3.6.1.2 Receptors

Question 1

Describe how a generator potential is established in a pacinian corpuscle

Answer 1

1.) mechanical stimulus (pressure) deforms lamellae and stretch mediated sodium ion channels
2.) Na + channels in membrane open and Na+ diffuse into sensory neurone
-greater the pressure, more ion channels open, more Na enters
3.) causes depolarisation leading to a generator potential
if generator potential reaches threshold, action potential is triggered.
therefore, receptors only respond to specific stimuli (pacinian corpuscle =mechanical pressure)

Question 2

what is the all or nothing principle

Answer 2

action potential is only sent if generator potential reaches threshold

Question 3

Why are rod cells more sensitive to light than cone cells?

Answer 3

Several rods are connected to a single neurone
spacial summation overcomes threshold and action potential is generated
only one cone cell is connected to a neurone , no spatial summation

Question 4

why do cone cells have a higher visual acuity than rod cells?

Answer 4

cone cells are connected to a single neurone. Therefore they send separate sets of impulses to the brain and can distinguish between light sources.
Several rod cells are connected to a single neurone (bipolar) and set out a single set of impulses. therefore cannot distinguish between separate sources of light

Question 5

Explain why rods and cone cells have different sensitivity to colours

Answer 5

3 type of cone cells (red, green. blue) with different optical pigments, so they absorb different wavelengths.
rods only have one pigment.

Question 6

what is an action potential ?

Answer 6

when a neurons voltage increases beyond a set point.

Question 7

Describe repolarization and refractory period in detail.

Answer 7

1. Repolarisation: 2xNa+ ion channells close
   (Voltage gated.) Nat out of avon.
   lx K- ion channellsopen.(K-into axon.
2. Refractory period. hyper polarisation. Potassium ions channells are slow to close