autonomic nervous systemgroupf2.yolasite.com/resources/foundation-autonomic.pdf · 2012-11-25 ·...
TRANSCRIPT
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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