PART 3

• Peripheral Nervous System (PNS)


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

  
• Components of the 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 the Autonomic Nervous System (ANS)

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

  
• Autonomic Nervous System (ANS)

  Involuntary branch of the peripheral efferent division

  
• Somatic Nervous System

  Branch of the efferent division subject to voluntary control

  
• Autonomic nerve pathway

  1. Preganglionic neuron: synapses with the cell body of the postganglionic fiber in a ganglion outside the CNS

  2. Postganglionic neuron: sends axons that end on the effector organ
• 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.)
• Sympathetic nervous system

  • Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are triggered
  • Group of changes induced by sympathetic control is called the fight-or-flight response
• Structure of Sympathetic nervous system

  • 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

  
• Adrenal medulla

  • Modified part of the sympathetic nervous system
  • Adrenal glands are endocrine glands
  • Adrenal medulla secretes catecholamine hormones on stimulation
• Structure of Parasympathetic division

  • Parasympathetic preganglionic neurons have dendrites and cell bodies in the gray matter of the brainstem and the sacral segments of the spinal cord

  
• Functions of Parasympathetic division

  • Dominates control of many visceral effectors under normal, everyday conditions
  • Counterbalances sympathetic function
• Divisions of the autonomic nervous system are usually reciprocally controlled

  
• Regions of the CNS involved in 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)