Genetics and reproduction

• Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes.
• Homeostasis is important for maintaining optimal conditions for enzyme action and all cell functions.
• Internal conditions that are controlled

  • Body temperature
  • Water content of the body
  • Blood glucose concentration
• Homeostasis


  The balancing act of maintaining constant internal conditions
• Control systems


  • Receptors
  • Coordination centres
  • Effectors
• Receptors


  Cells that detect changes in the internal or external environment
• Coordination centres


  Areas that receive and process information from receptors
• Effectors


  Muscles or glands that bring about responses to the stimulus
• Homeostasis involves coordination and control.
• Automatic control systems may involve nervous or chemical responses.
• Nervous system


  Enables you to react to your surroundings and coordinate your behaviour
• The nervous system uses electrical impulses to enable you to react quickly to your surroundings and coordinate your behaviour.
• Stimulus


  A change in the environment detected by receptors
• Neurones


  Special cells that carry electrical impulses
• Reflexes


  Automatic responses that happen quickly without conscious thought
• Reflex arc


  • Involves sensory neurones
  • Relay neurones
  • Motor neurones
• How reflexes work


  1. Stimulus

  2. Receptor

  3. Sensory neurone

  4. Relay neurone

  5. Motor neurone

  6. Effector

  7. Response
• Reflex actions control everyday bodily functions.
• Reflexes help you to avoid danger or harm because they happen so fast.
• Reflex actions are automatic and rapid and do not involve the conscious parts of the brain.
• Receptors are usually found clustered together in special sense organs.
• Neurones are not joined up directly to each other; there are junctions called synapses.
• The diffusion of the chemical across the synapse is slower than the electrical impulse in the neurones.
• When an impulse from the sensory neurone arrives at the synapse with a relay neurone, a chemical is released.
• The chemical diffuses across the synapse to the relay neurone where it sets off a new electrical impulse.
• When the impulse reaches the synapse between the relay neurone and a motor neurone, another chemical is released.
• The chemical diffuses across the synapse and starts a new electrical impulse travelling down the motor neurone to the effector.
• The whole reflex is very fast.
• An impulse also travels up the spinal cord to the conscious areas of your brain.
• This action moves the hand rapidly away from the source of pain
• If the effector organ is a gland, it will respond by releasing (secreting) chemical substances
• Reflex pathway


  Not very different from a normal conscious action
• In a reflex action the coordinator is a relay neurone either in the spinal cord or in the unconscious areas of the brain
• The whole reflex is very fast indeed
• An impulse travels up the spinal cord to the conscious areas of your brain
• You know about the reflex action, but only after it has happened
• Reflexes


  Important for controlling everyday bodily functions and avoiding danger
• Reflex pathway


  1. Stimulus

  2. Receptor

  3. Sensory neurone

  4. Relay neurone

  5. Motor neurone

  6. Effector

  7. Response
• Reflex actions


  • Automatic
  • Rapid
  • Do not involve conscious parts of the brain
• Reflexes


  • Involve sensory, relay and motor neurones