coordination and response

• Animals and plants


  • Need to be able to respond to changes in their internal and external environment
  • Need to coordinate the activities of their different organs
• Control and communication systems


  Ensure internal conditions are kept relatively constant to allow organisms to function properly and efficiently
• Homeostasis


  Physiological control system that maintains the internal environment within restricted limits
• Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function
• Physiological factors controlled by homeostasis in mammals


  • Core body temperature
  • Metabolic waste (eg. carbon dioxide and urea)
  • Blood pH
  • Concentration of glucose in the blood
  • Water potential of the blood
  • Concentration of respiratory gases (carbon dioxide and oxygen) in the blood
• Homeostatic mechanisms in mammals


  Require information to be transferred between different parts of the body
• Communication systems in mammals


  • Nervous system
  • Endocrine system
• Pathway through the nervous system


  1. Stimulus

  2. Sensory neurone

  3. Relay neurone

  4. Motor neurone

  5. Effector

  6. Response
• Stimulus


  Received by a sensory (receptor) neurone
• Receptors


  • Most are specialised to detect particular stimuli
• What happens when a receptor is stimulated


  It produces electrical impulses
• What happens to the electrical impulses

  They travel along a sensory neurone to the central nervous system (the coordinator is either the brain or the spinal cord)
• What happens in the CNS


  The impulses are passed on to a relay neurone
• What happens with the relay neurone

  It links to a motor neurone, along which the impulses travel until they reach the effector
• Effector


  What carries out the response (the effector may be a muscle or gland)
• Neurones do not actually come into direct contact with each other
• Synapse

  The junction where the dendrites of two neurones meet to make a connection between the neurones
• At a synapse, there is a very small gap between neurones
• Synaptic cleft or synaptic gap

  The very small gap between neurones at a synapse
• Electrical impulses cannot travel directly from one neurone to the next due to the synaptic cleft (electricity cannot 'jump' the gap)
• Signal transmission at a synapse

  1. Electrical signal briefly converted to a chemical signal

  2. Chemical signalling molecules (neurotransmitters) cross the synaptic cleft

  3. Chemical signal converted back into an electrical impulse
• Neurotransmitters

  Chemical signalling molecules used to transfer the signal between neurones at a synapse