Module D-10

Question 1

direct response

Answer 1

response on ipsilateral side

Question 2

Consensual response

Answer 2

response on contralateral side

Question 3

What are the 3 types of conjugate eye movements?

Answer 3

1) Saccadic eye movements (gaze)
2) vestibular reflex
3) optokinetic reflex (smooth pursuit)

Question 4

What is the function of optokinetic reflex?

Answer 4

keep the eyes focused on an object and keep it in the center of the visual field

Question 5

What is the optokinetic reflex?

Answer 5

movements involuntarily re-align the point of fixation during movements of either the whole visual surround, or an object within the visual surround, relative to the head

Question 6

Vestibulo-ocular reflex solely based on ________ info, the optokinetic reflex is based on _____ input

Answer 6

vestibular; Visual

Question 7

The parieto-occipital eye field, receives visual input of ?

Answer 7

Motion of the visual environment, or objects within the visual environment

Question 8

Where does the efferent limb of the optokinetic reflex come from?

Answer 8

parieto occipital eye field

Question 9

Describe pathway of efferent limb of optokinetic reflex

Answer 9

1) fibers originating in the parietooccipital eye field descend
ipsilaterally into the pons
2)They synapse on pontine nuclei (different from the PPRF) which project to the contralateral vestibulocerebellum
(flocculo-nodular lobe).
3) The vestibulocerebellum in turn sends fibers to a vestibular nucleus (the medial vestibular nucleus) on the same side.
4)Fibers from the vestibular nucleus cross the body’s midline and synapse in the contralateral abducens nucleus,
5) this activates the lateral rectus muscle of the ipsilateral eye. via the abducens nerve and the medial rectus muscle of the contralateral eye, via ascending fibers in the contralateral MLF, and the oculomotor nucleus and nerve.

Question 10

When does Optokinetic nystagmus occur?

Answer 10

• a physiological nystagmus.
• When, during the optokinetic reflex movements, the object in focus reaches the limit of eye movements towards one side, the fixation on the target is broken and the eyes
  move quickly in the opposite direction, resetting the focus of vision onto a new target, using the rapid saccadic circuitry.

Question 11

During the initial 30 sec of rotation of the head to the right, the endolymph is moving to the _________, which induces the _____________ reflex to the _______ and __________ nystagmus to the ________

Answer 11

left; Vestibulo-ocular ; left; Vestibulo-ocular ; right

Question 12

During the transition period of rotation of the head to the right, as the effect of visual stimuli increases it induces the _____________ reflex to the _______ and __________ nystagmus to the ________

Answer 12

Optokinetic; left; optokinetic; right

Question 13

At the stop of the rotation of the head to the right ___________ nystagmus takes over , and is to the ______

Answer 13

vestibulo-ocular; left

Question 14

Describe the pathway for the pupillary light reflex

Answer 14

1)Shining light into the right eye activates retinal ganglion cells.
2)The axons of retinal ganglion cells form the afferent limb of the reflex arc.
3)About 50 percent of the fibers forming the optic
nerve stay ipsilateral and continue in the optic tract of the same side.
4) The other 50 percent ganglion cell axons cross at the optic chiasm and then run along the contralateral optic tract.
5) Some of these fibers synapse in the pretectal nucleus of the midbrain.
6) Collaterals of axons originating in the pretectal nucleus bilaterally innervate the Edinger-Westphal nuclei, which are the accessory nuclei of the oculomotor nerve (CN III).
7) The Edinger-Westphal nuclei of CN III are the origin of parasympathetic fibers of the autonomic nervous system
8) Preganglionic fibers follow the path of the somatic
motor neurons of the oculomotor nerve, until they reach the ciliary ganglion,where they synapse on the second order neurons.
9)The postganglionic fibers form the short ciliary nerves,
10) innervate the circular smooth muscle of the pupil,
the constrictor muscle of the pupil,
11) the pupils constrict

Question 15

What is the function of the corneal or blink reflex?

Answer 15

protects the eye and the cornea from damage by inducing a closure of the eye lids and causes them to blink

Question 16

Describe the pathway for the corneal reflex

Answer 16

1) Sensory endings of nociceptors located in the cornea are activated
2) Their sensory signal enters the Pons via the ophthalmic division of the trigeminal nerve (CN V1).
3) The fibers descend within the pons and medulla,
to synapse in the spinal nucleus of CN V.
4) Fibers originating from there activate (directly or indirectly) both facial nuclei located in the lower pons.
5) The efferent axons originating in the facial nuclei run within the facial nerve (CN VII) and synapse in the orbicularis oculi muscles of both eyes,
6) cause the closure of the eye lids

Question 17

Which nerve forms the efferent limb of corneal reflex?

Answer 17

CN VII

Question 18

Which nerve forms the afferent limb of corneal reflex?

Answer 18

CN V

Question 19

Which muscle is responsible for closing the eye lid?

Answer 19

Orbicularis oculi

Question 20

Which muscles is responsible for opening the eye lid?

Answer 20

1) Levator palpebrae superioris

2) Tarsal muscles

Question 21

Which nerve innervates Orbicularis Oculi?

Answer 21

facial nerve and nucleus

Question 22

Which nerve innervates Levator palpebrae superioris?

Answer 22

Oculomotor nucleus and nerve (CN III)

Question 23

Which nerve pathway innervates Tarsal muscles?

Answer 23

Sympathetics:

1) Hypothalamus
2) T1–T3 of spinal cord
3) Superior cervical ganglion
4) Carotid plexus

Question 24

Damage to the __________ may be one of the causes interrupting the initiation of an optokinetic nystagmus

Answer 24

parieto-occipital eye field

Question 25

What causes Bell’s palsy?

Answer 25

a peripheral lesion of the facial nerve due to swelling and compression in the distal part of the bony facial canal

Question 26

Symptoms of Bell’s Palsy

Answer 26

1) total loss of the corneal reflex reaction (blink) on the affected side, but is not associated with ptosis (why?).
2) flattened nasolabial fold
3) unable to raise the eyebrow and wrinkle the forehead on the affected side.