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Psychology 304: Brain and Behaviour

Lecture 32

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Reminder

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From last class ….

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Olfactory Receptors and Pathways of the Olfactory System 4

Olfactory Epithelium

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1. What is the structure of the eye and where are the receptors for light? (continued)

The Visual System

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By the end of today’s class, you should be able to:

1. distinguish between cones and rods.

3. explain how an action potential is generated in the retinal cells of the visual system.

2. describe duplex retinal theory.

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What is the structure of the eye and where are the receptors for light? (continued)

8The Cellular Structure of the Retina

9A Section of the Retina

Front of Eye, Pupil,

Vitreous Humor

10A Section of the Retina and Optic Nerve

Front of Eye, Pupil,

Vitreous Humor

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• There are two types of receptors in the human retina: cones and rods.

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• Cones are associated with relatively high visual acuity because a single ganglion cell receives input from only one or a few cones (low convergence).

• Rods are associated with relatively high sensitivity to illumination because a single ganglion cell receives input from many rods (high convergence).

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Convergence of Cones and Rods on Retinal Ganglion Cells

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• The fovea is specialized for high-acuity vision.

• Visual acuity at the fovea is enhanced by:

1. the presence of cones.2. the “thinning” of the bipolar and ganglion cell layers

in this region.

15The Fovea

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Retinal Cells at the Fovea

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Cone vs. Rod Density at the Fovea

Nasal Half of Retina

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• When light reaches a receptor, photopigments (e.g., rhodopsin) are activated that hyperpolarize the

receptor cell. Reduced neurotransmission by the receptor cell results in depolarization of the adjacent

bipolar cell (see Figure 10.13 on p. 295 of textbook, left side ONLY, “on-center” cells).

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• In turn, depolarization of the bipolar cell results in depolarization of the adjacent ganglion cell.

• When the ganglion cell is stimulated, an action potential is triggered that passes down the cell’s axon, along the optic nerve—cranial nerve II.

20Generation of an Action Potential in the Retina

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1. What is the structure of the eye and where are the receptors for light? (continued)

The Visual System