I. Introduction

A. Overview

• System of motor neurons innervating smooth and cardiac muscle and glands
• Autonomic nerves make adjustments to many changes identified by the sensory division of the PNS

B. Comparison of SNS (Somatic Nervous System) to ANS (Autonomic Nervous System) Diagram

• ANS differs from the SNS in:
  • Thier effectors
    • SNS innervates skeletal muscle and ANS innervates smooth and cardiac muscle and glands
  • Efferent pathways
    • SNS - cell bodies of the motor neuron are in the CNS, and their axons extend in spinal nerves all the way to skeletal muscles
    • ANS - two neuron chain
      • The cell body of the first neuron (preganglionic neuron) resides in the brain or spinal cord
      • Its axon (preganglionic axon) synapses with the second motor neuron (ganglionic neuron) in an autonomic ganglion outside the CNS
      • The axon of the ganglionic neuron (postganglionic axon) extends to the effector organ
  • Target organ responses - neurotransmitter effects
    • SNS - acetylcholine released at their synapse
    • ANS - norepinephrine, epinephrine and acetylcholine

C. Divisions of the ANS

• Parasympathetic and sympathetic
• Action via ANS is by dual innervation (divisions counterbalance each other's activities)
• Parasympathetic division in general is most active in nonstressful situations
• Sympathetic division in general is most active in emergency or threatening situations - "fight-or-flight"
• ANS divisions characterized by:
  • Origin
  • Length of fibers
  • Location of their ganglia

 II. Parasympathetic (Craniosacral Division) Diagram

• Cranial Outflow
  • Oculomotor nerve (III)
    • Preganglionic fibers from oculomotor nuclei in the midbrain synapses in the ciliary ganglion (in eye), postganglionic fiber innervates smooth muscle of eye
      •  Pupil constriction and lens movement to cause focusing
  • Facial nerve (VII)
    • Preganglionic fibers from lacrimal nuclei in the pons synapses in the pterygopalatine ganglia, postganglionic fiber innervates lacrimal glands of eye
      • Lubrication of eye and tear formation
    • Preganglonic fibers from superior salivatory nuclei in the pons synapses in the submandibular ganglia, postganglionic fibers innervate submandibular and sublingual salivary glands
      • Production of saliva and secretion of salivary enzymes
  • Glossopharyngeal nerve (IX)
    • Preganglionic fibers from the inferior salivary nuclei in the medulla synapses in the otic ganglia, postganglionic fibers innervate the parotid salivary gland
  • Vagus nerve (X)
    • Preganglionic fibers from the dorsal motor nuclei of the medulla synapses in terminal ganglia located within the walls of the target organ
      • Intramural ganglia ....effects:
        • Heart -decreases/steadies heart rate and constricts coronary veins
        • Lung - constricts bronchioles
        • Gall bladder - expel bile
        • Stomach - stimulates secretion of enzymes
        • Intestines - increase motility (peristalsis) and relaxes sphincters
• Sacral Outflow
  • Preganglionic fibers from lateral gray matter of spinal cord in segments S2-S4 synapse in terminal ganglia within walls of the target organ
    • Intramural ganglia....effects:
      • Distal large intestines - relaxes sphincters
      • Bladder - contraction of smooth muscle of bladder wall; relaxes urethral sphincter - promotes voiding
      • Genitalia - causes penile and clitoral erection

III. Sympathetic Diagram

• Thoracolumbar Outflow
  • All preganglionic fibers of sympathetic division arise from cell bodies of preganglionic neurons located in spinal cord segments T1-L2
  • Preganglionic sympathetic neurons in grey matter of spinal cord produces lateral horns
    • Sympathetic neurons leave spinal cord via the ventral root and passes through white ramus communicans (rami communicantes) to enter paravertebral ganglion (forms part of sympathetic trunk)
  • Once a preganglionic axon reaches a paravertebral ganglion it can......
    • Synapse with a post ganglionic neuron within the same ganglion
    • Ascend/descend within sympathetic trunk to synapse with another paravertebral ganglion
    • Pass through the ganglion and emerge from the sympathetic chain without synapsing
• Synapses in Paravertebral (sympathetic chain) Ganglion:
  • Postganglionic axons enter the ventral ramus of the joining spinal nerves via communicating branches called gray rami communicantes
  •  Preganglionic fiber serving head, neck, and thorax emerge from spinal cord segments T1-T6 and ascend the sympathetic chain to synapse with postganglionic neurons within cervical ganglia (inferior, middle, and superior)
    • Superior cervical ganglion:
      • Stimulates dilator muscles of irises
      • Inhibits nasal and salivary glands
      • Stimulates copious sweating
      • Stimulates arrector pili muscle to contract
      • Causes blood vessel vasodilation
      • Provides branches to carotid body (oxygen sensor) and larynx & pharynx
    • Middle cervical ganglia - innervates heart and skin
    • Inferior cervical ganglia (stellate ganglion) innervates heart, aorta, dilates bronchioles, constrict esophageal sphincter
• Synapses in Prevertebral (Collateral) Ganglion:
  • Preganglionic fibers of T5-L2 synapse in prevertebral ganglia. Fibers enter and leave without synapsing and form several nerves collectively called splanchnic nerves (greater, lesser, and lumbar)
  • Splanchnic nerves synapse at abdominal aortic plexus that clings to surface of abdominal aorta
  • Synapses occur at ganglia of plexus:
    • Greater splanchnic nerve
      • Celiac ganglion - innervates stomach (decrease muscle activity/constricts pyloric sphincter), adrenal medulla (secretes epinephrine/norepinephrine), liver (epinephrine stimulates liver to release glucose), kidney (vasoconstriction, decrease urine output), intestine (decrease smooth muscle activity)
    • Lesser splanchnic nerve
      • Superior mesenteric (via celiac) ganglion - innervates small intestine
    • Lumbar splanchnic nerve
      • Inferior mesenteric ganglion - innervates large intestine
    • Lumbar splanchnic nerve 
    • Hypogastric ganglion - innervates bladder and urethra (causes relaxation of smooth muscle of bladder wall and constricts urethral sphincter/inhibits voiding), genitalia (causes ejaculation in males and vaginal contractions in females)