Biological Rhythms Flashcards
Explain what is meant by biological rhythms.
Cyclical patterns within biological systems that evolved in response to environmental influences (E.G. day and night)
There are 2 key factors that govern the biological rhythms:
Endogenous pacemakers (internal)
Exogenous zeitgebers (external)
Name and explain the 2 key factors that govern the biological rhythms.
Endogenous pacemakers (internal) >
the body’s biological clocks
Exogenous zeitgebers (external) >
changes in the environment
What are the types of biological rhythms?
Circadian
Infradian
Ultradian
What is the circadian rhythm? Give examples of circadian rhythms.
The 24-hour circadian rhythm which is reset by levels of light.
Sleep-wake cycle
Body temperature
Hormone production
Explain how body temperature is a circadian rhythm.
Human body temp is at its lowest in the early hours of the morning (36°C at 4:30am) and at its highest in the early evening (38°C at 6pm).
Sleep typically occurs when the core temp starts to drop, and the body temp starts to rise towards the end of a sleep cycle promoting alertness first thing in the morning.
What is the infradian rhythm? Give examples of infradian rhythms.
Lasts longer than 24 hours, and can be weekly, monthly, or annually.
A monthly infradian rhythm is the female menstrual cycle, which is regulated by hormones that either promote ovulation or stimulate the uterus for fertilisation
What is the ultradian rhythm? Give examples of ultradian rhythms.
Lasts fewer than 24 hours and can be found in the pattern of human sleep.
This cycle alternates between REM (rapid eye movement) and NREM (non-rapid eye movement) sleep, and consists of 5 stages.
The cycle starts at light sleep, progressing to deep sleep, then REM sleep, where the brain waves speed up and dreaming occurs. This repeats itself about every 90 minutes throughout the night.
Describe the stages of the ultradian sleep cycle [4 marks]
1 =
> Stage 1 & 2 are ‘light sleep’ stages.
> Brainwave patterns become slower and more rhythmic, starting with alpha waves progress to theta waves.
2 =
> Stage 3 & 4 are ‘deep sleep’ or slow wave sleep stages, where it’s difficult to wake someone up.
> This stage is associated with slower delta waves.
3 =
> Stage 5 is REM (or dream) sleep. Here the body is paralysed (to stop the person acting out their dream), and brain activity resembles that of an awake person.
On average, the entire cycle repeats every 90mins - experiencing up to 5 full cycles in a night.
What are examples of an endogenous pacemaker?
Suprachiasmatic nucleus (SCN)
Pineal gland
What is the suprachiasmatic nucleus (SCN)?
> The main endogenous pacemaker which is linked to the PINEAL gland, which both maintain the circadian sleep/wake cycle.
> SCN signals to the pineal gland - leads to an increase in melatonin production at night, helping to induce sleep.
> Found in the HYPOTHALAMUS - known as the ‘master clock’.
> Controls other bio rhythms as it links to other areas of brain responsible for sleep/arousal.
> SCN receives info about light levels (an exogenous zeitgeber) from the optic nerve which sets the circadian rhythm so that it’s in synchronisation w/ the outside world, e.g. day & night.
What are examples of exogenous zeitgebers?
Light
Social cues - such as meal times & social activities
Explain how an exogenous zeitgeber works.
> SCN contains receptors sensitive to light, and this external cue is used to synchronise the body’s internal organs & glands.
> Melanopsin, a protein in the eye, is sensitive to light and carries the signals to the SCN to set the 24-hour daily body cycle.
What is melanopsin?
A protein in the eye that is sensitive to light and carries the signals to the SCN to set the 24-hour daily body cycle.
Describe the stages of how sleep is induced from low levels of light [4 marks]
1 > Low levels of light detected from receptors on optic nerve.
2 > Melanopsin carries signals to the SCN.
3 > SCN sends signals to the pineal gland.
4 > Melatonin is produced by the pineal gland.
5 > Induced sleep
What is are endogenous pacemakers?
Internal mechanisms that GOVERN biological rhythms.
