The nervous system is a rapid communication system.
The central nervous system consists of:
- The brain,situated inside the skull.
- The spinal cord,which extends from the base of the skull to the lumbar region and is protected from injury by the bones of the spinal column.
The peripheral nervous system is a network of nerve fibres,which are:
- Sensory or afferent nerves that transmit signals from the body to the brain ,or
- Motor or efferent nerves,which transmits signals from the brain to the effector organs,such as muscles and glands.
The somatic senses are pain,touch,heat and cold,and they arise following stimulation of specialised sensory receptors at nerve endings found throughout the skin.
There are different receptors in muscles and joints that respond to changes in position and orientation of the body,maintaining posture and balance. Yet other receptors are activated by stimuli in internal organs and control vital body function eg heart rate,respiratory rate and blood pressure. Stimulation of any of these receptors sets up impulses that are conducted to the brain in sensory (afferent)nerves.
Reflex actions are fast,involuntary,and usually protective motor responses to specific stimuli. They include:
- Withdrawal of a finger from a very hot surface.
- Constriction of the pupil in response to bright light.
- Control of blood pressure.
