Receptors

Question 1

What are Pacinian corpuscles?

Answer 1

They are receptors on the skin that detect changes in pressure.

Question 2

Draw and label a pacinian corpuscle.

Question 3

Describe how the Pacinian corpuscles create an electrical impulse in response to a pressure change?

Answer 3

1. When the pressure increases the lamellae deforms.
2. This causes them to press onto the sensory nerve endings.
3. The stretch-mediated sodium ion channels are also deformed and open.
4. The sodium ions diffuse into the nerve cell and cause the charge to increase.
5. If the charge increases above the threshold, an action potential is triggered.
6. The greater the pressure, the more sodium ion channels open, and the threshold is more likely to be reached.

Question 4

What are photoreceptors?

Answer 4

They are receptors found in the eye that detect light.

Question 5

Where are rods usually found?

Answer 5

In the peripheral of the retina.

Question 6

Where are cones usually found?

Answer 6

They are concentrated in the fovea.

Question 7

How do cones allow humans to see different colours?

Answer 7

1. They are only green, red and blue sensitive cones in the human eye. If each one of those is stimulated individually we see those colours.
2. Any other colours are seen due to the stimulation of more than one type of cone in different proportions.

Question 8

Why do rods have a lower visual acuity and a higher sensitivity?

Answer 8

1. Multiple different rods are connected to open bipolar nerve.
2. The weak generator potentials that are triggered in each one due to a stimulus can be combined to reach the threshold and trigger an action potential. This means that the stimulus doesn’t have to be as strong to generate an action potential.
3. Since multiple rods are connected to one bipolar nerve, a single set of action potentials is sent to the brain via the optic nerve, meaning they can’t be told apart.

Question 9

Why do cones have a higher visual acuity and a lower sensitivity?

Answer 9

1. Each cone is connected to one binary nerve.
2. This means that the stimulus has to be very strong to raise the charge of the neuron to the threshold and trigger an action potential.
3. Each cone is connected to one bipolar nerve so separate action potentials are sent to the brain and can be told apart.

Question 10

How do rods detect a stimulus and send an electrical impulse to the CNS?

Answer 10

1. When the light hits the photoreceptors it triggers the breakdown of a pigment called rhodopsin in the rod cells.
2. This causes the sodium ion channels in the bipolar nerve to open. The charge inside increases, and if it reaches the threshold level, then an action potential is triggered.
3. The action potential travels along the bipolar nerve and into the optic nerve.
4. The optic nerve takes that electrical impulse to the CNS.

Question 11

How do cones detect a stimulus and send an electrical impulse to the CNS?

Answer 11

1. When the light hits the photoreceptors it triggers the breakdown of a pigment called iodopsin in the rod cells.
2. This causes the sodium ion channels in the bipolar nerve to open. The charge inside increases, and if it reaches the threshold level, then an action potential is triggered.
3. The action potential travels along the bipolar nerve and into the optic nerve.
4. The optic nerve takes that electrical impulse to the CNS.