Axia College Material Appendix C The Sleep Matrix Why do we sleep? What governs when or how long we sleep? This activity will assist you in understanding two common sleep theories, recuperation and circadian, which provide different answers to these questions. Depending on which one you support, it may change your outlook on sleep and your current sleeping habits.
Categorize each characteristic under the correct theory—recuperation or circadian—by placing an “ X” in the appropriate column. Then, answer the questions that follow.
Sleep restores the body to a state of homeostasis.
Sleep plays no role in physiological functioning.
We become tired when it is dark out.
Function of sleep is to restore energy levels
Function of sleep is to conserve energy
We become tired from wakefulness.
We sleep until the body is physiologically sound.
We sleep based on an internal timing mechanism.
Sleep depends on vulnerability from predators.
Sleep deprivation may cause behavioral disturbances.
We have a sleep-wake cycle.
When we sleep is based on some evolutionary aspects.
1. What are the main differences between the recuperation and circadian theories?
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The recuperation theory states that sleep restores homeostasis of a body and serves the purpose of restoring energy levels and repairs damage incurred during wakefulness. According to the Circadian theory, sleep is a result of evolution, developed for conserving energy and providing protection from predators. It states that sleep is a component of the 24 hour daily cyclic behavior that occurs due to an internal timing mechanisms which itself derives its cues from the daily cycle of daylight and night time darkness. Thus according to circadian theory, external environmental cues(zeitgeber) direct and guide our internal clocks and it recognizes the period of wakefulness as opportunity for an organism to fulfill their survival needs, and sleep as a mechanism which helps them tide over their vulnerabilities from predators during night time darkness.
The recuperation theory suggests that short term sleep deprivation results in physiological aberrations that may have serious consequences, and that missed sleep is usually regained later nd that species expending more energy should sleep more, however statistically the degree of correlation between the amount of energy expended and duration of sleep is very low. The circadian theory on the other hand suggests no such relation between sleep and physiological well-being and almost no compensation for lost sleep.
The recuperation theory does not take into consideration, the affect of any external stimuli whereas the circadian theory explicitly does and by extrapolation of this fact, the circadian theory suggests that by adjusting the duration of night and day, it is possible to alter the length of the circadian cycle within reasonable limits.
2. Which theory do you most agree with? Explain.
I agree with the circadian theory more than the recuperation theory as it is more statistically sound and can be supported by neurological data, and the theory can better explain occurrences related to sleep disorders.
The circadian theory correlates survival time and vulnerability with wakefulness and sleep respectfully, and this fact can be observed in herbivorous animals, who are extremely vulnerable to predators, hence sleep barely a couple of hours a day, whereas a koala bear which has no danger of predators, tend to sleep a very large part of the day.
Another fact that supports the circadian theory is the occurrence of jet lag, which occurs due to disruption in our internal clocks due to acceleration or de acceleration of environmental cues while travelling on east bound routes and west bound routes respectively. Large phase shifts also occurs with people working the night shift, where zeitgeber remain unvarying. Both lead to sleep disturbances, fatigue etc.
Also the neurological centre of the circadian clock has been located in the suprachiasmatic nuclei (SN) in the medial hypothalamus just above the optic chiasma. This tells us that visible cues of light or darkness picked up by our eyes is relayed through the optic nerves to the SN, which accordingly controls sleep pattern through secretion of hormones such as melatonin and epinephrine and various neurotransmitters.
Since sleep patterns are steered by cognitive functions, circadian theories are more apt in explaining sleep disorders arising out of sleep deprivation, anxiety rather than homeostatic imbalance as suggested by recuperation theory, however the only criticism of the circadian theory is the failure of acknowledgement of the facts that sleep serves any part in physiological conditioning of an organism, or its necessity for good health.