endogenous pacemakers and the stages of sleep

• Although endogenous pacemakers are internal biological clocks, they can be altered and affected by the environment. For example, although the circadian sleep-wave cycle will continue to function without natural cues from light, research suggests that light is required to reset the cycle every 24 hours. (See Siffre and Aschoff & Weber,
• The most important endogenous pacemaker is the suprachiasmatic nucleus, which is closely linked to the pineal gland, both of which are influential in maintaining the circadian sleep/wake cycle.
• The suprachiasmatic nucleus (SCN), which lies in the hypothalamus, is the main endogenous pacemaker (or master clock)
•  It controls other biological rhythms, as it links to other areas of the brain responsible for sleep and arousal
• The SCN also receives information about light levels (an exogenous zeitgeber) from the optic nerve, which sets the circadian rhythm so that it is in synchronisation with the outside world, e.g. day and night.
• The SNC sends signals to the pineal gland, which leads to an increase in the production of melatonin at night, helping to induce sleep
• he SCN and pineal glands work together as endogenous pacemakers; however, their activity is responsive to the external cue of light
• The SCN also receives information about light levels to ensure that biorhythms synchronise with the outside world, e.g. day and night
• • The SNC sends signals to the pineal gland, which increases production of melatonin secretion at night, helping to induce sleep
• SCN and the sleep/wake cycle

  A) low

  B) suprachiasmatic nucleus

  C) melatonin

  D) increase