Download MBBS Anatomy PPT 40 Autonomic Nervous System 1 Notes

Functions

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?Sympathetic & parasympathetic divisions typically

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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Diuresis


Functions

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?Sympathetic & parasympathetic divisions typically

function in opposition to each other.

?But this opposition is better termed

--- Content provided by FirstRanker.com ---

complementary in nature rather than antagonistic.

?Sympathetic as accelerator and parasympathetic as

--- Content provided by FirstRanker.com ---

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 release

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

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presynaptic neuron releases acetylcholine to act on
nicotinic receptors.

?Stimulation of adrenal medulla releases adrenaline

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(epinephrine) into bloodstream which acts on
adrenoceptors, 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, amylase

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

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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 (atria

only)

? 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, which

sends messages to muscles so that we may respond to
sensory information.

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?Second communication system is autonomic nervous

system. 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 neuroendocrine

system, 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 of
mobilization.

?Left mobilized and unchecked, these body functions

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could lead to disease. Some actions of calming branch
appear to reduce harmful effects of emergency branch's

response to stress.

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?Various "stress hormones" travel through blood and

stimulate 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 epinephrine

is 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 and

working 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 system

also 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