Coming out of the base of the brain is a cluster of nerves which spread all over the body forming the nervous system. The brain stem leads into the spinal cord which extends along the vertebrae upto the tail bone. From the central nerve stem peripheral nerves are extended to the other parts all across the body. These nerves carry messages back and forth from the brain through the spinal column. Each nerve contains various bundles of nerve fibres and blood vessels. Messages to the brain are carried by Sensory nerves and messages from the brain are carried to the muscle or effector organ by motor nerves which are attached to the muscle fibres through motor end plates.
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Our skin has various types of receptors in it, we have pressure receptors, touch receptors which give us the sessation of touch heat and cold receptors which allow us to feel the temperature and pain recptors which allow us the sensation of pain.
Certain parts of the body may have a greater number of receptors of a certain type, e.g., our lips and fingers have more touch receptors as compared to other parts. When we touch something, the touch receptors react and messages are sent to the brain, likewise for other receptors.
Most reactions are a result of a nerve message to the brain and a subsequent response from the brain. There are however some actions where the brain is not directly involved. If we touch something which is hot then the heat receptors convey the sensation to the brain through the nerves, but before the brain can respond the spinal cord sends impulses to the muscles in the arm which make us pull our hand back from the hot object.
Such actions are called ‘Refles actions’, they protect the body from harm or injury and they happen so fast that a person does not have the time to think about them.
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