A volume could easily be written on the different parts and functions of the brain. In fact, in our library we have a book on human neuroanatomy which amounts to nearly one thousand pages of solid facts and figures about the brain. Here we are only interested in briefly describing the basic functions so that you can appreciate the importance of perfect functional efficiency of the brain. Ifyou are interested in studying the subject further then you should read a suitable textbook.
The brain can be very roughly divided into three sections: the lower, middle and upper. At the lowest level are the activities which govern the blood pressure, the depth and rate of breathing, the body temperature, the digestive process and so forth. There are also many automatic or reflex centres in the spinal cord which cany out many body functions that have no need to be controlled from the brain itself.
The midbrain acts like an intricate switchboard. It receives impulses from every part of the body, sorts them out and transmits relevant impulses to the higher brain centres. It acts like a sluice gate that prevents unnecessary information going to the higher centres. It is the guardian of the gate, which only allows certain data to pass through. It thereby prevents the upper brain being overwhelmed by irrelevant information.
The upper or higher section of the brain is called the cerebral cortex. It is this part of the brain that structurally distinguishes man from animals. Fish and birds have little or no cerebral tissue; chimpanzees have the largest cerebral cortex of all animals; while man has easily the largest of all earthbound creatures.
The cerebral cortex fills the dome of the head and is divided down the middle; each half is automatically separated from the other. Each half is cross connected with nerves so that one side controls the other side of the body - the left side of the cerebral cortex controlling the right side of the body, and the right side of the cortex controlling the left side of the body. In most people the functions of the left hemisphere of the cortex are dominant; it is associated with speech, hearing and analytical undertakings such as mathematical problem solving. The right hemisphere is primarily concerned with spatial perception, synthesis of ideas and appreciation of art and music. The two hemispheres are connected together through a bundle of nerve fibres called the corpus callasum.
The cerebral cortex includes the centres that receive incoming data from the body via the midbrain and interpret them in a sensible manner. These centres decipher all external data coming from the surroundings through the sense organs of the eyes, ears, etc. All incoming information is interpreted by comparison with previous memories and from this suitable conclusions are reached. Appropriate actions are then instigated and carried out by the body. The cells and centres of the cerebral cortex act as receivers and transmitters of thought. They are the junction at which the mind-brain liaison takes place.
The brain is composed of two main types of tissue; one is called grey matter and the other white matter. The grey matter consists ofnerve cells and the white matter of nerve fibres
(lengths of nerve cellsjoined together). Unlike most other types of cells within the body, nerve cells do not regenerate or reproduce themselves. It is believed that each person is born with a full complement of these nerve cells to last the entire lifetime. They grow during childhood, but they do not multiply. If the cells die then the fibres will also die and vice versa. The nerve fibres connect the different cells together within the brain and also connect the brain to all parts of the body. They may be as long as fifty centimetres in length. It has been estimated that there are about two hundred million incoming and outgoing fibres linking the brain with the rest of the body.
The following is a brief description of the major functional areas of the brain.
The cerebellum is a fist-sized region located at the rear and lower part of the brain behind the top of the spine. It is concerned with maintaining muscular tone throughout the whole body. It supplies a continuous stream of nerve impulses to the motor nerves and thereby keeps the muscles in the appropriate state of partial contraction. The cerebellum also coordinates the movements of the muscles and harmonizes complex muscular actions. The entire process occurs automatically.
The thalamus is located at the top of the spine in the middle of the brain. It is the relay or transmitting station that sends information to the higher centres of the brain, having sorted out unwanted data. It is also the region where so-called protopathic sensations reach the threshold of conscious perception. The proto-pathic sensations are the instinctive signals which indicate pain, pleasure, etc. in different parts of the body without any discrimination regarding their importance, meaning, etc. Other more sensitive sensations are called epicritic; these are consciously perceived in the cerebral cortex, having passed through the thalamus.
The hypothalamus at the top of the spine is connected directly to the thalamus; it is part of the limbic system and is concerned with our emotional states and reactions. It is the centre that makes the emotional response of happiness, unhappiness, anger, etc. It is often inhibited by the higher brain centres, so that one suppresses emotional reactions. The reward (pleasure) and punishment (pain) areas of the brain are also located within the hypo-
thalamus. It is interesting to note that the pleasure centre is appreciably larger than the pain centre. The hypothalamus is also the central control centre of the sympathetic and parasympathetic nervous outflows. These two systems are associated with control and activation of all the organs of the body, from the heart to the eyes, from the skin to respiration.
