1

number 14

Done by ليان الجواودة

Corrected by

Al bakri Basil

Doctor

Dr.Omar Shaheen

2

THE EFFECT OF SYMPATHETIC STIMULATION

When we talk about effects we are concerned with nerves (how it goes to organs and how it

goes back...)

*As we said previously, the cell body of the sympathetic neurons exists in the CNS,

particularly in the spinal cord’s thoracic segments (T1-T12) and the upper 3 segments in the

lumbar region (L1-L3). The nerves exit the vertebral segments as presynaptic fibers on both

sides of the vertebral column reaching the ganglia which are distributed from the cervical

region (cervical ganglia) reaching all the way to the sacral region (sacral ganglia).

*The presynaptic neurons of the sympathetic nervous system are shorter than those of the

parasympathetic nervous system, why?

*The S.N.S. works as one unit meaning that it will affect many organs at the same

time. For this to occur, one presynaptic neuron must affect many postsynaptic

neurons that each goes to a specific organ throughout the body, because of this the

sympathetic ganglia are close to the vertebral column and so the presynaptic

neurons are short. While in the parasympathetic N.S. each presynaptic neuron

usually only affects one specific organ so the presynaptic neurons are long and the

ganglia are usually inside or near the effector organ.

The sympathetic effect on each organ :

1) Eye

Iris muscle , which controls the size of the pupil, has two types of involuntary

smooth muscles (the radial and the circular)

** IRIS radial m. attaches to the outer border of the iris and it widens (dilates)

the pupil when it contracts (By Sympathetic innervations) This state is called

MYDRASIS .

** CIRCULAR m. (also called iris sphincter m.) narrows (constricts) the pupil

when contracted (By Parasympathetic innervations) this state is called

MIOSIS

3

2) Salivary glands

They are 3 different salivary glands in our bodies (as shown in the picture below), and

under sympathetic effect they will secrete small amounts of salvia or no saliva at all

(when you are under stress like exams, war... you won’t need it.)

3) The heart

It will increase the heart’s output , By...

1) Increasing heart rate (positive chronotropy).

2) Increasing the cardiac contractility (force of contraction) (positive inotropy).

*The sympathetic N.S. also causes the coronary arteries to dilate because increased

activity of the heart tissue requires an increase in oxygen and nutrients.

4

4) Respiratory system

The smooth m. around the bronchioles and trachea will dilate (Bronchodilation), so

more oxygen will enter in order to send it to organs that need it (ex. muscles while

exercising).

5) Stomach & Small intestine

The sympathetic N.S. causes the inhibition of the activity of the G.I. tract by causing

the smooth muscles of the intestinal wall to relax, and causing the smooth muscles of

the sphincter (smooth muscle in the colon which controls the exit of feces) to contract.

6) Kidney & Supra Renal Medulla

* We need to increase blood pressure so the kidney releases rennin which causes

constriction of capillaries.

* We also need CATECHOLAMINES, so the Supra Renal Medulla will release

( adrenalin 80% , noradrenalin 20% ).

* Some effects of catecholamines :

7) Skeletal muscles

The sympathetic N.S will cause vasodilatation of blood vessels of these muscles (to

send more O2 to muscles to increase their activity during exercise for example)

8) The circulation of Skin & GI tract

The sympathetic N.S will cause vasoconstriction for circulation of Skin [note: the

frightened person looks yellowish because of leakage of blood flow to skin and

subcutaneous tissues]

Also, vasoconstriction will happen to circulation of the GI tract because we don’t need

to digest food at stress situation, it flows to other tissue as needed (brain, kidneys,

heart, muscles …)

Catecholamines cause general physiological changes that prepare the

body for physical activity (fight or fight response). Some typical effects

are increase in heart rate , blood pressure , blood glucose levels and

general reactions of the Sympathetic nervous system .

5

9) Genitourinary smooth muscles

a) Urinary bladder

Same effect as in the G.I. tract: relaxation of the wall and constriction of the

sphincter.

b) Uterus

Relaxation of the smooth muscles in the uterus

c) External Genitalia

In females the sympathetic N.S. activates orgasm while in males it activates

ejaculation. The parasympathetic N.S. stimulates erection in males, through

vasodilatation which causes the blood flow to increase)

10) Spleen

The spleen is an organ containing some blood supply, so the S.N.S causes some

smooth muscles surrounding it to contract squeezing the spleen causing the blood

supply to be released to the extracellular compartment.

11) Liver

An increase in blood glucose is necessary in fight or flight situations, so the

sympathetic nervous system causes an increase in glycogenolysis, which causes

hyperglycemia.

12) Sweat gland

The S.N.S. causes the body to increase energy production (ATP synthesis), this will

cause an increase in body temperature (shivering from stress, fear, cold, etc…), so to

modulate this the S.N.S. activates sweat glands to decrease body temperature to avoid

hyperthermia.

6

This figure is to review what we have studied

7

THE EFFECT OF PARASYMPATHETIC STIMULATION

*The parasympathetic nerves come from two regions: the cranial region which gives us

4 nerves and three sacral segments of the vertebral column (S2-S4) commonly referred to as

pelvic splanchnic nerves.

