Endogenous pacemakers/ zeitgebers

Question 1

AO1 endogenous pacemakers

Answer 1

• Main one is a tiny cluster of nerve cells called the suprachiasmatic nucleus which lies in the hypothalamus
  This plays an important role in generating the bodys circadian rhythm, acts as the master clock which links to other brain regions which control sleep and arousal
  Neurons in the SCN synchronise with each other so their target neurons in sites elsewhere in the body receive correctly time coordinated signals
• The SCN maintains a circadian rhythm for a long time because it has a built in one which only needs resetting when external light levels change, receives info about this via the optic nerve.
  SCN also regulates the manufacture and secretion of melatonin in the pineal gland via an interconnecting neural pathway

Question 2

SE role of the SCN
PM

Answer 2

Morgans study of hamsters 1995
Bred a strain of hamsters so that they had abnormal CR of 20hr rather than 24hr
SCN neurons from these abnormal hamsters were then transplanted into the brains of normal hamsters
Normal hamsters then displayed the same abnormal CR of 20 hrs implanted scn had imposed its pattern on normal brains
then did converse
Shows imp of scn in setting CR

Question 3

Dangers AO3
PM

Answer 3

Dangers of distrupted rhythms
Toutoui et a; argues that exposure to artificial light at night results in distruption of CR, bad effects on health
Research shows teenagers spend increasing amounts of time at night on electronic media, LED component has a blue light active on the circadian clock supressing melatonin, leading to shortened and irregular sleep
Proven by studies which shows the inc rate of depression heart disorders due to distrupted CR

Question 4

AO1 exogenous zeitgerbers

Answer 4

Origins are outside the organism, these are environmental events which are responsible for entraining a biological clock of an organism
Light- receptors in the scn are sensitive to changes in light levels during the day and use this information to synchronise the activity of the bodys organs and glands, light resets this keeping it on a 24 hour cycle
Melanopsin is critical, gauges overall brightness to entrain clock, found in retinal cells
Social cues and stimuli act as these EX zeitgerbers- e.g timing of meals, work schedules and excersise sessions, happen at certain times

Question 5

SE melanopsin AO3 ex zeitgerbers

Answer 5

Studies of blind people
Can entrain CR in response to light despite a lack of image forming visual perception
Skene and ardet estimate that the vast majority of blind people who have some light perception have normally entrained CR, shows pathway from retinal cells containing melanopsin to the SCN is still intact

Question 6

Research - Campbell and murphy 1998

Answer 6

15 sleeping pp were woken at various intervals throughout the night, light pad shon onto the back of their knees
Resulted in iriregular sleep wake cycles , light is an ex zeit
Even when it shines on the back of the knee and not being detected by the eye
compelling evidnece shows significance, direct effect on the SW cycle