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The human eye


Structure and function of the human eye

Eye is not the same eye in the animal kingdom. The human eye Although it belongs to the vertebrate eyes, it differs in structure and function partly from the eyes of other vertebrates. For example, in terms of day-night vision (cats as excellent night hunters), color vision (dogs are red-green-blind) or the size of the visual field (fruit with almost 360 * view). In addition, there are many other types of eyes: light sensor cells (in rainworms), shallow eyes (in starfish) or compound eyes (in flies).
The sensory eye can, for reasons of clarity in eyeball, appendages and Sehbahn be divided.

Structure of the eye

eyeball:
Cornea: to the cornea belongs the first, visible part of the eye. The cornea fulfills two essential functions. On the one hand it protects against the entry of foreign bodies and on the other hand the cornea ensures the refraction of light.
Glaskцrper: the glass body gives the eye its round shape. The gelatinous liquid consists almost exclusively of water and the protein collagen, which gives the glass body a certain firmness.
lens: is located between the iris and the glass body. The dished lens bundles the incident light on the retina.
pupil: the pupil is in the middle of the eye and is surrounded by the iris. Their main task is the regulation of light. By dilating or narrowing the pupil can increase or decrease the amount of light entering.
Iris (iris): surrounds the pupil. The iris closes the pupil through its musculature, thus it is also involved in the regulation of the light incidence. Stored pigments are responsible for the individual Augenfärrung.
Appendages::
eyelid: The eyelids consist of connective tissue and muscles. Through the eyelid reflex they cover the eyes at a regular interval of about 3-4 seconds to keep the eyeball moist. Even in startle reactions it comes to the blinking reflex, which protects in these cases the sensitive eye from external influences and foreign bodies.
conjunctiva: the conjunctiva is located immediately behind the eyelids. As a mucous membrane, it moisturizes the eye, more precisely the cornea, with tears at every blink of an eye. Without this permanent moistening the cornea would become brittle and could no longer break the incoming light.
Trдnenapparat: on the one hand the troughs which are responsible for production of tears and the trough ways which again divert tears belong to a trommel apparatus. The Trendendrьse is on the left eye on the left, and the right eye on the right above the eye. Every day the drinkers produce between 300 and 500ml. On the inside of the eyes the tears are drained into the nose.
Sehbahn:
Retina: The retina is a dense, multi-layered neural tissue that converts light waves into electrical excitement. It is located on the inside of the eye. The bipolar cells of the retina process the information from the photoreceptors (sticks and cones) and relay them to the retinal ganglion cells. These ganglion cells pass directly into the optic nerve.
optic nerve: The optic nerve (optic nerve) receives the electrical excitations of the retina and forwards them to the brain. At the optic nerve junction (chiasma opticum) both optic nerves cross each other. There the optic nerve "ends" and passes into an optic tract. The optic nerve consists of about 1 million nerve fibers.