Biological Rhythms
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- Biological Rhythms - cyclical changes in the way that biological systems behave. These rhythms have evolved because the environment in which organisms live has cycles eg. day/night
- Circadian Rhythm - a pattern that occurs every approx. 24 hours and is reset by environmental light eg. sleep/wake, temperature
- Sleep wake cycle - refers to the alternating sleep and waking that are dependent on the 24 hour circadian cycle
- Circadian Rhythm:
- Light (exogenous zeitgeber) is detected by the eye's optic nerve
- Brightness level message is sent to the suprachiasmatic nuclei (SCN), found in the hypothalamus
- SCN informs the pineal gland, which secretes melatonin causing us to become sleepy
- Biological rhythms are regulated by endogenous pacemakers and exogenous zeitgebers
- Endogenous Pacemaker (internal cues) - internal mechanism eg. SCN that governs biological rhythms e.g sleepwake cycle
- Exogenous Zeitgeber (external cues) - environmental events that are responsible for resetting the biological clock of an organism eg. social cues (meal times), light
- Sleep Cycle (Stage 1): 4 - 5% (NREM)
- light sleep
- muscle activity slows down/occasional twitching
- starting with alpha waves progressing to theta waves
- Sleep Cycle (Stage 2): 45 - 55% (NREM)
- light sleep
- Breathing and heart rate slows
- slight decrease in body temperature
- starting with alpha waves progressing to theta waves
- Sleep Cycle (Stage 3): 4 - 6% (NREM)
- Deep sleep begins
- brain begins to generate slow delta waves
- Sleep Cycle (Stage 4): 12 - 55% (NREM)
- very deep sleep
- rhythmic breathing
- limited muscle activity, brain produces delta waves
- Sleep Cycle (Stage 5): 20 - 25% (REM)
- rapid eye movement
- brainwaves speed up and dreaming occurs
- muscle relax and heart rate increases
- breathing is rapid and shallow
- Sleep cycle is a form of an ultradian pattern including REM and NREM and repeats every 90 mins for 5 stages
- (REM) - Rapid Eye Movement
- (NREM) - Non Rapid Eye Movement