Guyton Chapter 50: The Eye - Receptor And Neural Function Of The Retina

Question 1

What are the rods and cons and where are they situated?

Answer 1

Cones: responsible for colour vision
Rods: can detect dim light and are mainly responsible for black and white vision and vision in dark!

Situated in the retina

Question 2

What are the layers of the retina?

Answer 2

1. Pigmented layer
2. Layer of rods and cones projecting to the pigment
3. Outer nuclear layer containing the cell bodies of the rods and cones
4. Outer plexiform layer
5. Inner nuclear layer
6. Inner plexiform layer
7. Ganglionic layer
8. Layer of optic nerve fibres
9. Inner limiting membrane

Question 3

What are the major functional segments of either a rod or cone?

Answer 3

1. Outer segment
2. The inner segment
3. The nucleus
4. The synaptic body

Question 4

Where is the nutrient blood supply for the internal layers of the retina derived from?

Answer 4

From the central retinal artery, which enters the eyeball through the centre of the optic nerve and then decides to supply the entire inside retinal surface.

The inner layers of the retina have their own blood supply independent of the other structures of the eye.

Question 5

Which blood flow do the outer layers of the retina depend mostly on?

Answer 5

The outermost layer of the retina is adherent to the choroid which is also a highly vascular tissue lying between the retina and the sclera. The outer layers of the retina especially the outer segments of the rods and cones, depend mainly on diffusion from the choroid blood vessels for their nutrition especially for their oxygen.

Question 6

What are the different neuronal cell types in the neural circuitry of the retina?

Answer 6

-the photoreceptors themselves (the rods and cones) which transmit signals to the outer plexiform layer where they synapse with bipolar cells and horizontal cells

• The horizontal cells which transmit signals horizontally in the outer plexiform layer from the rods and cones to bipolar cells
• The bipolar cells which transmit signals vertically from the rods, cones and horizontal cells to the inner plexiform layer where they synapse with ganglion cells and amacrine cells
• the amacrine cells which transmit in two directions either directly from bipolar cells to ganglion cells or horizontally within the inner plexiform layer from axons of the bipolar cells to dendrites of the ganglion cells or to other amacrine cells

-the ganglion cells which transmit output signals from the retina through the optic nerve into the brain

Question 7

What neurotransmitter substance is released by the rods and cones?

Answer 7

Glutamate is released at their synapses with the bipolar cells.

Question 8

Which are the only retinal neurons that always transmit visual signals by means of action potentials?

Answer 8

Ganglion cells

Question 9

How do the retinal neurons (beside the ganglion cells) conduct their visual signals?

Answer 9

Electric conduction