The structure and function of the nervous system
The conditions inside our body must be carefully controlled if the body is to function effectively. The conditions are controlled in two ways with chemical and nervous responses.
All control systems include:
- cells called Organs which recognise and respond to stimuli., which detect Something that sets off a reaction in the nervous system, for example, light, heat, sound, gravity, smell, taste, or temperature. These changes in the environment are detected by receptors in an organism. The plural is stimuli.
- the coordination centre, such as the brain, spinal cord or pancreas, which receives and processes information from receptors around the body
- The organ, tissue or cell that produces a response. bring about responses, which restore The best or most appropriate - for instance, the conditions under which an enzyme works best (eg temperature and pH). levels, such as core body temperature and blood glucose levels
- effectors include muscles and glands, and so responses can include muscle contractions or hormone release
Nerve cells
Nerve cells are called Nerve cells. They carry an electrical message or impulse when stimulated.. They are adapted to carry electrical impulses from one place to another. A bundle of neurones is called a nerve.
There are three main types of neurone:
- sensory
- motor
- relay
They have some features in common:
- A long fibre (axon) which is insulated by a fatty (myelin) sheath. They are long so they can carry messages up and down the body.
- Tiny branches (dendrons) which branch further as dendrites at each end. These receive incoming impulses from other neurones.
Where two neurones meet there is a small gap called a A tiny gap at the junction between two nerve cells, which nerve signals must cross.. Here the electrical signal must be converted into a chemical one, which is converted back to an electrical one on the other side of the synapse where the next neurone starts.
- an electrical impulse travels along the first The long part of a nerve cell along which the electrical signal quickly moves.
- this triggers the nerve-ending of a neurone to release chemical messengers called Chemical involved in passing nerve impulses from one nerve cell to the next across a synapse.
- these chemicals When particles spread out from a region of higher concentration to a region of lower concentration. across the synapse (the gap) and bind with receptor molecules on the A selectively permeable membrane surrounding the cell and controlling the entry and exit of materials. of the second neurone
- the receptor molecules on the second neurone bind only to the specific neurotransmitters released from the first neurone
- this stimulates the second neurone to transmit the electrical impulse.
Receptors to effectors
Receptor cells detect a change in the environment (a stimulus) and start electrical signals along neurons. These move towards the central nervous system (CNS). The CNS is the brain and spinal cord. It coordinates the responses. Messages are then sent back along different neurones to muscles which contract or relax, and glands which secrete hormones. Muscles and glands are called effectors.
The diagram summarises how information flows from receptors to effectors in the nervous system.
Receptors are groups of specialised cells. They detect a change in the environment and stimulate electrical impulses in response. Sense organs contain groups of receptors that respond to specific stimuli.
| Sense organ | Stimulus |
| Skin | Touch, temperature |
| Tongue | Chemicals (in food and drink, for example) |
| Nose | Chemicals (in the air, for example) |
| Eye | Light |
| Ear | Sound |
| Sense organ | Skin |
|---|---|
| Stimulus | Touch, temperature |
| Sense organ | Tongue |
|---|---|
| Stimulus | Chemicals (in food and drink, for example) |
| Sense organ | Nose |
|---|---|
| Stimulus | Chemicals (in the air, for example) |
| Sense organ | Eye |
|---|---|
| Stimulus | Light |
| Sense organ | Ear |
|---|---|
| Stimulus | Sound |
Effectors include muscles and glands. They produce a specific response to a detected stimulus. For example:
- a muscle contracting to move an arm
- muscle squeezing saliva from the salivary gland
- a gland releasing a hormone into the blood.