L31 Ocular Reflexes Flashcards
What is the function of the optokinetic reflex (smooth pursuit)
involuntarily realign the point of fixation during movement of the entire visual field or an object within the visual field
what forms the afferent limb of the OKR?
magnocellular parallel pathway (motion) M Cells
what forms the efferent limb of the OKR
parieto-occipital eye field
what is an example of naturally occurring optokinetic nystagmus
trying to follow a passing telephone pole outside while in a train
what is the slow phase of the Optokinetic nystagmus
controlled by OKR - attempts to keep object within visual field
what is the fast phase of the optokinestic nystagmus
reset, driven by saccadic circuitry in opposite direction - used to catch the next pole
what happens in the rotating chair experiment?
the start of rotation (endolymph going opposite direction of spin)= VOR
VOR will continue until the endolymph rotates at the same speed as the head (VOR stimulation stops) = OKR takes over
what happens when the spinning is stopped?
the endolymph will again begin to flow but now in the OPPOSITE direction (same direction as original spin) = VO nystagmus will start in other direction
what is the function of the pupillary light reflex?
limits the amount of light falling on the retina and prevents potential damage by excessive light intensities
what is the afferent limb of the pupillary light reflex?
CN 2 - optic n.
what is the efferent limb of the pupillary light reflex?
CN 3 - oculomotor n.
what is the function of the corneal reflex?
causes the eyelid to blink if something touches the cornea
what is the afferent limb of the corneal reflex?
trigeminal n.(CN V) V1 (pain fibers)
what is the efferent limb of the corneal reflex?
facial n. (CN VII)
how can optokinetic nystagmus be tested?
using OKN tape or a spinning drum with stripes - just move the tape and you should see OKN in healthy people
