Neurophysiology Flashcards
What are the 3 planes and corresponding axes of rotation of extraocular muscles?
-horizontal = vertical
-vertical = horizontal
-torsional = visual
what does Sherrington’s law of reciprocal innervation state?
For each eye, ‘antagonist’ muscles receive equal but opposite innervation
what does herring’s law of motor correspondence state?
For conjugate movements, ‘synergist’ muscles receive equal innervation (from CNS), i.e. certain muscles must co-contract (or co-relax) = “yoked” pairs Oculomotor Coordination
name the ipsilateral antagonists
-medial rectus
-lateral rectus
-superior rectus
-inferior rectus
-superior oblique
-inferior oblique
for each of the RE extraocular muscles name the contralateral synergists so state the yoked muscle pairs of the two eyes
-medial rectus = lateral rectus
-lateral rectus = medial rectus
-superior rectus = inferior oblique
-inferior rectus = superior oblique
-superior oblique = inferior rectus
-inferior oblique = superior rectus
why are there two sub divisions of the medial rectus?
because it is involved in both horizontal alignment and vergence
how are eye movements different to other muscle movements in the body?
there is a lack of a monosynaptic stretch reflex in extraocular muscles
give 3 devices that can measure eye movements and what are they all sampled at? What exactly can these measure?
-tobii pro spectrum
-eye link 1000+
-skalar
pupil boundary
pupil centre
gaze direction
why does the optic nerve have to be cushioned and protected?
as it moves alot when the eyes move
how do eye trackers work?
uses an image of the eye and by working out the center of the pupil and the geometry of the reflex, to find pupil boundary, centre and gaze direction, it can calculate how the eye is moving and where it’s looking.
what is the function of eye movements in general?
to provide a good, stable image
why do chickens move their bodies while keeping their heads completely still?
as they achieve stable image with their head instead of their eyes like us humans with foveal fixation
give an example in animals of how eye orientation in the head affects how a stable image is achieved
pigeons have eyes on the side of their head as every time they take a step forward, the image moves back so they bob their head to compensate
what are the two categories of eye movements and which eye movements fall in them?
-compensatory = stabilising
vestibulo-ocular reflex and optokinetic nystagmus
-targeting = fixation
saccades, smooth pursuit and vergence
what is gaze
where the fovea is looking independent of where the eyes are in terms of orientation or head movement
what is vestibulo-ocular reflex?
where your gaze remains unchanged even though the position of the eyes in the head changes due to fast, transient head movement
give an example that explains what vestibular nystagmus is
if you were to rotate 360 degrees, then you get a slow phase to compensate for the head movement and then a quick phase to reset the eyes because you have ran out of room and this maximises the amount of time you get a stable view of the world
what drives the vestibulo-ocular reflex?
a non visual stimulus - driven by afferent signal from inner ear canals
what is optokinetic nystagmus?
where gaze gets stabilised by generating an eye movement that’s in the same direction as the movement of the field - Occurs in all animals. When it reaches its max limit, it resets (saccades)
what is optokinetic nystagmus driven by?
retinal slip so has a visual stimulus
what are the two types of saccade?
-involuntary = anticompensatory reset during head rotation (or in OKN)
-voluntary = redirecting the foveal line of sight via reflex, visual (normal scanning) and memory (making saccadic movements in the dark)
what makes saccades different from other eye movements?
They are the only eye movement you can make to a non stimulus I.e. you don’t actually have to have something to look at for your eyes to make a saccade. This is the memory aspect of voluntary saccades
what kind of movement are saccades?
a ballistic movement
how long do saccades take to happen?
1/5 of a second