Lecture 7 - Vision II

Question 1

What are the different cell layers of the retina and what does each do?

L7 S4 LO1

Answer 1

Photoreceptors (rods/cones):
-synapses with bipolar cells and horizontal cells in outer plexiform layer

Horizontal cells:

• signals from photoreceptors to bipolar cells
• inhibitory

Bipolar cells:
-synapses with amacrine and ganglion cells in inner plexiform layer

Amacrine cells:
-transmits from bipolar cells to ganglion cells

Ganglion cells:

• axons make up the optic nerve and synapse in the brain
• only cells in retina that use action potentials

Question 2

What is the signal pathway for cones and rods in the retina?

L7 S9 LO1

Answer 2

Cones:

• cones
• bipolar cells
• ganglion cells

Rods:

• rods
• bipolar cells
• amacrine cells
• ganglion cells

Question 3

What neurotransmitter is used between photoreceptors and bipolar cells?

L1 S4 LO1

Answer 3

Glutamate

Question 4

What is the general function of amacrine cells?

L7 S11 LO2

Answer 4

Interneurons that analyze visual signals before leaving the retina

Question 5

What are the functions of he different types of ganglion cells and what is their relative abundance?

L7 S12-15 LO2

Answer 5

W ganglion cells:

• stimulated by several rods by way of bipolar and amacrine cells
• broad field
• ~40%

X ganglion cells:

• stimulated by at least one cone cell
• small field
• ~55%

Y ganglion cells:

• responds to rapid changes in visual information
• approximately no accuracy with location of field
• ~5%

Cells get larger and faster from W to Y

Question 6

What proportion of axons in the optic nerve decussate in the optic chiasm? What general rule determines if an axon decussates?

L7 S16 LO3

Answer 6

Approximate 50% decussate.

In general, axons from the nasal portion of the retina decussate while axons from the later portion don’t decussate.

This effectively separates the axons into right and left visual fields being processed in the opposite side of the brain.

Question 7

What path do visual signals take from the eye?

L7 S16 LO3

Answer 7

• optic nerve
• optic chiasm
• optic tract
• lateral geniculate body
• optic radiation
• visual cortex

Question 8

What relationship do each of the different nuclear layers of the lateral geniculate nucleus have with which portion of the retinas they receive information form?

L7 S16 LO3

Answer 8

Ipsilateral retina (lateral portion):
-layers II, III, and V

Contralateral retina (nasal portion)
-layers I, IV, and VI

Question 9

What do each of the cell layers of the later geniculate nucleus do?

L7 S17 LO3

Answer 9

Layers I and II:

• magnocellular layer
• receive input from Y ganglion cells
• transmit BLACK and WHITE vision
• poor point to point transmission

Layers III to VI:

• parvocellular layer
• receive input from X type ganglion cells
• transmits COLOR vision
• accurate point to point transmission