The Nervous System
The human nervous system is a complex communication network consisting of two systems interconnected with each other:
1. Central Nervous System (CNS)
The CNS consists of the brain and spinal cord. It is the command centre; interpreting all incoming sensory information such as from our eyes and ears, and controling all the commands transmitted to the muscles. The communication takes place via nerve impulses, i.e. electrical signals, which are transmitted along the nerve tracks. The brain also performs complex functions such as learning, memory, feelings and abstract thought.
Peripheral Nervous System (PNS)
The PNS consists of sensory and motor nerves: sensory nerves transmit incoming information absorbed by seeing, hearing, tasting, feeling and touching to the CNS. Motor nerves then transmit command signals from the CNS to the muscles.
The reflex arc
A simple way of testing the function of the nervous system is to check the spinal cord reflex arc. This can determine whether the patient is suffering from a disorder of the nervous system or not.
Reflex reactions are those which do not demand any conscious thought or willed response. A known reflex, for instance, is the reaction to touching something very hot:
1. The sensory nerve in the skin indicates possible danger
2. A nerve impulse is transmitted from the skin to the spinal cord, where it is transferred from the sensory to the motor nerve
3. Motor nerves transmit the impulses to the muscles; these trigger the hand muscles to jerk the hand away from the source of heat.
Reflex functions can also be tested by tapping the elbow or knee with a narrow reflex hammer.
