Definition
The Nervous System consists of two parts: the CNS (Central Nervous System) which is the brain and spinal cord, and other nerves to and from the CNS.
The nervous system is an Automatic Control System.
- First the receptor cells detect a stimulus.
- The receptor sends Electrical Impulses down Neurones to the CNS - The co-ordination centre of the nervous system.
- The CNS now sends Electrical Impulses down other Neurones to an effector.
- The effector carries out a response (Usually a muscle which contracts or a gland which secretes a hormone).
Reflexes
A reflex action is a protective, automatic and rapid response to a stimulus. It follows the same general sequence as a normal reaction but circumvents the brain as to be faster. It does still go through the CNS via the Relay Neurone
The Reflex Arc is:
- Stimulus
- Receptor
- Sensory Neurone
- Synapse - located at the end of the sensory neurone where a chemical (neurotransmitter) is released which diffuses to a relay neurone.
- Relay Neurone - located in CNS, when the chemical is received it triggers an electrical impulse.
- Synapse - the electrical impulse passes across the relay neurone to another synapse. A chemical is released
- Motor Neurone - when the chemical is received it triggers an electrical impulse
- Effector - electrical impulse received which causes effector to bring a response