Autonomic Nervous System

• The autonomic nervous system is part of the peripheral nervous system and has two main divisions: the sympathetic nervous system and the parasympathetic nervous system
• Somatic nervous system


  Helps control voluntary skeletal muscles and sensations
• Autonomic nervous system


  Controls involuntary functions like heart rate, blood vessel diameter, and digestion
• Autonomic nervous system structure

  1. Preganglionic neuron (from central nervous system)

  2. Ganglion (collection of neuron cell bodies)

  3. Postganglionic neuron (to target organ)
• Divisions of the autonomic nervous system

  • Sympathetic (fight-or-flight)
  • Parasympathetic (rest-and-digest)
• Sympathetic nervous system


  • Preganglionic neurons originate in thoracic and lumbar regions of spinal cord
  • Prepares body for stressful/emergency situations
• Parasympathetic nervous system


  • Preganglionic neurons originate in brainstem and sacral region of spinal cord
  • Promotes resting, relaxing, and digesting functions
• Preganglionic neurons can synapse with multiple postganglionic neurons, allowing for more complex control
• Preganglionic neurons can also bypass the first ganglion and synapse with postganglionic neurons in other ganglia
• Prevertebral ganglia


  Located in front of the spinal column, anterior to the spinal column
• Sympathetic trunk ganglia


  Located on the sides, vertically on the sides of the spinal column
• Pathway of preganglionic neuron


  1. Can synapse with postganglionic neuron in first ganglion reached

  2. Can go up or down to higher or lower ganglion to communicate with different postganglionic cell

  3. Can go through ganglion and to somewhere else like adrenal glands
• Autonomic nervous system


  • Part of the peripheral nervous system
  • Involves collections of nerves called plexuses
• Plexuses


  Collections of nerves
• Names of plexuses often indicate their location near arteries
• Autonomic nervous system is a two-neuron pathway
• Neurotransmitters released by autonomic neurons

  • Acetylcholine
  • Norepinephrine (also called noradrenaline)
• Neuron classifications based on neurotransmitter release

  • Cholinergic (acetylcholine)
  • Adrenergic (norepinephrine)
• Preganglionic neurons in sympathetic nervous system release acetylcholine
• Postganglionic neurons in sympathetic nervous system can release acetylcholine or norepinephrine
• Preganglionic and postganglionic neurons in parasympathetic nervous system release acetylcholine
• Differences between sympathetic and parasympathetic nervous systems

  • Neurons and neurotransmitters
  • Physiological effects
• Sympathetic nervous system


  Also called "fight-or-flight" system, prepares body for emergency situations
• Effects of sympathetic nervous system

  • Increases heart rate and contractility
  • Dilates pupils
  • Dilates airways
  • Inhibits digestion
• Parasympathetic nervous system


  Also called "rest and digest" system, promotes normal body functions
• Effects of parasympathetic nervous system

  • Decreases heart rate
  • Decreases respiratory rate
  • Stimulates digestion
  • Constricts pupils
• Sympathetic and parasympathetic nervous systems can work together, e.g. in male reproduction
• Autonomic nervous system functions as a reflex arc to maintain homeostasis