Autonomic Nervous System

I. Comparison between somatic and autonomic nervous system

• A. Effectors differ• 1. somatic system• 2. ans• B. Number of neurons between CNS and effector• 1. somatic• 2. ans• C. Location of nerve cell bodies• 1. somatic• 2. ans• D. Ganglia present• 1. somatic• 2. ans

• E. Nature of response• 1. Somatic• 2. Ans• F. Presence of myelin• 1. somatic• 2. ans• G. Transmitter substance• 1. somatic is acetycholine• 2. ans: acetycholine from preganglionic fiber,

either acetycholine or norepinephrine from postganglionic fiber

Comparison between somatic and autonomic nervous systems

II. Structure of the ANS-Sympathetic Division

• A. Location of preganglionic nerve cell bodies

• B. Two ganglia in system

• 1. sympathetic chain or paravertebral ganglia

• 2. collateral ganglia• C. Relative length of

fibers

D. Outflow from CNS

• 1. Gray ramus communicans

• 2. sympathetic nerves to thoracic organs

• 3. splanchnic nerves• 4. special case of the

adrenal medulla

III. Structure of the parasympathetic division

• A. Location of the preganganglionic nerve cell bodies

• B. Craniosacral division• C. Lengths of fibers• D. Location of ganglia• E. Terminal or intramural

ganglia• F. Very little divergence in

the parasympathetic division when compared to the sympathetic

IV. Physiology of ANS

• A. Transmitter substances

• 1. All presynaptic fibers-acetycholine

• 2. postsynaptic fibers of para=acetycholine

• 3. postsynaptic of sym=most are adrenergic but a few are cholinergic to sweat glands

B. Receptor sites in the ANS

• 1. Cholinergic receptors• a. Bind acetycholine• b. Two categories-nicotinic and muscarinic• c. Nicotinic sites all postganglionic membranes and skeletal

muscle-possess an excitatory affect• d. Muscarinic sites- membranes of effectors responding to

acetycholine released from postganglionic fibers of ANS-response to binding of acetycholine to these receptors may be inhibitory or excitatory

• e. Effects relatively short-lived because it is destroyed by cholinesterase

2. Adrenergic receptor sites

• a. Located on membranes of effectors innervated by sympathetic division

• b. Respond to epinephrine or norepinephrine• c. May be excitatory or inhibitory depending on effector• d. These receptors can respond to ANS or to adrenalin

released from the adrenal medulla• e. Sympathetic stimulations tend to be more widespread• f. Sympathetic reactions tend to be longer lasting because

transmitter substance is not directly broken down but diffuses away

V. Generalizations about the ANS

• A. Many organs possess dual innervation• 1. two divisions will have opposing effects• 2. if one is stimulatory, other is inhibitory• 3. parasympathetic is rest and recovery• 4. sympathetic produces the effects of “fight or

flight”

B. Sympathetic division produces longer lasting and more widespread effects

• 1. The adrenergic receptor sites of the sympathetic division can respond to adrenal gland secretions

• 2. if adrenalin is circulating in the blood stream, disperses to many glands

• 3. one sympathetic preganglionic fiber synapses with multiple postganglionic fibers travelling to many different effectors

• 4. the transmitter substances of the sympathetic fibers degrades by diffusing from the receptor site

C. Blood vessel diameter is regulated solely by the sympathetic division of ANS

• 1. always basal level of sympathetic activity• 2. if greater sympathetic activity, generally vasoconstriction• 3. less sympathetic activity, vasodilation• 4. generalizations don’t always hold when considering blood

vessels• 5. during fight or flight• a. Blood vessels in skeletal muscle dilate• b. Blood vessels in digestive system constrict to limit flow