Reflexes

• Reflexes


  Rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain
• Reflexes can reduce the chances of being injured
• Reflexes


  • Pupils getting smaller when a bright light is shone in the eyes
  • Body releasing adrenaline when getting a shock
• Reflex arc


  The passage of information in a reflex (from receptor to effector)
• Reflex arc


  1. Stimulus detected by receptors

  2. Impulses sent along sensory neurone to CNS

  3. Impulses trigger chemicals released at synapse between sensory and relay neurone

  4. Impulses sent along relay neurone

  5. Impulses trigger chemicals released at synapse between relay and motor neurone

  6. Impulses travel along motor neurone to effector

  7. Effector (muscle) contracts
• Reflexes are quicker than normal responses because you don't have to think about the response
• Investigating Reaction Time


  1. The person being tested should sit with their arm resting on the edge of a table

  2. Hold a ruler vertically between their thumb and forefinger

  3. The person being tested should try to catch the ruler as quickly as they can as soon as they see it fall

  4. Repeat the test several times then calculate the mean distance that the ruler fell

  5. The person being tested should then have a caffeinated drink (c.g. 300 ml of cola)

  6. After ten minutes, repeat steps 1 to 5
• Reaction time


  The time it takes to respond to a stimulus-it's often less than a second
• Factors that can affect reaction time

  • Age
  • Gender
  • Drugs
• Caffeine is a drug that can speed up a person's reaction time
• With a little bit of maths, it's possible to work out the reaction time in seconds using the mean distance
• Variables to control


  • Use the same person to catch the ruler each time, and that person should always use the same hand to catch the ruler
  • The ruler should always be dropped from the same height
  • Make sure that the person being tested has not had any caffeine or anything else that may affect their reaction time before the start of the experiment
• Too much caffeine can cause unpleasant side-effects, so the person being tested should avoid drinking any more caffeine for the rest of the day after the experiment is completed
• Measuring Reaction Time Using a Computer

  1. The person being tested has to click the mouse (or press a key) as soon as they see a stimulus on the screen, e.g. a box change colour

  2. Computers can give a more precise reaction time because they remove the possibility of human error from the measurement

  3. Using a computer can also remove the possibility that the person can predict when to respond
• Advantages of using a computer to measure reaction time

  • Computers can record reaction time in milliseconds, so it can give a more accurate measurement
  • Computers can remove the possibility of human error from the measurement
  • Computers can remove the possibility that the person can predict when to respond