Sleeping Process

What does the Brain do when we sleep ?

 We all know from experience that sleep varies from drowsiness to sound sleep from which it is very difficult to wake. its an important part of our daily routine—we spend about one-third of our time doing it and it is essential for survival.
 

Sleep is important to a number of brain functions, including how nerve cells (neurons) communicate with each other.  In fact, our brain and body stay  active while we sleep.  Recent researches suggest that sleep plays a important role that removes toxins in your brain that build up while you are awake. According to Sigmund Freud; our all unfulfilled desires, unsocial wishes , unacceptable thoughts etc which are not allowed adequate fulfilment in waking life. Therefore they are represssed during sleep and become unconscious.
 

Everyone needs sleep, but its biological purpose remains a mystery.  Sleep affects almost every type of tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Recently , However, experimenters studying sleep have learned that the Electroencephalogram (EEG) a tracing of the electrical activity of the brain ( or “brain waves”), provides a good index of the depth of sleep. since the tracing can be made without disturbing the sleeper, the EEG has become a standard measure of sleep depth. The tracings have also made it possible for investigators to know when someone is dreaming during sleep.

Variations in the activity of the ARAS( Ascending reticular activating system) play a large role in the control of the levels of sleep and the EEG pattern which accompany them. The ARAS also has an important influence on the brain activity that occurs during dreaming.
 
In general, as a person falls into deeper and deeper sleep during the night, the “brain waves” becomes progressively slower and higher in voltage. Starting with the Alpha rhythm (10 Hz)  of the drowsy waking state, the brain waves slow until they may have a frequency of only 1 to 3 Hz.

Based on EEG patterns, investigators have divided sleep into 4 stages. In stage 1, a relatively- large proportion of the “brain wave” activity is fairly fast; in stage 2 and 3, the proportion of slower activity increases; and stage 4 is characterized by a large proportion of very slow ( 1 to 3 Hz) activity.
 

 

 

Sleep Stages

There are two basic types of sleep:  Non-REM sleep (which has three different stages) and REM sleep- rapid eye moment (the 4^th stage) Each is linked to specific brain waves and neuronal activity.

 

Stage 1 non-REM sleep is the changeover from wakefulness to sleep.  During this short period (lasting several minutes) of relatively light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches.  Your brain waves begin to slow from their daytime wakefulness patterns. Relatively- large proportion of the “brain wave” activity is fairly fast.

Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep.  Your heartbeat and breathing slow, and muscles relax even further.  Your body temperature drops and eye movements stop.  Brain wave activity slows but is marked by brief bursts of electrical activity, in stage 2, the proportion of slower  electrical activity increases in brain.

 

Stage 3 non-REM sleep is the period of deep sleep that you need to feel refreshed in the morning.  It occurs in longer periods during the first half of the night.  Your heartbeat and breathing slow to their lowest levels during sleep.  Your muscles are relaxed and it may be difficult to awaken you.  Brain waves become even slower than stage 2.

MRI of Brain

 

REM sleep first occurs about 90 minutes after falling asleep. Mixed frequency brain wave activity becomes closer to that seen in wakefulness.it is characterized by a large proportion of very slow ( 1 to 3 Hz) electrical activity. Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels.  Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep.  Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams.   Memory consolidation most likely requires both non-REM and REM sleep. New born baby spend 50% of sleep in their REM stage and adult 20-25%.

 One of the striking facts about the sleep pattern through the night is its cyclical nature, it moves from stage 1 to stage 4 and back again several times.

The EEG(electroencephalogram) is a record of the slowly changing electrical activity of millions of nerve cells, all functioning at the same time in the brain, with suitable amplification of the electrical activity, the EEG can be recorded by attaching electrodes to the scalp.  These brain waves are really very small voltage changes, in the range of millionths of a volt. The number of alternations of voltage per second, or the frequency of the electrical changes, varies from 1 or 2 in deep sleep to 50 or more in highly aroused states. The range of frequencies of the EEG is from about 1 to 50 Hz.