How do photoreceptors in the eye respond to light stimuli?

Photoreceptors in the eye respond to light stimuli by converting light into electrical signals that the brain can interpret.

Photoreceptors are specialised cells located in the retina, the light-sensitive layer at the back of the eye. There are two main types of photoreceptors: rods and cones. Rods are responsible for vision in low light conditions, while cones are responsible for colour vision and detail in brighter light.

When light enters the eye, it passes through the cornea and the lens, which focus the light onto the retina. The light then strikes the photoreceptors. The photoreceptors contain a pigment called photopigment, which undergoes a chemical change when it absorbs light. This chemical change triggers an electrical signal.

In rods, the photopigment is called rhodopsin. When rhodopsin absorbs light, it splits into two components: opsin and retinal. This splitting process is called bleaching. The bleaching of rhodopsin triggers a series of chemical reactions that generate an electrical signal. This signal is then transmitted to the brain via the optic nerve.

In cones, the process is similar, but there are three different types of photopigment, each sensitive to a different range of wavelengths. This allows us to perceive different colours. When light strikes a cone, the photopigment undergoes a chemical change, triggering an electrical signal that is sent to the brain.

The brain then interprets these electrical signals to form a visual image. It's important to note that the photoreceptors do not 'see' the image; they simply convert light into electrical signals. The process of vision - the interpretation of these signals into a coherent visual image - occurs in the brain.

In summary, photoreceptors in the eye respond to light stimuli by undergoing a chemical change that triggers an electrical signal. This signal is then transmitted to the brain, which interprets it to form a visual image.