lecture 14 & 15 dr. zahoor ali shaikh 1. central nervous system (cns) – brain and spinal cord....

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Lecture 14 & 15

Dr. Zahoor Ali Shaikh

AUTONOMIC NERVOUS SYSTEM (ANS)

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Central Nervous System (CNS) – brain and spinal cord.

Peripheral Nervous System (PNS) – afferent and efferent branch.

PNSAfferent branch takes message to CNS.Efferent branch brings message from CNS to

Effector organ.

NERVOUS SYSTEM GENERAL INTRODUCTION

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Skeletal muscle is innervated by efferent division of PNS, but it is voluntary – somatic nervous system.

Autonomic Nervous System (ANS) is the part of efferent division of PNS, but it is involuntary.

We will discuss ANS

NERVOUS SYSTEM GENERAL INTRODUCTION

4FUNCTIONAL COMPONENTS OF NERVOUS SYSTEM

Autonomic nerve pathwayExtends from CNS to an innervated organTwo-neuron chain

Preganglionic fibers arise from CNS – they synapses with cell body (ganglion) of second neuron

Postganglionic fiber arise from ganglia and innervates Effector organ

ANS

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Autonomic Nervous System (ANS) has two major sub- divisions:

1. Sympathetic Autonomic Nervous System2. Parasympathetic Autonomic Nervous

System

We will discuss each one.

AUTONOMIC NERVOUS SYSTEM(ANS)

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We will discuss Sympathetic and Parasympathetic ANS under following headings:

1. Origin 2. Organization 3. Chemical Transmitters 4. Actions 5. Receptors 6. Exceptions in ANS 7. Comparison between Sympathetic &

Parasympathetic ANS


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ANS supplies cardiac muscle, smooth muscle, blood vessel, GIT, salivary glands, sweat glands, most exocrine glands and some endocrine glands, adipose tissue (fat).


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SYMPATHETIC AUTONOMIC NERVOUS SYSTEM

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1. Origin Sympathetic nerve fiber originate in the

spinal cord from lateral horn cell from thoraco lumber region.

T1 - T12 and L1 – L2/L3 Therefore, called thoraco lumber outflow.


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SYMPATHETIC ANS

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2. Organization Sympathetic ANS is Two - neuron system.The cell body of first neuron is located in the

CNS (spinal cord at lateral horn cell). Its axon, the preganglionic fiber makes the synapse with the cell body of second neuron which lies within sympathetic chain ganglion (collection of neuronal cell bodies).

The axon of the second neuron, the post ganglionic fiber arises from the ganglion and innervates the Effector organ.


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SYMPATHETIC ANS ORGANIZATION

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In Sympathetic ANS - Preganglionic fibers are short and post

ganglionic fibers are long. - Preganglionic fibers synapse with

sympathetic ganglion chain also called Sympathetic trunk which is located on either sides of spinal cord.

- Post ganglionic fibers are large and originate in the ganglion chain and go to the Effector organ.


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SYMPATHETIC ANS

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NOTESome preganglionic fiber pass through the

ganglion chain without synapsing.Instead they synapse with sympathetic

collateral ganglion and post ganglionic fiber arises from collateral ganglion and innervates the Effector organ.


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3. Chemical TransmittersChemical transmitter at - preganglionic sympathetic nerve ending

is acetylcholine - postganglionic sympathetic nerve

ending is nor-epinephrine.Sympathetic fibers which release nor

adrenaline (nor epinephrine) are called adrenergic fibers.


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SYMPATHETIC ANS CHEMICAL TRANSMITTERS

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4. ActionsSympathetic and Parasympathetic ANS,

generally have opposite effects in a particular organ.

ImportantInstead of memorizing, it is better to see the

actions of Sympathetic ANS by understanding the circumstances under which it dominates.


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Time of sympathetic dominance Sympathetic ANS dominates in the stressful

situation e.g. fighting, frightened, examinations.

Therefore, sympathetic response is called fight or flight response (makes body ready to fight or run away from the threat).


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sympathetic dominance

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When there is more sympathetic activity, there is

- increased heart rate, increased force of contraction of heart

- increased blood pressure (due to vasoconstriction)

- respiratory airways are open (broncho dilation to increase air flow)

- Pupils dilate

SYMPATHETIC AUTONOMIC NERVOUS SYSTEM - ACTIONS

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- Sweating is increased- Glycogen and fat stores are broken down- Blood vessel to skeletal muscle are dilated to

increase blood flow in anticipation of increased physical activity

- Digestive and urinary activities are inhabited at the time of threat by sympathetic ANS

SYMPATHETIC AUTONOMIC NERVOUS SYSTEM (cont)

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Structures Innervated by Sympathetic & Parasympathetic ANS

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Structures Innervated by Sympathetic & Parasympathetic ANS

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5. ReceptorsTwo major types of adrenergic receptors on

which nor-epinephrine acts are: - Alpha (α) – sub divided in α1 and α2

- Beta (β) – sub divided in β1 and β2

They are present on the cell membrane of the Effector organs.

Alphaα1 are excitatory e.g. blood vessels (vasoconstriction)

α2 are inhibitory e.g. intestine smooth muscle (relaxation)


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Beta adrenergic receptors - β1 are excitatory – heart (increase Heart Rate)

- β2 inhibitory – lungs, broncho dilation

Remember - Type“1” e.g. α1, β1 – excitatory

- Type “2” e.g. α2, β2 – inhibitory

- Preganglionic sympathetic fibers which are cholinergic i.e.

secretes acetylcholine (ACH). This activates nicotinic receptors present in the ganglion.


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SYMPATHETIC ANS RECEPTORS

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It is modified part of sympathetic ANS.There are two adrenal glands, each lying

above the kidney. They are endocrine glands.