*Parasympathetic presynaptic neurons are longer than those of the sympathetic N.S.

because in the parasympathetic N.S. organs are usualy activated seperately, so the ganglia is

usually near or inside the affected organ.

*Cranial nerves :

Oculomotor nerve III

Facial nerve VII

Glossopharyngeal nerve IX

Vagus nerve X

The Parasympathetic effect on each organ :

1. eye

**Remember as we said previously the circular m will contract when

parasympathetic N.S is working and causes Miosis (constriction of the

pupil)

** lacrimal gland will stimulate and secrete tears under parasympathetic effect

[note: when something enters your eyes it starts releasing tears ]

2. Salivary glands

It will increase releasing salivation ( copious* watery secretion )

*copious means abundant (it may reach one to two liters per day)

Parasympathetic & sympathetic Both cause Contraction of the eye muscles ,

but one of them causes the contraction of the radial m (sympathetic) and the

other (parasympathetic) causes contraction of the circular m.

8

3. The heart

Vagus nerve firstly innervates the heart , via SA node [note: there are SA

nodes, AV nodes , pukinje fibers (but these fibers are not innervated

neither from the vagus nerve nor from any other nerve)

So the vagus nerve will decrease the heart rate (from 120 to 70 or 60 bps)

in normal situations. all of the contractile properties of the heart will

decrease, such as number and force of contractions, thus the heart will be

relieved from stresses.

3. Smooth M of bronchioles and trachea

It will be constricted ( there is no need for extra oxygen but the secretion of

the gland will increase).

4. GI tract

Remember this is rest and digest system so the digestion rate will increase

so it will constrict the smooth muscles of the walls of the GI and relax the

sphincter.

5. colon

it will increase contractility of the wall of GI and relax the sphincter via

pelvic nerve

6. Urinary bladder

Increases the contractility of the wall for urintation and inhibits the

sphincter.

7. External genitalia

Induces male erection

*Extra

information in

picture :

9

10

*Physiological function of sympathatic N.S

It is a dynamic system (continuosly active) which means that it works non

stop, especially for blood pressure, and stressful situations ( fear ,

hypoglycemia , exercise ….etc) = (fight or flight).

The S.N.S. either works directly (through nerves affecting the organ

directly) or indirectly (by affecting the supra renal medula.)

* Supra Renal Medulla is a gland not a ganglia when it is stimulated by

acetylcholine it secretes Catecholamine ( Epinephrine 80% & Norepinephrine

20% ) which are secreted directly into the blood then transported to all parts

of the body , the cells that receive it have (α , β adrenergeic receptors) which

the Catecholamines will bind to and activate.

Stimulation of Sympathetic N.S will cause:

1. Increase in heartrate

2. Increase in blood prussure

3. Increase in blood flow to the skeletal m.

4. Increase to the heart via the coronory heart dilation

5. Decrease in blood flow to the skin

6. Dilation of the pupil

7. Derease in the blood flow to the GI

8. Bronchi dilation

9. Hyperglycemia through to glycogenolsis.

Stimulation of Parasympathetic N.S will cause:

1. Stimulates the digestion mechanism

2. Stimulates the urintation according to the body’s need. [note: the

parasympathatic stimulation only affects the organ we need \and not to

all organs that are stimulated by it. ( in this example we are only

disucssing the urinary bladder)]

3. Dominates in maintaining the heart rate.

11

Neurotransmitters

*1*Act as (Local hormones) these are substances that the cell secretes and act on the same

cell they are secreted from. Its action ends within seconds like histamine and Prostaglandins

*2*A substance that is secreted by endocrine glands directly to the blood then to other body

parts .( like pancreas which is an endocrine gland producing several important hormones

like insulin and glucagon.)

*3* A substance that is secreted by exocrine cells which releases its contents at the cavities

of the body (for ex. the pancreas which is composed of “exocrine” cells that produce

enzymes to help with the digestion of food.)

*4*there is no continuous transmission between neurons or between the neuron and the

effector organ , so How is the electrical current transduced?

By chemicals called (neurotransmitters)

Finally ..This is a brief introduction about what will be discussed next lecture:

You know that neurotransmitters are transported from the (presynaptic neuron) to the (post

synaptic neuron) via the synapse but how does this occur exactly?

The neurotransmitter will be pumped into the nerve ending by the active transport

mechanism then it is stored in vesicles until an action potential reaches the presynaptic

ending , then this vesicles will bind to the presynaptic membrane and will be released to the

postsynaptic membrane by diffusing through the synapse to bind finally with the

postsynaptic membrane receptors to cause action potential in the second neuron .

Chemical signals between cells

Autacoids

Hormones

Exocrine

12

How will the signal stop??

If the neurotransmitter is acetylcholine then it will be degraded by an acetylcholine-esterase

enzyme to (acetate & choline)

While if the neurotransmitter is (epinephrine or norepinephrine) it will be reuptaken by α

receptors on the presynaptic membrane (where it came from)

This sheet was talked TOTALLY about last year’s physiology Our

colleague )لجين العضايلة( has written physiology sheet for us Doctor 2016

Please remember that she helped us one a day

اذكروها بدعوة