The basic anatomy and Physiology of Autonomic nervous system (Sympathetic and parasympathetic nervous system)

ANATOMY

• Sympathetic Division
• leave CNS at thoracic or lumbar levels (“thoracolumbar system”)
• preganglionic neurons are SHORT. Postganglionic neurons are long, traveling rest of the way to body organs, glands, & vessels.
• almost all release NE as their transmitter (except those to sweat glands)

• Parasympathetic Division
• leave CNS from the brain or from sacral cord (“craniosacral”).
• preganglionic neurons are LONG and go all the way out to body organs to reach ganglia.
• postganglionic neurons are short, going from those ganglia to nearby organ/gland cells.
• All release ACh.
• Parasympathetic nerves tend to operate individually, as needed.
• Parasympathetic ganglia are near to organs.

FUNCTIONS

 A. SYMPATHETIC DIVISION (Thoracolumber):

 Also called fight, fright and flight response

 

• Easy to remember and understand that when you are nervous, you sweat; when afraid, hair stand; when excited blood pressure rises (vasoconstriction):  these are sympathetic processes.
• Also causes: dry mouth, pupils to dilate, increased heart & respiratory rates to increase O2 to skeletal muscles, and liver to release glucose.

•          ･Acceleration of heart and lung action･Inhibition of stomach and intestinal action

•          ･Constriction of blood vessels in many parts of the body

•          ･Dilation of blood vessels for muscles

•          ･Inhibition of tear glands and salivation

•          ･Dilation of pupil

•          ･Relaxation of bladder

•          ･Inhibition of erection

B. PARASYMPATHETIC DIVISION (Craniosacral):

Also called Rest and digest response

• Cranial outflow
• III ( Oculomotor) - pupils constrict
• VII (Facial)  - increasing tears, nasal mucus, saliva
• IX (Glossopharyngeal) – parotid salivary gland
• X (Vagus) – visceral organs of thorax & abdomen:
• Stimulates digestive glands
• Increases motility of smooth muscle of digestive tract
• Decreases heart rate
• Causes bronchial constriction
• Sacral outflow (S2-4):
• Supply 2^nd half of large intestine (stimulation of intestinal secretion)
• Supply all the pelvic (genitourinary) organs:

e.g. erection ( due to vasodilatation), contraction of bladder.

Summary of the Major Types of Autonomic Receptors & Drugs:

Branch	Type	Location	Typical Agonist Drugs	Typical Antagonist Drugs
Sympathetic (adrenergic)	Alpha 1	Most vascular arterioles, Eye Sphincters of bladder & GI tract	Norepinephrine Epinephrine	Phenoxybenzamine Phentolamine Prazosin
	Alpha 2	GI tract, presynaptic sympathetic neurons, pancreas	Clonidine Epinephrine	Yohimbine
	Beta 1	Heart muscle Salivary glands Fat cells	Norepinephrine Isoproteronol Dobutamine Epinephrine	"Beta blockers" Propranolol Metoprolol
	Beta 2	Bronchioles of lung Arterioles of skeletal muscles, brain and lungs Bladder wall GI tract	Epinephrine Isoproteronol Albuterol	"Beta blockers" Propranolol Butoxamine
Parasympathetic (cholinergic)	Muscarinic (M)	Heart muscle Sphincters of bladder & GI tract Bronchioles of lung Sweat glands Iris constrictor	Acetylcholine Muscarine Carbachol	Atropine Scopolamine
	Nicotinic (N)	Neuromuscular junctions Autonomic ganglia	Acetylcholine Nicotine Carbachol	Curare