AUTONOMIC NERVOUS SYSTEMgroupf2.yolasite.com/resources/Foundation-Autonomic.pdf · 2012-11-25 · Autonomic nervous system (ANS) manages our physiology By regulating organs & organ

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Somatic NS have their cell

bodies within CNS

Send axon to SK.M Conduct impulses along single axon from spinal cord to neuromuscular junction

Muscles consciously

induced to contract or relax

When motor nervous severed (cut, damaged), SK. Ms enter state of paralysis & atrophy

ANS Outline

Introduction

ANS Neurons

Divisions of ANS

ANS Neurotransmitters

ANS Innervation of Organs

Higher Control of ANS

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Nervous system

Central NS Peripheral NS

Autonomic NS Somatic NS

Sympathetic NS Parasympathetic NS

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Autonomic nervous system (ANS) manages our physiology ◦ By regulating organs & organ systems, & their smooth

muscles & glands ◦ Majority of organs (effectors) that receive efferent fiber

from ANS are hollow (heart, blood vessels, stomach, bladder, uterus, glands) & located within viscera so ANS= visceral NS

◦ Most of these organs can not be controlled consciously ANS= involuntary NS

9-4

Autonomic Nervous system (ANS):

That controls involuntary body activities i.e..

controls visceral activities (heart , gastrointestinal tract , blood vessels ………).

Somatic Nervous System:

That controls voluntary body activities

(skeletal muscle).

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Smooth muscle maintains resting tone in absence of nerve stimulation i.e. effectors are independent of their innervation

◦ Smooth becomes more sensitive when ANS input is cut (= denervation hypersensitivity)

Many types of smooth are spontaneously active & contract rhythmically without ANS input ◦ ANS input simply increases or decreases intrinsic

activity

ANS has 2 neurons in its efferent pathway

1st neuron (=preganglionic neuron) has cell body in brain or spinal cord ◦ Synapses with 2nd

neuron (=postganglionic neuron) in an autonomic ganglion

Autonomic ganglion= is a collection of cell bodies outside CNS

Postganglionic axon extends from autonomic ganglion to target tissue

Preganglionic fibers originate in: ◦ midbrain, hindbrain

(pons, cerebellum & medulla oblengata), & upper thoracic to 4th sacral level of spinal cord

Autonomic gangli located in head, neck & abdomin

Depending on origin of preganglionic fibers & location of autonomic ganglia

ANS can distinguish between sympathetic & parasympathetic divisions

Usually have antagonistic effects ◦ These coordinate physiology with what’s going on

in person's life

◦ Sympathetic mediates "fight, flight, & stress" reactions

◦ Parasympathetic mediates "rest & digest" reactions

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Fight & flight division.

It prepare the body to deal with stress.

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Is also called thoracolumbar division because its preganglionics exit spinal cord from thoracic (T)1 to lumber

(L)2

Most of these preganglionics then synapse on postganglionics in the paravertebral ganglia

Which form chain of interconnected ganglia paralleling spinal cord i.e located on either side of spinal cord

Is characterized by divergence & convergence which cause Symp to mostly act as a unit (mass activation)

Divergence: preganglionics branch to synapse with number of postganglionic neurons

Convergence: postganglionics receive synaptic input from large number of preganglionics

Some postganglionics do not synapse in paravertebral ganglion but go to outlying collateral ganglion form splanchnic nerves

The adrenal medulla, located in adrenal gland on top of kidney, appears to be a modified collateral ganglion

Its secretory cells appear to be modified

postganglionics

That release 85% epinephrine (Epi) or adrenaline & 15% norepinephrine (Norepi) or noradrenaline into blood in response to preganglionic stimulation

Stimulated during mass activation

Epi is made by methylating Norepi

Parasympathetic NS is called the rest & sleep division of the ANS.

It allows the body to recover from stress

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Is also called craniosacral division because long preganglionics originate in midbrain, medulla, pons, involving cranial nerves III

, VII , IX & X &

sacral (S)2 - S4

Synapse on postganglionic in terminal ganglia located next to or within target organ

Postganglionic has short axon that innervates target

The long vagus nerve (X) carries most Parasymp fibers ◦ Innervates heart, lungs, esophagus, stomach,

pancreas, liver, small intestine, & upper half of the large intestine

Preganglionic fibers from S2-4 innervate lower half of large intestine, rectum, urinary & reproductive systems

Sympathetic division of the ANS is called the fight & flight division.

