?But this opposition is better termed
complementary in nature rather than antagonistic.
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?Sympathetic as accelerator and parasympathetic as
brake.
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?Sympathetic quick responses.?Parasympathetic functions with actions that do not
require immediate reaction.
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?Sympathetic "fight or flight"
?Parasympathetic "rest and digest".
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Autonomic Nervous System
? 2 divisions:
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? Sympathetic?"Fight or flight"
?"E" division
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? Exercise, Excitement,
Emergency &
Embarrassment
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? Parasympathetic
?"Rest and digest"
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?"D" division? Digestion, Defecation, &
Diuresis
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Functions
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?Sympathetic & parasympathetic divisions typicallyfunction in opposition to each other.
?But this opposition is better termed
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complementary in nature rather than antagonistic.
?Sympathetic as accelerator and parasympathetic as
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brake.?Sympathetic quick responses.
?Parasympathetic functions with actions that do not
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require immediate reaction.
?Sympathetic "fight or flight"
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?Parasympathetic "rest and digest".Receptors
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?Parasympathetic nervous system uses only acetylcholine(ACh) as its neurotransmitter.
?ACh acts on two types of receptors, muscarinic and
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nicotinic cholinergic receptors.
?Most transmissions occur in two stages:
?When stimulated, preganglionic nerve releases ACh at
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ganglion, which acts on nicotinic receptors of
postganglionic nerve.
?Postganglionic nerve then releases ACh to stimulate
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muscarinic receptors of target organ.
Neurotransmitters
?At effector organs, sympathetic ganglionic neurons release
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noradrenaline (norepinephrine) to act on adrenergic
receptors, with exception of sweat glands and adrenal
medulla:
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?At sweat glands, it is acetylcholine muscarinic receptors.?At adrenal cortex, there is no postsynapic neuron. Instead
presynaptic neuron releases acetylcholine to act on
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nicotinic receptors.?Stimulation of adrenal medulla releases adrenaline
(epinephrine) into bloodstream which acts on
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adrenoceptors, producing a widespread increase insympathetic activity.
?In parasympathetic system, ganglionic neurons use
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acetylcholine, to stimulate muscarinic receptors.Sympathetic (adrenergic, with exceptions)
? cardiac output increases
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? SA node: heart rate (chronotropic) 1, 2: increases
? cardiac muscle: contractility (inotropic )1, 2: increases
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? conduction at AV node 1: increases? vascular smooth muscle M3: contracts; = contracts & 2 =
relaxes
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? smooth muscles of bronchioles 2: relaxes (major
contribution); 1: contracts (minor contribution)
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? pupil of eye 1: relaxes? ciliary muscle 2: relaxes
? salivary glands: secretions: stimulates viscous, amylase
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secretions; 1 = stimulates potassium cation
? smooth muscles of GI tract - , 2: relaxes
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? sphincters of GI tract - 1: contracts? glands of GI tract - inhibits
Parasympathetic (muscarinic)
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? cardiac output M2: decreases? SA node: heart rate (chronotropic) M2: decreases
? cardiac muscle: contractility (inotropic) M2: decreases (atria
only)
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? conduction at AV node M2: decreases
? smooth muscles of bronchioles M3: contracts
? pupil of eye M3: contracts
? ciliary muscle M3: contracts
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? salivary glands: secretions stimulates watery secretions? GI tract motility M1, M3: increases
? smooth muscles of GI tract M3: contracts
? sphincters of GI tract M3: relaxes
? glands of GI tract M3: secretes
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Autonomic regulation & stress
?A stressful situation activates three major communication
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systems in brain that regulate bodily functions.?First of these systems is voluntary nervous system, which
sends messages to muscles so that we may respond to
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sensory information.?Second communication system is autonomic nervous
system. It combines sympathetic or emergency branch,
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which gets us going in emergencies, and parasympatheticor calming branch, which keeps body's maintenance
systems, such as digestion, in order and calms body's
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responses to the emergency branch.?Third major communication process is neuroendocrine
system, which also maintains body's internal functioning.
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Specific task
?Emergency branch causes arteries to muscles to relax in
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order to deliver more blood, allowing greater capacity to
act and At same time,reduces blood flow to skin,
kidneys, and digestive tract.
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?In contrast, calming branch helps to regulate bodilyfunctions and soothe body once stressor has passed,
preventing body from remaining too long in a state of
mobilization.
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?Left mobilized and unchecked, these body functions
could lead to disease. Some actions of calming branch
appear to reduce harmful effects of emergency branch's
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response to stress.
?Various "stress hormones" travel through blood and
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stimulate release of other hormones, which affect bodilyprocesses such as metabolic rate and sexual functions.
Stress reaction
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? When stress occurs,sympathetic nervous
system is triggered.
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? Norepinephrine is released
by nerves, and epinephrine
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is secreted by adrenalglands. By activating
receptors in blood vessels
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and other structures, these
substances ready heart and
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working muscles for action.? Acetylcholine is released in
parasympathetic nervous
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system, producing calming
effects.
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? Digestive tract isstimulated to digest a meal,
heart rate slows, and pupils
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of eyes become smaller.
? Neuroendocrine system
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also maintains the body'snormal internal
functioning.
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Chronic stress
?When glucocorticoids or adrenaline are secreted in
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response to prolonged psychological stress commonly
encountered by humans, results are not ideal.
?Normally, bodily systems gear up under stress and release
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hormones to improve memory, increase immune
function, enhance muscular activity and restore
homeostasis.
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?If you are not fighting or fleeing, but standing frustratedin a supermarket checkout line or sitting in a traffc jam,
you are not engaging in muscular exercise.
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?When stimulated chronically, there are consequences:?Memory is impaired,
?Immune function is suppressed, and
?Energy is stored as fat.
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Response to stress