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Autonomic Nervous System
Chapter 14
Human Nervous System Divisions
Nervous System
Info in & out
Integration & Command
Peripheral
Nervous
System (PNS)
Central Nervous
System (CNS)
Brain
Spinal Cord
Motor (efferent)
Autonomic
(involuntary)
Sympathetic
(Fight or flight)adrenergic
Sensory (afferent)
Somatic
(voluntary)
Parasympathetic
(Rest and digest)cholinergic
Comparing Somatic and Autonomic
• Effectors
– Innervates skeletal muscle
– Innervates visceral organs and glands
• Efferent pathways
– Single axon = faster signal
– Two axons = slower signal
• Target organ responses
– Cholinergic (ACh) synapses  exite
– Cholinergic, epinephrine, or norepinephrine synapses
 excite or inhibit
Autonomic Nervous System
• Stabilize internal environments
• Adjustments from changes to sensory stimuli
• Dual innervation
– 2 divisions counter the effects of each other
• Parasympathetic
– Nonstressful situations (rest and digest)
• Sympathetic
– Emergency or threatening situations (fight or flight)
– Rare in actuality
• Antagonistic relationship with continuous adjustments by both
• Anatomical characterizations
– Origin: craniosacral or thoracolumbar regions
– Length of fibers: long preganglionic, short post- or
opposite
– Location of ganglia: in effectors or close to spinal cord
Parasympathetic Roles
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D division (digest, defecate, diuresis)
Pupils constrict
Stimulates salivary, lacrimal, and pancreas glands
Decrease heart rate
Causes contraction and emptying of hollow
organs:
– Bladder, gallbladder, stomach, intestines (peristalsis)
• Vasodilation of penis (erection)
• No effect on blood vessels
Sympathetic Roles
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E division (exercise, excitement, emergency, embarrassment)
Dilates pupils
Inhibits secretion of glands
Stimulates sweating
Stimulates arrector pili
Stimulates medulla of adrenal gland to secrete epi- and
norepinephrine
Increases heart rate
Decreases digestive processes
Decreases urine output
Causes ejaculation
Stimulates glycogenolysis in liver (glucose release)
Blood vessel constriction/dilation and blood coagulation
Bronchiole dilation
Craniosacral Division
• CN III (oculomotor)
– From midbrain  ciliary ganglia
• CN VII (facial)
– From pons  pterygopalatine and
submandibular ganglia
• CN IX (glossopharyngeal)
– From medulla  otic ganglia
• CN X (90%) (vagus)
– From medulla  cardiac, pulmonary, and
celiac plexuses
• S2 – S4
– Lateral gray spinal mater  pelvic splanchnic
nerves into the inferior hypogastric plexus
Thoracolumbar Division
• Pre- from gray matter in lateral
horns of T1 – L2 to sympathetic
trunk via rami communicates
• Synapse varies
– W/ a postganglionic neuron w/i
same ganglion (1)
– Ascend/descend w/i sympathetic
trunk to another ganglion (2)
– Pass through ganglion w/o synapsing
(collateral ganglia or adrenal
medulla)(3)
Trunk Ganglia
• Post- enter rami via rami
communicates
• Superior cervical ganglion
– Dilates pupils
– Inhibit nasal and salivary secretions
– Stimulates sweating, arrector pili
muscles, and vasodilation
• Middle cervical ganglion
– Heart and skin
• Inferior cervical ganglion
– Heart, aorta, bronchiole dilation, and
esophageal sphincter constriction
Collateral Ganglia
• Pre- form splanchnic nerves which synapse w/ collateral ganglia
• Post- from collateral ganglia to effectors
• Greater splanchnic nerve
– Celiac ganglia
• Stomach, adrenal medulla, liver,
kidney, and intestine
• Lesser splanchnic nerve
– Superior mesenteric (via celiac)
• Small intestine
• Lumbar splanchnic nerve
– Inferior mesenteric ganglion
• Large intestine
– Hypogastric ganglion
• Bladder, urethra, and genitalia
ANS Neurotransmitters
• Acetylcholine (cholinergic fibers)
– All pre- and all parasympathetic post– Nicotinic receptors (stimulatory)
• Skeletal muscle, all ganglionic neurons, and adrenal medulla
– Muscarinic receptors (stimulatory or inhibitory)
• All parasymapthetic targets and some sympathetic organs
• Norepinephrine (adrenergic fibers)
– Most sympathetic post– Alpha (generally stimulatory)
– Beta (generally inhibitory)
Select ANS Effecting Drugs
• Atropine
– Anticholinergic (blocks muscarinic receptors)
– Prevent salivation, dilate pupils, and dry up respiratory
secretions
• Neostigmine
– Anticholinesterase
– Treat myasthenia gravis by preventing ACh degradation
• Ephedrine
– Stimulates alpha adrenergic receptors
• Beta-blockers
– Inhibit beta receptors
– Reduce heart rate and arrhythmias w/o disrupting other
sympathetic effects