How many stimuli do receptors detect + why?
One - they're specific
What + where are receptors?
2) On cell surface membrane
How do receptors communicate?
- Via Nervous System
1) Resting state : difference in charge inside + outside = meaning there is a voltage across membrane (potential difference)
2) At rest called resting potential
3) Cell membrane excited by stimulus = becomes permeable
4) Ions in + out alter potential difference
5) Generator potential: changes in potential difference
6) Big enough G.P triggers A.P if exceeds threshold
Explain Pacinian Corpuscles
- It's a pressure receptor in skin
1) When stimulated lamelle deforms + press on sensory nerve ending
2) Causing stretch-mediated sodium ion channels to open + ions to diffuse = G.P
3) G.P reaches threshold = triggers A.P
Explain/Define Photoreceptor, Iris and Lens
Photoreceptor - Light receptor in eye
Iris - controls amount of light that enters
Lens - Focuses rays onto retina
Explain/Define Retina and Blind Spot
Retina - contains loads of photoreceptors in fovea
- Nerve impulses carried from retina to brain by optic nerve, a bundle of neurones
Blind spot - NO photoreceptors = not sensitive to light
Explain how photoreceptors convert light into impu
- Light hits photo.rec + absorbed by light sensitive optical pigment
- Causing chemical change - alterning membrane permability to sod ions
- G.P reaches threshold + nerve impulse sent along bipolar neurone
- This N connects photoreceptors to optical nerve - takes impulses to brain
Name types of photoreceptors
Where is the rod + cone found?
Rod - Peripheral part, Retina
Cone - Fovea
How do rods + cones give information?
Rods - Black + White
Cones - Coloured
What types of cones are there?
Red, blue + green sensitive
Sensitivity - Rod
Very - work in dim light - bc many rods join to one N = weak G.P combines
Sensitivity - Cone
Low - only fires A.P in bright light - one cone to one N = more needed to reach threshold
Acuity - Rod
Low - many rods join to one N - meaning light from two points cannot be told apart
Acuity - Rod
High - cones are close together + one cone joins to one N - when light from two points hit two cones two A.P = so can distinguish between two points