The nervous system

• What does the human nervous system consist of?

  The central nervous system (CNS) and the peripheral nervous system.
• What is in the central nervous system? (CNS)

  The brain and the spinal cord
• What is the peripheral nervous system?

  Nerve cells that carry information to and from the CNS
• What are nerves?

  Bundles of neurones.
• What are neurones?

  Long cells which carry electrical impulse signals.
• What is a synapse?


  A gap where 2 neurones meet.
• How are electrical impulses passed?

  Chemically.
• What are sense organs?

  Group of receptor cells (specialised) which produce electrical impulses.
• What is the stimulus for skin?

  Temperature, pressure and pain.
• What is the stimulus for tongue?

  Chemicals in the mouth.
• What is the stimulus for nose?

  Chemicals in the air.
• What is the stimulus for eye?

  Light.
• What is the stimulus for ear?

  Sound.
• What are effectors?


  Parts of the body, like glands/ muscles which produce a response to a detected stimulus.
• What are 3 examples of effectors?

  1. A muscle contracting to move an arm
  2. A muscle contracting to alter pupil size
  3. a gland releasing a hormone into the blood.
• What are the main stages in a reflex arc?

  1. Stimulus
  2. Receptor cells
  3. Electrical impulse along sensory neurone
  4. Synapse
  5. Relay neurone
  6. Synapse
  7. Motor neurone
  8. Effector
  9. Response
• What is a reflex action?


  Usually protective, involuntary and fast.
• What doesn’t a reflex response need?

  The brain- instead the spinal cord coordinates the response so that the electrical impulse can reach the effector quickly
• How is light entering the eye controlled?

  By a reflex response through the muscles in the Iris. It changes in response to bright or dim light
• What does the cornea?

  Clear part of sclera, refracts light
• What does the lens do?

  Focuses light onto the retina
• What does the optic nerve do?


  Carries impulses between retina and the brain
• What is the sclera?

  White, tough, protective layer
• What does the choroid do?

  Pigmented middle layer, absorbs light to avoid reflection
• What is The blind spot?

  Where the optic nerve leaves the retina and lacks receptor cells
• What is the pupil?

  A small hole at the centre of the iris, where light enters eye
• How might reaction time be affected?


  Age and if the person has had stimulants (e.g caffeine)