Topic 5-homeostatis and response

• Homeostasis is maintaining a stable internal environment
• Cells need the right conditions to function properly, including the right conditions for enzyme action
• Homeostasis


  • Regulation of the conditions inside your body (and cells) to maintain a stable internal environment
  • Automatic control systems in your body that regulate your internal environment
• Components of automatic control systems


  • Receptors
  • Coordination centres (including the brain, spinal cord and pancreas)
  • Effectors
• Negative feedback


  1. Receptor detects a stimulus

  2. Coordination centre receives and processes the information, then organises a response

  3. Effector produces a response which counteracts the change and restores the optimum level
• Stimulus


  A change in the environment
• Negative feedback counteracts changes to maintain a steady condition
• Nervous system


  • Allows organisms to react to their surroundings and coordinate their behaviour
  • Made up of the central nervous system (brain and spinal cord) and sensory/motor neurones
• Sensory neurones


  Carry information as electrical impulses from receptors to the central nervous system
• Motor neurones


  Carry electrical impulses from the central nervous system to effectors
• Effectors


  Muscles and glands that respond to nervous impulses
• Reflex arc


  1. Stimulus detected by receptor

  2. Impulses travel along sensory neurone

  3. Impulses passed to relay neurone in central nervous system

  4. Impulses travel along motor neurone

  5. Effector (muscle) contracts
• Reflexes are rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain
• Reaction time is the time it takes to respond to a stimulus
• Measuring reaction time


  1. Person sits with arm resting on table

  2. Hold ruler vertically between thumb and forefinger

  3. Let go of ruler without warning

  4. Person tries to catch ruler as quickly as possible

  5. Measure distance ruler fell to get reaction time

  6. Repeat with caffeine and compare
• Computers can measure reaction time more precisely than manual methods
• The person being tested should avoid drinking any more caffeine for the rest of the day after the experiment is completed
• Simple computer tests can also be used to measure reaction time
• Reaction time test


  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
• Computers for measuring reaction time


  • They remove the possibility of human error from the measurement
  • They can record the reaction time in milliseconds, giving a more accurate measurement
  • They can remove the possibility that the person can predict when to respond
• Measuring reaction time with a computer


  1. Student repeats the test five times before having an energy drink

  2. Student repeats the test five times after having the energy drink
• Along with the spinal cord, the brain is part of the central nervous system
• The brain is made up of billions of interconnected neurones
• The brain

  • It controls and coordinates everything you do - running, breathing, sleeping, remembering your gym kit
  • Different regions of the brain carry out different functions
• Regions of the brain and their functions


  • Cerebral cortex (responsible for consciousness, intelligence, memory and language)
  • Medulla (controls unconscious activities like breathing and heartbeat)
  • Cerebellum (responsible for muscle coordination)
• Methods used to study the brain


  • Studying patients with brain damage
  • Electrically stimulating the brain
  • MRI scans
• Knowledge of how the brain works has led to the development of treatments for disorders of the nervous system
• The brain is incredibly complex and delicate, and investigation of brain function and treatment of brain damage or disease is difficult and carries risks
• Sclera


  The tough, supporting wall of the eye
• Cornea


  The transparent outer layer found at the front of the eye, which refracts (bends) light into the eye
• Iris


  Contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye
• Lens


  Focuses the light onto the retina
• Ciliary muscles and suspensory ligaments


  Control the shape of the lens
• Optic nerve


  Carries impulses from the receptors on the retina to the brain
• Iris reflex - adjusting for bright light


  1. Circular muscles in the iris contract and radial muscles relax, reducing the pupil size to limit light entering the eye

  2. Radial muscles contract and circular muscles relax, widening the pupil in dim light
• Focusing on near and distant objects


  1. Ciliary muscles contract, slackening suspensory ligaments, making the lens more curved to focus on near objects

  2. Ciliary muscles relax, allowing suspensory ligaments to pull tight and make the lens less curved to focus on distant objects
• Long-sightedness


  Occurs when the lens is the wrong shape and doesn't refract light enough, or the eyeball is too short, causing images of near objects to focus behind the retina
• Short-sightedness


  Occurs when the lens is the wrong shape and refracts light too much, or the eyeball is too long, causing images of distant objects to focus in front of the retina
• Treatments for vision defects


  • Glasses
  • Contact lenses
  • Laser eye surgery
  • Replacement lens surgery
• The body has to keep its insides at around 37°C - the optimum temperature for enzymes in the body