Nerve cells are called neurons, which make up much of the brain. They conduct the electrical impulses which allow us to see, as well as think. Neurons have three main sections. These are the dendrites, cell body, and axon. The dendrites are like long fingers that extend from the cell body and connect to other neurons' axons. When a neuron fires, an electrical impulse travels down its axon into the dendrites of the next neuron. This next neuron usually then fires as a result of the stimulation caused by the signal from the first neuron. Neurons carry complicated electrical signals all over the brain.

Diagram of Neurons and Their Parts

Photoreceptors are a type of neuron, except they are stimulated not by other neurons, but by light. When the photoreceptor cells fire, they activate cells called bipolar cells, which fire in turn and activate ganglion cells. Ganglion cells make up the optic nerve, which extends into the brain. Thus, the original light is detected by photoreceptors in the eye and then the corresponding electrical signals travel from the photoreceptors to the optic nerve, where they are carried to the brain.

Other neurons in the eye are also important. One such type of cell is the horizontal cell. It lies perpendicular to the photoreceptors and allows them to communicate. It is thought that horizontal cells help to increase the contrast with which we see, allowing us to distinguish objects better. Another type of neuron in the eye is the amacrine cell, which also lies perpendicular to the photoreceptor-bipolar-ganglion pathway. It provides a means for ganglion and bipolar cells to communicate and is thought to help us distinguish movement.