Vision

Question 1

How do Rods transduce light?

Answer 1

Question 2

Characteristics of Retinal Cells:

1. Photoreceptors
2. Bipolar cells
3. Ganglion cells

Answer 2

Photoreceptors

• Graded membrane potentials (no AP’s)
• Release glutamate
• Hyperpolarized by light!

Bipolar Cells

• Graded membrane potentials (no AP’s)
• Release glutamate
• ON or OFF center BP cells

Ganglion Cells

• Generate Action Potentials!
• Axons project to thalamus
• ON or OFF center RGCs

Question 3

Answer 3

Question 4

How do Off-center cells respond to light in center of RF? (3)

How do On-center cells respond to light in center of RF? (3, same yet opposite)

Answer 4

How do Off-center cells respond to light in center of RF?

• Photoreceptor hyperpolarizes, less gluatamate released.
• Off-center Bipolar cells have ionotropic depolarizing glutamate receptors
• Less glutamate = OFF-BP cell hyperpolarization = OFF-BP cell releases less glutamate = OFF-Ganglion Cell fires fewer action potentials

How do On-center cells respond to light in center of RF?

• Photoreceptor hyperpolarizes, less glutamate released
• On-center bipolar cells have metabotropic hyperpolarizing glutamate receptors
• Less glutamate = ON-BP cell depolarization = ON-BP cell releases more glutamate = ON-Ganglion cell fires more action potentials

Question 5

Answer 5

Question 6

How do ON-center cells respond to light in surround of RF?

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Answer 6

How do ON-center cells respond to light in surround of RF?

• Surround Photoreceptor hyperpolarizes, less glutamate released
• Horizontal cell reduces its inhibitory activity which leads to depolarization of the center Photoreceptor
• Photoreceptor in turn releases more glutamate = ON-BP hyperpolarizes and releases less glutamate (b/c they have hyperpolarizing glutamate receptors) = ON-GC fires less action potentials

Question 7

What is the role of Horizontal Cells?

Remember:

The surround region of a bipolar or ganglion cell
receptive field is defined by the locations of the
photoreceptors that do not signal directly to those cells

Also, the receptive fields of retinal ganglion cells overlap resulting in high acuity/small receptive field!

Answer 7

What is the role of Horizontal Cells?

Inhibition of the photoreceptors in surround region.

Graded membrane potential (no APs)

Depolarized by glutamate from surround photoreceptors

Release GABA onto center photoreceptors (inhibiting them)

Question 8

How do we process shape?

Answer 8

We process shape through processing edges of objects.

RGCs most affected by the stimulus are those along an edge which creates edges of shapes

Detection Luminance Contrast