divisions of the nervous system

• central nervous system(CNS)


  origins of commands and decisions, includes brain and spinal cord

  • brain = responsible for consciousness and awareness
  • spinal cord = responsible for reflexes
• peripheral nervous system (PNS)


  takes info into the CNS and takes messages back out of the CNS. includes the somatic nervous system and the autonomic nervous system
• somatic nervous system


  within PNS, voluntary actions, includes ...

  • sensory neurons = carry messages from PNS to CNS
  • motor neurons = connect CNS to effectors eg. muscles and glands
• autonomic nervous system


  within PNS, vital functions (heart rate, breathing), includes ...

  • sympathetic division = fight or flight, prepares for action
  • parasympathetic division = rest and digest
• when stressed...


  • hypothalamus triggers chain of activity from sympathetic NS
  • readies body for action by shutting down unnecessary tasks (digestion) and makes body physiologically aroused
  • when calming down, brain uses parasympathetic branch of ANS to one by one reset each organ to its normal resting state
  • only one can be active at a time, seesawing pair
• effects of parasympathetic NS


  • constricts pupils
  • slows heartbeat
  • no adrenaline
  • constricts bladder
• effects of sympathetic NS

  • dilates pupils
  • speeds up heartbeat
  • releases adrenaline
  • dilates bladder