The hypothalamus also contains the centre of wakefulness, consisting of sympathetic nerves, and the centre of sleep, consisting of parasympathetic nerves. The hypothalamus is therefore a very important part of the brain.
Other parts of the brain include the fissure of Roland, parietal lobe and the occipital lobe, where most of the functions concerned with skin sensations such as touch, temperature and pressure, hearing, seeing, eye movements, sense of smell and taste, speech and so forth are received and interpreted.
The most well-known area of the brain is called the frontal lobe, located behind the forehead. It is this centre that most clearly differentiates man from animals. It is this area that is concerned with human traits such as truth, honesty, morality, justice, discretion, friendship and many other characteristic human attributes. This is the so-called silent area of the brain which determines the nature of an individual. Any injury or malfunction of this area can cause the individual to become careless, mentally deranged, depressed, anxious, or lose all sense of values. It is the centre of personality. It is also believed to be the instrument or centre which picks up the memory of the mind; this is demonstrated by the fact that electrical or nervous stimulation of this area brings about recall of past experiences, good and bad. This part of the brain acts as the switchboard of the mind.
The nervous system is an extension of the brain, though the brain can also be considered to be part of the nervous system - it is a matter of definition. The brain communicates with the rest of the body through the nerves of the spine and a multitude of others outside the spine. The brain is like the telephone exchange and the nerves are like the thousands of telephone lines that connect the telephone exchange to individual telephones. Innumer able messages pass to and from the brain, bringing all organs, muscles and all parts of the body into direct communication with the "brain. Most of these messages occur below the level of conscious perception.
There are two main groups of nerves. One group is the sensory nerves which transmit information to the brain concerning the state and happenings in the outside environment and about the physical condition of the body, such as temperature, pain, etc. Each type of sensory perception requires a special receptor. The sensations connected with pain, pleasure and touch of objects depend on specific sensors; these cannot detect other sensations. There are thousands of these different sensors throughout the whole body. Nerve impulses from these detectors travel to the brain along specific nerve pathways; from there they are redirected to the particular brain centre connected with that type of sense. They are then interpreted according to previous experience.
The second group of nerves are called motor nerves. These come into play if action is required in response to the interpretation of nerve impulses from the sensory nerves. The motor nerves carry explicit commands from the brain to the muscles telling them to move in a certain manner. Let us give an example. You are reading a book. Your eyes are attracted to something interesting. Sensory information is transmitted to the brain. The brain responds by sending a series of messages to the muscles of the fingers, hands and arms, directing them to turn the pages of the book for more information. The sensory and motor nerves act as a continuous feedback system.
This same feedback operates with the nerves of taste and smell located in the mouth and nose. If we taste some food, we immediately know whether we like it or not. The taste buds on the tongue are sensory receptors that immediately flash a message to the brain; from this we know whether to continue eating or not. The pleasant odour of a well-cooked meal acts in the same way. Both of these sensations not only allow one to enjoy food, they also cause the digestive organs to prepare for the process of digestion.
It is the nervous system that allows the brain to receive information from the eyes. Within each eve there are millions of small receptors that are sensitive to light; they detect all the different colours. When the eyes look at something, then a picture or image is formed on these sensors in the screen (retina) at the back of the eye. These sensors transmit messages to the brain where they are interpreted. In this way, one understands the nature of the object.
It is the same with the ears; they contain thousands of tiny sensory nerves that are sensitive to differences of pitch, tone and quality of sound. All the different sounds that occur at any one moment are transmitted to the brain, where they are interpreted and recognized as being a sound that has been heard before. If it is a pleasant sound such as beautiful music, it will produce a joyful emotional response. Without the brain we would never be able to recognize any sounds.
A most important section of the nervous system is the autonomic nervous system, comprising the sympathetic and paras-ympathetic nerves. They are essential for maintaining perfect balance and harmony in the functioning of all physical organs-.
It should be abundantly clear that without the brain and the nervous system, we would be totally unable to experience the outside world; also the functioning of the inner organs would not be synchronized so that they work together for the overall health and well-being ofthe entire body. The degree to which we can live to the full depends on the efficiency of the brain. Various yogic practices, especially sirshasana, help the brain to function as a perfect instrument.
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