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Rheum from a cat's eyes. Rheum ( / ruːm /; from Greek: ῥεῦμα rheuma 'a flowing, rheum') is a thin mucus naturally discharged from the eyes, nose, or mouth, often during sleep (contrast with mucopurulent discharge ). [ 1][ 2][ 3] Rheum dries and gathers as a crust in the corners of the eyes or the mouth, on the eyelids, or under the nose ...
Circadian clock. A circadian clock, or circadian oscillator, also known as one’s internal alarm clock is a biochemical oscillator that cycles with a stable phase and is synchronized with solar time . Such a clock's in vivo period is necessarily almost exactly 24 hours (the earth's current solar day ).
In neuroanatomy, the optic chiasm, or optic chiasma ( / ɒptɪk kaɪæzəm /; from Greek χίασμα 'crossing', from Ancient Greek χιάζω 'to mark with an X '), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. [ 1] The optic chiasm is found in all ...
The resulting eye is a mixture of a simple eye within a compound eye. Another version is the pseudofaceted eye, as seen in Scutigera. This type of eye consists of a cluster of numerous ocelli on each side of the head, organized in a way that resembles a true compound eye. Asymmetries in compound eyes may be associated with asymmetries in behaviour.
Rapid eye movement sleep ( REM sleep or REMS) is a unique phase of sleep in mammals (including humans) and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vividly. The REM phase is also known as paradoxical sleep ( PS) and sometimes ...
Nature versus nurture is a long-standing debate in biology and society about the relative influence on human beings of their genetic inheritance (nature) and the environmental conditions of their development .
Non-rapid eye movement sleep ( NREM ), also known as quiescent sleep, is, collectively, sleep stages 1–3, previously known as stages 1–4. Rapid eye movement sleep (REM) is not included. There are distinct electroencephalographic and other characteristics seen in each stage. Unlike REM sleep, there is usually little or no eye movement during ...
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better 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. On average, there are approximately 92 million rod cells (vs ~6 million cones) in the ...