Retinal Anatomy - Introduction

Tutorial 14: Retinal Anatomy

Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test

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The retina forms the inside lining of the back of the eye and is composed of light-sensitive neurons. The retina processes the light emitted from visual images and transmits this information to the brain for perceptual awareness of the images. The light must pass through all layers of the retina before it reaches the cells that systematically absorb the light energy. By the time light that has passed into the eye through the cornea reaches the retina, almost 90% has been scattered or otherwise lost! The retina is organized into three layers. The first layer is made up of rods and cones. Two deeper layers transmit impulses from the receptor cells of the first layer to the optic nerve. These inner layers consist of four different cell types that form a network of circuits. This network contributes to the processing of the image information, transmitting this information to the optic nerve. These cells feed into a number of optic fibers that collect at a hole in the back of the eye (the optic disk) to form the optic nerve.

Figure 14 illustrates the layers of cells that compose the retina. This tutorial describes the structural and functional relationships that underlie the reception and transduction of light into a neural code.

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There are two types of Receptor Cells in the retina, rods, and cones. These cells detect light energy and absorb this energy for use by the nervous system. The collection of rods and cones that convey signals to a particular visual cell of the retina and then ultimately to a neuron within the primary visual cortex, comprise that visual cell's receptive field. Although the receptive fields of visual cells are found with a variety of shapes and sizes, they are typically arranged in two concentric circles with light falling on the center opposing the effect of light falling on the outside circle. This arrangement is called "center-surround". Sometimes the stimulation of receptor cells in the center results in excitation of an impulse (depolarization of the visual cell) and stimulation of receptor cells in the surrounding circle results in the inhibition of an impulse (hyperpolarization of the cell). Other times the excitatory and inhibitory influence of the concentric circles is reversed, so that stimulation of the center results in inhibition and stimulation of the peripheral circle results in excitation. Either arrangement results in lateral communication between retinal cells and a refinement of the signal that reaches the primary visual cortex.

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Tutorial 14: Retinal Anatomy

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