Chapter 4: physiology Autonomic Nervous System

Girmay F.

Out line presentation

1. Introduction

2. Division of ANS

Sympathetic nervous system

Parasympathetic nervous system.

3. Adrenal medulla

4. Neurotransmitters and Receptors in ANS

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Introduction

The human internal environments is regulated in

large measure by the:

• ANS

• Endocrine glands and

N.B. Integrated activities of these two systems

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The subdivision of the Peripheral NS that regulates body

activities independently (autonomously) and continuously

without conscious effort.

ANS innervate

Smooth muscle, Cardiac muscle

Glands (eg, sweat glands, salivary glands)

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mediates visceral reflex responses that are involuntary

and largely unconscious.

Although survival is possible without an ANS, the

ability to adapt to environmental stressors and other

challenges is severely compromised.

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The ANS affects the following:

Heart rate, Respiration rate

Digestion, Salivation

Perspiration

Diameter of the pupils

Micturition (urination)

Sexual arousal

Basic difference ANS VS SNS

Somatic division:

operates under our conscious (voluntary) control.

Cell bodies of motor neurons reside in CNS

One motor neuron extends from the CNS to skeletal

muscle.

Axons are well myelinated, conduct impulses rapidly.

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Autonomic system:

chains of two motor neurons

1st = preganglionic neuron (in brain or spinal cord)

2nd = ganglionic neuron (cell body in ganglion outside

CNS) .

Slower because lightly or unmyelinated.

functions are involuntary

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Preganglionic neurons :

the first neuron and its cell bodies in CNS

Myelinated.

Postganglionic neurons:

The second neuron

its cell bodies in the autonomic ganglion

Unmyelinated

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The nerve impulse transmitted from pre-to-post ganglion

occur via Acetyl choline (ACH).

N.B

1. Ganglion: the collection of nerve cell bodies in the

peripheral nervous system.

2. Nuclei : collection of nerve cell bodies in CNS.

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Divisions of Autonomic Nervous System

The ANS has two major divisions: the sympathetic and

parasympathetic nervous systems.

Sympathetic division (speeds up)

• Prepares body for ‘fight or flight’ situations

Parasympathetic division (slows down)

• Prepares body for ‘resting and digesting’ activities.

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some target organs are innervated by both divisions

(Dual innervation), Opposing effects on the same

organ.

others are controlled by only one.

It has also Enteric division and has role in digestive

tract.

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Sympathetic nervous system

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You come across a gangster with sharp materials @Gcmhs campus

at 8:00 pm on your walk to GCMHs library ………… what

happens ???

1. Heart rate

2. Breathing rate

3. Size of pupil

4. Bronchiole smooth muscle

5. Digestive system

6. Skeletal system

7. Cutaneous circulation

8. Cerebral circulation

Sympathetic nervous system

mobilization & increased metabolism “fight, flight or

fright”.

Involves in activities of exercise, excitement,

emergency, and embarrassment.

Non-essential activities are dampened (GI/urinary).

Promotes adjustments during exercise – blood flow to

organs is reduced, flow to muscles is increased

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Its activity is illustrated by a person who is threatened

HR increase and breathing is rapid and deep.

The skin is cold and sweaty, and the pupils dilate.

Bronchioles dilate which increasing ventilation,

delivering more oxygen to cells.

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Constriction of visceral & cutaneous blood vessels

(blood is shunted to skeletal muscle ).

Liver releases more glucose into blood to provide

more readily avail energy

Targets adipocytes for lipolysis.

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Basic organization

Issues from T1-L2 ( thoraco lumbar division )

Preganglionic fibers form the lateral gray horn.

Supplies visceral organs and structures of superficial body

regions.

Contains more ganglia than the parasympathetic division

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Parasympathetic Division

Cranial outflow

Supplies the visceral structure in the head, neck and face

via the oculomotor, facial and glossophryngeal nerves.

Thorax and upper abdomen via vagus nerves.

Sacral outflow

Supplies pelvic organ via the pelvic branches of the

second to fourth sacral spinal nerves.

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Cranial Outflow

Preganglionic fibers run via:

Oculomotor nerve (III)

Facial nerve (VII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)

Cell bodies located in cranial nerve nuclei in the brain stem.

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oculomotor nerve

ciliary ganglion

Ciliary muscle, accommodation for near vision

Pupillary constrictor of iris(sphincter), miosis

(contraction of pupil).

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Facial nerve

Submandibular and sublingual glands via Submandibular

ganglion

Lacrimal gland via Pterygopalatine ganglion .

