The central nervous system and nerve impulsesSpec 2.87, 2.88
The nervous system lets you react to your surroundings and coordinate your behaviour. The central nervous system (CNS) is made up of the brain and spinal cord. It is linked to the sense organs (such as the eye and the skin) by nerves.
When a receptor in a sense organ is stimulated, it sends electrical impulses along neurones in the nerves into the CNS. The CNS sends electrical impulses out along nerves to effectors. Effectors are muscles (which contract) or glands (which secrete). Impulses travel quickly, so the response is rapid.
- Stimulus (a change in the surroundings)
- Receptor in a sense organ is stimulated
- Electrical impulses travel along nerves into the CNS (brain and spinal cord)
- Electrical impulses travel out along nerves to an effector
- Effector (muscle or gland) produces the response
| Part | Job |
|---|---|
| Receptors | Detect a stimulus and start electrical impulses |
| Nerves | Bundles of neurones that carry impulses to and from the CNS |
| CNS (brain and spinal cord) | Receives impulses and coordinates the response |
| Effectors | Muscles or glands that carry out the response |
Exam tip:
The CNS is the brain and spinal cord only. Nerves are not part of the CNS; they link it to the sense organs and effectors.