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Quick Revision:-

We`ve started talking about the Autonomic Nervous System:

First: There are two divisions of the Autonomic Nervous System:

Sympathetic ANS:- { Thoracolumber origin}

Parasympathetic ANS: - {Craniosacral origin}

Second: Each sympathetic and parasympathetic pathway from the brain or the

cord to the stimulated tissue is composed of two neurons, a preganglionic neuron

{the first one} and a postganglionic neuron {the second one} , forming the axis

of both systems.

Third: Physiologic Anatomy of Sympathetic NS:

Paravertebral ganglia: Chains of ganglia that is located near the vertebral

column in both sides where we have the synapse of the first and second

neurons.

Prevertebral ganglia : Some preganglionic fibers that enter ganglia pass

without any synapse at the paravertebral ganglia and continue to these

ganglia which are located in the abdomen where they have the synapse with

the second neuron > there are three solitary ( unpaired ) prevertebral ganglia

: celiac , superior mesenteric and inferior mesenteric ganglia .

Some preganglionic fibers pass without synapse in either location, these fibers

continue directly toward the suprarenal gland where they synapse with

endocrine cells that release the Epinephrine hormone.

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The sympathetic NS have short preganglionic axons (fibers) and long

postganglionic axons.

Fourth: Physiologic Anatomy of Parasympathetic NS:

The preganglionic fibers leave the central nervous system and go toward

the stimulated organ where they synapse with the second postganglionic

neuron located within the tissue of the effector organ.

The preganglionic fibers are long compared to the short postganglionic

fibers.

Fifth: The General function of the ANS is: Control and Adaptation of

body systems to internal and external changes.

Finally: In the sympathetic NS we have characteristic organizations

such as Convergence and Divergence. This organization is very important

in the function of the sympathetic NS to generate a Diffused response,

while in the parasympathetic we don`t have this type of organization so its

effect is limited to the specific stimulated organ.

Now we will continue our journey of exploring our ANS

What are the Effects of Sympathetic stimulation??

1- Effects on Blood pressure : the sympathetic NS have an effect

on the : blood vessels supplying skeletal muscle , heart muscles and the

conductive tissue of the heart .So it change the blood pressure via :

Changing the rate of contraction of the heart muscles

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Changing the propulsion of blood by the heart {Contractility or the

force of contraction and propelling of blood }

Changing the diameter of the blood vessels { By controlling the

smooth muscles of the vessels }

Note:-

Because blood vessels are widely distributed tissues these structures have only

sympathetic innervations as it is the widely distributed neural system .In fact all

widely distributed tissues in our body are innervated by the sympathetic NS such as

skin , sweat glands, piloerector muscles ……etc.

2- Control Body temperature : the sympathetic NS have many

mechanisms by which it can regulate body`s temperature :-

If the temperature goes high our body can get rid of excessive

heat by :

Vasodilation of cutanous blood vessels

Stimulating the sweat glands to secret large quantities of

sweat.

Our body can reduce heat loss by vasoconstriction for example.

3- Effects on the Cardiovascular system :-

Effects on blood vessels will result in redistribution of blood by

enhancing blood flow to skeletal muscle and reducing blood flow to

skin and mesentery {cause vasoconstriction in these vessels}.

Effects on heart: - In general sympathetic stimulation increases

the overall activity of the heart. This is accomplished by

increasing the rate of contraction by affecting the conductive

tissue of the heart, and increasing the force of contraction by

affecting the heart muscles.

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Note:- The parasympathetic NS can only affect the conductive tissue of

the heart but not the heart muscles them self.

4- Effects on the respiratory system: sympathetic stimulation causes

relaxation of the bronchial smooth muscles which result in

bronchodilation.

5- Effects on Digestive system: - It is not important in the fight

and flight reaction so the main effect is inhibitory, it cause inhabitation

of motility and secretion of the gastrointestinal tract.

6- Metabolic effects : These include :

Mobilization of glucose for the sake of energy for muscles.

Mobilization of Lipids {Lipolysis} as source of energy.

Metabolic activities are increased {Set of chemical reactions that

maintain life in any organism. Two types of metabolic processes

are anabolism and catabolism }

NOW what are the effects of PARASYPMATHETIC STIMULATION?

