Structure and Function

• The nervous system enables humans to react to their surroundings and coordinate their behaviour.
• The CNS is the brain and spinal cord
• The CNS coordinates the response of effectors which may be muscles contracting to glands secreting hormones.
• stimulus -> receptor -> coordinator -> effector -> response
• Reflex actions are automatic and rapid, they of not involve the conscious part of the brain
• sensory neurones - the neurones that carry information as the electrical impulses from the receptors to the CNS
• effectors - all of the muscles and glands which respond to nervous impulses
• receptors and the cells that detect stimuli
• there are many different types if receptors, such as taste receptors on the tongue and sound receptors in the ears
• Information from receptors passes along cells (neurones) as electrical impulses to the CNS.
• receptors can form part of larger, complex organs, like the retina of an eye which is covered in light receptor cells
• Effectors respond to nervous impulses and bring about a change
• muscles and glands are known as effectors - they respond in different ways. Muscles contract in response to a nervous impulse, and glands secrete hormones
• synapses connect neurones
• the nerve signal is transferred by chemicals which diffuse across the gap. these chemicals then set of a new signal in the next neurone
• reflexes help prevent injury
• the passage of information in a reflex - from receptor to effector - is called a reflex arc
• Reflex arc


  1. Stimulus detected by receptors

  2. Impulses sent along sensory neurone to relay neurone in CNS

  3. Chemicals released at synapse between sensory and relay neurone

  4. Impulses sent along relay neurone

  5. Chemicals released at synapse between relay and motor neurone

  6. Impulses sent along motor neurone

  7. Effector (usually muscle) contracts
• Neurones in reflex arcs

  • Go through the spinal cord or through an unconscious part of the brain
• The reflex arc goes through the CNS
• Investigating Reaction Time:

  • Testee should sit with their arm on resting on the edge of a table to stop their arm from moving up and down during the experiment
  • Hold a ruler vertically between their thumb and forefinger, making sure that the zero end is level with their fingers, then let go without warning
  • They should try to catch the ruler as quickly as they can
  • Reaction time is measured by the number on the ruler where it is caught
  • Repeat and calculate the mean distance
  • Then the person being tested should have a caffeinated drink, and after 10 minutes, repeat steps 1-5