Sensory receptors

Features of sensory receptors

• Specific to a single type of stimulus

• Act as transducer, by converting stimulus into electrical impulse

Sensory receptors role as a transducer

Receptor converts stimulus into nervous impulse called a generator potential

• Creates an action potential that passes along sensory neurone

  • Given it reaches the threshold of -55mV

Main types of sensory receptor present in an animals

Where is Pacinian corpuscle found?

• Deep within skin, fingers, soles of feet, genitals, joints, nipples

What is found within membrane of P.C.’s neurone and why?

• Sodium ion channels

• Responsible for transporting sodium ions across membrane

What does P.C. neurone ending have?

• Stretch-mediated sodium channel

  • When it changes shape, permeability changes

Generator Potential

Change in potential difference due to stimulus

• Na+ channels open 

• Na+ ions diffuse into cell, increasing p.d. to -55mV

• Once reaches threshold of -55mV, action potential generated 

How a sensory receptor (P.C.) pressure into nervous impulse

1. In resting state, stretch-mediated Na+ channels in sensory neurone’s membrane too narrow to have Na+ passing thru. HAS A RESTING POTENTIAL

2. When pressure applied, corpuscle changes shape ; membrane surrounding neurone stretches

3. Na+ channels widen, Na+ ions diffuse into neurone

4. This depolarises membrane (changes p.d.). RESULTS IN GENERATOR POTENTIAL 

5. Once generator potential big enough, triggers action potential that passes along sensory neurone.