It prepare the body to deal with stress.

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Parasympathetic NS

• Parasympathetic NS is

called the rest and

sleep division of the

ANS.

• It allows the body to

recover from stress

It is a collection of neurons outside the CNS.

It is the site of synapse between preganglionic & postganglionic neurons

It act as a distributing

center.

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1- Lateral ganglia

(sympathetic chain)

3- Terminal ganglia

Types of autonomic ganglia

2-Collateral ganglia

(Prevertebral)

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Chemical Transmission in ANS

Parasympathetic NS

Sympathetic NS

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Sites of the Cholinergic Autonomic Fibers

All preganglionic fibers

Some postganglionic sympathetic fibers such as sweat glands & blood vessels of skeletal muscles

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Adrenergic fibers

All postganglionic

sympathetic fibers except

(sweat glands & blood vessels Of

skeletal muscle)

Sites of the Adrenergic Fibers

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The postganglionic effect of sympathetic NS is mediated mainly by noradrenaline, so it is called adrenergic system.

The majority of

adrenal medulla secretion is adrenaline 85% & 15% noradrenaline.

Chemical Transmission in Sympathetic NS

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The postganglionic effect of parasympathetic NS is mediated mainly by acetyl choline, so it is called the cholinergic system.

Chemical Transmission in Parasympathetic NS

◦ Two subdivisions

Sympathetic nervous system

Parasympathetic nervous system

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Autonomic Receptors

• They are chemical structures found mainly on the cell membrane of the effector organs.

• They are affected by chemicals or drugs.

• They are classified into 2 main groups:

Cholinergic

receptors Adrenergic

receptors

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Cholinergic Receptors

• It is the division of the autonomic receptors which can be stimulated by acetyl choline.

• It is classified into 2 types according to its sensitivity to drugs.

Muscarinic – Rs

Stimulated by muscarine

Nicotinic – Rs

Stimulated by nictotine

Muscarinic receptors

Nicotinic receptors

Site Effector organs supplied by:

-All parasympathetic postganglionic fibers.

-Sympathetic cholinergic fibers (sweat glands & blood vessels of skeletal muscles)

-All autonomic ganglia.

-Adrenal medulla.

-Motor end plate.

Stimulated by:

-Acetyl choline.

-Muscarine.

-Acetyl choline.

-Nicotine small dose.

Blocked by: Atropine Curare; Nicotine large dose

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Adrenergic Receptors

• It is the division of the autonomic receptors which can be stimulated by catecholamine (epinephrine & norepinephrine).

• It is classified into 2 types according to its sensitivity to

drugs

Alpha (α) –Rs

α1 & α2 Beta (ß)- Rs

ß 1 and ß 2

- α1 & ß 1 receptors have excitatory actions.

- α2 & ß 2 receptors have inhibitory actions.

Subdivided

Alpha (α) receptors

Beta (ß) receptors

Action They are mostly excitatory.

i.e. on stimulation, they cause smooth muscle to contract.

They are mostly inhibitory.

i.e. on stimulation, they cause smooth muscle to relax.

Site -Blood vessels (vasoconstriction).

-Splenic capsule (contraction).

-GIT sphincter ( contraction).

-Blood vessels (vasodilation).

-Bronchi (bronchodilation).

-GIT wall (relaxation).

Exception: cardiac muscle

(increase its contraction

force) ß 1

Stimulated by:

Mainly by noradrenaline. Mainly by adrenaline.

Blocked by:

Phentolamine Propranolol.

