Muscles, nerves and hormones

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  • Muscles, nerves and hormones
    • Responding to environmental stimuli:
      • Responses of mammals to environmental stimuli are coordinated and balanced to ensure survival.
      • Coordination of responses to stimuli from external environment is mainly the result of brain activity to assess the most appropriate response.
      • Brain also regulates endocrine responses through action of the hypothalamus and its control on the pituitary gland.
    • Fight or flight response
      • Threat to safety of a mammal leads to physiological changes to prepare the organism to deal with the threat, escaping or challenging it.
      • Aterioles to digestive system + skin are constricted whilst those to muscles and liver are dilated.
      • Pupils dilate.
      • Heart rate & blood pressure increase.
      • Blood glucose levels increase.
      • Metabolic rate increases.
      • Erector pili muscles in skin contract, making hairs stand up.
      • Ventilation rate and depth increase.
      • Endorphins (natural painkillers) are released in the brain.
      • Sweat production increases.
    • Coordination of the physiological changes:
      • Cerebral understanding of a threat activates hypothalamus which stimulates increased activity in sympathetic nervous system + triggers release of adrenaline from adrenal medulla into blood.
      • Hypothalamus releases corticotropin-releasing factor (CRF) into pituitary gland, stimulating release of adreno-corticotropic hormoone (ACTH) from pituitary gland. Stimulates release of hormones from adrenal cortex which help body to resist stressors.
      • Effects of sympathetic nervous system + adrenaline release and hormones into blood is responsible for physiological changes of fight or flight response.
    • Timing of fight/flight response:
      • On perception of threat, there is a period of heightened awareness.
      • The threatened animal assess the threat which is an autonomic assessment.


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