ANS

• Nervous system components


  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)
  • Autonomic nervous system (ANS)
  • Somatic nervous system

  
• Autonomic nervous system (ANS)


  • Critical for survival
  • Regulates homeostasis and reproduction
• Homeostasis


  The maintenance of an optimal internal environment, including body temperature and chemical composition of tissues and fluids
• Control of internal body processes

  • Blood pressure
  • Heart and respiratory rates
  • Body temperature
  • Digestion
  • Metabolism
  • Balance of water and electrolytes
  • Production of body fluids
  • Urination
  • Defecation
  • Sexual response
• Mechanoreceptors


  Response to pressure and to stretch
• Nociceptors


  Responsive to stretch and ischemia
• Chemoreceptors


  Sensitive to chemical concentrations in the blood
• Thermoreceptors


  Respond to changes in temperature
• Afferent pathways


  1. Information enters CNS via dorsal roots

  2. Information enters CNS via cranial nerves

  
• Efferent pathways


  1. Autonomic efferent neurons classified as sympathetic and parasympathetic

  2. Two-neuron pathway from CNS to effectors

  
• Preganglionic neuron


  The neuron extending from the CNS to the ganglion

  
• Postganglionic neuron


  The neuron connecting the ganglion with the effector organ
• Somatic motor system vs autonomic efferent system

  • Autonomic functions are typically nonconscious
  • Many internal organs function independently of CNS input
• Heart can continue to beat without neural connections
• Gastrointestinal tract can operate independently
• Neurotransmitters


  • Acetylcholine
  • Norepinephrine
  • Epinephrine
• Cholinergic neurons


  Neurons that secrete acetylcholine
• Adrenergic neurons


  Neurons that secrete norepinephrine or epinephrine
• Cholinergic receptors


  • Muscarinic
  • Nicotinic
• Adrenergic receptors


  • Most sympathetic postganglionic neurons release norepinephrine
  • Adrenal medulla releases epinephrine and norepinephrine

  
• Sympathetic and parasympathetic nervous system

  • Work independently
  • Perform opposite roles
  • Release different neurotransmitters
  • Different lengths of pre and postganglionic nerve fibers

  
• Sympathetic nervous system


  Flight, fight, freeze response
• Parasympathetic nervous system


  Rest and digest response

  
• Sympathetic nervous system


  • Cell bodies in lateral horn of spinal cord
  • Thoracolumbar outflow
  • Short preganglionic neurons
  • Long postganglionic neurons

  
• Functions of the sympathetic nervous system

  • Maintain optimal blood supply in organs
  • Regulation of body temperature
  • Regulation of blood flow in skeletal muscles
  • Metabolism
• Increasing sympathetic activity


  Constriction of vessels
• Decreasing sympathetic activity


  Allows vasodilation
• Fear response


  • Prepares for fight or flight
  • Increases blood flow to active muscles
  • Increases blood glucose levels
  • Dilation of bronchi and coronary vessels
• Parasympathetic nervous system


  • Uses a two-neuron pathway
  • Preganglionic cell bodies in brainstem nuclei and sacral spinal cord
  • Craniosacral outflow

  
• Functions of the PNS

  • Energy conservation and storage
  • Vagus nerve innervates heart, lungs, and digestive system
• Comparison of sympathetic and parasympathetic effects

  • Synergistic actions on thoracic and abdominal viscera
  • Opposing actions balance for optimal organ function

  
• Effector cells = muscle or gland
• Acetylcholine


  Neurotransmitter for both pre and postganglionic neurons

  
• The principal function of the PNS is energy conservation and storage
• Vagus nerve efferent fibers


  Innervate the heart, smooth muscle of lungs, and digestive system
• Vagus nerve activity to the heart

  Can cause bradycardia or decreased cardiac contraction force
• Respiratory system stimulation


  Causes bronchoconstriction and increased mucus secretion
• Vagus activity in the digestive system

  Increases peristalsis, glycogen synthesis, and glandular secretions
• Sympathetic and parasympathetic effects on organ function

  • Activities on thoracic and abdominal viscera, bladder, bowels, and pupil are synergistic
  • Opposing actions are balanced for optimal organ function

  
• Before exercise


  Sympathetic signals increase heart rate and contractility, while parasympathetic signals that would slow heart rate decrease