Topics: Sleep, Circadian rhythm, Melatonin Pages: 8 (2240 words) Published: April 25, 2013

Awareness of the environment, ones own existence, sensations, thoughts

States of Consciousness
Distinctive or discrete patterns in the function of consciousness

Biological Rhythms

Endogenous cycles
Bio Rhythms: endogenous rhythms are systematic changes in the brain’s function that are vastly internal brain mechanisms. One of the things that does alter conscious states are actually these bio rhythms.

1. Circadian
24hr. cycle. Sleep, temperature

2. Infradian
Less often that 24hrs. E.g., migration in animals, Fertility cycle

3. Ultradian
More frequent than 24hrs. Stomach contractions, hunger, performance, alertness, daydreaming, within sleep cycle

Circadian cycle / rhythm
Sleep-wake cycle. In free running experiments averaged 25hrs.

Controlled by a tear drop shaped area in the hypothalamus called The Suprachiasmatic Nucleus (SCN)

All other clocks take their cue from SCN. The SCN itself is kept in synch with day-night patterns by a hormone ‘Melatonin’ secreted by the Pineal gland.
Insomnia is correlated with and has been treated with low Melatonin levels • Way to test these cycles: Free running experiments. Here you very carefully remove people from the natural environmental stimuli. You take them to a building where everything is independent of the environment. There is not external stimuli – nothing to signal what time it is – eg day light and sound etc. The experiment showed that the endogenous cycle of sleeping is actually internal and lasts 25 hours. • There are time keeping mechanisms within the brain. It is a tear-brain shaped area within the hypothalamus, it is called Supachiasmatic Nucleus called the SCN. There are a series of neurons which stimulate themselves in a cycle and after a number of cycle they shoot of signals to other parts of the brain. Amongst other place, the SCN tells inhibitory signals to the base of the brain which tells it when to shut down. • You have a number of light detection neurons in the eye and these neurons send a signal to the Pinneal gland which is in the brain and this pineal gland secretes a hormone called melatonin. This thing has a 24 hour cycle and melatonin in turns sends a signal to the SCN to send of the alarm signal to sleep. • An example is that if you put a person after he has just had three hours of sleep in bright sunlight, he’ll become active somewhat and a person who has just slept 8 hours, if put into a cozy environment with low light which is very conducive to sleep, he will go to sleep / get drowsy. • The phenomenon of insomnia is when your melatonin cycles and SCN cycles are completely out of sync.

Jet lag: Hormonal and temperature cycles take the longest to get into synch

Most accidents occur with alterations in this cycle. It is not open to frequent change and in general lengthening it (25hrs) is easier to adjust to that shortening it. The SCN is not the only time keeping neural mechanism in the brain. There are other time keeping cycles in other parts of the brain as well. If you reset the SCN, it starts rescynchronizing other cycles in the brain with itself. We all know for example that one can have jetlag. When you go to a new timezone your SCN is doing something else and your melatonin is doing something else, your SCN soon starts readjusting. It also starts adjusting other clocks as well. Jet lag is the phenomenon by which this system goes out of sync. Sleep recovers the fastest from such a phenomenon. However, other aspects get back into sync a little slowly.

Example of one randomly feeling hungry at 3 am in the night and waking up for the reason. Your immune system at times takes some time to readjust as well so it is very much possible to catch a lot of infections whenever you go into a new timezone. Your hormonal cycle is one that takes a lot of time to readjust. As we would expect from free running experience, the SCN has a tendency to...
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