Näköelimistö

The näköelimistö, or visual system, is the part of the sensory nervous system that enables vision. It is composed of the eyes and the neural pathways that run from the eyes to the brain. The eyes detect light and convert it into electrochemical impulses. These impulses are then transmitted through the optic nerves to the brain, where they are interpreted as images.

The eye itself is a complex organ. Light enters through the cornea, a transparent outer layer, and then passes through the pupil, an opening in the iris. The iris, a colored muscular diaphragm, controls the size of the pupil, regulating the amount of light that enters. The lens, located behind the iris, focuses the light onto the retina, a light-sensitive tissue lining the back of the eye. The retina contains photoreceptor cells called rods and cones. Rods are responsible for vision in low light conditions, while cones detect color and detail in brighter light.

When light strikes the photoreceptor cells, it triggers a chemical reaction that generates nerve impulses. These impulses are processed by other cells in the retina before being sent along the optic nerve. The optic nerves from each eye meet at the optic chiasm, where some fibers cross over. This allows information from both eyes to be processed by both hemispheres of the brain. The impulses then travel to various areas of the brain, including the thalamus and the visual cortex, where they are ultimately perceived as vision. The näköelimistö allows us to perceive the world around us, enabling navigation, recognition of objects and individuals, and appreciation of visual stimuli.