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Many useful drugs have been developed to affect ANS receptors ◦ Drugs that

promote actions of a NT are agonists

◦ Drugs that inhibit actions of a NT are antagonists

Agonists

Bind to same receptor as neurotransmitter

Elicit an effect that mimics that of neurotransmitter

Antagonists

Bind with receptor

Block neurotransmitter’s response

People with hypertension propranolol (block receptor)

1 located in heart decrease cardiac rate

& blood pressure

2 located in bronchioles of lungs reduce bronchodilation • Produce asthma in susceptible people

More selective 1 antagonist (atenolol) is now

used to decrease cardiac rate & lower blood pressure

People with asthmatics inhaled epinephrine (stimulate receptor)

stimulate 1 receptor located in heart

stimulate 2 receptor located in air way

Drugs such as terbutaline selectively function as 2 agonist are commonly used

What is the difference between adrenaline and noradrenaline ?

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Adrenaline Noradrenaline

Site of release -Adrenal medulla (80% of its secretion ).

-Adrenal medulla (20% of its secretion ).

-Sympathetic postganglionic nerve endings.

Action on adrenergic-Rs

Acts on both α & β receptors. Acts mainly on α receptors.

Effect on heart

More strong Less strong

Effect on blood vessels

Vasoconstriction , but it causes vasodilation in blood vessels of skeletal muscle & liver

Vasoconstrictor only.

Relaxing effect on GIT

More strong Less strong

Metabolic actions

Glycolytic lipolytic & increasing metabolic rate

More strong Less strong

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Functions of the sympathetic NS

• Sympathetic NS is characterized by: It discharges during emergency & stress

(fear, fight & flight reaction). It acts as one unit (generalized action).

It has catabolic action.

Delays evacuation of visceral content.

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Sympathetic NS is divided into 4 divisions:

• Cervical division head & neck.

• Cardiopulmonary division heart & lung.

• Splanchnic division abdomen & pelvis.

• Somatic division skeletal muscle.

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Cervical division ( 3X3 )

Head & neck

Eye Salivary glands Skin

1- Pupil dilation

(contraction of

radial muscle;

mydriasis = prolonged dilation of pupil

of eye ).

2- Widening of the

palpebral fissure

(فتحة الجفن )

3- Exophthalmos.

(جحوظ)

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Cervical division ( 3X3 )

Head & neck

Eye Salivary glands Skin

1- Stimulate viscid

(لزج) salivary

secretion.

(thick saliva rich in

mucus)

2- Squeezing of the

salivary ducts.

3- Vasoconstriction

1- Pupil dilation

(contraction of

radial muscle;

mydriasis) .

2- Widening of the

palpeberal fissure.

3- Exophthalmos.

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Cervical division ( 3X3 )

Head & neck

Eye Salivary glands Skin

1- Stimulate viscid

salivary secretion.

(thick saliva rich in

mucus)

2- Squeezing of the

salivary ducts.

3- Vasoconstriction

1- Increase sweat

secretion.

2- Hair erection.

3- Vasoconstriction

1- Pupil dilation

(contraction of

radial muscle;

mydriasis)

2- Widening of the

palpeberal fissure.

3- Exophthalmos.

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Thorax

Heart Ooooooooooooooooooooo

Lung

1- Increase in cardiac activities:

Increases heart rate & force of contraction.

2- Vasodilatation of coronary blood vessels

indirectly by increasing cardiac work &

accumulation of metabolites.

1- Bronchodilatation.

2- Decreased bronchial

secretion.

3- Vasoconstriction of

bronchial blood

vessels.

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3- sympathetic function to abdomen &

pelvis

Abdomen (supplied by greater splanchnic (= visceral حشوى)

nerve):

• Liver: Glycogenolysis.

• Gall bladder: Relaxation of the wall &

contraction of the sphincter.

• GIT: Relaxation of wall & contraction

of sphincter i.e. inhibition of motility

& delay of evacuation.

• Spleen : Contraction of its capsule.

• Pancreas : net decrease insulin

secretion.

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Adrenal medulla

• It is supplied by preganglionic

cholinergic fibers.

So it is considered as modified

sympathetic ganglia).

• Its stimulation causes release of

catecholamine to blood (80% of its

secretion is adrenaline & 20%

noradrenaline).

• It augments & potentiates the effects

of sympathetic stimulation.

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Pelvis (supplied by lesser splanchnic

nerve) :

• Urinary bladder : Relaxation of wall & contraction

of internal sphincter

i.e. urine retention.

