If the external causes are removed, the sleep-wake cycle in humans?
Correct Answer: Continue with cycle length of more than 24 hours
Description: Ans. d. Continue with cycle length of more than 24 hours (Ref: R L Bijlani 4/e p730; Principle of Neural Science by Kandel 4/e p936)If the external causes are removed, the sleep-wake cycle in humans continue with cycle length of more than 24 hours."The sleep-wakefulness cycle follows a 24-hour, or circadian rhythm, and is related to the light-dark cycle. If the external cues in the form of light and darkness are removed, the sleep-wakefulness cycle still remains circadian although it has a tendency to lengthen to 25-30 hours."- R L Bijlani 4/e p730Sleep-wake cycleSleep and wakefulness have a circadian periodicity of about 24 hours.Sleep-wake cycle, like other circadian rhythms, is endogenous.The biological or the internal clock controlling the circadian rhythms is the suprachiasmatic nucleus of the anterior hypothalamus.The circadian rhythms are endogenous and can persist without environmental cues: however, under normal circumstances the rhythms are modulated by external timing cues (called 'zeitgeher's or time givers) that adapt the rhythm to the environment.Sunlight is a powerful external timing cue.Light entrains this rhythm by means of the retino-hypothalmic tract, a pathway from the retina to the suprachiasmatic tract, a pathway from the retina to the suprachiasmatic nucleus of the hypothalamus.The sleep-wakefulness cycle follows a 24-hour, or circadian rhythm, and is related to the light-dark cycleQ.If the external cues in the form of light and darkness are removed, the sleep-wakefulness cycle still remains circadian although it has a tendency to lengthen to 25-30 hoursQ.
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