In this video, I cover the anatomy and physiology of the retina. I discuss the five major types of neurons found in the retina: photoreceptor cells (i.e. rods and cones), bipolar cells, ganglion cells, horizontal cells, and amacrine cells. I also briefly describe the fovea, our area of highest visual acuity, and the optic disc, which creates a natural blind spot in our visual field.

**CORRECTION** The image of the cell layers of the retina at 0:12-0:15 is reversed. The photoreceptors should be at the very back of the retina; light must travel through the other cell layers of the retina before reaching the photoreceptors. Note that the images throughout the rest of the video (after 0:15) are correct. Follow this link to see a corrected image: https://www.neuroscientificallychallenged.com/retina-correction

For an article (on my website) that explains the retina, click this link: https://neuroscientificallychallenged.com/posts/know-your-brain-retina

TRANSCRIPT:

Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics in 2 minutes or less. In this installment I will discuss the retina.

The retina contains the neural component of the eye. When light reaches the back of the eye, it enters the cellular layers of the retina.

The cells of the retina that detect and respond to light, known as photoreceptors, are located at the very back of the retina. There are two types of photoreceptors: rods and cones. Rods allow us to see in dim light, but don't allow for the perception of color. Cones, on the other hand, allow us to perceive color under normal lighting conditions. Throughout most of the retina, rods outnumber cones. In one area called the fovea, however, there are no rods but many cones. The fovea represents the area of the retina that provides our highest acuity vision, and thus is at the center of our gaze.

When light hits photoreceptors, it interacts with a molecule called photopigment, which begins a chain of events that serves to propagate the visual signal. The signal is transmitted to cells called bipolar cells, which connect photoreceptors to ganglion cells. Bipolar cells pass the signal on to ganglion cells, which leave eye in a large cluster at an area called the optic disc. The optic disc doesn't contain any photoreceptors, and so represents an area on the retina that can't process visual information, creating a natural blind spot. However, we normally don't notice our blind spot. The brain uses information from surrounding photoreceptors and the other eye to fill in the gaps in images that are processed by the retina. After leaving the retina, the ganglion cell fibers are called the optic nerve. The optic nerve carries visual information toward the brain to be processed.

There are two other cell types in the retina that should be mentioned: horizontal and amacrine cells. Horizontal cells receive input from multiple photoreceptor cells. They integrate signaling from different populations of photoreceptor cells, make adjustments to the signals that will be sent to bipolar cells, and regulate activity in photoreceptor cells themselves. Amacrine cells receive signals from bipolar cells and are involved in the regulation and integration of activity in bipolar and ganglion cells.

REFERENCE:

Nolte J. The Human Brain: An Introduction to its Functional Anatomy. 6th ed. Philadelphia, PA. Elsevier; 2009.