Biological rhythms

biological rhythm definition

cyclical changes in body processes or behaviour in response to cues

What are the cues that change behaviour or bodily processes?

endogenous pacemakers and exogenous zeitgebers

endogenous pacemaker

cues within the body

exogenous zeitgebers

cues in the external environment

example of EZ

light

Circadian rhythms

physical, mental and behavioural changes that follow roughly a 24 hour cycle

circannual

cycle of a year e.g hibernation

circalunar

monthly

circatidal

twice daily

chronobiology

study of circadian rhythms

example of a circadian rhythm

sleep/wake cycle

EZs affecting sleep/wake cycle

natural light and social time cues

EPs regulating sleep/wake cycle

release of melatonin at night, metabolic rate, body temperature

core body temperature

lowest around 4:30 am and highest at 6 pm, links with warmer temperatures and cognitive ability

Relationship between EPs and EZs

EPs can be triggered by EZs but can also function without them

most influential EP

suprachiasmatic nucleus (SCN)

what is the Suprachiasmatic nucleus?

bundle of nerve cells in the hypthalamus

function of SCN

regulated by light and argued to be our internal body clock

how is the SCN examined?

SCN is shared in mammalian species so it is removed from animals

pineal gland and SCN

SCN passes on info about day length and light to pineal gland

pineal gland function

pineal gland increases melatonin production at night

melatonin affects

induces sleep and is inhibited in periods of wakefulness

Entrainment

there is an adjustment of the body clock in line with the environment

light therapy

used as a clinical treatment for depression

infradian rhythms

cycle lasts longer than

ultradian rhythms

cycle lasts under 24 hours so can happen more than once a day

example of infradian rhythms

menstrual cycle, hibernation and breeding

which biological system is the menstrual cycle governed by?

endocrine system

which hormones are involved in the menstrual cycle?

progesterone, FSH, LH, oestrogen

EZs that impact menstrual cycle

stress, weight, odours and light

pheromone

a chemical substance produced and released into the environment by an animal that affects the behaviour or physiology of others of its species

menstrual synchronicity

females menstrual cycles are synchronised

evolutionary advantage to menstrual synchronicity

women ovulating at the same time would increase chance of pregnancy

advantage of menstrual synchronicity in collectivist cultures

shared responsibility of child rearing practices such as breast feeding

SAD type of cycle

an infradian rhythm - circannual

SAD effects

more melatonin is released affecting alertness and sleep/wake cycle

melatonin and depression

melatonin effects production of serotonin which affects mood and sleep which increases chance of depression

example of ultradian rhythm

sleep cycle

example of infradian rhythm

sleep/wake cycle

how many stages of sleep?

5

length of each cycle

90 minutes

how many cycles potentially a night?

5

stage one

light sleep

length of stage one

5-15 minutes

stage one brain activity

alpha waves

stage one physiological activity

heart rate slows and muscles relax, people are easily woken

stage two

light sleep

stage two length

5-15 minutes

stage two brain activity

theta waves

stage two physiological effects

body continues to relax and still easy to wake

stage three

deep sleep

stage three length

5-15 minutes

stage three brain activity

slow delta waves

stage three physiological effects

body relaxes further but is harder to wake

stage four

deep sleep

stage four length

40 minutes

stage four brain activity

delta waves, activity is slower

stage four physiological effects

metabolic rate is very low, very difficult to wake, growth hormones released

stage five/REM

rapid eye movement

REM length

15 minutes but lengthens throughout the night with less time spent in other stages

REM brain activity

more brain activity than in any other stage

REM physiological effects

complete paralysis of the trunk, irregular breathing and heart rate, probability of dreams

order of sleep stages

1, 2, 3, 4, 3, 2, REM