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HBIO4 > Flight or Fight
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Flight or Fight - anger or fear

Nervous System

  • Central nervous system (CNS)
    • Brain
    • Spinal cord
  • Peripheral nervous system
    • Motor
      • Autonomic nervous system (involuntary)
        • Parasympathetic (cholinergic → acetylcholine) - inhibition/relaxation
        • Sympathetic (adrenergic → noradrenaline) - excitation/stress
      • Somatic nervous system (voluntary)
    • Sensory

Autonomic nervous system

Effect on target organ

Parasympathetic (ACh)

Sympathetic (NA)

Iris of eyes

Constricts pupil

Dilates pupil



Bronchodilation (↑air flow)

Blood vessels


Vascular smooth muscle



Arterioles supplying skin and gut


Vasoconstriction (require less blood)

Arterioles supplying muscles



Coronary arteries




↓heart rate

↑heart rate

Salivary glands






Sweat glands

No effect

↑sweat production


  • Receives information from cerebral cortex
  • Passes on impulses to sympathetic nerve fibres
  • Sympathetic nerves synapse with target organ
  • Release noradrenaline (NA) into synaptic cleft

Adrenal medulla

  • Located just above the kidneys
  • Innervated by sympathetic nerves
  • Stimulation causes the release of adrenaline (ADR) into blood

Role of Hormones

  • Steroid hormones
    • Lipid soluble
      • Diffuse though plasma membrane and bind to receptors in cytoplasm
      • Regulate transcription
    • Cortisol → stress hormone, turns protein and fat into glucose
    • Testosterone and oestrogen
  • Protein hormones
    • Bind to plasma membrane
      • Causes cascade of signals
      • Activates enzymes within the cell
    • Adrenaline (released from adrenal glands)
      • Increases sensitivity of nervous system
      • Stimulates release of cortisol
      • Stimulates glycogenolysis in liver and muscles
      • Note: ADR is a hormone while NA acts as a hormone and neurotransmitter
    • Insulin
  • Hormone vs Nervous System
    • Hormones
      • Produce delayed and prolonged responses
      • Travel throughout the body and produce widespread effects
      • May cause permanent and irreversible effects
    • Nervous System
      • Instant response
      • Usually act locally
      • Temporary and reversible effects