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Watford
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The function of the nervous system is to recieve messages from outside the body and after analysing them, to cause the animal to respond in an appropriate way. The nervous system is essentially divided into two parts:
1. The central nervous system
This consists of the brain and spinal cord, both of which are protected by bone - the skull in the case of the brain and the bony canal through the vertebrae in the case of the spinal cord.
2. The peripheral nervous system
This consists of nerves which connect the central nervous system to the rest of the body. If a ball is thrown for a dog to catch, messages are sent through the sensory nerves from the light-sensitive nerve endings in the eye to the brain. This in turn sends messages via the motor nerves to the muscles which move the dog into the right place and open its mouth at the correct time.
Some nerve impulses are sent automatically from an organ, for example the stomach, when it is full, and the central nervous system responds, also automatically, to send a nerve impulse to the muscles in the organ to make them contract and empty it. In some cases, eg the urinary bladder, the brain can override the automatic response, as occurs in house trained animals. In other cases, for example the filling and emptying of the stomach, the nervous impulses which case contraction of the muscles and dilation of the sphincter are purely automatic and cannot be overridden consciously.
