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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 our 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 the 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 of 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.