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 receptors, which detect stimuli (changes in the environment).
  • The coordination centre, such as the brain, spinal cord or pancreas, which receives and processes information from receptors around the body.
  • Effectors bring about responses, which restore optimum 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 neurones. They are adapted to carry electrical impulses from one place to another.

A bundle of neurones is called a nerve.

An image of the inside of a nerve

There are three main types of neurone: sensory, motor and relay.

  • 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.
Diagram of a motor neuroneA motor neurone

Receptors to effectors

Information from receptors passes along neurones, as electrical impulses to co-ordinators such as the central nervous system or CNS. The CNS is the brain and spinal cord. Muscles contracting or glands secreting hormones are the response of effectors coordinated by the CNS.

Stimulus → receptor → coordinator → effector → response

The diagram summarises how information flows from receptors to effectors in the nervous system.

Diagram of how information flows from receptors to effectors in the nervous system

Receptors

Receptors are groups of specialised cells. They detect a change in the environment (stimulus) and stimulate electrical impulses in response. Sense organs contain groups of receptors that respond to specific stimuli.

Sense organStimulus
SkinTouch, temperature and pain
TongueChemicals (in food and drink, for example)
NoseChemicals (in the air, for example)
EyeLight
EarSound and position of head

Effectors

Effectors include muscles and glands - that produce a specific response to a detected stimulus.

For example:

  • a muscle contracting to move an arm
  • a muscle squeezing saliva from the salivary gland
  • a gland releasing a hormone into the blood