Reticular Activating System.

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RETICULAR ACTIVATING SYSTEM

R.A.S.  is very susceptible to damage.

                  

          Is suppressed by chemicals during sleep.

Acts as a filter of sensory messages    passing through to the cerebral cortex.

Function of R.A.S.

                                                        Cut/lesion above R.A.S.

This would cause a permanent coma.

                                                        Cut/lesion below R.A.S.

This would cause paralysis from the point below the lesion.  

                                                        Cut/lesion through RAS

Damage to this will keep a person awake.

Diagram including location of R.A S., pons, & Raphe nuclei.

Chemical analysis of the RAPHE found SEROTONIN.  (This was investigated to find a cur for coma victims).  Serotonin is a neurotransmitter.  This acts an inhibitor on the R.A.S.  This leads to a gradual decrease in arousal. This is the mechanism for falling asleep.

R.A.S. is also inhibited by nor-adrenalin, released by the pons. This closes the RAS system down further.

Noradrenalin acts as and exitory agent on motor/sensory pathways and could cause REM/dreaming sleep.

Havever found a system which reinhibits the motor pathwau after it has been stimulated by noradrenalin.  (This stops you acting out your dreams.)  He damaged this area in animals and they seemed to act out their dreams. (see animal experiments.)

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There is a lot of complex bio-chemistry in the base of the brain controlling sleep.  But they can hardly be there by accident of merely as remnants of past evolution!

People on amphetamines (speed etc.) have difficulty on sleeping. These are given as an appetite suppressant.  But patients soon get used to them and sleep normally.  When they stop taking them they get a massive REM/Dream sleep rebound, (nightmares etc.)

Line graph to show R.E.M. rebound and subsequent return to pre-amphetamine taking levels.

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0          1                2           3                 4            5                  6                7

R.E.M. is maintained at a set level and therefore must be useful for something.

Alcohol also caused lack of REM sleep. When prolonged drinking (heavy for several weeks) stops, REM sleep is increased to possibly and unpleasant level.  

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FUNCTIONS OF DREAMS

Psychological approach

FREUD  

He believed that Dreams are the guardians of sleep.  He also believed that they provided an insight into the motives of a persons behaviour.  He described it as  the royal road to the unconscious. He believed that no matter how absurd a dream was it always possessed meaning and logic.  He warned that dreams had to be analysed in the context of a person s waking life.  According to Freud the mind had 3 components.

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Id:        This is concerned with basic instinctive urges such as the need for food, comfort and sexual gratification.  It works at an unconscious level. It is not driven by logic and is the pre-socialized part of the personality. He felt that we are driven by unconscious urges, and that through dreams the unconscious desires are expressed, Thus relieving psychic tensions.

        The Id works on the   Pleasure principle

Superego:

        Its components are the conscience.  This threatens the Ego with punishment, in the form of guilt, for bad behaviour. The other component is the ego-ideal which promises rewards, in the form of pride and ...

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