topic 8 - detection of light ( rods and cones) Flashcards
define receptors
specialised cells that can generate an electrical impulse when stimulated
describe the route of light in the eye
pupil - retina - fovea - light receptors and photoreceptors
what controls the amount of light that can enter the eye?
circular and radial muscles in the iris
what are the two types of photoreceptor?
rod cells and cone cells
what to rod cells detect?
light intensity - in black and white
what to cone cells detect?
wavelength of light in colour
photorceptors generate light if … ?
light is bright enough
light is of the correct wavelength
what main pigment do rod cells contain ?
rhodopsin
what happens whehn light falls on rhodopsin?
it gets “bleached” splitting it into retinal and opsin
what does a rod cell do in light? (1)
generates an action potential which travels along the bipolar neurone
describe the process that happens at rod cells in the dark (5)
- Na+ actively pumped out of the cell against conc gradient
- Na+ channels open so Na+ diffuses back in down gradient
- there is little difference in charge between inside and outside of cell so cell is depolarised
- inhibitory neurotransmitter released into the synapse
- no action potential transmitted to bipolar neurone
describe the process that happens at rod cells in the light (6)
- rhodopsin “bleached” into retinal and opsin
- Na+ actively pumped out of the cell against concentration gradient
- Na+ channels closed so cannot diffuse back into the cell
- Inside of the cell become sincreasingly negative so cell becomes hyperpolarised
- No inhibitory neurotransmitter released into the synapse
- Action potential generated and can be passed to the bipolar neurone
EQ explain why current decreases in a rod cell as light intensity increases (4)
- rhodopsin bleached into opsin
- opsin binds to receptors on Na+ voltage gated channels
- Na+ voltage gated channels close
- reducing influx of Na+
