Photoreceptor cell

Photoreceptor cells are specialized type of neuron found in the retina that are capable of photo transduction. More specifically, they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. The two classic photoreceptor cells are rod cells and cone cells, but other photoreceptors exist, including the photosensitive ganglion cells in the retina of mammals.

Types of Photoreceptor Cells

There are three types of photoreceptor cells in mammalian eyes:

1. Rod cells: Rod cells are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision.
2. Cone cells: Cone cells, or cones, are one of the two types of photoreceptor cells that are in the retina of the eye which are responsible for color vision. They are less sensitive to light than rod cells in the retina (which support vision at low light levels), but allow the perception of color.
3. Photosensitive ganglion cells: These cells contribute to the regulation of circadian rhythms, pupillary light reflex, and other non-image-forming visual functions.

Function

Photoreceptor cells capture photons and convert them into electrical signals, which are then processed by other neurons, sent to the brain, and translated into the visual images we see. The process by which this happens is called phototransduction.

Diseases and Disorders

Photoreceptor cells can be affected by a number of diseases and disorders. These include:

• Retinitis pigmentosa: This is a genetic disorder that causes loss of vision. Symptoms include trouble seeing at night and decreased peripheral vision.
• Macular degeneration: This is a medical condition which may result in blurred or no vision in the center of the visual field. It generally occurs in older adults and results in a loss of vision in the center of the visual field because of damage to the retina.
• Color blindness: This is the decreased ability to see color or differences in color. It is often inherited and affects a significant percentage of the population.

See Also

• Neuron
• Retina
• Rod cells
• Cone cells
• Photosensitive ganglion cells
• Phototransduction
• Retinitis pigmentosa
• Macular degeneration
• Color blindness

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