Endegenous Pacemakers Amd Exogenous Zeitgebers Flashcards
Describe the suprachasmstic nucleus
• Tiny bundle of nerve cells in the hypothalamus
• Maintains circadian rhythms like the sleep/wake cycle
How does the suprachasmatic nucleus work
• Nerve fibres connected to the eye cross in the optic chiasm on their way to the visual areas of the cerebral cortex
Where is the suparachasmatic nucleus
• The SCN lies just above the optic chiasm (‘supra’ = above)
What Informatiom does the suprachasmic nucleus store
• Receives information about light, even when our eyes are closed, enabling the biological clock to adjust to changing daylight patterns when we are asleep
Decoursey et al 2000
Destroyed the SCN connections in the brain of 30 chipmunks who were then returned to their natural habitat for 80 days.
The sleep/wake cycle of the chipmunks disappeared and by the end of the study a
significant proportion of them had been killed by predators (likely because they were awake and vulnerable to attack when they should have been asleep).
What does the pineal gland produce/do
The SCN passes the information it receives regarding day length and light to the pineal gland
During the night, the pineal gland increases production of melatonin - a chemical that induces sleep and is inhibited during periods of wakefulness.
Involvement of light (key exogenous zietgeber)
• It can reset the body’s main endogenous pacemaker, the SCN
• It has an indirect influence on key processes in the body that control such functions as hormone secretion and blood circulation
Campbell and Murphy 1998
Demonstrated that light may be detected by skin receptor sites on the body
15 participants were woken at various times and a light pad was shone on the back of their knees.
The participants’ usual sleep/wake cycle changed by up to 3 hours.
Suggests that light is a powerful exogenous zeitgeber that need not necessarily rely on the eyes to exert its influence on the brain.
Describe infants sleep/wake cycle
• At ~ 6 weeks old, the circadian rhythms begin
• By ~ 16 weeks, most babies are entrained
• The schedules imposed by parents are likely to be a key influence here, including adult-determined mealtimes and bedtimes
What is delayed sleep phase disorder
Delayed Sleep-Phase Disorder (DSPD) is a circadian rhythm sleep disorder affecting the timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily rhythms. People with DSPD generally fall asleep some hours after midnight and have difficulty waking up in the morning. Patients can sleep well and have a normal need for sleep. However, they find it very difficult to wake up in time for a typical school or work day.
Describe DSPD investigation
20 patients who suffered from DSPD
Researchers randomly allocated the 20 patients into 2 groups: Group A (the treatment group) and Group B (the control group).
Group A were given a course of drugs that increased melatonin production for 6 weeks at bed time (around 11pm). Group B were given a placebo for the same period of time. At the end of the 6 weeks, all the participants were assessed on a number of self-report measures. These examined their performance at work, their attention levels during the day, and their relationship with their families.
Jet lag
Jet lag is another important form of desynchronisation that can disrupt the sleep/wake cycle, causing sleepiness, irritability and nausea, as the body struggles to adapt to changing time zones.
