Chapter 15 (1)

• Autonomic


  Self-governed; the autonomic nervous system (ANS) is independent of our will
• Autonomic nervous system (ANS)


  • Regulates fundamental states and life processes such as heart rate, BP, and body temperature
• Visceral motor system


  Another name for the autonomic nervous system
• Primary organs of the ANS

  • Viscera of thoracic and abdominal cavities
  • Some structures of the body wall
  • Cutaneous blood vessels
  • Sweat glands
  • Piloerector muscles

  
• Visceral effectors


  Do not depend on the ANS to function; only to adjust their activity to the body's changing needs
• Denervation hypersensitivity


  Exaggerated responses of cardiac and smooth muscle if autonomic nerves are severed
• Visceral reflexes


  Unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors
• Components of a visceral reflex arc

  • Receptors
  • Afferent neurons
  • Integrating center
  • Efferent neurons
  • Effectors
• Baroreflex


  1. High blood pressure detected by arterial stretch receptors

  2. Afferent neuron carries signal to CNS

  3. Efferent signals on vagus nerve of ANS travel to the heart

  4. Heart then slows, reducing blood pressure
• Baroreflex


  Example of a homeostatic negative feedback loop
• Sympathetic division


  Prepares body for physical activity: exercise, trauma, arousal, competition, anger, or fear
• Sympathetic division


  • Increases heart rate, BP, airflow, blood glucose levels, etc.
  • Reduces blood flow to the skin and digestive tract
  • "Fight-or-flight"
• Parasympathetic division


  Calms many body functions reducing energy expenditure and assists in bodily maintenance
• Parasympathetic division


  • Digestion and waste elimination
  • "Resting and digesting" state
• Autonomic tone


  Normal background rate of activity that represents the balance of the two systems according to the body's needs
• Types of autonomic tone

  • Parasympathetic tone
  • Sympathetic tone
• Parasympathetic tone maintains smooth muscle tone in intestines and holds resting heart rate down to about 70 to 80 beats per minute
• Sympathetic tone keeps most blood vessels partially constricted and maintains blood pressure
• Sympathetic division excites the heart but inhibits digestive and urinary function, while parasympathetic has the opposite effect
• ANS


  • Has components in both the central and peripheral nervous systems
  • Control nuclei in the hypothalamus and other brainstem regions
  • Motor neurons in the spinal cord and peripheral ganglia
  • Nerve fibers that travel through the cranial and spinal nerves

  
• Somatic motor pathway


  A motor neuron from brainstem or spinal cord issues a myelinated axon that reaches all the way to skeletal muscle
• Autonomic pathway


  • Signal must travel across two neurons to get to the target organ
  • Must cross a synapse where these two neurons meet in an autonomic ganglion
  • Presynaptic neuron: the first neuron has a soma in the brainstem or spinal cord
  • Synapses with a postganglionic neuron whose axon extends the rest of the way to the target cell
• Differences between somatic and autonomic efferent innervation

  • Somatic effectors (skeletal muscles)
  • Visceral effectors (cardiac muscle, smooth muscle, glands)

  
• ANS has two neurons from CNS to effector: presynaptic neuron cell body is in CNS, postsynaptic neuron cell body is in peripheral ganglion
• Sympathetic division


  Also called the thoracolumbar division because it arises from the thoracic and lumbar regions of the spinal cord
• Sympathetic division


  • Relatively short preganglionic and long postganglionic fibers
  • Preganglionic neurosomas in lateral horns and nearby regions of spinal cord gray matter
  • Fibers exit spinal cord by way of spinal nerves T1 to L2
  • Lead to nearby sympathetic chain of ganglia (paravertebral ganglia)
• Sympathetic chain ganglia

  • 3 cervical
  • 11 thoracic
  • 4 lumbar
  • 4 sacral
  • 1 coccygeal ganglion
• Sympathetic nerve fibers


  Distributed to every level of the body
• Communicating rami


  • Two branches that connect each paravertebral ganglion to a spinal nerve
  • Preganglionic fibers travel from spinal nerve to the ganglion by way of the white communicating ramus (myelinated)
  • Postganglionic fibers leave the ganglion by way of the gray communicating ramus (unmyelinated)
• Sympathetic preganglionic fibers


  1. May follow any of three courses after entering the sympathetic chain

  2. Some end in ganglia which they enter and synapse immediately with a postganglionic neuron

  3. Some travel up or down the chain and synapse in ganglia at other levels

  4. Some pass through the chain without synapsing and continue as splanchnic nerves
• Routes of sympathetic nerve fibers

  • Spinal nerve route
  • Sympathetic nerve route
  • Splanchnic nerve route
• Autonomic


  Self-governed; the autonomic nervous system (ANS) is independent of our will
• Autonomic nervous system (ANS)


  • A motor nervous system that controls glands, cardiac muscle, and smooth muscle
  • Also called visceral motor system
  • Primary organs of the ANS are the viscera of thoracic and abdominal cavities, some structures of the body wall, cutaneous blood vessels, sweat glands, and piloerector muscles

  
• Visceral reflexes


  Unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors
• Visceral reflex arc


  1. Receptors: nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli

  2. Afferent neurons: lead to CNS

  3. Integrating center: interneurons in the CNS

  4. Efferent neurons: carry motor signals away from the CNS

  5. Effectors: carry out end response
• High blood pressure detected by arterial stretch receptors

  Afferent neuron carries signal to CNS, efferent signals on vagus nerve of ANS travel to the heart, heart then slows, reducing blood pressure
• Baroreflex


  Example of homeostatic negative feedback loop
• Divisions of the ANS


  • Sympathetic division
  • Parasympathetic division
• Sympathetic division


  • Prepares body for physical activity: exercise, trauma, arousal, competition, anger, or fear
  • Increases heart rate, BP, airflow, blood glucose levels, etc.
  • Reduces blood flow to the skin and digestive tract
  • "Fight-or-flight"
• Parasympathetic division


  • Calms many body functions reducing energy expenditure and assists in bodily maintenance
  • Digestion and waste elimination
  • "Resting and digesting" state