of the ribs at that level.
Now, we want to shift our attention to movements
of the thoracic wall as well as the diaphragm.
The way the thoracic wall is constructed,
along with the diaphragm, these structures
are well suited to change thoracic volume
that is necessary for respiratory movements.
The diaphragm is shown here. It is in its
superior most location after normal expiration
and one of the changes that has to occur for
inspiration is to increase your thoracic volume.
The diaphragm participates in this maneuver
by contracting. It will then undergo a downward
excursion, downward movement, thereby increasing
the vertical dimension or volume of the chest.
We also have two other movements that are
produced by the osteology of our thoracic
wall. And so, here, we're looking at the relevant
osteology and we have two kinds of movements
that can be described with the osteology.
If we take a look at the sternum and look
at the xiphoid process and consider that is
a pump handle and pull up and out on that
pump handle, we will increase the anterior–posterior
dimension of the thoracic cavity, also increasing
the thoracic volume for inspiration. We can
also describe a bucket handle movement
to the ribcage, and if we look at the lateral
aspects of the ribs on either side and put
our hand under the inferior margin of a rib
and lift up and out, that is a bucket handle
type of movement that will increase the transverse
diameter of the thoracic cavity, also assisting
And certainly, instead of using our hands
to describe these movements of the pump handle
or the bucket handle, we have muscles of the
thoracic wall that will produce those given
movements. For expiration, you want to decrease
your thoracic volume collectively. So, the
diaphragm relaxes, moves upwards, decreasing
the vertical dimension, the ribs fall down
and toward the back, thereby decreasing the
transverse as well as the AP, anterior
to posterior dimensions.
Based on the architecture of the osteology,
there are two apertures in the thoracic wall.
The superior thoracic aperture is shown here.
This is termed the thoracic inlet. It is the
smallest of the two in diameter, so it’s
very restricted. But, it will allow the passage
of structures between the neck and the thoracic
cavity such as the esophagus, for example,
or some of your blood vessels such as the
common carotid arteries. They’re going to
have a vertical course through this thoracic
There are also some structures that are going
to be distributed to the upper extremity.
They are going to course outwards and up and
over the thoracic inlet and the thoracic inlet
is bounded by the first thoracic vertebra,
the first pair of ribs, as well as the superior
aspect of your manubrium.
The thoracic outlet is much wider than the
thoracic inlet and it is bounded by T12, rib
12, the anterior most aspect of rib 11 and
then the costal margin that we see here. And
the costal margin is formed by the costal
cartilages of ribs T7 through T10. And then
the most anterior boundary of your thoracic
outlet would be your xiphoid process and then
we’d repeat that as we go around to the
opposite side of the thoracic wall.
Now, we’ll shift our attention to the muscles
of the thorax and when we look at muscles