The nervous system or the central-line of communication amidst all the receptors and effectors controls and coordinates all body functions and activities including all reflexes and instincts like any thought or feelings, any judgment or reasoning. It directs tasks to all tissues working towards a common function.
Basically, the nervous system is a network of neurons that keep us informed about environmental changes and directs us as to how to react to them. Suppose you keep your hand on a pan full of hot boiling water. Sensory cells within the skin will respond, impulse will be transmitted along to the brain via sensory nerves. This impulse is interpreted by the brain and a response is sent from the brain to the muscles in the hand and palm, along the motor nerves to remove your hand from the pan.
The neuron or nerve cell is the main component of the nervous system. A cluster of many neurons together form nerve fibers that carry impulses in different body parts. Some sections of the nerve fiber are insulated with some fatty substance called myelin that acts as a protective cover over it.
Nerve cells have specialized regions or synaptic terminals at their ends. The synaptic terminals have many very small membranous sacs filled with neurotransmitter chemicals that help in transmitting impulses from a neuron to the next neuron. When an electrical impulse travels across a neuron, it goes to the terminal stimulating and releasing the neurotransmitters from the sacs. These neurotransmitters travel along the synapse, stimulating the generation of electrical charge that will carry the impulse ahead. Only once the sensory impression gets recorded by the brain or a muscle moves or relaxes based on the impulse, the process stops repeating. These electrochemical actions are like a "language" to the nervous system, by which message or information is communicated.
The nervous system can be divided into the central nervous system (CNS) that is made up of the spinal cord and the brain, and the peripheral nervous system (PNS) that comprises of both spinal nerves and cranial nerves.
The brain rests within a skull governing the body roles by receiving and sending messages via the spinal cord. Both the spinal cord and the brain is protected by cerebrospinal fluid, sheets of tissues and bones. After the message leaves the central nervous system, the nerves of the peripheral nervous system carry and convey the information from receptor cells back to the central nervous system. Motor impulses are also transported to the body, from the CNS, for the glands and muscles to react to the impulse.
The autonomic nervous system, a part of the PNS, controls all involuntary activities that are necessary for living and other internal organs activities and functioning of glands. All these divisions work together, coordinating adjustments and reactions with the body to deal with external and internal environmental conditions.
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Essortment: Anatomy Of Human Nervous System