The Autonomic Nervous System

The Autonomic Nervous System

Assess Prof. Fawzia Al-Rouq

Department of Physiology

College of Medicine

King Saud University

Autonomic Nervous System

LECTUR (1)

Functional Anatomy & Physiology of Autonomic NS

INTRODUCTION

THE NERVOUS SYSTEM •INTRODUCTION

•The nervous system monitors and controls almost every organ / system through a series of positive and negative

feedback loops.•The Central Nervous System (CNS): Includes the brain

and spinal cord. •The Peripheral Nervous System (PNS): Formed by

neurons & their process present in all the regions of the body.

•It consists of cranial nerves arises from the brain & spinal nerves arising from the spinal cord.

•The peripheral NS is divided into •Somatic Nervous system

•Autonomic nervous system

OBJECTIVES

• Anatomy and physiology of Autonomic Nervous System

• At the end of this lectutre (1)the student should be able to:-

• -appreciate the anatomy of symathetic& parasympathetic nervous system.

• -explain physiological functions of Symathetic &parasympathetic nerves in head&neck,chest,abdomen and pelvis

FUNCTIONAL ANATOMY OF THE

AUTONOMIC NERVOUS SYSTEM

Basic anatomical difference between the motor pathways of the voluntary somatic nervous system (to skeletal muscles) and those of the autonomic nervous system

• Somatic division:– Cell bodies of motor neurons reside in CNS (brain

or spinal cord)– Their axons (sheathed in spinal nerves) extend all

the way to their skeletal muscles• Autonomic system: chains of two motor

neurons– 1st = preganglionic neuron (in brain or cord)– 2nd = gangionic neuron (cell body in ganglion

outside CNS)– Slower because lightly or unmyelinated 8

Basic anatomical difference between the motor pathways of the voluntary somatic nervous system (to skeletal muscles) and those of the autonomic nervous system

The Autonomic Nervous System

The Autonomic Nervous System

1.Visceral sensory

2.Visceral motor

• ANS is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control

• Visceral motor innervates non-skeletal (non-somatic) muscles

• Composed of a special group of neurons serving: – Cardiac muscle (the heart)– Smooth muscle (walls of viscera and blood vessels)– Internal organs– Skin

11

• Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron

• Axon of 2nd (ganglionic) neuron extends to the organ it serves

12

this dorsal root ganglion

is sensory

LOCATIONS OF AUTONOMIC GANGLIASympathetic Ganglia:

Trunk (chain) ganglia near vertebral bodies

Prevertebral ganglia near large blood vessel in gut :celiac

,superior mesenteric &

inferior mesenteric

Parasympathetic Ganglia:

Terminal ganglia in the wall of organ

Sympathetic Innervation of Visceral Targets

• Ganglia close to spinal cord

• Short, lightly myelinated preganglionic neurons

• Long, unmyelinated postganglionic neurons

Spinal

Cord

Parasympathetic Innervation of Visceral Targets• Ganglia close to or on target organs

• Preganglionic neurons - long

• Post ganglionic neurons - short

SYMPATHETIC & PARASYMPATHETIC NERVOUS SYSTEM ORIGIN

Blue= Para symp; Red symp

Sympathetic - Origin• Thoracolumbar lateral horns of the spinal segments T1-L2.

• Nerve fibers originate between T1 & L2

Parasympathetic - OriginCraniosacral Cell bodies of the motor nuclei of the cranial nerves III, VII,

IX and X in the brain stem Second, third and fourth [S2-S4] sacral segments of the spinal cord

• Nerve fibers emerge from brain & • sacrum cranio-sacral outflow

PARASYMPATHETIC NERVOUS SYSTEM

The cranial nerves III, VII and IX affect the pupil and salivary gland secretion

Vagus nerve (X) carries fibres to the heart, lungs, stomach, upper intestine and ureter

The sacral fibres form pelvic plexuses which innervate the distal colon, rectum, bladder and

reproductive organs.

