Sensory Receptors

Question 1

What are the 2 main features of sensory receptors?

Answer 1

All have a unique stimulus

Act as transducers - convert stimulus into a nervous impulse

Question 2

What are the 4 types of sensory receptors?

Answer 2

Mechanoreceptor: responds to pressure and movements. E.g. Pacinian corpuscle (detects pressure). Sense organ: Skin

Chemoreceptor - responds to chemicals. E.g. Olfactory receptor (detects smell). Sense organ: Nose

Thermoreceptor - responds to heat. E.g. End-bulbs of Krause (nerve terminals in skin, mucosa of oral cavity). Sense organ: Tongue

Photoreceptor - responds to light. E.g. Cone cells (detects different light wavelengths). Sense organ: Eyes

Question 3

What is the role of a transducer?

Answer 3

After sensory receptors detect stimuli, the receptor converts it into a nervous impulse called a generator potential. The magnitude of the potential determines the intensity of the stimulus

Question 4

What is a Pacinian Corpsucle?

Answer 4

Located within your skin and are most abundant in fingers and soles of feet

They are also found in joints so you know which direction they are moving in

• The sensory neurone is in the centre of the corpsucle surrounded by layers of connective tissue
• Each layer of tissue separated by a gel
• The neurone ending has a special sodium channel called a stretch mediated sodium channel, as they stretch the permeability to sodium changes

Question 5

How does a Pacinian Corpuscle convert mechanical pressure to a nervous impulse?

Answer 5

1. In the resting state, the stretch mediated sodium ion channels in the sensory neurone membrane are too narrow for Na+ ions to pass through. The PC neurone has a resting potential
2. Once pressure is applied, the corpsucle changes shape causing the membrane in the neurone to stretch
3. As the membrane stretches, the sodium ion channels widen so Na+ ions can diffuse into the neurone
4. The influx of positive charge changes the potential - making it depolarised - results in a generator potential
5. The generator potential creates an action potential (nervous impulse) that passes along a sensory neurone
6. Action potential is transmitted along neurones to the CNS.