Glands of nasal cavity, mouth, and palate

Glossopharyngeal nerve

Parotid gland via otic ganglion

Outflow via the Vagus Nerve (X)

Fibers innervate visceral organs of the thorax and most of the

abdomen.

Stimulates - digestion, reduction in heart rate and blood pressure.

Preganglionic cell bodies

Located in dorsal motor nucleus in the medulla.

Ganglionic neurons

Confined within the walls of organs being innervated.

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Sacral Outflow

Emerges from S2-S4

Innervates organs of the pelvis and lower abdomen

Preganglionic cell bodies

Located in visceral motor region of spinal gray matter.

Form pelvic splanchnic nerves.

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SNS VS PNS

Sympathetic

1. Thoracolumbar

2. Short preganglionic and long

post ganglionic neurons.

3. Sympathetic axons – highly

branched , Influences many

organs

4. Location of Ganglia: Close to

the spinal cord

Parasympathetic

1. Craniosacral

2. Long preganglionic and short

postganglionic fibers

3. Parasympathetic axons – few

branches , Localized effect.

4. Location of ganglia: In the

visceral effector organs 34

SNS VS PNS cont’d…

Neurotransmitter released by preganglionic axons

Acetylcholine for both branches (cholinergic)

Neurotransmitter released by postganglionic axons

Sympathetic – most release norepinephrine (adrenergic).

Parasympathetic – release acetylcholine .

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Adrenal medulla

Major organ of the sympathetic nervous system.

Secretes great quantities epinephrine (a little

norepinephrine)

Stimulated to secrete by preganglionic sympathetic

fibers.

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Neurotransmitters & Receptors in ANS

1. Neurotransmitter

chemical messengers produced by the cell bodies of

neuron and have role in communication between neurons

and neuron, muscle coordination.

Neurotransmitters are released by the presynaptic cell.

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Bind to specific receptors in the postsynaptic cell

membrane.

Binding has either an excitatory or an inhibitory effect on

the effector, depending on the specific receptor.

Acethylcholine(ACh) and Norepinephrine( NE) are the

major neurotransmitters in autonomic nervous system.

A. Both the preganglionic and postganglionic axons in the

parasympathetic division release acetylcholine and thus

are called Cholinergic.

B. The preganglionic axon and a few postganglionic axons

in the sympathetic division are also cholinergic(blood

vessels of skeletal muscle and sweat gland).

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C. Most of the postganglionic axons of the sympathetic

division release Norepinephrine and are called

Adrenergic.

D. The postganglionic chromaffin cells at the adrenal

medulla secrete Adrenaline(epinephrine).

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Acetylcholine

ALL preganglionic neurons

ALL parasympathetic postganglionic neurons

Blood vessels of muscle and sweat gland.

ACH is rapidly hydrolyzed by a membrane-associated

Acetylcholinesterase in the synaptic cleft.

Effects are short and localized.47

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Norepinephrine (= Noradrenalin):

Most sympathetic postganglionic neurons

Exceptions: Sweat glands (Acetylcholine), Renal

arteries (Dopamine).

Epinephrine (= Adrenaline):

– Adrenal medulla upon sympathetic impulses

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2. Receptors

A. Cholinergic Receptors:

Receptor for Ach.

classified as nicotinic, muscarinic.

Muscarinic (M): at the target organ named after activation

by Muscarine (poison of Amanita muscaria).

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Hetrotrimeric G protein-coupled

CNS, gastric mucosa: M1

Cardiac: M2

Glandular/Smooth muscle: M3

The effect of ACh binding:

Can be either inhibitory or excitatory.

Depends on the receptor type of the target organ52

Nicotinic (N) receptors

All ganglionic neurons of both sympathetic and

parasympathetic

At the neuromuscular junction

The hormone-producing cells of the adrenal medulla

The effect of ACh binding to nicotinic receptors is always

stimulatory

named after activation by Nicotine. 53

The effect of ACh binding to nicotinic receptors is

always stimulatory (excitatory ).

Stimulation of muscarinic receptors produces a longer

lasting effect than does stimulation of nicotinic

receptors.

The effects produced by the PS division center on

relaxation, food processing and energy absorption.

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B. Adrenergic receptors: respond to norepinephrine/epinephrine

Subdivided in to α and β.

α Adrenergic receptors

α receptors are located postsynaptically at sympathetic

neuroeffector junctions of many organs.