PHYSIOLOGICAL FUNCTIONS OF THE

AUTONOMIC NERVOUS SYSTEM

SYMPATHETIC NERVOUS SYSTEM FUNCTIONS

The sympathetic system enables the body to be prepared for fear, flight or fight

Sympathetic responses include an increase in heart rate, blood pressure and cardiac output Diversion of blood flow from the skin and splanchnic vessels to those supplying skeletal

muscle Increased pupil size, bronchiolar dilation,

contraction of sphincters and metabolic changes such as the mobilisation of fat and glycogen.

FEAR, FLIGHT OR FIGHT

FUNCTIONS OF SYMPATHETIC NERVOUS SYSTEM

Bronchioles dilate, which allows for greater alveolar oxygen exchange.

It increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a

mechanism for the enhanced blood flow to skeletal muscles.

Sympathetic nerves dilate the pupil and relax the lens, allowing more light to enter the eye.

PARASYMPATHETIC NERVOUS SYSTEM FUNCTIONS

The parasympathetic nervous system has "rest and digest" activity.

In physiological terms, the parasympathetic system is concerned with conservation and restoration of

energy, as it causes a reduction in heart rate and blood pressure, and facilitates digestion and absorption of

nutrients, and consequently the excretion of waste products

The chemical transmitter at both pre and postganglionic synapses in the parasympathetic system

is Acetylcholine (Ach).

Subdivision

Nerves Employed

Location of Ganglia

Chemical Messenger

General Function

Sympathetic

Thoracolumbar

Alongside vertebral column

Norepinephrine

Fight or flight

Parasympathetic

Craniosacral On or near an effector organ

Acetylcholine

Conservation of body energy

THE AUTONOMIC

NERVOUS SYSTEM

PHYSIOLOGICAL FUNCTIONS OF THE

AUTONOMIC NERVOUS SYSTEM

The Autonomic Nervous System

Structure

Sympathetic Stimulation Parasympathetic Stimulation

Iris (eye muscle)

Pupil dilation Pupil constriction

Salivary Glands

Saliva production reduced

Saliva production increased

Oral/Nasal Mucosa

Mucus production reduced

Mucus production increased

HeartHeart rate and force increased

Heart rate and force decreased

LungBronchial muscle relaxed

Bronchial muscle contracted

The Autonomic Nervous System

Structure Sympathetic Stimulation Parasympathetic Stimulation

Stomach

Peristalsis reducedGastric juice secreted; motility increased

Small Intes

Motility reduced Digestion increased

Large Intes

Motility reduced Secretions and motility increased

LiverIncreased conversion ofglycogen to glucose

Kidney Decreased urine secretion Increased urine secretion

Adrenal medulla

Norepinephrine andepinephrine secreted

BladderWall relaxedSphincter closed

Wall contractedSphincter relaxed

LECTUR (2)

MECHANISM OF ACTIONS

The neurotransmitters & receptors of Autonomic NS

OBJECTIVES

OBJECTIVES• describe neurotransmitters that can

release at pre and post ganglionic of Autonomic NS.

• Describe Autonomic NS receptors.

Sympathetic Neurotransmitters• Preganglionic neurons - • Cholinergic = ( release acetylcholine ) • Postganglionic neurons:

– release norepinepherine at target organs – ie. Adrenergic

Parasympathetic Neurotransmitters

• Pre & Postganglionic neurons release acetylcholine = Cholinergic

ANS Neurotransmitters

Cholinergic Nor Adrenergic

The neurons that are cholinergic are Are pre ganglionic neurons Anatomicallt para syampatheic post ganglionic neuron Anatomical;lt syampatheic post ganglionic neuron ineervate sweet glands Anatomically syampatheic neurons that end on blood vessels in skeletal muscles & produce vasodilatation The remaining post ganglionic sympathetic neurons are nor adrenergic

 Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released

ANS Neurotransmitters:  Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released

Adrenergic

Cholinergic

Chemical or neural transmitter

• All preganglionic fibers release acetylcholin (Ach).

• All parasympathetic postganglionic release Ach.

• All sympathetic postganglionic release noradrenalin except sweat glands & bl vessels to skeletal muscles

The parasympathetic nervous system uses only acetylcholine (ACh) as its neurotransmitter.

The ACh acts on two types of receptors, the muscarinic and nicotonic choloinergic receptors. Most transmissions occur in two stages: When

stimulated, the preganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of the

postganglionic nerve. The postganglionic nerve then releases ACh to

stimulate the muscarinic receptors of the target organ.The Sympathetic NS Acts on tow types of receptors :

α and β.

