What is an Electroencephalogram-EEG?

            An instrument called electroencephalograph is used to record the electrical activity of the brain. Electroencephalography is a bio-medical process of recording minute electric currents produced by the brains of human beings and other animals. This was discovered by Hans Berger of Jena now in East Germany in 1929, and found to have important clinical significance in the diagnosis of brain diseases.

Electroencephalogram-EEG

            The brain constantly generates feeble electrical currents, even during sleep and in deep coma. These can be recorded from the surface of the skull by means of small wires electrodes attached to the scalp. In normal persons, there is an electrical potential of about 100 microvolt’s. So to make such recording doctors use a machine that has about 20 equally spaced electrodes, which are attached on the scalp’s surface in accordance with the standard positions adopted by the international federation of EEG? Electrode positions are measured so that subsequent recordings for the same person can be compared with the earlier ones. The electrodes are connected to an amplifier, which amplifies the voltages 1,000,000 times. The current runs an electromagnetic pen that makes a graph on a roll of chart paper.

            In a normal adult person, most of the EEG recordings are made up of rhythmic oscillating waves regularly repeated at about 10 Hertz (hertz is the unit of frequency). They are called alpha waves. They are best obtained from the back of the central nervous system brain when a person is in a relaxed position with the eyes closed. The waves disappear or are blocked when the eyes are opened.

            Normally EEG reveals more rapid rhythmical movement. It consists of smaller waves called beta waves, which are repeated at every 18-25 hertz. These are related to the function of sensory motor part of the brain. During sleep, the central nervous system cells generate electrical wave’s f eve higher voltage but they re slowed down to 2 or 3 hertz. During coma, very feeble waves are produced.

            The irregular slow waves, one to three per seconds, which arise form the localized area of the damaged region of the brain, are called delta waves. Rhythmic slow waves with frequencies between 4 and 7 hertz are called theta waves. Slow waves suggest some abnormally in case of adult but it is not so in infants or young children. EEG patterns change gradually in the growing child until he has attained the age of 8 to 12 years. That is when the adult patterns appear. Every person has a different EEG pattern. Identical at twins have identical pattern.

            EEG has proved to be very useful for studying the working of the brain and detecting many brain diseases. A doctor can figure out the working of a person’s brain by looking at the pattern of the graph. The graph also shows whether the brain is functioning properly or not.

            EEG provides indications about any abnormalities in the brain. It can be used to detect epilepsy and abnormal metabolic conditions. Coma conditions can be studied from EEGs. If we get a flat EEG, it indicates brain death. Nowadays, CAT computerized axial tomography scanning is more frequently used, as it has been found to be more useful than EEG. Better than IAT is MRI magnetic resonance imaging which gives better information of brain disorders.

How does Our Nervous System Function?

            Whatever it is the heat from a candle or fire that is sensed by you or the pain when a pin pricks your finger, it is all because your nerves are passing the messages to the brain. The nervous system is a network of nerve cells called neurons that send information to and from all parts of the body to the brain. The messages are in the form of electrical signals or nerve impulses. They travel through the cells and are passed on to the other cells. The body has millions of nerve cells linked together to make up the nervous system. The human brain itself contains about ten thousand million nerve cells.

Nervous System in our body

            The human nervous system is divided into two parts- the central nervous system and the peripheral nervous system. The central nervous system comprises the brain and the spinal cord, whereas eh nerve cells and nerve fibers at the periphery. The tough bones of the skull protect the bran, and the bones of the spinal column protect the spinal cord.

            There are two kinds of nerve cells or neurons- sensory neurons and motor neutrons. Sensory neurons carry messages form distant parts of the body towards the brain.

            These relate to pain, temperature, pressure and other messages from the sense organ. The motor neurons carry messages to the muscles, telling them to contract; and to the glands, telling them to produce secretions. The nerves of the central and peripheral nervous system are a mixture of sensory and motor neurons traveling together.

            The nervous system can also be divided on the basis of the nature of work of the neurons. If the nerves are all concerned with conscious sensations, it is called the voluntary nervous system. They carry out orders given by the brain that are directed by will. When we want to walk, write or talk, we use the neurons of the voluntary system. The neurons of the autonomic system help in carrying out the routine activities we do not normally think about. The autonomic system regulates the heartbeat, respiration, digestion, blood pressure, and other unconscious activities.

            The autonomic nervous system has two main divisions- the sympathetic and parasympathetic systems. Their activities balance each other. Nerve impulses in the sympathetic system tend to increase the rate of heartbeat and the blood pressure. On the other hand, the impulses in the parasympathetic system tend to have the opposite effect. Under different conditions each system takes control of the unconscious activities. With the help of prescribed physical exercises, training and to some extent will power, it is possible to control some of the activities of the autonomic nervous system.

What Causes a Reflex Action?

            If you accidentally touched a hot stove, what would you do? You would immediately jerk your had away even before you have had time to think about it. This action is called a reflex action. A reflex action is an automatic nervous action, in which a stimulus causes a rapid and totally involuntary response. In this case, the hot stove is a stimulus, and the jerk is the response.

Reflex Action

            Reflexes such as the pupil reflex are quite common. When a bright beam of light hits a person’s eye, his pupil automatically becomes smaller, i.e., it contracts. When the light is taken away and his eyes are shaded, the pupils return to their normal size. In this example, the light is the stimulus and the reaction of the pupil is the response.

            Reflex actions re of two types- unconditioned ad conditioned. Unconditioned reflex actions re exemplified by the reflex tests of the physician. When a doctor tests a person’s reflexes, he makes sure that the different parts of his nervous system are functioning properly.

            One reflex action frequently tested is the knee-jerk action. In this, the doctor lightly strikes an area just below the kneecap with rubber hammer. This cases the lower part of the leg to jerk upward suddenly. This is because the nerve impulses move via the spinal cord directly to the leg muscle and are not controlled by the brain.

             Conditioned reflex actions are a result of particular internal or external stimuli. The Russian physiologist Ivan Pavlov and his associates popularized such conditioning process. Pavlov believed that whenever there was a response to a particular stimulus, a kind of reflex was established in the brain. However, most psychologists today believe that the mechanism of learning is much more complicated than what was explained by him.

            Now the question arises- what cause a reflex action?

            To explain it in simple terms, four basic processes are involved in a reflex action. These are- reception, conduction, transmission, and response. The stimulus is received by receptors nerve ending. Energy from the stimulus is changed into nerve impulses and carried from the receptor to the central nervous system. The nerve impulses are then sent to the motor nerves. The motor nerves control muscle action, causing the muscles and gland respond. Most reflex actions, however, are much complicated and also involve other parts of the nervous system, like the brain. More than 90% of all our actions are performed by our nervous system, through reflex actions.