function 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".Autonomic Nervous System
? 2 divisions:
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? Sympathetic
?"Fight or flight"
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?"E" division? Exercise, Excitement,
Emergency &
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Embarrassment? Parasympathetic
?"Rest and digest"
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?"D" division
? Digestion, Defecation, &
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DiuresisFunctions
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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
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?At effector organs, sympathetic ganglionic neurons releasenoradrenaline (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
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presynaptic neuron releases acetylcholine to act onnicotinic receptors.
?Stimulation of adrenal medulla releases adrenaline
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(epinephrine) into bloodstream which acts onadrenoceptors, producing a widespread increase in
sympathetic activity.
?In parasympathetic system, ganglionic neurons use
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acetylcholine, to stimulate muscarinic receptors.
Sympathetic (adrenergic, with exceptions)
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? cardiac output increases? 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 =
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relaxes? 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
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? salivary glands: secretions: stimulates viscous, amylasesecretions; 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
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Parasympathetic (muscarinic)
? cardiac output M2: decreases
? SA node: heart rate (chronotropic) M2: decreases
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? cardiac muscle: contractility (inotropic) M2: decreases (atriaonly)
? conduction at AV node M2: decreases
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? smooth muscles of bronchioles M3: contracts? pupil of eye M3: contracts
? ciliary muscle M3: contracts
? salivary glands: secretions stimulates watery secretions
? GI tract motility M1, M3: increases
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? smooth muscles of GI tract M3: contracts? sphincters of GI tract M3: relaxes
? glands of GI tract M3: secretes
Autonomic regulation & stress
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?A stressful situation activates three major communication
systems in brain that regulate bodily functions.
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?First of these systems is voluntary nervous system, whichsends messages to muscles so that we may respond to
sensory information.
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?Second communication system is autonomic nervoussystem. It combines sympathetic or emergency branch,
which gets us going in emergencies, and parasympathetic
or calming branch, which keeps body's maintenance
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systems, such as digestion, in order and calms body's
responses to the emergency branch.
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?Third major communication process is neuroendocrinesystem, which also maintains body's internal functioning.
Specific task
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?Emergency branch causes arteries to muscles to relax in
order to deliver more blood, allowing greater capacity to
act and At same time,reduces blood flow to skin,
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kidneys, and digestive tract.?In contrast, calming branch helps to regulate bodily
functions and soothe body once stressor has passed,
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preventing body from remaining too long in a state ofmobilization.
?Left mobilized and unchecked, these body functions
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could lead to disease. Some actions of calming branchappear to reduce harmful effects of emergency branch's
response to stress.
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?Various "stress hormones" travel through blood andstimulate release of other hormones, which affect bodily
processes such as metabolic rate and sexual functions.
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Stress reaction? When stress occurs,
sympathetic nervous
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system is triggered.
? Norepinephrine is released
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by nerves, and epinephrineis secreted by adrenal
glands. By activating
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receptors in blood vessels
and other structures, these
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substances ready heart andworking muscles for action.
? Acetylcholine is released in
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parasympathetic nervous
system, producing calming
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effects.? Digestive tract is
stimulated to digest a meal,
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heart rate slows, and pupils
of eyes become smaller.
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? Neuroendocrine systemalso maintains the body's
normal internal
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functioning.
Chronic stress
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?When glucocorticoids or adrenaline are secreted in
response to prolonged psychological stress commonly
encountered by humans, results are not ideal.
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?Normally, bodily systems gear up under stress and release
hormones to improve memory, increase immune
function, enhance muscular activity and restore
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homeostasis.?If you are not fighting or fleeing, but standing frustrated
in a supermarket checkout line or sitting in a traffc jam,
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you are not engaging in muscular exercise.?When stimulated chronically, there are consequences:
?Memory is impaired,
?Immune function is suppressed, and
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?Energy is stored as fat.Response to stress