Receptors

Question 1

Describe how receptors convert energy from a stimulus into electrical energy that is used by the neurones.

Answer 1

1. When a receptor is at rest there is a difference in charge between the inside and outside of the cell.
2. The inside is slightly negative and the outside is slightly positive.
3. This creates a potential difference which is known as the resting potential.
   4 . When the stimulus is detected the cell becomes excited and the membrane becomes more permeable to ions.
4. The increased movement of ions in and out of the cell changes the resting potential and creates a generator potential.
5. If the change goes above the threshold level then an action potential is triggered.

Question 2

What are Pacinian corpuscles?

Answer 2

Receptors on your skin that detect mechanical stimuli.

Question 3

Draw the structure of a Pacinian corpuscle.

Question 4

How does a paciniac corpuscle detect and action potential?

Answer 4

1. When the corpuscle is stimulated the lamellae are deformed and press on the sensory nerve ending.
2. This causes the cell membrane of the neurone to stretch and that deforms the stretch-mediated sodium ion channels.
3. This allows more sodium ions to move into the cell and that changes the resting potential.
4. If the potential reaches above the threshold level then an action potential is triggered.

Question 5

What are photoreceptors?

Answer 5

receptors in your eye that detect light

Question 6

Draw the structure of an eye.

Question 7

Why is the blind spot not sensitive to light?

Answer 7

There are no photoreceptors on that part of the eye.

Question 8

How do photoreceptors work?

Answer 8

1. Light enters the eye and is absorbed by the light-sensitive pigments in the photoreceptors.
2. The light bleaches the pigments and causes a chemical change that alters the permeability of the cell to sodium ions.
3. The sodium ions diffuse into the cell and change the resting potential.
4. If the generator potential goes above the threshold level an action potential will be sent along the bipolar nerve.

Question 9

Where are rods found in the eye?

Answer 9

In the peripheral parts of the eye

Question 10

Where are cones found in the eye?

Answer 10

packed together in the fovea

Question 11

Why are rods responsible for monochromatic visions?

Answer 11

They only give information in black and white.

Question 12

Why are cones responsible for coloured vision?

Answer 12

There are three types of cones; red-sensitive, blue-sensitive and green-sensitive. The colour we see depends on how much each one is stimulated.

Question 13

Why are rods very sensitive to light?

Answer 13

Many rods are connected to one bipolar neurone meaning that many weak generatior potentials can be combined to trigger an action potential.

Question 14

Why do rods have a low visual acuity?

Answer 14

Many rods are connected to one bipolar neurone meaning that it is hard to tell light from two points apart.

Question 15

Why do cones have low sensitivity to light?

Answer 15

Each cone is connected to an individual bipolar neurone meaning that to trigger an action potential the intensity of the light must be high.

Question 16

Why do cones have high visual acuity?

Answer 16

Each cone is connected to an individual bipolar neurone meaning that when light from two different points hits a different cone two different action patterns will be triggered.