[14.4] (1/2) receptors: the pacinian corpuscle

Question 1

what are features of sensory receptors, illustrated by the pacinian corpuscle?

Answer 1

• specific to a single type of stimulus (PC = mechanical pressure)
• produces a generator potential by acting as a transducer

Question 2

how does a receptor act as a tranducer?

Answer 2

• all stimuli involve a change in form of energy (heat, light, sound, mechanical)
• transducers convert the change in form of energy by the stimulus into a nerve impulse known as a generator potential that the body can understand
• receptors convert (tranduce) one form on energy into another

Question 3

where are pacinian corpuscles found?

Answer 3

• most abundant on fingers, soles of feet and external genitalia
• joints, ligaments and tendons, where they enable the organism to know which joints are changing direction

Question 4

describe the structure of a pacinian corpuscle

Answer 4

• sensory neurone in centre
• capsule: many layers of phospholipid membranes
• layers of connective tissue with viscous gel between
• blood capillary
• myelin sheath

Question 5

what is special about the sensory neurone ending at the centre of the PC?

Answer 5

• has a special type of sodium channel in its plasma membrane
• this is called a stretch-mediated sodium channel

Question 6

why are stretch-mediated sodium channels called so?

Answer 6

their permeability to sodium changes when they are deformed eg. when stretched

Question 7

how does a pacinian corpuscle work?

Answer 7

1. in resting state, SMSC in membrane around neurone are too narrow to allow Na+ to pass along them
2. when pressure is applied, PC is deformed and membrane around neurone becomes stretched
3. stretching widoens Na channels in membrane, Na+ diffuse into neurone
4. influx of Na+ changes potential of membrane (becomes depolarised), thus producing a generator potential
5. GP creates an action potential (nerve impulse) that passes along neurones then to CNS