Anatomy & Physiology: The Unity of Form and Function, 7th Edition

Published by McGraw-Hill Education
ISBN 10: 0073403717
ISBN 13: 978-0-07340-371-7

Chapter 14 - Section 14.5 - Study Guide - Assess Your Learning Outcomes - Page 554: 2

Answer

Sleep is a physiological state of temporary unconsciousness that occurs in humans, on a 24 hour cycle ( nearly/circadian). Other features of sleep are closed eyes, and muscular paralysis. Usually, humans sleep lying down, but some people can sleep sitting or even standing. In any case a sleeping person can usually be awakened with various degrees of stimulation. In a regular period of nightly sleep, the the sleeping process exhibits several stages with well-characterized physical and EEG features. The well-known stages of sleep are Stages I-!V. Also, of great interest is the so-called rapid eye movement (REM) sleep. As one is falling asleep, EEG waves show frequency decreases during the first 40 minutes of sleep. However, there is a rise in amplitude as the sleeper experiences the four sleep stages. Stage I. This sage is dominated by alpha waves. Eyes are closed, the sleeper is drowsy and is easily awakened. Stage II.This is the stage of light sleep. EEG wave frequencies fall, and amplitudes increase. Also, the EEG traces exhibit occasional 1-2 hour bursts of high amplitude spikes. Stage III. Moderate to deep sleep occurs in this stage. . Frequency of high level spikes decreases, and the EEG displays theta and delta waves. In addition, muscles relax, and the following vital signs-- temperature, blood pressure, heart rate, and respiratory rate-- all decline. Stage IV. This is the slow wave sleep stage. It is dominated by low frequency, high amplitude, delta waves. In this stage muscles are very relaxed, vital signs are at their lowest, and sleepers are most difficult to wake. Paradoxical or rapid eye movement sleep REM), usually occurs several time in a normal period of nightly sleep. In this phenomenon, the sleeper reverses sleep stages-- going from stage 3 or 4 back to stage 2 about five time in a sleep episode . In REM sleep, the eyes oscillate back and forth, the sleeper is very difficult to wake,, and sleep paralysis of muscles is very strong. Sleepers dream in both REM, and non-REM sleep. However, in general, REM dreams are more vivid, longer lasting, and more emotional.

Work Step by Step

Regulation of the sleep cycle and the rhythms of sleep are controlled by interactions between cerebral cortex, thalamus, hypothalamus, and the reticular formation (RF). A central role is played by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. The SCN uses input from the optic nerves to synchronize the rhythms of several physiological functions with the time of day. These functions include sleep, body temperature, and urine production. Orexins hypocretins) are brain neuropeptides that play a role in sleep production. They are produced by the lateral and posterior hypothalamus ; they stimulate wakefulness, and increase the metabolic rate. Lack of orexins ,or blocking of orexin receptors can lead to abnormal sleepiness, as in the disorder narcolepsy. Although it is vital for human health and ultimately for human life., sleep is still poorly understood physiological phenomenon. Nonetheless, there several theories-- but little evidence-- explaining the function of, and the necessity for sleep. For example, it is clear that non-REM sleep is restorative to the degree, and in a manner that quiet rest is not. It seems that the peculiar restorative powers of sleep are somehow linked to the loss of consciousness. But this has not been proven. It has been shown, however, that during waking hours levels of glycogen and ATP ( energy stores) fall while adenosine ( a sleep inducing chemical) rises in concentration. In contrast, during sleep, glycogen and ATP concentrations return to high levels, and adenosine levels go down. This energy restoration theory seems to make sense, but comparative mammalian physiological experiments do not support this theory completely.
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