11

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Muhammad Abed

Osama Al-khader

Muhammad khatatbeh

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-Some points from the previous lecture: -

In the previous lecture, we have seen how we can get excitatory post synaptic

potentials (EPSP) and inhibitory post synaptic potentials (IPSP), also the types of

summation which are spatial summation and temporal summation.

-The action potential generates in the axon hillock.

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“The new lecture”

Two notes to know: -

*when we have many presynaptic neurons synapsing with one neuron, we call this

synaptic organization as convergence. Results in many inputs from presynaptic neurons

received by single postsynaptic neuron.

*when we have one neuron with its many terminals synapsing with many neurons, we

call this synaptic organization as divergence. It results in converting the signal from one

neuron to many postsynaptic neurons.

In our nervous system, we have many divergence and convergence between our neural

network structures.

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Compound action potential: -

It is a recording for action potential with multiple peaks or waves.

We can do it by performing a stimulus to the skin which will stimulate all

neurons of a nerve, then we put a sensor away from the stimulus.

Each wave reflects the activity of a group of fibers with a similar conduction

velocity. So, we have many waves because of the difference in the velocity of

conduction of the action potential due to the difference in the type of the

neuron and the diameter of it.

This reading helps us to check whether the neurons of a person of a nerve is

working properly or not.

More details with Dr. Faisal. We don’t have to know much right now.

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Autonomic nervous system (ANS) The autonomic nervous system is the portion of the nervous system that

controls most visceral functions of the body. This system helps to control

arterial pressure, gastrointestinal motility, gastrointestinal secretion, urinary

bladder emptying, sweating, body temperature, and many other activities,

some of which are controlled almost entirely and some only partially by the

autonomic nervous system.

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The general function of it is the Control and Adaptation of body systems to

internal and/or external changes. These changes include fear, stress, eating,

digesting, etc.

The system is divided into two subdivisions sympathetic and parasympathetic.

-Physiological characteristics of ANS: -

*speed of onset: ANS can produce dramatic changes in the level of activity of

organs they innervate within seconds.

*Autonomic nature: functions and the regulation by this system occurs

without conscious control as the name indicates.

*Tonic activity (of each division): means certain level of activity over the body.

As example, sometimes the level of activity of the sympathetic nervous

systems increases and the level of activity of the parasympathetic nervous

system decreases. So, this system is continually active. The value of this

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feature is that it allows a single nervous system both to increase and decrease

the activity of a stimulated organ. For instance, sympathetic tone normally

keeps almost all the systemic arterioles constricted to about one-half their

maximum diameter. By increasing the degree of sympathetic stimulation

above normal, these vessels can be constricted even more; conversely, by

decreasing the stimulation below normal, the arterioles can be dilated.

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Examples on some situations when the system works:

When your eye is exposed to intense light your pupil constricts, an in the low

light situation your eye pupil dilates.

Constriction of the pupil is known as miosis, while the dilation of the pupil is

known as mydriasis.

Temperature: in warm environment, cutaneous vasodilation and sweating

occurs, and vasoconstriction in cold.

vaso-vessel

Stress (mainly for sympathetic nervous system and adrenal medulla): as in

fight or flight situation many responses happen. As an increase in the heart

rate tachycardia, widely dilated pupils, pallor (pale of fear due to low blood

flow to skin), goose pimples (hair standing over skin), cold sweat(because of

the low blood flow to the sweat so it won’t be heated) and dry mouth (low

activity of salivary gland because it is not the perfect time to digest food)

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Sympathetic and parasympathetic nervous systems (general overview)

sympathetic nervous system- SNS

parasympathetic nervous system- PNS

there are 3 differences and 1 similarity between them.

The similarity is that the two types have two neurons starting from the place

of origin to the effector organ, this pathway from the origin to the effector

organ is called the Axe. The Axe in both types consists of two neurons. (There

is an exception in SNS will be noticed later).

