Disc shedding

Cone Cells

Diagram of a cone cell

Cone cells, or cones, are one of the two types of photoreceptor cells in the retina of the eye that are responsible for color vision. They function best in relatively bright light, as opposed to rod cells, which work better in dim light. Cone cells are concentrated in the fovea centralis, a small pit in the center of the macula of the retina.

Structure

Cone cells are elongated, conical structures that contain photopigments in their outer segments. The outer segment is connected to the inner segment by a ciliary stalk. The inner segment contains the cell's metabolic machinery, including the mitochondria and endoplasmic reticulum.

The outer segment of a cone cell contains stacks of membrane-bound discs, where the photopigments are located. These discs are continuously renewed, with new discs being formed at the base of the outer segment and old discs being shed at the tip. This process is known as disc shedding.

Function

Cone cells are responsible for photopic vision, which is vision under well-lit conditions. They are also responsible for color discrimination, as they contain different types of photopigments that are sensitive to different wavelengths of light. Humans typically have three types of cone cells, each sensitive to different parts of the visible spectrum:

• S-cones (short-wavelength sensitive) are most sensitive to blue light.
• M-cones (medium-wavelength sensitive) are most sensitive to green light.
• L-cones (long-wavelength sensitive) are most sensitive to red light.

The combination of signals from these three types of cones allows the brain to perceive a wide range of colors through a process known as trichromatic vision.

Distribution

Cone cells are unevenly distributed across the retina. They are densely packed in the fovea, where they provide the highest visual acuity and color discrimination. The density of cone cells decreases towards the periphery of the retina, where rod cells become more prevalent.

Related pages

• Rod cell
• Photoreceptor cell
• Retina
• Color vision
• Fovea centralis