1- Effects on the gastrointestinal system: Parasympathetic

stimulation in general increases overall degree of activity of

the gastrointestinal tract by promoting motility and secretary

activity.

Remember!!!!

The parasympathetic effect is limited, that means for example

stimulating the neurons innervating the stomach will cause a

limited response changes the activity of the stomach only!!

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2- Effects on Glands of the body : The nasal,

lacrimal,salivary and many gastrointestinal glands are strongly

stimulated by the parasympathetic nervous system ,usually

resulting in increased secretary activity of these glands { BUT

REMEMBER : sweat glands are under sympathetic control }

3- Effects on heart: - It causes mainly the opposite effects of

the sympathetic NS Decreased heart rate and force of

heart contraction. Its effect is limited to the conductive

tissue of the heart.

How Does this Happen??

Conduction tissue of the heart has the special property of depolarizing without any

external influence. This is known as cardiac muscle automaticity {Automatic

generation of action potential by some structures in this tissue}

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In the Diagram:

Phase 4: is slow depolarization which continues till reaching threshold.

Phase 0: is the upstroke of the action potential.

Phase 3: is repolrization going back to the lowest point then slow depolarization

again.

What` s the effect of the parasympathetic NS???

It slows the rate of {SLOW depolarization} this means less number of heart beats

per minute.

BUT the sympathetic NS increases the rate of depolarization so increasing the

number of heart beats per minute.

4- Effects on pupil :- parasympathetic NS controls pupil

diameter by papillary light reflex (myosis){ This reflex

regulate the amount of light falling on retina }

In fact, our parasympathetic NS is adapting our eyes to

increased light intensity by causing constriction of the pupil

opening to decrease amount of light that strikes the retina.

5- Lens: focusing of the lens is controlled almost entirely by

the parasympathetic NS. It is involved in the accommodation

of the lens for near vision .this is usually achieved by changing

the convexity of the eye lens.

6- Urinary Bladder: cause contraction of the urinary bladder

which results in micturation.

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MOLECULAR BASIS of PHYSIOLOGICAL ACTIONS of the

ANS:

Sympathetic NS:-

All the sympathetic preganglionic autonomic nerve endings

secrete the neurotransmitter Acetylcholine.

Most of the sympathetic postganglionic autonomic nerve

endings release the neurotransmitter Norepinephrine.

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An exception is the postganglionic fibers innervating

sweat glands and piloerector muscles their autonomic

nerve endings secretes Acetylcholine.

Parasympathetic NS:

All the parasympathetic preganglionic autonomic nerve

endings secrete the neurotransmitter Acetylcholine.

All the parasympathetic postganglionic autonomic nerve

endings secrete the neurotransmitter Acetylcholine.

Remember!!!! Sweat glands are under the control of the sympathetic

but stimulated by Acetylcholine.

Receptors and Signal transduction mechanism:

At ganglia:-

Sympathetic and parasympathetic have nicotinic receptors at the post synaptic

membrane for acetylcholine.

{{It`s called nicotinic because they can be stimulated by

nicotine}}

The Ach cause the generation of action potential on the

second neuron`s membrane that`s mean that these

receptors are linked to Na+ channels.

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Note that:

In skeletal muscles somatic fibers release acetylcholine which have receptors

on the skeletal muscle`s cells those receptors are also nicotinic.

On effector cells:-

First (Ach):

Sympathetic and parasympathetic have Muscarinic receptors for acetylcholine on the

effector cell`s membrane {{They are called Muscarinic because they can be

stimulated by muscarine [A natural product found in toxic types of mushrooms ]}}

Clinical Application:

If someone gets intoxicated by these toxic mushrooms the Muscarinic receptors in

his body will be stimulated and this will cause: _

Stimulation of parasympathetic fibers and sympathetic fibers innervating sweat

glands. So the major symptoms of this case are:-

Vomiting and diarrhea as a result of increased gastrointestinal motility.

