The Autonomic Nervous System
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Transcript of 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
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
• 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 ¶sympathetic nerves in head&neck,chest,abdomen and pelvis
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
• 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 - 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.
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
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
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
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)