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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 majority of animal species are invertebrates; one estimate puts the figure at 97%. [1] Many invertebrate taxa have a greater number and diversity of species than the entire subphylum of Vertebrata. [2] Invertebrates vary widely in size, from 10 μm (0.0004 in) [3] myxozoans to the 9–10 m (30–33 ft) colossal squid. [4]
Many animals alternate between sleeping and waking in a daily cycle. Arousal and alertness are also modulated on a finer time scale by a network of brain areas. [8] A key component of the sleep system is the suprachiasmatic nucleus (SCN), a tiny part of the hypothalamus located directly above the point at which the optic nerves from the two ...
Invertebrate paleontology - the study of fossil invertebrates These divisions are sometimes further divided into more specific specialties. For example, within arachnology, acarology is the study of mites and ticks ; within entomology, lepidoptery is the study of butterflies and moths , myrmecology is the study of ants and so on.
Sleep is a highly conserved behavior across animal evolution, [6] likely going back hundreds of millions of years, [7] and originating as a means for the brain to cleanse itself of waste products. [8] In a major breakthrough, researchers have found that this cleansing may be a core purpose of sleep. [9]
Though these criteria are difficult to measure in nonhuman animals, cephalopods are the most intelligent invertebrates. The study of cephalopod intelligence also has an important comparative aspect in the broader understanding of animal cognition because it relies on a nervous system fundamentally different from that of vertebrates. [3]
One of the important questions in sleep research is clearly defining the sleep state. This problem arises because sleep was traditionally defined as a state of consciousness and not as a physiological state, [14] [15] thus there was no clear definition of what minimum set of events constitute sleep and distinguish it from other states of partial or no consciousness.
Ectothermic animals also undergo periods of metabolic suppression and dormancy, which in many invertebrates is referred to as diapause. Some researchers and members of the public use the term brumate to describe winter dormancy of reptiles, but the more general term hibernation is believed adequate to refer to any winter dormancy. [ 8 ]