In general, alpha receptors mediate excitation or increased

activity of the effector cells.

Vascular smooth muscle is an important site of alpha

receptors. 56

They are subdivided into two types:

1

Located in the vascular smooth muscle of the skin and

splanchnic regions, the gastro intestinal(GI) and bladder

sphincters, and the radial muscle of the iris.

Produce excitation( e. g. contraction or constriction).

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2

Are located in presynaptic nerve terminals, platelets, fat

cells and pancreatic islets.

Effects

platelet aggregation

Vasoconstriction

inhibition of norepinephrine release and of insulin

secretion.

Often produce inhibition ( e. g. relaxation or dilation).

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β adrenergic receptors

are also located postsynaptically at sympathetic

neuroeffector junctions of many organs.

In general, beta receptors mediate relaxation or

Decreased activity of the effector cells. Thus, Blood

vessels dilate and Uterine smooth muscle

relaxes in response to activation of beta receptors.

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A notable exception – NE binding to receptors of the heart

is stimulatory.

There are three known types of beta receptor, designated β1,

β2 and β3.

β1-Adrenergic receptors : are located mainly in the heart.

Produce excitation ( e. g. increased HR, increased

conduction velocity, increased contractility).

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β2-Adrenergic receptors: are located on the vascular

smooth muscle of skeletal muscle, bronchial smooth

muscle, and in the wall of GI tracts and bladder.

Produce relaxation( e.g. dilation of vascular smooth

muscle, dilation of bronchioles, relaxation of the bladder

wall.

β3- adrenergic Receptors are located in fat cells.

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Rhythm disturbances are a major concern with drugs that activate the beta1 receptor. 64

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Alpha receptor activation leads to smooth muscle

contraction

Activation of beta 1 leads to smooth muscle

contraction(especially in heart).

Activation of beta 2 receptors lead to smooth muscle

relaxation.

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Dual Innervation

Most of viscera receive nerve fibers from both

parasympathetic and sympathetic divisions.

Both divisions do not normally innervate an organ equally.

Antagonistic effects

oppose each other

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Exerted through dual innervation of same effector

Heart rate decreases (parasympathetic)

Heart rate increases (sympathetic)

Exerted because each division innervates different cells

pupillary dilator muscle (sympathetic) dilates pupil

constrictor pupillae (parasympathetic) constricts pupil

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Cooperative effects seen when 2 divisions act on different

effectors to produce a unified effect

parasympathetics increase salivary serous cell secretion

sympathetics increase salivary mucous cell secretion

ANS cooperation is best seen in control of the external

genitalia

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Parasympathetic fibers cause vasodilation and are

responsible for erection of the penis and clitoris.

Sympathetic fibers cause ejaculation of semen in males and

reflex peristalsis in females

Some effectors receive only sympathetic

adrenal medulla, arrector pili muscles, sweat glands and

many blood vessels.

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SympatheticPreganglionic Postganglionic

Noradrenaline

α,β1 β2

receptors

Nicotinicreceptor

ACh

Effector Organ

ParasympatheticPreganglionic Postganglionic

ACh

Muscarinicreceptors

Nicotinicreceptor

ACh

Effector Organ

Summary

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Adrenal glandACh

Nicotinicreceptor

Adrenalin (80%)Noradrenalin (20%)

Skeletal muscle

Nicotinicreceptor

ACh

Summary Cont.

Somatic

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Receptor Location Response

Adrenergic Receptorsα1

α2

β1

β2

Widespread, found in most tissues

Sympathetic neuroeffector junctionsParasympathetic neuroeffector Junctions

Heart, kidneys, liver, adipose tissue*

Smooth muscle in vessels of heart and skeletal muscle; smooth muscle layers in the intestines, lungs, and bronchi

Excitation, stimulation of metabolism

Inhibition of effector cell

Inhibition of neurotransmitter release

Stimulation, increased energy consumption

Inhibition, relaxation

Cholinergic Receptors

Nicotinic

Muscarinic

All autonomic synapses between preganglionic and ganglionic neurons; neuromuscular junctions of the SNS

All parasympathetic neuroeffector junctions; cholinergic sympathetic neuroeffector junctions

Stimulation, excitation; muscular contraction

Variable

Adrenergic and Cholinergic Receptors of the ANS

Recall

Describe the main functions of ANS.

Distinguish the division of the ANS

Appreciate the difference between the sympathetic

nervous and parasympathetic nervous system.

Identify the neurotransmitters and its receptors in ANS.

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