Autonomic Nervous System Effectors.
Now, we get to talk a lot about all this different
things that happen throughout the body
that will able to be doing something.
We are not just gonna look at things.
We are gonna look it action today.
The Autonomic Nervous System is a large cohort that’s
controlling a number of aspects of the body.
What we have here are two different columns.
These are spinal cord columns.
The first one is the autonomic nervous systems,
And then, on the other side, we have
the parasympathetic component.
The sympathetic component you know because it has
paravertebral chain ganglia on both sides of the spinal cord.
This will act as relay spots and sometimes where
the soma or cell body of the nerve will be.
The parasympathetic nervous system, remember,
primarily comes from cranial nerve number 10.
So this vagus nerve will innervate many
of the different organs in the body.
These are the same organs that would innervated
by those particular sympathetic fibers
that come off of the spinal cord.
In the parasympathetic nervous system then you also
have the splanchnic nerve and some that come from
the sacral area. And they will innervate things like
the bottom portion of the GI track,
places like the bladder and the reproductive organs.
So we go through this process, I think it’s best to
do this one organ at a time.
And so, we do one organ, the next organ, and
keep going through those.
We’ll talk about what’s function that’s involve, as well as
what receptors will mediate that particular function.
Let’s start off with the heart.
The heart is going to be innovated by both the
sympathetic and parasympathetic nervous system.
The SA node, and this is again the area
that’s going to control heart rate.
If it’s engage by the sympathetic nervous system it’s
through Beta-1 (β1) adrenergic receptors,
and this will increase heart rate.
In contrast, the parasympathetic nervous system,
is mediated through muscarinic receptors
and that decreases heart rate.
The conduction system of the heart especially
around the AV node,
velocity can change in response to sympathetic
comparison sympathetic stimulation.
Beta-adrenergic receptors here also increase conduction
velocity in the sympathetic nervous system.
While muscarinic receptors, this decrease
the conduction velocity.
In terms of contractility, which is the contraction,
the strength of the heart,
this is gonna be mediated also by beta-adrenergic receptors.
But now, this increases contractility or an atrophy.
Muscarinic reflects don’t really have anything to do
with the ventricles, to push blood around
to the body or to the lungs.
What happens to the blood flow that goes
to the skin in the muscle?
Here we need to talk through which things
cause constrictions and dilations.
So in the skin, we mainly have alpha-adrenergic
receptors that cause vasoconstriction.
So vasoconstriction is going to be decreasing the
luminal diameter of a blood vessel
that reduces the amount of blood flow.
Beta-2 (β2) adrenergic receptors are located in
skeletal muscle and they can cause a vasodilation.
That said, they are usually not engaged in normal physiology.
You have to give us supra physiological dose of
a drug to get this receptors to be in acted.
So normally, our response is having a vasoconstriction
in response the blood vessels of skeletal muscle.
So you vasoconstrict them in terms of the
sympathetic nervous systems response.
Hopefully, you’ve looked now on the parasympathetic side
and notice there is no intervention of blood vessels
to the skin or to the muscle from the
parasympathetic nervous system.
That’s said, there are some relaxing factors that
can be released. And some of this have been associated
with some parasympathetic innervation especially
in the facial region.
The Autonomic Nervous System and the Lung.
So what changes happen with the lung in regards to a
sympathetic and parasympathetic nervous system?
The main component with the lung are the bronchioles.
If you dilated a bronchiole, what will get is an increase
in a diameter. And if you have an increase in diameter,
you'll have a reduction and a resistance and
therefore more flow.
And this sympathetic nervous system does just that
by dilating bronchioles.
It does that through beta-adrenergic receptors.
The opposite response is a constriction.
And this is mediated by this parasympathetic
nervous system through muscarinic receptors.
What about the GI Tract?
How does the autonomic nervous system both the
sympathetic and parasympathetic mediate this?
We have to throw one caveat in this before we
go through the table. And that is,
remember, there is another division of the
autonomic nervous system which is known as the
enteric nervous system.
The enteric nervous system gives information from the
sympathetic and the parasympathetic.
But it also operates on its own. So I have to throw
that caveat in as we go through this particular table.
So what are the effects on smooth muscle walls?
The sympathetic nervous system relaxes them.
The parasympathetic nervous system contracts them.
So what does that mean?
Practically, if you have a smooth muscle wall relaxation,
You’re going to slow down the food,
slow down the food as it travels to the GI tract.
If you have a contraction, it will speed it up. So
as you speed up food that travels through the GI Tract.
So this effects gastric motility.
If you want to think about this in terms of these sphincters.
Now, this are the areas of
a gastrointestinal tract that act as gates.
You will get a sympathetic nervous system will
cause of vasoconstriction,
or sorry, a constriction
and with this dose is prevent the food stuff
form going through that particular gate.
The parasympathetic nervous system relaxes those gates.
So that food will move through the GI system.
In terms of secretions, it’s kind of interesting, but both
the sympathetic and parasympathetic nervous system
increase salivary secretions.
They do it via little different mechanisms though.
The beta-adrenergic increase from the sympathetic
nervous system, creates a more mucusy saliva.
And the parasympathetic nervous system
secretes more of a watery saliva.
And so this are differences that can happen in salivary
secretion but both tend it increase it.
It’s just, what type, watery or serous solutions
or more mucusy solutions.
In terms of stomach secretions, the parasympathetic
nervous systems increases gastric secretions.
Also pancreatic secretions is the
parasympathetic nervous system.
