Structure of nervous system

• • 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.
• neurons have

  • 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.
• 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
• 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.
• Effectors include muscles and glands - that 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