Nerv 3

• Peripheral Nervous System (PNS)


  The nerve connecting the brain and spinal cord to other part of the body
• Components of PNS


  • Cranial nerves
  • Spinal nerves
• Cranial nerves


  • Twelve pairs
  • Attached to undersurface of the brain
  • Connect brain with the neck and structures in the thorax and abdomen
• Spinal nerves


  • Thirty-one pairs
  • Contain dendrites of sensory neurons and axons of motor neurons
  • Conduct impulses necessary for sensations and voluntary movements
• Dermatome


  Skin surface area supplied by a single cranial or spinal nerve
• Divisions of Autonomic Nervous System

  • Sympathetic division
  • Parasympathetic division
  • Enteric nervous system
• Sympathetic division


  • Serves as the emergency or stress system
  • Controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are triggered
• Fight-or-flight response


  Group of changes induced by sympathetic control
• Sympathetic nervous system structure

  • Dendrites and cell bodies of sympathetic preganglionic neurons are located in the gray matter of the thoracic and upper lumbar segments of the spinal cord
  • The adrenal medulla is a modified part of the sympathetic nervous system
• Adrenal medulla


  A modified sympathetic prevertebral ganglion that releases epinephrine and norepinephrine into the blood (about 4:1) in response to sympathetic stimulation
• Parasympathetic division


  • Dominates control of many visceral effectors under normal, everyday conditions
  • Counterbalances sympathetic function
• Parasympathetic division structure

  • Preganglionic neurons have dendrites and cell bodies in the gray matter of the brainstem and the sacral segments of the spinal cord
• Sympathetic and parasympathetic nervous systems

  Dually innervate most visceral organs
• Dual innervation


  Innervation of a single organ by both branches of the autonomic nervous system
• Times of sympathetic dominance

  Fight-or-flight response (adrenergic)
• Times of parasympathetic dominance

  Rest-and-digest response (The body performs activities like digesting, detoxifying, eliminating, and building immunity.)
• Many regions of the CNS are involved in the control of autonomic activities
• Some autonomic reflexes are integrated at the spinal-cord level
• Medulla within the brain stem is the region most directly responsible for autonomic output
• Hypothalamus plays a role in integrating autonomic, somatic, and endocrine responses
• Autonomic Nervous System as a Whole

  • Regulates the body's automatic functions in ways that maintain or quickly restore homeostasis
  • Many visceral effectors are doubly innervated (i.e., they receive fibers from parasympathetic and sympathetic divisions and are influenced in opposite ways by the two divisions)