To know where a smooth muscle is located,
which is throughout many different
areas in the body, let’s start with
something easy like blood vessels.
Blood vessel smooth muscle here helps
control the diameter of the vessel,
which regulates the blood flow.
If it increases the diameter of
the vessel, more flow can happen.
If it decreases the diameter,
less flow happens.
Airways are controlled in a
similar manner in which you can
bronchodilate or bronchoconstrict
and that regulates airflow.
The urinary system also
has smooth muscle in it,
such as the ureter and bladder, and
this will help, not only the stretching
to be able to load the bladder,
but also to get rid of the urine.
In both the male and female,
there is smooth muscle in the
reproductive tract to help things
like sperm move along the tract
or in terms of the female
for labor processes.
The eyes have smooth muscle and this
causes an increase in pupil diameter.
This will allow either more
or less light into the eye.
The kidney also uses
smooth muscle to regulate
blood flow through the
and those will be discussed
more in the renal section.
In the skin, you use small amounts of
smooth muscle to cause hairs to stand up.
These are many of the
different locations of smooth
muscle and some of the
functions that are involved.
But hopefully, you get the
appreciation that smooth
muscle is located almost
everywhere in each of these
organ systems and this will
allow for the movement
of other types of processes
along a certain track.
Besides the different locations
of where smooth muscle is,
smooth muscle can operate as a
single unit or as a multiunit.
The single units are known as
phasic and the reason why these are
act together is they’re connected
by small little gap junctions.
Those gap junctions are
denoted in the figure above.
Tonic smooth muscle acts
more like multiunits
and these are because
there are individual
nerve fibers that innervate the various
portions of that smooth muscle.
And so, they won’t operate as a single
unit but rather as a multiunit process.
Autonomic nerve fibers can innervate these
single unit or phasic smooth muscle
causing these gap junctions to share
information versus tonic smooth muscle,
which again use autonomic fibers
and they are connected to
various smooth muscle cells.