the nervous system

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The nervous system allows the body to respond to changes in the environment. In humans it consists of:

  • the brain
  • the spinal cord
  • all of the nerves that branch off from the spinal cord

The Central Nervous System (CNS) refers to the first two of these, i.e. the brain and spinal cord.

There are two ways in which the nervous system handles these changes, depending on how urgently a reaction is needed:

  1. A response coordinated by the brain. This is the usual and slower way of responding.
  2. Reflex actions, which are extra-rapid responses to stimuli that by-pass the brain.

Stimuli are things that set off a reaction in the nervous system - for example, light, heat, sound, gravity, smell, taste, or temperature. The singular is stimulus.

Now look at the following sub-topics:

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