Module D-10 Flashcards
direct response
response on ipsilateral side
Consensual response
response on contralateral side
What are the 3 types of conjugate eye movements?
1) Saccadic eye movements (gaze)
2) vestibular reflex
3) optokinetic reflex (smooth pursuit)
What is the function of optokinetic reflex?
keep the eyes focused on an object and keep it in the center of the visual field
What is the optokinetic reflex?
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
Vestibulo-ocular reflex solely based on ________ info, the optokinetic reflex is based on _____ input
vestibular; Visual
The parieto-occipital eye field, receives visual input of ?
Motion of the visual environment, or objects within the visual environment
Where does the efferent limb of the optokinetic reflex come from?
parieto occipital eye field
Describe pathway of efferent limb of optokinetic reflex
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.
When does Optokinetic nystagmus occur?
- 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.
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 ________
left; Vestibulo-ocular ; left; Vestibulo-ocular ; right
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 ________
Optokinetic; left; optokinetic; right
At the stop of the rotation of the head to the right ___________ nystagmus takes over , and is to the ______
vestibulo-ocular; left
Describe the pathway for the pupillary light reflex
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
What is the function of the corneal or blink reflex?
protects the eye and the cornea from damage by inducing a closure of the eye lids and causes them to blink
Describe the pathway for the corneal reflex
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
Which nerve forms the efferent limb of corneal reflex?
CN VII
Which nerve forms the afferent limb of corneal reflex?
CN V
Which muscle is responsible for closing the eye lid?
Orbicularis oculi
Which muscles is responsible for opening the eye lid?
1) Levator palpebrae superioris
2) Tarsal muscles
Which nerve innervates Orbicularis Oculi?
facial nerve and nucleus
Which nerve innervates Levator palpebrae superioris?
Oculomotor nucleus and nerve (CN III)
Which nerve pathway innervates Tarsal muscles?
Sympathetics:
1) Hypothalamus
2) T1–T3 of spinal cord
3) Superior cervical ganglion
4) Carotid plexus
Damage to the __________ may be one of the causes interrupting the initiation of an optokinetic nystagmus
parieto-occipital eye field
What causes Bell’s palsy?
a peripheral lesion of the facial nerve due to swelling and compression in the distal part of the bony facial canal
Symptoms of Bell’s Palsy
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.