Adrenal glands has two parts - Adrenal cortex (outer portion) - Adrenal medulla (inner portion)

ADRENAL MEDULLA

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It is modified sympathetic ganglion.It does not give postganglionic fibers, but

secretes epinephrine and nor-epinephrine directly into the blood, therefore, it is called Endocrine gland.

Adrenal medulla secretes - 80% Epinephrine - 20% NorepinephrineThese hormones increase the activity of

sympathetic ANS.

ADRENAL MEDULLA

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PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM

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1. Origin Parasympathetic ANS – preganglionic fibers

originates from the nuclei of cranial nerves III, VII, IX, X (midbrain, pons and medulla) and spinal cord sacral segments S2,3,4.

Therefore, called craniosacral outflow. Major nerve of parasympathetic ANS is 10th cranial

nerve (vagus).

NOTE (Names of Cranial nerves)III – Oculomotor VII – FacialIX – Glassophyrangeal X – Vagus


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PARASYMPATHETIC ANS

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2. Organization Parasympathetic ANS is Two - neuron

system.Preganglionic fibers are longer Postganglionic fibers are shorterPreganglionic fibers end on the ganglia that

lies in or near the Effector organ.Postganglionic fibers are very short that they

end on the Effector organ.


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PARASYMPATHETIC ANS

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3. Chemical TransmittersChemical transmitter at - preganglionic parasympathetic nerve

ending is acetylcholine - postganglionic parasympathetic nerve

ending is acetylcholineParasympathetic fibers which release

acetylcholine are called Cholinergic fibers.

PARASYMPATHETIC ANS

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4. ActionsSympathetic and Parasympathetic ANS,

generally have opposite effects in a particular organ.

ImportantInstead of memorizing, it is better to see the

actions of Parasympathetic ANS by understanding the circumstances under which it dominates.


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Time of parasympathetic dominance Parasympathetic ANS dominates at the time

of relaxation, digestion, rest and sleep.At the time of rest and digestion Heart - heart rate decreases, force of

contraction of heart decreases GIT – increases digestion, gut motility,

secretions and promotes defecation. - promotes diuresis


43parasympathetic dominance

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5. ReceptorsThere are two types - Nicotinic receptors – are present in

autonomic ganglion. Preganglionic parasympathetic fibers which secrete acetylcholine act on nicotinic receptors.

- Muscarinic receptors – are found in target organs that is the cell membrane of cardiac muscle, smooth muscle, glands. Post ganglionic parasympathetic fibers which are cholinergic i.e. secrete acetylcholine act on muscarinic receptors.

PARASYMPATHETIC ANS

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PARASYMPATHETIC ANS RECEPTORS

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What is the advantage of dual ANS supply, whose actions oppose each other?

It is like accelerator and brake of car, to have precise control of activity of the organ.

ADVANTAGE OF DUAL (symp & parasymp) AUTONOMIC INNERVATION

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Blood vessels – most arterioles and veins are innervated by sympathetic ANS, but not by parasympathetic ANS.

Sympathetic ANS causes vasoconstriction (α1 receptors) in blood vessels, but causes vasodilatation in skeletal muscle blood vessels (β2 receptors).

The only blood vessels which receive both sympathetic and parasympathetic fibers are male and female sex organs.

Exceptions in ANS

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Salivary Glands are supplied by both sympathetic and parasympathetic ANS but both stimulate salivary secretion.

Parasympathetic – causes increased amount of watery secretion.

Sympathetic causes little increase of thick saliva secretion.

Exceptions in ANS (cont)

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Sweat glands – are supplied by sympathetic ANS only and chemical transmitter at postganglionic sympathetic nerve ending is acetylcholine

(NOT Norepinephrine).

Exceptions in ANS (cont)

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Drugs are available which work as agonist and antagonist at the receptor site.

Agonist give effect like neurotransmitter.Antagonist block the receptor, therefore, no

effect of neurotransmitters occurs.Example of drugs acting in sympathetic ANS: - β1 blocker e.g. metoprolol, decreases heart rate

- salbutamol (Ventolin) activates β2 adrenergic receptors and causes broncho dilatation, therefore used in bronchial asthma

CLINICAL NOTE

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Example of drugs acting in parasympathetic ANS:

- atropine blocks the effect of acetylcholine at the muscarinic receptors (postganglionic parasympathetic effect of acetylcholine), therefore atropine decreases salivary and bronchial secretion

Ganglionic Blocker - Hexamethonium blocks the nicotinic

receptors at autonomic ganglion

CLINICAL NOTE

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Many regions of central nervous system are involved in control of ANS, they are

1. Prefrontal association cortex – influences emotional expression (mediated through hypothalamus, medullary pathways).

2. Hypothalamus – affects emotions and behavioral state e.g. increase heart rate, blood pressure with anger or fear (via medulla)

Control of Autonomic Nervous System

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3. Medulla In brain stem – directly responsible for autonomic output. It has center for control of cardiovascular, respiratory and digestive activity

4. Spinal cord – some autonomic reflexes are integrated at spinal cord level, therefore, called spinal reflexes e.g. urination, defecation, male and female sex organ function.

All these spinal reflexes are controlled by higher level of consciousness.

Control of Autonomic Nervous System

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SYMPATHETIC ANS

1. Origin2. Organization 3. Chemical

Transmitters4. Actions5. Receptors6. Dominance7. Drugs acting on

adrenergic and muscarinic receptors

COMPARISON OF SYMPATHETIC & PARASYMPATHETIC ANS

PARASYMPATHETIC ANS

Do the comparison yourself

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THANK YOU

lecture 14 & 15 dr. zahoor ali shaikh 1. central nervous system (cns) – brain and spinal cord....

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