RECEPTORS

Neurotransmitters and Receptors

TYPES OF MUSCARINIC RECEPTORS

The three main types of muscarinic receptors:

M1 muscarinic receptors: located in the neural system.

M2 muscarinic receptors: located in the heart, and act to bring the heart back to normal after the actions of

the sympathetic nervous system: slowing down the heart rate, reducing contractile forces of the atrial

cardiac muscle, and reducing conduction velocity of the SA and AV node.

Note, they have no effect on the contractile forces of the ventricular muscle.

TYPES OF MUSCARINIC RECEPTORS

M3 muscarinic receptors: located at many places in the body, such as the smooth muscles of the blood

vessels, as well as the lungs, which means that they cause vasoconstriction & bronchioconstriction and.

They are also in the smooth muscles of the GIT, which help in increasing intestinal motility and dilating

sphincters.

M3 receptors are also located in many glands that help to stimulate secretion in salivary glands and other

glands of the body.

Types of -adrenergic receptor

-adrenergic receptors are adrenergic receptors that respond to norepinephrine and to such blocking agents as phenoxybenzamine.

• They are subdivided into two types:

1, found in smooth muscle, heart, and liver, with effects including vasoconstriction, intestinal relaxation, uterine contraction and pupillary dilation,

2, found in platelets, vascular smooth muscle, nerve termini, and pancreatic islets, with effects including platelet aggregation, vasoconstriction, and inhibition of norepinephrine release and of insulin secretion.

-receptor types -adrenergic receptors respond particularly to epinephrine and to

such blocking agents as propranolol.

• There are three known types of beta receptor, designated β1, β2 and β3.

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

• β2-Adrenergic receptors are located mainly in the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, and skeletal muscle.

• β3-receptors are located in fat cells.

Sympathetic (adrenergic,Parasympathetic (

muscarinic)

circulatory system

cardiac output increases M2: decreases

SA node: heart rate (chronotropic)

β1, β2: increases M2: decreases

cardiac muscle: contractility (inotropic)

β1, β2: increasesM2: decreases (

atria only)

conduction at AV node

β1: increases M2: decreases

vascular smooth muscle

M3: contracts; α = contracts; β2 = relaxes ---

platelets α2: aggregates ---

mast cells - histamine β2: inhibits ---

Sympathetic (adrenergic, Parasympathetic (muscarinic)

respiratory system

smooth muscles of bronchioles

β2: relaxes (major contribution); α1: contracts (minor contribution) M3: contracts

nervous system

pupil of eye α1: relaxes M3: contracts

ciliary muscle β2: relaxes M3: contracts

Sympathetic (adrenergic,Parasympathetic (muscarinic)

digestive system

salivary glands: secretions

β: stimulates viscous, amylase secretions; α1 = stimulates potassium

stimulates watery secretions

lacrimal glands (tears) decreases M3: increases

kidney (renin) secretes ---

parietal cells --- M1: secretion

liver α1, β2: glycogenolysis, gluconeogenesis ---

adipose cells β3: stimulates lipolysis ---

GI tract motility decreasesM1, M3: increases

smooth muscles of GI tract

α, β2: relaxes M3: contracts

sphincters of GI tract α1: contracts M3: relaxes

glands of GI tract inhibits M3: secretes

Sympathetic (adrenergic,Parasympathetic (muscarinic)

ENDOCRINE

pancreas (islets) α2: decreases secretion ---

adrenal medulla N: secretes epinephrine ---

urinary system

bladder wall β2: relaxes contracts

ureter α1: contracts relaxes

sphincter α1: contracts; β2 relaxes relaxes

reproductive system

uterus α1: contracts; β2: relaxes ---

genitalia α: contracts M3: erection

sweat gland secretionsM: stimulates (major contribution); α1: stimulates (minor contribution)

---

arrector pili α1: stimulates ---

What do the receptors do?

Activation of receptors leads to smooth muscle contraction

Activation of 2 receptors leads to smooth muscle relaxation

Activation of 1 receptors leads to smooth muscle contraction (especially in heart)