Hi, welcome to pharmacology by Lecturio. We are going to
cover the autonomic nervous system. I'm Dr. PJ Shukle,
I'm an internal medicine specialist and we are going to
cover how drugs work in the body. Specifically today,
we are going to look at the autonomic nervous system. In terms
of an overview let's take a look at how the parasympathetic
system works. The parasympathetic system starts as nerves
coming out of the spine and they meet at a nicotinic cholinergic
receptor to give you a post-synaptic neuron that hooks
up to the cardiac, smooth muscle or gland of it's choice.
The parasympathetic nervous system has preganglionic fibres
and these originate in cranial nerve nuclei III, VII, IX and X.
There are also some sacral segments at S2 to S4 of the spinal
cord as well. These ganglionic synapses respond to nicotine.
So they are called nicotinic cholinergic receptors. And
effector synapses responds to muscarine. So they are the
muscarinic cholinergic receptors. Let's take a look at the
sympathetic system. This is the opposite system to the
parasympathetic system. They also work through the spine and
they come off many of thoracic and lumbar vertebrae
and they meet at a ganglia. The ganglia are nicotinic cholinergic
as well. And from there they proceed on to the different targets.
The muscarinic cholinergic receptors in the sweat glands, the
epinephrine and norepinephrine target organs in the cardiac
muscle, smooth muscles some glands and nerve terminals, and
the dopamine receptors in renal vascular smooth muscle.
This stuff is hard to remember, so let's use a little mnemonic.
The gangos out to smoke. So that's how I remember that ganglionic
neurons are nicotinic cholinergic. And people smell a little
musky when they sweat. So the sweat glands are muscarinic
cholinergic receptors. Of course, norepinephrine works on the
heart so that's easy to remember. And dopamine works on the
renal vascular system. And we're going to talk about that
certain drugs that are used to bring up blood pressure.
Sympathetic nervous systems work through sweat glands, cardiac
and vascular tissue, other glands, nerves and renal tissue.
These preganglionic fibers originate in the thoracic vertebrae
or in the lumbar vertebrae segments of the cord. The ganglionic
synapses are always nicotinic. Effector synapses are always
muscarinic, noradrenergic, adrenergic or dopaminergic.
Let's move on to the adrenal medulla. The adrenal medulla is
sort of part of the sympathetic system but we're going to
separate it out because it's important to know that there is
a nerve that directly connects the spine to adrenal medulla.
And the adrenal medulla releases then epinephrine and
norepinephrine. The sympathetic adrenal system
has preganglionic that originate from the thoracic segments.
These are nicotinic receptors. And those nicotinic receptors
on the adrenal medulla itself end up releasing adrenaline and
noradrenaline into the blood stream. Finally we have the
voluntary system. In the diagram here it looks like it's
coming out of the sacral nerve segments but you all know
that it is every level of the spinal cord right from the
cervical vertebrae right down to the sacral vertebrae.
The preganglionic fibers originate from all levels of the
spine and the brain. The nicotinic receptors are the receptors
on the surface of the muscle. And the effectors are the
skeletal muscles themselves. Okay, so now let's get into
a little bit more detail because this is going to be relevant
when we start looking at drugs. The dopaminergic receptors
are D1 receptors in the smooth muscle of the kidney
vasculature. The adrenergic receptors are either alpha
or beta and they can be alpha 1 or alpha 2, or beta 1,2 or 3.
The parasympathetic nervous system is either nicotinic
or muscarinic as I mentioned to you before. And the muscarinic
can be M1, M2 or M3. Now, we spoke about adrenergic receptors
and dopaminergic receptors and cholinergic receptors. There is
actually another category of receptors that are in the autonomic
nervous system. They go by the acronym NANC transmission.
They are the non-adrenergic, non-cholinergic transmission.
And so they will use different types of organic molecules.
One of them are the purine receptors. So purine receptors
1 through 7 are spread out throughout the body and we're
going to talk about them individually in each of the lecture
segments that we are going to go through. The peptide based
NANC transmission agents are things like adenosine triphosphate,
vasoactive intestinal peptide, neuropeptide Y and
substance P which is a sensory or local effect fiber.