muscles in both eyes
What happens in trochlear nerve palsy
What happens if the nucleus is affected
Paralysis of superior oblique
Normally depresses and medially rotates eyeball, this ability is lost
If nucleus affected => contralateral sup oblique paralysis
What happens in abducens nerve palsy
Why
Paralysis of lateral rectus muscle
Unopposed action of medium rectus
Longest cranial nerve with furthest to travel, vulnerable to injury.
What happens in oculomotor nerve palsy
Results in limited eye movement => strabismus => diplopia and ptosis
Pupillary abnormalities
