coordinating responses

• 'fight or flight' response


  • detecting threat to survival stimulates 'fight or flight' response.
  • in mammals, this leads to a range of physiological changes that prepare animal for activity.
  • Activity may be running away
• coordination of fight or flight response


  receptors that detect external threat include eyes, ears and nose. Internal receptors may detect a threat, such as pain or sudden increase or decrease in blood pressure. Cerebrum uses such sensory input to coordinate a suitable response:

  • inputs feed into sensory centres in cerebrum
  • cerebrum passes signals to association centres
  • if threat recognised, cerebrum stimulates hypothalamus
  • hypothalamus increases activity in sympathetic nervous system and stimulates release of hormones from anterior pituitary gland
• role of sympathetic nervous system


  • autonomic nervous system controls many physiological mechanisms
  • increasing stimulation of sympathetic nervous system increases activity of effectors
  • nervous communication is used for rapid responses
  • fight or flight from danger may need prolonged response - achieved through endocrine system
  • sympathetic nervous system stimulates adrenal medulla. Adrenaline released from adrenal medulla has wide range effects on cells
• mechanism of adrenaline action


  adrenaline is a first messenger. it's an amino acid derivative so it is unable to enter target cell; must cause an effect inside cell, without entering cell itself

  1. adrenaline binds to adrenaline receptor on plasma membrane. receptor is associated with G protein on inner surface of plasma membrane, which is stimulated to activate enzyme adenyl cyclase
  2. adenyl cyclase converts ATP to cyclic AMP (cAMP) which is second messenger inside the cell
  3. cAMP causes an effect inside cell by activating enzyme action
• release of hormones from anterior pituitary 


  • hypothalamus secretes releasing hormones into blood. these pass down portal vessel to pituitary gland and stimulate release of tropic hormones from anterior part of pituitary gland
• corticotropin-releasing hormone (CRH)


  • from hypothalamus causes release of adrenocorticotropic hormone (ACTH)
  • ACTH passes around blood and stimulates adrenal cortex to release different hormones - include glucocorticoids such as cortisol which regulate metabolism or carbohydrates
  • more glucose released from glycogen stores
• thyrotropin-releasing hormone (TRH)


  • causes release of thyroid-stimulating hormone (TSH) which stimulates thyroid gland to release more thyroxine.
  • thyroxine acts on nearly every cell of the body, increasing metabolic rate and making cells more sensitive to adrenaline