Receptors

One - they're specific

1) Proteins 

2) On cell surface membrane 

• 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 

• 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 

Photoreceptor - Light receptor in eye 

Iris - controls amount of light that enters 

Lens - Focuses rays onto retina 

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 

• 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

1) Rod 

2) Cone 

Rod - Peripheral part, Retina 

Cone - Fovea 

Rods - Black + White 

Cones - Coloured 

Red, blue + green sensitive 

Very - work in dim light - bc many rods join to one N = weak G.P combines 

Low - only fires A.P in bright light - one cone to one N = more needed to reach threshold

Low - many rods join to one N - meaning light from two points cannot be told apart 

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