- The nervous system is a complex network of nerves and cells that perform three overlying functions of sensory input, integration, and motor output. This process is generally the same even at a very primitive level of the nervous system.
- The sensory input is sensing the environment and changes in an organism and is carried out by sensory organs like eyes, ears, nose, tongue, and skin, some of them performing simultaneously.
- The integration involves the processing of information and is carried out by the central nervous system (CNS), which is composed of the brain and the spinal cord.
- Moto-neuron output is the conduction of signals from the integration centre, the central nervous system, and is carried out by a group of effector cells, the muscle cells or gland cells, which actually carry out body’s responses to external stimuli. Both sensory input and motor output signals are carried through nerves, which are long rope-like structures made from nerve cells. Nerve cells are of two types – neurons and glia.
- Neurons are the cells which actually carry through signals, whereas glial cells provide supporting structures and maintenance of neuronal cells. Nerves, many times, are made from end to end connection between neurons, supported by the glial cells. The nerves that communicate sensory and motor signals between the central nervous system and the rest of the body are collectively referred to as the peripheral nervous system (PNS). Sensory inputs are received by receptor cells located in sensory organs. For examples, light receptor cells are located in eyes, or chemical receptor cells are located on the surface of the tongue.
- Signals from these receptors are carried through sensory neurons of the peripheral nervous system into the central nervous system, and after processing, the instructions are communicated through the motor neurons of the peripheral nervous system to effector cells, such as muscles. Communication from the receptor cells to effector cells is carried in two forms – chemical and electrical. Since communication of information involves more than one cells, the communication is through special chemicals called neurotransmitters or a specialized form of an electrical signal called an action potential.
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