Receptors and action potentials

What is a generator potential

The change in potential diffference across the cell surface membrane of a receptors. Result of a stimulus

Depolarisation of cell

Describe the structure of the pacinian corpuscle

Describe what happens in a pacinian corpuscle to generate an action potential

Pressure from touch causes lamellae to be deformed and press on sensory neurone ending

Stretches the membrane of the neurone

Increase in pressure deforms stretch mediated NA+ channels causing them to widen and open

Na+ ions diffuse into the axon

depolarises the cell creating a Generator potential

If generator potential reaches threshold an action potential is triggered

What is the retina

Layer of photoreceptor cells found at the back of the eye

Where are rod cells found 

Periphery of the retina

Can trigger action potential at low light intensities

Where are cone cells found and why

In the fovea

High light intensity needed

What is the name of the pigment in rods + cones

Rhodopsin

Iodopsin

Describe light sensitivity in rod cells

High so more sensitive

Several rods connected to a singer bipolar cell ,type of spatial summation 

Even at low light intensities many generator combine  so more likey to exceed threshold +sends impulse to optic nerve 

-rhodospin needs lower intensity to be broken down

Describe sensitivity to colour in rod cells 

Low

Only sensitive to light

Describe visual acuity in rod cells

Low

Several rod cells connected to single bipolar cell

Spatial summation

Single impulse sent, unable to distinguish between light from two points

Describe light sensitivity in cone cells

Low

One cone cells connected to connected to one bipolar cell,no spatial summation Even at

Low light intensities more light required to reach threshold and generate action potential,impulse not sent to optic nerve

Describe colour sensitivity in cones 

High 

3 types of cones with different pigments-iodopsin 

Red blue green

When stimulated in different proportions see different colours

Describe visual acuity 

One bipolar connected to one cone 

Many action potentials ,receives many impulses which can be distinguished 

Send separate impulses to the brain

Describe how a pacinian corpuscle produces a generator potential when stimulated (3)

Increased pressure deforms stretch mediated sodium ion channel

Sodium channels open and sodium ions flow iN

Depolarisation leading to generator potential