Rhythms Flashcards
Biological Rhythms
- Recurring patterns of behaviour in the body’s systems (eg. endocrine, immune)
- In humans, evolutionary pressure on these rhythms included avoiding predators and repair/recovery/growth
Circadian Rhythms
- Latin term meaning a pattern or cycle that lasts around (circa) a day (dies)
- Biological clock responds to sunlight
- Melatonin levels vary depend on time of day
Light & Rhythms
- Rods and cones in eye use chemicals called opsins to detect light
- We have a third photoreceptor cell called ipRCGs - contain melanopsin, a non-visual opsin to detect intensity and wavelength of light
Role of Suprachiasmatic Nucleus (SCN)
- The body’s ‘master circadian clock’ - located in hypothalamus
- Contains neurons that fire in synchronised pattern
- These neurons communicate with other pacemakers all over the body
- All pacemakers keep time but SCN sets them - regulation of circadian rhythm
Role of Pineal Gland
- Receives signals from SCN to produce melatonin according to light levels
- Melatonin derived from serotonin - inhibitory NT
- Inhibits many ares of brain that are responsible for wakefulness
- Inhibition of these areas leads to sleep
Endogenous Pacemaker
Internal body clocks that allow us to keep pace with changing cycles in the environment - eg. SCN, pineal gland
Exogenous Zeitgeber
External cues that are responsible for entraining internal biological clock of an organism - eg. light, social cues
Ralph (199) - SCN as main endogenous pacemaker
- Tau mutation hamsters have 20 hr circadian rhythm compared with 24 hrs in normal hamsters
- SCN from normal hamsters transplanted into Tau mutants - Tau mutants gained 24 hr circadian rhythm
- Normal hamster given Tau SCN gain 20 hr circadian rhythm
Steps of the Circadian Rhythm
1) SCN receives info from optic nerve about light levels (even if eyes are shut)
2) SCN sends impulses to pineal gland
3) Pineal gland release/inhibits melatonin production depending on light levels
4) Melatonin induces sleep by inhibiting brain activities that promote wakefulness
Social Cues: Aschoff et al (1971)
Individuals are able to compensate for absence of zeitgebers such as natural light by responding to social zeitgebers instead
Social Cues - Klein & Wegmann (1974)
- Circadian rhythms of air travellers adjusted more quickly if they went outside at their destination
- Exposed to social cues of their timezone (eg, when people go home for the night)
Ultradian Rhythms
Span a period of less than one day
Infradian Rhythms
Span a period longer than a day
90 Minute Sleep Stages - Ultradian
1&2) Light sleep, brainwave patterns slower and more rhythmic - alpha to theta waves
3&4) Deep sleep, slow wave sleep, difficult to wake someone up, slower delta waves
5) REM (or dream) sleep, body is paralysed to prevent acting out the dream, brain activity resembles that of someone who is awake
* A person can experience up to 5 full cycles per night
Weekly Testosterone Rhythms - Infradian
- Testosterone levels higher at weeekends
- Young couples reported more sexual activity at the weekend than in the week
- Little evidence, many other possible variables