Again mediated by muscarinic receptors.
the sympathetic nervous system doesn’t have anything to do
with the secretion end only with the motility
and for the GI Tract.
What about the bladder?
The autonomic nervous system also engages the bladder
so that if you have urinary contents,
you need to know, is it appropriate time or
not to void that bladder?
The bladder. What we’re gonna do here is
cause either a relaxation or a contraction.
Remember, if you are relaxing the bladder,
you are not then wanting to have that urge to void.
If you are contracting it, this is the time where you may
wanted then, if it’s socially appropriate to void your bladder.
These sphincters are also involve in
that same kind of a maneuver.
There will be a constriction portion
and a relaxation portion.
Now again, this is the autonomic sphincter.
There is also a voluntary or skeletal muscle component
that you control from your cortex.
So this is just the one part of being able to void
the bladder but not the voluntary component.
What about the reproductive organs?
The autonomic nervous system both the
sympathetic and para sympathetic nervous system
innervate the reproductive organs
for both males and females.
If you think about for the male genitalia,
the sympathetic nervous system has to do with ejaculation.
The parasympathetic nervous system has to do
with the erection or increasing blood flow.
In terms of the female genitalia, it’s very similar.
You during contractions are sympathetically mediated event.
While increasing this secretions and
increasing the amount of blood flow is a
parasympathetic nervous system.
These is one of the organ systems that I think
or should be most highlighted
because there is a duo activation and needs to happen.
So in this case, you need to have both in
increase of blood flow and ejaculation to happen.
So they are working together in concert. Rather than,
working in an opposition to each other.
So a lot of the different of the organ systems
we saw that one constricted and one dilated.
and so they seemed to be opposites.
But in the reproductive organs, they can
work in concert to do a function.
The eyes, also innervated by the sympathetic
and parasympathetic nervous systems.
This is an important process in being able to get
more light into the eye when you need to see more
or protect it when you need to see less.
The Eye. Sympathetic and parasympathetic
innervation both affect the eye.
The sympathetic nervous system affects radial muscles
and this will dilate the pupil, so you get more light in.
And as you do this, this increases via
The opposite is a pupil constriction.
This constriction is mediate by muscarinic receptors
from the parasympathetic nervous system.
Finally, as you think about ciliary muscles,
They’ve can be dilation or occurrence
from the sympathetic nervous system and constriction
for the parasympathetic nervous system.
So you can see here that dilation seems to
be more sympathetically mediated.
And the constrictions and contractions
more parasympathetically nervous mediated.
Now, let’s address some of the skin specific components.
We already talked about blood vessels in
the previous one. But now, we are gonna go through
and talk about the skin appendages.
And you might ask, appendages
I don’t have anything growing off my skin.
Maybe you do.
Sweat glands are called skin appendages because
they are part of the glandulous structure.
But they will end up being a structure of their own.
They are mediated by the sympathetic nervous system
and muscarinic receptors.
Wait, wait, wait, wait, wait.
I said muscarinic receptors.
Did you mean it?
Yes I did.
This is a rare time when the sympathetic nervous system
is using a muscarinic receptor.
Typically, these are for the parasympathetic
nervous system, right.
But in this case, this is an exception to the rule.
We’re you use acetylcholine as a primary neurotransmitter
and bind the muscarinic receptors. And it’s
still under sympathetic control.
The other type of skin appendage is hair.
And so hair is sticking off the skin. You can modulate
the hair though by contracting pilliary muscles.
This Pilomotor muscles, allow for hair to standup.
And this would be in a time that when you are very cold
or if you are nervous, and your hair starts standing up,
and this also can make little kind of pillary bumps
or we leagues call goose bumps.
This are mediated by alpha-adrenergic receptors and
this is contraction of that smooth muscle.
You notice that the parasympathetic nervous system
here doesn’t activate skin appendages.
Let’s now move on to tear glands.
So lacrimal glands are innervated by
the parasympathetic nervous system,
and muscarinic receptors increase their secretions.
The liver is important in being able to do a
lot of different functions for the body.
In this case, it is gonna be innervated by
the sympathetic nervous system.
It is going to be involve in gluconeogenesis,
which is the production of the new glucose.
It is also involve in glycogenolysis. And that
is the breakdown of glycogen.
Both of these two things will do increasing blood glucose.
Either gluconeogenesis making new glucose or
breaking down glycogen into glucose
the liver then can release it, so the rest
of the body can neutralize it.
Adipose tissue is innervated by the autonomic nervous system.
You will necessarily think of this, would you?
Why would fat be innervate by the autonomic nervous system?
But there are couple of times from a sympathetic event that
it makes it important. Let’s go through those.
Adipose tissue has beta-3 adrenergic receptors.
These receptors, if engage, by epinephrine
or norepinephrine cause lipolysis.
Lipolysis is the breakdown of fat. Then what you would
do is the adipose tissues will release
free fatty acids into the blood.
Another tissue as also adipose tissue
is called a brown adipose tissue.
Brown adipose tissue, especially in infant,
is important for thermos regulation.
They utilize these same beta-3 adrenergic receptors
and end up causing heat production.
So both white fat and brown fat are innervated
by the sympathetic nervous system.
The kidney is innervated by the sympathetic nervous system.
and it does this to help regulate things like
blood flow and glomerular filtration rate.
The other thing that it does is
stimulate the release of renin.
And remember, when was such important molecule
in starting the Renin Angiotensin Aldosterone System.
The RAAS system allows you to reabsorb sodium and water.
And this is an important process that is mediated
by beta-1 adrenergic receptors.