Excitable cells 17: (McLean) Eye movement Flashcards
Label the parts of the eye
Iris Cornea Pupil Lens Retina (has several layers)
Describe the layers and cells of the retina
Sclera
- white of the eye, protective outer layer of collagen and elastin fibres
Choroid
- vascular layer, provides O2 and nutrients especially to fovea
Pigment epithelium
- pigmented layer for light absorption, reduces oxidative stress, supports photoreceptors
Photoreceptors
- cones (3 types, blue, red ,green) (high acuity, day vision, colour vision, concentrated at fovea)
- rods (dark vision, not present in central retina)
Horizontal cells
- connect interneurons laterally
Bipolar cells
- connect photoreceptors to retinal ganglion cells
Amacrine cells
- Interneurons connecting bipolar cells laterally
Retinal Ganglion cells
- output cells from the retina
Fovea
- area/pit of densely packed photoreceptors
Why do eyes move?
1) bring an image onto fovea
2) keep it there
Types of eye movement?
Saccade - bring image to fovea
Fixations Smooth pursuit Optokinetic Nystagmus Vestibulo-ocular reflex Vergence movements - all to keep image on fovea
Match eye movement to behaviour
- reading
- when head or whole body moves
- single object of interest moving
- whole visual field moving
Reading - Saccades and fixations
Head/whole body moves - vestibulo-ocular reflex
Single object of interest moving - smooth pursuit
Whole visual field moving - optokinetic nysteagmus
3 components of fixational eye movement? What do they prevent?
Microsaccade - small saccades to bring image back to fovea
Drift - slower than microsaccades and more random
Tremor - fine oscillations superimposed on the drift
- Prevent retinal adaptation -> red dot grey halo
What is required to make a smooth pursuit movement?
A moving target
Eye movement during smooth that helps ‘catch up’ if object is going too fast?
Catch-up saccades
what does each eye movement look like on a graph?
look at the graphs blud
Which parts of the vestibular system respond to
- Head rotation
- Head translation
Head rotation
- semicircular canals
Head translation
Horizontal movement - utricle
Verticle movement - saccule
(both together called otolith organs)
Purpose of Bárány chair?
Diagnose balance disorders
How to OKN and VOR work together?
complement eachother
rapid immediate response = VOR
slow build up = OKN
responds best to brief stimulation = VOR
respond best to sustained stimulation = OKN
sensory drive
OKN = visual
VOR = vestibular
What is vergence?
the simultaneous movement of the pupils of the eyes towards or away from one another during focusing.
inward - convergence
outward - divergence
