reflexes, nervous system and reactions

• pathway of a reflex arc

  stimulus -> receptor -> sensory neurone -> relay neurone (in CNS) -> motor neurone -> effector -> response
• what is a sensory neurone


  The neurones that carry information as electrical impulses from the receptors to the CNS
• what is a receptor


  an organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve.
• what is a relay neurone


  Neurones that carry impulses from the sensory neurone to the motor neurone.
• CNS is made up of

  brain and spinal cord
• what is a motor neurone


  The neurones that carry electrical impulses from the CNS to effectors
• what is an effector


  Muscles or glands that bring about a response after getting a signal from a motor neurone
• retina of eye is covered in

  light receptor cells
• what is a synapse


  Gap between neurons
• process at synapse


  - nerve signal is transferred by chemicals which diffuse across gap

  - these chemicals set off an electrical signal in the next neurone
• reflexes are


  rapid automatic responses to a stimulus

  - don't involve conscious part of brain
• reflexes bypass conscious brain when a quick response is essential
• investigating reaction time


  - arm rest on edge of table (to stop arm moving up or down)

  - hold ruler vertically between thumb and forefinger. make sure zero is level with fingers. let go without warning

  - test person catch ruler as quick as possible

  - reaction time is measured by number they caught it on (higher number lower reaction)

  - repeat and calculate mean

  - give person caffeine and test again 10 mins later
• control variables in reaction test


  - person being tested

  - same hand

  - ruler dropped from same height

  - person not had caffeine before test
• reaction times can also be measured by

  tests on a computer