I. AUTONOMIC NERVOUS SYSTEM
A. General classification & function
PNS, visceral efferent to smooth muscle, cardiac muscle and glands
B. Preganglionic & postganglionic neurons
Preganglionic neuron begins at CNS to ganglion and is myelinated. Postganglionic neuron begins at ganglion to effector and is unmyelinated.
C. Sympathetic division{expends energy}
1. Preganglionic neurons T1-L2 [short]
2. Sympathetic chain ganglia or trunk
a. White & Gray ramus communicans
White ramus is the branching of the preganglionic neuron from the spinal nerve; Gray ramus is the branching of the postganglionic neuron to rejoin the spinal nerve
b. Directly to postganglionic neuron [long]
c. Up or Down sympathetic chain ganglia
d. Through chain ganglia to Collateral =Prevertebral Ganglia
1. Splanchnic nerves -pertaining to viscera
2. Celiac ganglion
3. Superior mesenteric ganglion
4. Inferior mesenteric ganglion
e. Adrenal medulla
Preganglionic neuron only
3. Divergence
D. Parasympathetic division{conserves energy}
1. Cell body location
2. Not to skin, blood vessels
3. Brain stem {3,7,9,10}
4. S2-S4, Pelvic splanchnic nerves
E. Comparisons of anatomy between SNS & PNS
Short preganglionic neurons SNS, long postganglionic neurons SNS; opposite in PNS. More localized effects in PNS due to anatomy.
F. Neurotransmitters
1. Acetylcholine – Cholinergic
a. Parasympathetic {pre/postganglionic fibers}
b. Preganglionic fiber – SNS
2. Norepinephrine – Adrenergic
a. Postganglionic fiber – SNS
3. Adrenal medulla
Releases norepinephrine and epinephrine to exaggerate the fight or flight response
4. Receptors
a. Acetylcholine
1. Muscarinic [blocked by atropine]
2. Nicotinic [blocked by curare in somatic system]
b. Norepinephrine/epinephrine
1. Alpha
-Alpha 1 are most common and have a stimulatory response [constricts muscles]
-Responds to norepinephrine & epinephrine
2. Beta 1
-Heart
Stimulatory effect
-Responds to norepinephrine & epinephrine
-Propranolol – B1 blocker
3. Beta 2
-Most common beta receptor
-Generally inhibitory
-Responds to only epinephrine
G. Functions
Heart – SNS increases rate and force of contraction, PNS decreases rate and force.
Airways – SNS dilates airways, PNS narrows airways
Digestive structures – SNS decreases secretions and peristalsis, PNS increases secretions and motility
Pupil – SNS dilates pupil, PNS constricts pupil
Sweat glands – SNS increases sweat secretion
Adrenal medulla – SNS causes release of epinephrine and norepinephrine from adrenal medulla
Urinary bladder – SNS causes wall to relax and sphincter to contract, PNS causes wall to contract and sphincter to relax
Cutaneous and abdominal blood vessels – SNS causes vasoconstriction
Skeletal muscle blood vessels – SNS causes vasodilation
H. Controls
Hypothalamus