3.5.3 Pharmacology I
Lab 8 Determination the prolongation action of Diazepam on Pentobarbitone induced sleeping time
Sleep is a state of partial unconsciousness or altered consciousness of the brain, from where one can arouse. There are two main stages of sleep, non rapid eye movement sleep (NREM) and rapid eye movement (REM) sleep. The NREM sleep is further divided into four consecutive stages:
Stage I: This is the transitional stage between sleep and wakefulness, lasting for 1-7 minutes, when one can be awaken easily. Fleeting thoughts appear in this stage.
Stage II: This is the first stage of true sleep, called the light sleep stage. One experiences fragments of dreams in this stage.
Stage III: This is the period of moderately deep sleep, which occurs after 20 minutes after falling asleep. It is difficult to awaken one easily from this stage. The blood pressure and body temperature decrease in this stage.
Stage IV: This is the deepest stage of sleep, when the brain metabolism, muscle tone and body temperature decrease from the normal. But the motor reflexes appear to be intact during sleeping.
REM sleep is characterized by the increased metabolic and electrical activities of the brain, increased muscle tone, increased cerebral blood flow and fluctuating cardiac and respiratory rates. It is initiated by the action of acetylcholine and dopamine has an altering effects.
The complete cycle of sleep during night (7-8 hours) includes four consecutive stages of NREM sleep for about 60 minutes, followed by REM sleep for about 90-120 minutes and further stages of NREM sleep from about 60 minutes. There is total 3-5 REM sleep in the cycle, which increases from 90 to 120 gradually, the final one lasting for 50 minutes. The percentages of REM sleep decreases gradually with age (50% in infant, 35% in 2 years children and 25% in adults).
Reticular formation is the part of brain stem, which includes reticular activating system (RAS), involved in consciousness, attention and alertness, muscle tone regulation, wakefulness and arousal from the sleep. Inactivation of RAS causes the state of sleep and damage of RAS causes the state of coma. RAS is composed of sensory axons, which are sensitive to the auditory, visual, pain, touch and pressure stimuli, which control the state of arousal. It is also sensitive to the mental activities like stress, thoughts, anxiety etc. Beside this the combined action of dopamine and acetylcholine in the CNS help in wakefulness.