Example receptors: Pacinian Corpuscle + Photoreceptors

What are pacinian corpuscles?

Pressure receptors in the dermal layer of the skin enabling you to sense changes in pressure all over your body.

Label the pacinian corpuscle

1. Sensory neurone ending

2. Sensory neurone axon

3. Blood capillary

4. Capsule

5. Layers of connective tissue with gel between

Describe the generator potential in the pacinian corpuscle

1. The lamellae deform, pressing on the sensory neurone ending.

2. This stretches the neurone’s membrane, causing it to change shape.

3. This opens stretch-mediated sodium ion (Na+) channels in the membrane, increasing its permeability to Na+.

4. Na+ diffuses into the neurone, depolarising it and resulting in a generator potential.

5. If this change in ion concentration, and so charge, reaches the threshold, an action potential is triggered.

Label the structures of the eye

1. Pupil

2. Iris

3. Lens

4. Retina

5. Fovea

6. Optic nerve

Where are the photoreceptors located in the eye?

1. Rods- located around the peripheral of the retina

2. Cones- densely packed in the fovea

Describe the generator potential in photoreceptors

1. Light hits photopigments, which are light- sensitive proteins in photoreceptor cells.

2. Light bleaches and causes a chemical change in the photopigments.

3. This increases the permeability of photoreceptor cells to sodium ions.

4. An influx of sodium ions causes a generator potential.

5. If this reaches threshold, a bipolar sensory neurone carries a signal to the optic nerve and then the brain.

What happens if too much light is picked up by these receptors?

The photopigment can basically run out, making the receptors exhausted. This can lead to temporary or permanent blindness.

How many cone cells are connected to a neurone? How does this help?

One cone cell connected to a single sensory neurone. This gives cone cells a high visual acuity as separate impulses will be sent to the brain for each cone cell receiving the stimulus. But, it gives cone cells a low light sensitivity, as the impulse received from one cone cell is unlikely to generate an action potential in the sensory neurone.

How many rod cells are connected to a neurone? How does this help?

There are multiple rod cells connected to a single neurone. This gives rod cells a low visual acuity as one single impulse will be sent to the brain for all the rod cells receiving the stimulus. But, it gives rod cells a high light sensitivity, as the impulses received from many rod cells are more likely to generate an action potential in the sensory neurone.