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Sleep can follow a physiological or behavioral definition. In the physiological sense, sleep is a state characterized by reversible unconsciousness, special brainwave patterns, sporadic eye movement, loss of muscle tone (possibly with some exceptions; see below regarding the sleep of birds and of aquatic mammals), and a compensatory increase following deprivation of the state, this last known ...
The brain might not be able to do this while still assailed by new stimuli and new information to process. Therefore, the role of sleep would be to periodically shut down sensory input to allow the brain to form memories. Pelagic species swim in an open-water environment wherein novel stimuli is uncommon. In such species, the sensory input is ...
Many sharks can contract and dilate their pupils, like humans, something no teleost fish can do. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some species have nictitating membranes. This membrane covers the eyes while hunting and when the shark is being attacked.
The Somniosidae are a family of sharks in the order Squaliformes, commonly known as sleeper sharks. [1] The common name " sleeper shark " comes from their slow swimming, low activity level, and perceived non-aggressive nature.
Grey reef sharks become more active as night approaches. Grey reef sharks are active at all times of the day, with activity levels peaking at night. [4] At Rangiroa, groups of around 30 sharks spend the day together in a small part of their collective home range, dispersing at night into shallower water to forage for food.
Using unihemispheric slow-wave sleep, birds are able to maintain environmental awareness and aerodynamic control of wings while obtaining the necessary sleep they need to sustain attention during wakefulness. Their sleep is more asymmetric in flight than on land, and they sleep mostly while circling air currents during flight.
Most attacks involve sharks biting the legs or feet of waders, apparently mistaking them for their natural prey, and do not result in serious injury. [3] In the Marshall Islands, native islanders avoid blacktip reef shark attacks by swimming rather than wading through shallow water, as a way of discouraging these sharks is to submerge one's body.
From my understanding sharks do not sleep, but shut down parts of their brain in certain intervals while remaining active, I will work on locating the source for this. -- Starchild12345 ( talk ) 06:37, 22 September 2008 (UTC)