Download MBBS Anatomy PPT 40 Autonomic Nervous System 1 Notes

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Functions

?Sympathetic & parasympathetic divisions typically

function in opposition to each other.

?But this opposition is better termed

complementary in nature rather than antagonistic.

?Sympathetic as accelerator and parasympathetic as

brake.

?Sympathetic quick responses.

?Parasympathetic functions with actions that do not

require immediate reaction.

?Sympathetic "fight or flight"

?Parasympathetic "rest and digest".

Autonomic Nervous System

? 2 divisions:

? Sympathetic

?"Fight or flight"

?"E" division

? Exercise, Excitement,

Emergency &
Embarrassment

? Parasympathetic

?"Rest and digest"

?"D" division

? Digestion, Defecation, &

Diuresis


Functions

?Sympathetic & parasympathetic divisions typically

function in opposition to each other.

?But this opposition is better termed

complementary in nature rather than antagonistic.

?Sympathetic as accelerator and parasympathetic as

brake.

?Sympathetic quick responses.

?Parasympathetic functions with actions that do not

require immediate reaction.

?Sympathetic "fight or flight"

?Parasympathetic "rest and digest".


Receptors

?Parasympathetic nervous system uses only acetylcholine

(ACh) as its neurotransmitter.

?ACh acts on two types of receptors, muscarinic and

nicotinic cholinergic receptors.

?Most transmissions occur in two stages:
?When stimulated, preganglionic nerve releases ACh at

ganglion, which acts on nicotinic receptors of
postganglionic nerve.

?Postganglionic nerve then releases ACh to stimulate

muscarinic receptors of target organ.

Neurotransmitters

?At effector organs, sympathetic ganglionic neurons release

noradrenaline (norepinephrine) to act on adrenergic
receptors, with exception of sweat glands and adrenal
medulla:

?At sweat glands, it is acetylcholine muscarinic receptors.

?At adrenal cortex, there is no postsynapic neuron. Instead

presynaptic neuron releases acetylcholine to act on
nicotinic receptors.

?Stimulation of adrenal medulla releases adrenaline

(epinephrine) into bloodstream which acts on
adrenoceptors, producing a widespread increase in
sympathetic activity.

?In parasympathetic system, ganglionic neurons use

acetylcholine, to stimulate muscarinic receptors.

Sympathetic (adrenergic, with exceptions)

? cardiac output increases

? SA node: heart rate (chronotropic) 1, 2: increases

? cardiac muscle: contractility (inotropic )1, 2: increases

? conduction at AV node 1: increases

? vascular smooth muscle M3: contracts; = contracts & 2 =

relaxes

? smooth muscles of bronchioles 2: relaxes (major

contribution); 1: contracts (minor contribution)

? pupil of eye 1: relaxes

? ciliary muscle 2: relaxes

? salivary glands: secretions: stimulates viscous, amylase

secretions; 1 = stimulates potassium cation

? smooth muscles of GI tract - , 2: relaxes

? sphincters of GI tract - 1: contracts

? glands of GI tract - inhibits


Parasympathetic (muscarinic)

? cardiac output M2: decreases
? SA node: heart rate (chronotropic) M2: decreases
? cardiac muscle: contractility (inotropic) M2: decreases (atria

only)

? conduction at AV node M2: decreases
? 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
? smooth muscles of GI tract M3: contracts
? sphincters of GI tract M3: relaxes
? glands of GI tract M3: secretes

Autonomic regulation & stress

?A stressful situation activates three major communication

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
sensory information.

?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

systems, such as digestion, in order and calms body's

responses to the emergency branch.

?Third major communication process is neuroendocrine

system, which also maintains body's internal functioning.

Specific task

?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,
kidneys, and digestive tract.

?In contrast, calming branch helps to regulate bodily

functions and soothe body once stressor has passed,
preventing body from remaining too long in a state of
mobilization.

?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

response to stress.

?Various "stress hormones" travel through blood and

stimulate release of other hormones, which affect bodily
processes such as metabolic rate and sexual functions.

Stress reaction

? When stress occurs,

sympathetic nervous

system is triggered.

? Norepinephrine is released

by nerves, and epinephrine

is secreted by adrenal

glands. By activating

receptors in blood vessels

and other structures, these

substances ready heart and

working muscles for action.

? Acetylcholine is released in

parasympathetic nervous

system, producing calming

effects.

? Digestive tract is

stimulated to digest a meal,

heart rate slows, and pupils

of eyes become smaller.

? Neuroendocrine system

also maintains the body's

normal internal

functioning.


Chronic stress

?When glucocorticoids or adrenaline are secreted in

response to prolonged psychological stress commonly
encountered by humans, results are not ideal.

?Normally, bodily systems gear up under stress and release

hormones to improve memory, increase immune
function, enhance muscular activity and restore
homeostasis.

?If you are not fighting or fleeing, but standing frustrated

in a supermarket checkout line or sitting in a traffc jam,
you are not engaging in muscular exercise.

?When stimulated chronically, there are consequences:
?Memory is impaired,
?Immune function is suppressed, and
?Energy is stored as fat.

Response to stress

This post was last modified on 05 April 2022