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A N S NERVOUS SYSTEM

PNS CNS EFFERENT AFFERENT

ANS SOMATIC ENTERIC PARASYMPATHETIC SYMPATHETIC

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Efferent neurons of ANS brain stem or spinal cord preganglionic neuron ganglionic transmitter

Post ganglionic neuron neuroeffector transmitter effector organ

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ANSANS

–   –   Controls involuntary body Controls involuntary body functionsfunctions

BPBP

DigestionDigestion

EliminationElimination

Some voluntary controlSome voluntary control

ThermoregulationThermoregulation

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ANS AnatomyANS Anatomy

Sympathetic & ParasympatheticSympathetic & Parasympathetic

–   –   Sympathetic (Thoracolumbar)Sympathetic (Thoracolumbar)

Neurons in thoracic and upper lumbar Neurons in thoracic and upper lumbar spinespine

–   –   Parasympathetic (Craniosacral)Parasympathetic (Craniosacral)

»   Neurons in midbrain, brainstem, »   Neurons in midbrain, brainstem, sacral region of spinesacral region of spine

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Efferent neuron—from cns to effector organs Afferent—neurons—important for reflex

regulation of the system Sympathetic neurons—originate in the cns and

emerge from two different spinal cord regions==thoracic and lumbar regions of the spinal cord

Parasympathetic neurons—preganglionic fibers arise from cranium and sacral areas of spinal cord

Enteric neurons—collection of nerve fibers which innervate the gi tract, pancreas and gall bladder.

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Functional Aspects of SNS & PNS

»   »   SNSSNS_ _ fight or Flightfight or Flight –   –   Increased cardiac outputIncreased cardiac output

–   –   Decreased visceral blood flowDecreased visceral blood flow

-- Increased cellular metabolism

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»   PNS»   PNS

  REST AND DIGESTREST AND DIGEST

_  Conserves energy_  Conserves energy

–   –   Slows heart rateSlows heart rate

–   –   Increased digestionIncreased digestion

_Increased absorption

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PARASYMPATHETIC RESPONSES

slows heart rate lowers blood pressure increases gastrointestinal motility empties the bowel and bladder promotes absorption of nutrients

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NERVE TERMINAL

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Cholinergic transmission: acetylcholine is the neurotransmitter primary means of terminating action is break down of

acetylcholine into acetate & choline by acetylcholine esterase (AchE), found principally in neurons & neuromuscular junctions

cholinergic receptors are present in the parasympathetic nervous system, brain, ganglia of the sympathetic nervous system, and skeletal muscle

two main types of receptors present – muscarinic (principally autonomic nervous system) – nicotinic (principally skeletal muscle)

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Adrenergic transmission: catecholamines (dopamine, norepinephrine,

epinephrine) are the neurotransmitters primary means of terminating action is by neural

membrane reuptake of the transmitter, although metabolism by catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) is important in some tissues.

adrenergic receptors – alpha-1: principally found in peripheral vascular

smooth muscle – alpha-2:

• occur both presynaptically & postsynaptically

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beta-1: located in the myocardium, SA node, ventricular conduction system, and adipose tissue

beta-2: vascular smooth muscle of the skin, muscles, mesentery & bronchial tree; stimulation results in vasodilation and bronchodilation

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Function of the Adrenal Medulla –   –   Synthesizes and secretes Epi & NESynthesizes and secretes Epi & NESympathetic controlSympathetic control»   Fight or flight: pumps out Epi & NE to fight»   Fight or flight: pumps out Epi & NE to fight

»   »   EpinephrineEpinephrine: Adrenaline: Adrenaline

–   –   Increases cardiac function & cellular Increases cardiac function & cellular metabolism more effectively than NEmetabolism more effectively than NE–   –   Higher affinity for beta receptorsHigher affinity for beta receptors

»   »   Norepinephrine (NE): Norepinephrine (NE): NoradrenalineNoradrenaline

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Autonomic ReceptorsAutonomic Receptors

      2 main types2 main types

–   –   Cholinergic:Cholinergic:»   ACH synapses»   ACH synapses

–   –   Adrenergic:Adrenergic:»   NE synapses»   NE synapses

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      Cholinergic receptorsCholinergic receptors

–   –   2 main categories2 main categories

»»      Nicotinic:Nicotinic:      Junction btwn preganglionic & Junction btwn preganglionic & postganglionic neurons in PNS & SNSpostganglionic neurons in PNS & SNS

–   –   Any drug that affects nicotinic receptors Any drug that affects nicotinic receptors affects both PNS & SNSaffects both PNS & SNS

      2 types of Nicotinic receptors:2 types of Nicotinic receptors:

–   –   Type I (NType I (NNN): ANS): ANS

–   –   Type II (NType II (NMM): skeletal NMJ): skeletal NMJ

»   »   MuscarinicMuscarinic

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  –     –   MuscarinicMuscarinic

»   All synapses btwn cholinergic »   All synapses btwn cholinergic postganglionic neurons & terminal postganglionic neurons & terminal effector cellseffector cells

      PNS & SNSPNS & SNS

–    –    55 subclasses: M subclasses: M11, M, M

22 to M5 to M5

»   Muscarinic receptors mediate »   Muscarinic receptors mediate effect on tissueeffect on tissue

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Adrenergic Receptor Sub classifications

      2 Main Classes2 Main Classes

–   –   Alpha (Alpha ())

»   »   -1-1

»   »   -2-2

–   –   Beta (Beta ())

»   »   -1-1

»   »   -2-2

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RESPONSES ASSOCIATED WITH TYPES OF ADRENOCEPTORS

Alpha1 arterial and arteriolar constriction

(cutaneous, visceral, skeletal & pulmonary) venous constriction uterine contraction pupillary dilation ( mydriasis ) (contraction of radial smooth muscle of iris) contraction of ureter contraction of spleen contraction of pilomotor muscles

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Alpha 2

inhibition of NE release inhibition of ganglionic

transmission vasoconstriction

(quantitatively less important than α1)

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Beta 1

cardiac stimulation (chronotropic, inotropic,

dromotropic) stimulation of lipolysis stimulation of renin secretion

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Beta 2 arteriolar dilation (skeletal muscle, coronary visceral beds) intestinal relaxation bronchiolar relaxation uterine relaxation bladder body relaxation Decrease of insulin release skeletal muscle tremor stimulation of glycogenolysis

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chief therapeutic uses

vascular smooth muscle contraction………………………. α1

inhibition of transmitter release……………………………… α2

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chief therapeutic uses

cardiac stimulation…………………………… β1

vascular smooth muscle relaxation…………………………. Β2

bronchiolar smooth muscle relaxation………………………. Β2