How can you define sleep?
Sleep is one of the most important physiological functions in humans. Sleep is a regulated behavior that is controlled by two components, the circadian component, and the homeostatic component. Homeostasis is the maintenance of stable conditions in the internal environment. Defined homeostasis as the dynamic constancy of the internal environment, the term dynamic is used due to internal conditions fluctuating between narrow limits it is not a constant. The Autonomic Nervous System is vital in sleep physiology it is responsible for the control of the awake / sleep cycle. This essay will discuss the two types of sleep and the differences between them, the circadian rhythm which is regulated Suprachiasmatic Nucleus located in the brain, how the wake/sleep cycle is regulated and how changes in the internal or external environment effects normal sleep physiology.
Lee 1997 defined sleep as being a period of reduced awareness and responsiveness. Sleep has been considered a restorative or a recovery phase that prepares the body for the next episode of wakefulness. Cell division is more rapid during non-REM sleep and sleep has an important function on the immune system.
Synchronization of cortical activity during non-REM sleep may result in some way coordinate cortical connections. The prefrontal cortex is inactive during all phases of sleep (this may also confer some benefit). During REM sleep the cerebral cortex is open to sensory inputs and forms loose associations that cannot be formed during wakefulness. Both phases of sleep are involved in memory consolidation. Very little new information is gained during sleep, but consolidation and maintenance of memory from experiences of the previous day is considerable. It is known that learning of visual information is improved during the first night of sleep and that sleep deprivation impairs recall of the information. Different types of sleep have a different effect on memory consolidation and retention of information. Retention is best if stage 3 and four non-REM sleep occurs in the first 2 hours of sleep and if the last 25% of sleep is REM s.