Differences: The origin: the sympathetic nervous system originates from the spinal cord

from the thoracolumbar region (from T1 to L2) *In the handout to L3. The

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parasympathetic nervous system originates from the sacral region (the lower

most region of the spinal cord S2, S3) and from certain nuclei in the cranial

region, so the parasympathetic nervous system has a craniosacral origin.

Note: - in the handout, the origin for the PNS is S3, S4 (sometimes S2 and S5)

in the book, S2, S3.

the most important is to know that it is craniosacral.

The second difference is the function and the level of activity in certain

situations. For example, SNS mainly active during “fight or flight” situations

which involves stress and fear … , while PNS is specialized in “rest and digest”.

The third difference is the length of the first and the second neuron as we said

in the similarity between PNS and SNS. In the SNS, the first neuron is short

very near to the spinal cord and the second neuron is long. The opposite in the

PNS where the first neuron extends from its origin to a very close position near

the effector organ or in it, where it synapses with the second short neuron.

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Sympathetic nervous system in more details

Physiological anatomy: Two neurons carry impulses of the SNS from CNS to the

effector organ. The first is known as preganglionic (before the ganglion) neuron

and the second is known as the postganglionic neuron (after ganglion).

The ganglion: a cluster of cell bodies.

For the SNS there are three possibilities for the synapsing condition.

*Look at the picture below.

The two neurons may meet in the paravertebral ganglia, the paravertebral

ganglia are closer to the spinal cord than prevertebral ganglia.

(Ganglia is the plural for ganglion).

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The two neurons will pass from the paravertebral ganglia without synapsing then

meeting in the prevertebral ganglia (located in the abdomen).

note: the prevertebral ganglia are free ganglia that are not connected to each

other, unlike the paravertebral ganglia. Also, they are three in number, celiac

ganglion, superior and inferior mesenteric ganglia.

The third case which is the exception mentioned in the beginning of the sheet. In

this case, there is no two neurons only one neuron passing from the spinal cord

to the adrenal gland where they synapse with cells called chromaffin cells results

in releasing epinephrine (adrenaline) in the blood stream.

Note1- in the SNS we have a lot of divergence and convergence to do the

diffuse reaction which is a

characteristic of SNS. While in PNS,

almost no convergence and

divergence.

Note2- in the first situation

where two neurons meet in the

paravertebral ganglia, the first

neuron (the preganglionic neuron)

might synapse with the second

neuron at the same, lower or

above segmental level; i.e. some

terminals of some preganglionic

neurons synapse at a higher

segmental level, lower segmental

level or above the segmental level. ----------------------------------------------

Effects of sympathetic stimulation

(Fight or Flight)

SNS innervates widely distributed

tissues including sweat glands,

smooth muscles of blood vessels

supplying skeletal muscles, skin,

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etc. and smooth muscle cells of hair follicles. All of these target tissues don’t have

any parasympathetic innervation. So, the effects are:

Controlling blood pressure. As an example, by changing the diameter of the

blood vessels.

Body temperature by effecting cutaneous blood vessels and sweat glands.

Handling stress (fight or flight reaction)

the main goal is to promote the production of energy for muscular work and to

shut down organs with nonessential function. (You don’t need to digest food

while facing a lion). Effects include: -

*cardiovascular system: by redistributing blood to skeletal muscles and reducing

blood flow for skin and mesentery. Also, increasing the heart rate and the force

of contraction.

*Respiratory system: by relaxation of bronchial muscle which results in

bronchodilation (increasing in the diameter of bronchi) to get more oxygen.

*Digestive system: inhibition of motility and secretion. (Results in dry mouth due

to low salivation.

*Metabolic effects: increase in the rate of mobilizing glucose and lipids because

we need nutrients for the muscles.

Glucose is stored in the form of glycogen in our bodies.

If it was easy, everyone would do

it, but it is the hardness that makes

it great.