Urination as a result of urinary bladder contraction

Slowing of the heart rate {Bradycardia}

Contraction of pupil

Increased secretory activity causing :

Sweating

Salivation

Tearing

Nasal and bronchial discharge

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All these symptoms can be reversed by blocking muscarine receptors by ATROPIN

this will prevent the effect of muscarine on these receptors and reverse all these

effects

BUT Atropin has some side effects such as

Increase heart rate {Trachycardia}

Inhibition of glandular secretion dry mouth ,dry eyes ,dry nasal

passages

Loss of papillary light reflex and cause dilation of pupil { actually the drop we

use for eye therapy is composed of atropine }

Loss of ability to focus the lens for near vision

Subtypes of Muscarinic receptors: _

There is five subtypes of Muscarinic receptors have been identified numbered

{M1 --- M5}

Inhibitory:

M2 is an example of inhibitory receptor for Ach.

It is found in the conductive tissue of the heart.

It slows the rate of depolarization.

It function via G proteins :: The Gi protein binds to the enzyme

Adenylyl Cyclase and inhibits it , now the enzyme will stop converting

ATP to cAMP so the concentration of c AMP will decrease .

The final effect is decreasing the rate of depolarization and this can be

achieved in two methods :-

First: - Inactivating sodium channels

Second: - Activating potassium channels

Excitatory:-

{M1, M3, M5} are examples of excitatory receptors for Ach.

They are found in smooth muscle and glands.

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They are linked to Gq protein which when these receptors are

activated will dissociate and bind to the enzyme Phospholipase C

and activate it to break PIP2 and increase the concentration of

IP3 and this will result in increasing the calcium concentration in

the cytosol and causing the smooth muscles to contract .

SO…. We might have an inhibitory or excitatory effect of Ach depending on the

type of receptor.

Second {Norepinephrine}:

Both the hormone epinephrine and the neurotransmitter Norepinephrine which are

called Catecholamines have the same receptors called adrenergic receptors.

These Adrenergic receptors have many subtypes:

Alpha receptors:

The Alpha 1 adrenergic receptor (α1) :- It is excitatory linked to the Gq

protein which when bind to Phospholipase C enzyme it activate it and increase

the concentration of IP3 causing smooth muscles contraction

Note that:

During fight & flight reaction the cutanous blood vessels undergo

vasoconstriction so this means they have more alpha 1 receptors

The Alpha 2 adrenergic receptor (α2):- It is found in the nervous system on

the membrane of neural cells and it has inhibitory effect on neural activity.

Example:-

If we get any injury during any activity as long as our body is moving and

having stress we don`t feel pain .Pain sensation occurs in the relaxation state.

The reason is during stress Norepinephrine & epinephrine are binding to alpha

2 receptors over sensory neurons inhibiting the transmition of pain sensation.

Alpha 2 Heteroreceptors: - They are inhibitory for Adenylyl Cyclase enzyme

and they are noradrenergic.

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Beta receptors:-

Beta 1 receptor (β1):- It is found in heart and it is excitatory increasing the

rate of heart beats.

Beta 2 receptor (β2):- It is found in tracheal and bronchial smooth muscles,

in the gastrointestinal tract and on smooth muscles of blood vessels supplying

skeletal muscles. It is inhibitory of adenylyl Cyclase causing relaxation of

smooth muscles.

So receptors have excitatory or inhibitory effects over cells what determines

the final effect is the concentration of each type of receptor on these cells.

Note:-

Asthmatic patients usually have bronchoconstriction in order to cause

bronchial relaxation sometimes we give these patients epinephrine but we

have to be careful not to increase the heart rate as a side effect .

Blood vessels supplying muscles respond by vasodilation but vessels

supplying the skin are responding by vasoconstriction this difference

although this response is for the same hormone or neurotransmitter is

due to the difference in the type of receptors they bear

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Doctor`s answers to some questions:

Q: What is the difference between equilibrium potential and resting membrane potential??

A: The resting membrane potential includes the activity of the sodium-potassium

pump without this activity we get the equilibrium potential only

So resting membrane potential = equilibrium potential +activity of Na-K pump

Q: When can we use the Nernst or Goldman equation??

A: To see the activity of the membrane for one ion we use the Nernst equation but

for many ions we use Goldman equation.

Q; what is meant by Enteric Nervous System??

A: It is a subdivision of the ANS that directly controls the gastrointestinal system ,

If we removed the ANS the GI will function normally because it have its own

nervous system but the ANS have some effects on the GI like inhibition of motility

and secretion .

Bye …. Bye DR Khatatba ……….

Forgive Me for Any Mistakes

YOUR Colleague: - Rowa2 Lahaseh <3 <3