ANS: Sympathetic Division

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ANS Sympathetic Division
Figure 163
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Structure of the Sympathetic Division

• Cell bodies of preganglionic neurons in lateral
  gray horns
• between thoracic and superior lumbar segments of
  spinal cord
• Axons enter ventral roots of segments
• Ganglionic neurons near vertebral column
• Short pre-ganglionic fibers

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Ganglionic Neurons

• Occur in 3 locations
• sympathetic chain ganglia
• collateral ganglia
• adrenal medullae
• Long post-ganglionic fibers to reach effectors
• Exception adrenal medullae

Figure 164
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Sympathetic Chain Ganglia

• Paired ganglia on both sides of vertebral column
• Control effectors
• in body wall
• Inside thoracic cavity
• in head
• in limbs

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Collateral Ganglia

• Are anterior to vertebral sections
• Innervate tissues and organs in abdominopelvic
  cavity

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The Adrenal Medullae

• At the center of each adrenal gland in area known
  as adrenal medulla
• Very short axons
• When stimulated, release neurotransmitters into
  bloodstream (not at synapse)
• Functions as hormones affect target cells
  throughout body

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Organization of Sympathetic Chain

• Ventral roots of spinal segments contain
  preganglionic fibers
• Give rise to myelinated white ramus
• Carry myelinated preganglionic fibers into
  sympathetic chain ganglion
• Synapse at collateral ganglia or adrenal medullae

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Postganglionic Fibers

• Postganglionic fibers control visceral effectors
  in body wall, head, neck, or limbs
• enter gray ramus and return to spinal nerve for
  distribution
• Innervate effectors like sweat glands of skin and
  smooth muscles in superficial blood vessels

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• Postganglionic fibers innervating structures in
  the thoracic cavity, such as the heart and lungs
  form bundles called sympathetic nerves

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• Abdominopelvic Viscera
• Receive sympathetic innervation via sympathetic
  preganglionic fibers
• Synapse in separate collateral ganglia

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• Preganglionic fibers extend through chain
  ganglion
• Do not synapse in chain ganglion
• Form splanchnic nerves that synapse with
  collateral ganglia
• Innervate variety of visceral organs in
  abdominopelvic cavity
• Reduction of blood flow and energy
• Release of stored energy reserves

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• 3 Collateral Ganglion
• Celiac Ganglion
• Postganglionic fibers innervate stomach, liver,
  gallbladder, pancreas, and spleen
• Superior Mesenteric Ganglion
• Postganglionic fibers innervate small intestine
  and superior large intestine
• Inferior Mesenteric Ganglion
• Postganglionic fibers innervate inferior large
  intestine, kidney, urinary bladder, and sex organs

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Adrenal Medulla

• Preganglionic fibers pass through chain and
  collateral ganglia to enter adrenal gland
• proceed to center adrenal medulla which is a
  modified sympathetic ganglion
• Preganglionic fibers synapse on neuroendocrine
  cells which are specialized neurons that secrete
  hormones into bloodstream
• epinephrine (E) and norepinephrine (NE)

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Sympathetic Innervation
Figure 165
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What activities of the CNS are altered by
sympathetic activation?
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• Increased alertness
• Feeling of euphoria
• Increased activity in cardiovascular and
  respirator centers in brain stem
• General elevation in muscle tone
• Release of energy reserves

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What neurotransmitters are released in the
sympathetic division?
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• Preganglionic neurons release ACh at synapses
  with ganglionic neurons
• cholinergic
• Most postganglionic neurons secrete epinephrine
  (E) and norepinephrine (NE)
• adrenergic
• Some postganglionic neurons release ACh

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• Some postganglionic release nitric oxide (NO)
• Nitroxidergic
• vasodilation and increased blood flow
• Response of effectors to neurotransmitter depends
  on membrane receptors
• Alpha or Beta receptors
• Both G-proteins activated by second messenger
  systems

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What are the structures and functions of the
parasympathetic division of the autonomic nervous
system?
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ANS The Parasympathetic Division
Figure 167
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Autonomic Nuclei

• Pre-ganglionic neurons in brainstem and lateral
  gray horns of sacral spinal segments
• Long preganglionic fiber synapses on ganglionic
  neurons near target organ (terminal) or embedded
  in tissues of target organ (intramural)
• Postganglionic fibers are short to reach effectors

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• Preganglionic fibers leaving brainstem as
  components of cranial nerves
• Innervate visceral structures in head
• Synapse in ciliary, pterygopalatine,
  submandibular, and otic ganglia

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• Vagus Nerve innervates structures in
• neck
• thoracic and abdominopelvic cavity
• distal portion of large intestine
• Provides 75 of all parasympathetic outflow
• Branches intermingle with fibers of sympathetic
  division
• Form autonomic plexus

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• Preganglionic fibers leaving spinal cord as
  components of pelvic nerves
• Innervate
• kidneys
• urinary bladder
• lower portions of large intestine
• sex organs

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Parasympathetic Innervation
Figure 168
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What are the effects of parasympathetic
neurotransmitters on target organs and tissues?
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Effects of Parasympathetic Activation

• Constriction of pupils
• restricts light entering eyes
• Secretion by digestive glands
• exocrine and endocrine
• Secretion of hormones
• Changes in blood flow and glandular activity
• associated with sexual arousal

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• 5. Increases smooth muscle activity
• along digestive tract
• 6. Defecation
• stimulation and coordination
• Contraction of urinary bladder
• during urination
• Constriction of respiratory passageways

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• Reduction in heart rate
• and force of contraction
• Sexual arousal
• stimulation of sexual glands

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• Parasympathetic neurons all release ACh as
  neurotransmitter
• Effects vary widely due to variations in
  receptors
• Nicotinic
• Also seen in sympathetic and somatic divisions
• Directly bind to and open gated channels
• Muscarinic
• Also seen in sympathetic division
• G proteins

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Comparing Divisions

• Sympathetic
• widespread impact
• reaches organs and tissues throughout body
• Pre-ganglionic release Ach
• Post-ganglionic varies
• Parasympathetic
• innervates only specific visceral structures
• all release ACh