6.2: Receptors

What is the function of a Pacinian Corpuscle and what does it demonstrate?

• It is used as a pressure receptor in the skin

Demonstrates that

• Receptors only respond to specific stimuli as the pacinian corpuscle only responds to mechanical pressure

• Stimulation of a receptor leads to the establishment of a generator potential as when the threshold is reached, action potentials are sent

What is the structure of a Pacinian Corpuscle? (label diagram)

How is a generator potential established in a Pacinian Corpuscle?

• A mechanical stimulus deforms the lamalle and stretch-mediated sodium ion channels

• So sodium ion channels in the membrane open and Na+ diffuses into the sensory neuron

• An increase in pressure causes more Na+ channels to open and more Na+ to enter

• This causes depolarisation, leading to a generator potential 

• If the generator potential reaches threshold it triggers an action potential

What are the differences between rod and cone cells?

• Greater number of cone cells than rod cells

• Rod cells mainly at the periphery of the retina, cone cells mainly at the fovea with fewer at the retina

• Rod cells give poor visual acuity, cone cells give good visual acuity

• Rod cells are sensitive to low intensity light, cone cells are not sensitive to low intensity light 

• Only one type of rod cells, three types of cone cells responding to different wavelengths of light

What is spatial summation?

When multiple presynaptic neurons form a junction with a single neurone

Explain the differences in sensitivity to light for rods and codes in the retina

• Several rods are connected to a single neurone

• So spatial summation overcomes threshold to generate an action potential

• One cone is connected to a single neurone

• No spatial summation, so does not reach threshold, so no action potential produced

What is visual acuity?

How clearly a person can see at a specific distance

Explain the differences in visual acuity for rods and codes in the retina

• Several rods are connected to a single nuerone

• So several rods send a single set of impulses to the brain 

• So they cannot distinguish between seperate sources of light 

• One cone is connected to a single neurone 

• Sp they send separate sets of impulses to the brain

• So they can distinguish between seperate sources of light 

Explain the differences in sensitivity to colour for rods and codes in the retina

• Rods have only 1 type with 1 pigment 

• So they allow for monochromatic vision

• Cones have 3 types (red, green and blue sensitive)

• Different optical pigments absorb different wavelengths

• Stimulating different combinations of cones gives a range of colour perception