Cranial nerves II

Question 1

where is the oculomotor nuclear complex?

Answer 1

rostral midbrain, ventral to the PAG

Question 2

where is the trochlear nucleus?

Answer 2

caudal midbrain

Question 3

where is the abducens nucleus?

Answer 3

caudal pons

Question 4

where is the facial nucleus?

Answer 4

caudal pons

Question 5

the oculomotor complex is made up of what nuclei? what fibers do they carry?

Answer 5

1. oculomotor nucleus - motor 2. Edinger-Westphal nucleus - parasympathetic

Question 6

what are the symptoms of a CN 3 lesion?

Answer 6

wrinkled forehead, raised eyebrow, ptosis, dilated pupil, downward abducted eye

Question 7

what are the components of the parasympathetic pupillary light (constriction) reflex?

Answer 7

1. ganglion cells axons of retina go to ipsilateral and contralateral pretectal areas of midbrain 2. ganglion cell axons synapse at pretectal neurons that project bilaterally to EWN to stimulate preganglionic parasympathetic cell bodies 3. axons from parasympathetic cell bodies run via CN 3 to terminate in ciliary ganglion

Question 8

what are the components of the sympathetic pupillary (dilation) reflex?

Answer 8

1. cell bodies of hypothalamus descend to spinal cord and terminate at T1 2. preganglionic sympathetic neurons in lateral horn of spinal cord give rise to axons that enter sympathetic trunk 3. sympathetic trunk neurons ascend to superior cervical sympathetic ganglion to synapse with postganglionic sympathetic neurons which ascend via the internal carotid to innervate Muller’s muscle, dilator pupillae

Question 9

where does the trochlear nerve leave the brainstem?

Answer 9

just inferior to inferior colliculus

Question 10

what are the courses of axons leaving the abducens nucleus?

Answer 10

1. motor neurons forming abducens nerve 2. interneurons joining the medial longitudinal fasciculus and ascending to rostral midbrain and terminating in oculomotor nucleus to innervate MR muscles

Question 11

what minimizes horizontal diplopia resulting from an abducens nerve lesion?

Answer 11

turning head in direction of lesion

Question 12

what is the result of a lesion to an abducens nucleus?

Answer 12

deficit in ipsilateral LR and contralateral MR

Question 13

what nucleus is responsible for conjugate horizontal eye movement? what is the higher center modulation?

Answer 13

1. abducens nucleus 2. frontal and parietal motor eye fields (via reticular formation)

Question 14

what is the mechanism of internuclear opthamalmoplegia? what is the result? does it affect convergence?

Answer 14

1. lesion to one MLF disconnecting the abducens nucleus and the contralateral oculomotor nucleus 2. deficit in conjugate horizontal eye movement 3. does NOT affect convergence

Question 15

what controls LMNs during conjugate horizontal eye movement? convergence?

Answer 15

1. conjugate horizontal eye movement - MLF 2. convergence - higher brain centers via reticular formation

Question 16

what is the deficit involved in one-and-a-half syndrome? what is the cause?

Answer 16

1. ipsilateral lateral gaze paralysis and internuclear opthalmoplegia 2. lesion involving one entire abducens nucleus and MLF fibers from contralateral abducens nucleus

Question 17

what is required for successful convergence?

Answer 17

1. intact MR 2. intact LMNs innervating the MRs 3. intact oculomotor nucleus