It is essential that the organism be able to detect stimuli in the environment and react to those stimuli. The function of the nervous system is made up of: the central nervous system composed of the brain and spinal cord and the peripheral nervous system composed of the cranial, spinal nerves and the autonomic nervous system.
The nervous system works on this basic plan:
The receptor picks up the stimulus and initiates an impulse along a sensory neuron which carries it into the CNS In the CNS the sensory neuron synapses with the inter neuron which in turn synapses with a motor neuron The motor neuron then carries the impulse to the effector organ (muscle or gland) causing it to react.
The impulse, an electrical depolarization or message passes along specialized cells of the nervous system called neurons. Neurons which carry impulses toward the CNS are called sensory or affect end neurons, while those which take the impulses away from the CNS are termed motor neurons or efferent neurons. Inter neurons lie within the CNS and conduct the impulse from the sensory to the motor neuron. The area where the two neurons meet is called a synapse which is a microscopic gap.
Structure of the sensory neuron
The cell body which contains the nucleus and missal grannuels which produces granules is housed in the dorsal root ganglion of the spinal nerve, just outside the spinal cord. Extending from the receptor to the cell body of the neuron is the dendrite. Carrying the impulse from the cell body is the axon. The axon and dendrite are surrounded by a myelin sheath composed of Schwann cells which wind around them and secrete a fatty myelin. The neurolemma is the cellular part of the Schwann cell and contains the nucleus of the Schwann cell.
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