4 - Receptors

Question 1

What is resting potential?

Answer 1

The potential difference across a cell membrane when the cell is at rest

Question 2

What is the potential difference also known as?

Answer 2

Voltage

Question 3

What is the generator potential?

Answer 3

The change in potential difference across a cell membrane due to the presence of a stimulus

Question 4

What is an action potential?

Answer 4

An electrical impulse along a neurone

Question 5

What is a Pacinian Corpuscle?

Answer 5

A type of receptor found in your skin which detects mechanical stimuli e.g.. Pressure and vibrations
(mechanoreceptor)

Question 6

What are photoreceptors?

Answer 6

Receptors in the eye that detect light

Question 7

What are the two types of photoreceptors found in the human eye?

Answer 7

Rods and Cones

Question 8

Summarise the main features of Rods

Answer 8

• Mainly located in the peripheral parts of the retina
• Give information in black and white
• Many rods join one bipolar neurone
• High sensitivity to light
• Give low visual acuity

Question 9

Summarise the main features of Cones

Answer 9

• Mainly located in the fovea
• Give information in colour
• One cone joins one bipolar neurone
• Low sensitivity to light
• Give high visual acuity

Question 10

How do photoreceptors work?

Answer 10

• Light enters the eye, hits the photoreceptors and is absorbed by light sensitive optical pigments
• Light bleaches the pigments causing a chemical change and altering the membrane permeability to sodium ions
• A generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone, which connect photoreceptors to the optic nerve, which takes impulses to the brain

Question 11

Are Rods sensitive to light and why?

Answer 11

Rods are sensitive to light (they fire action potentials in dim light) because many rods join one bipolar neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential

Question 12

Are Cones sensitive to light and why?

Answer 12

Cones are less sensitive to light than rods (they only fire action potentials in bright light) because one cone joins one bipolar neurone so it takes more light to reach the threshold and trigger and action potential

Question 13

Do Rods give a high or low visual acuity and why?

Answer 13

Rods give low visual acuity because many rods join the same bipolar neurone which means light from two points close together can’t be told apart

Question 14

Do Cones give a high or low visual acuity and why?

Answer 14

Cones give a high visual acuity because cones are close together and one cone joins one bipolar neurone. When light from two points hits two cones, two action potentials (one from each cone) go to the brain - so you can distinguish two points that are close together as two separate points

Question 15

What is visual acuity?

Answer 15

The ability to tell apart points that are close together