• Rectum : Relaxation of wall & contraction of

internal sphincter.

• Male sex organ : ejaculation.

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• It increases blood flow to skeletal muscles through vasodilation of its blood vessels (sympathetic cholinergic fibers).

• So when sympathetic NS is activated skeletal muscles will have:

Better contraction force. Delayed fatigue. Rapid recovery from fatigue.

4- Sympathetic action on blood vessels of skeletal muscles

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• Parasympathetic NS is characterized by:

It discharges during rest & sleep. Its action is localized.

It has anabolic action (conserve body stores).

It increases gastrointestinal secretion &

motility i.e. secretomotor.

Functions of the parasympathetic NS

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3rd cranial nerve (Occulomotor nerve):

Eye: 1-constriction of the pupil (contraction of circular muscle)

2-Accommodation of eye to near vision due to contraction of ciliary

muscle.

7th cranial nerve (Facial nerve) :

Submandebular & sublingual salivary glands: Increases its secretion of

watery saliva (large volume).

9th cranial nerve (Glossopharyngeal nerve):

Parotid salivary glands: Increases its secretion of watery saliva (large volume)

Cranial division

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Thorax

Heart Ooooooooooooooooooooo

Lung

• Bronchoconstriction

• Increase mucous

secretion from

bronchial glands.

• Decrease heart rate.

• Decrease force of

contraction of atria.

• Vasoconstriction of

coronary blood

vessels indirectly due

to decreased cardiac

work & O2 demand

10th Cranial nerve (X) (= vagus nerve) (supply viscera in thorax & abdomen)

Cranial division

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Abdominal Viscera

• Gall bladder : Contraction

of wall & relaxation of

sphincter.

• GIT : Contraction of wall

& relaxation of sphincter

(increase its secretion &

motility).

• Pancreas : Increase

insulin secretion.

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Sacral division (supply pelvic organs):

• Urinary bladder : Contraction of wall & relaxation of internal sphincter.

• Rectum : Contraction of wall & Relaxation of internal sphincter.

• External genitalia : Vasodilatation of blood vessels

induce erection.

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Dual innervation

• Almost all visceral organs are supplied by both sympathetic & parasympathetic divisions of autonomic NS.

• Which division predominate at any given time is

determined by the body demands at that time.

• The parasympathetic discharge to heart is more powerful at rest (vagal tone)

• While sympathetic discharge to blood vessels is more potent at rest (sympathetic tone)

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Dual innervation

• Most visceral organs receive dual innervation (supplied by both Symp & Parasymp)

• While 2 branches are usually antagonistic, such as their effects on heart rate • Can be complementary (cause similar effects)

such as with salivation • Or cooperative (produce different effects that

work together to cause desired effect) such as with sexual function Parasym stimulate erection (dilation of blood

vessels) while Sym stimulate ejaculation & orgasmic both

division work to ensure complete sexual function

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Structures supplied only by sympathetic nervous system

• Skin

• sweat glands sympathetic cholinergic)

• Pilo erector muscle.

• Blood vessels all over the body except the penis.

• Dilator pupillae muscle (= radial muscle of iris).

• Blood vessels of the skeletal muscles sympathetic cholinergic.

• Adrenal medulla.

• Capsule of the spleen .

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Structures supplied only by Parasympathetic nervous system

• Constrictor pupillae muscle (= iris sphincter muscle;

circular muscle of iris) .

Regulation achieved by increasing or decreasing firing rate

Adrenal medulla, arrector pili muscle, sweat

glands, & most blood vessels receive only sympathetic innervation

Some postganglionics do not use Norepi or ACh

◦ Called nonadrenergic, noncholinergic fibers

◦ Appear to use ATP, VIP (vasoactive intestinal peptide), or NO as NTs

NO produces smooth muscle relaxation in many tissues

Medulla most directly controls activity of ANS ◦ It has centers for control of cardiovascular,

pulmonary, urinary, reproductive, & digestive systems

Hypothalamus has centers for control of body temperature, hunger, & thirst; & can regulate medulla

Limbic system is responsible for visceral responses that reflect emotional states

Cerebral cortex & cerebellum also influence ANS