Tissues constituting the nervous system
The nervous system is made up, predominantly, of tissue that has the special property of being able to conduct impulses rapidly from one part of the body to another. The specialised cells that constitute the functional units of the nervous system are calledneurons. Within the brain and spinal cord neurons are supported by a special kind of connective tissue that is calledneuroglia.Nervous tissue, composed of neurons and neuroglia, is richly supplied with blood. It has been taught that lymph vessels are not present, but the view has recently been challenged.
The nervous system of man is made up of innumerable neurons. The total number of neurons in the human brain is estimated at more than 1012. The neurons are linked together in a highly intricate manner. It is through these connections that the body is made aware of changes in the environment, or of those within itself; and appropriate responses to such changes are produced e.g., in the form of movement or in the modified working of some organ of the body. The mechanisms for some of these relatively simple functions have come to be known as a result of a vast amount of work done by numerous workers for over a century. There is no doubt that higher functions of the brain, like those of memory and intelligence, are also to be explained on the basis of connections between neurons, but as yet little is known about the mechanisms involved. Neurons are, therefore, to be regarded not merely as simple conductors, but as cells that are specialised for the reception, integration, interpretation and transmission of information.
Nerve cells can convert information obtained from the environment into codes that can be transmitted along their axons. By such coding the same neuron can transmit different kinds of information.
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