Professor Dave again, let’s look at the muscular system.
It’s been quite a task, but we just finished learning about the structure of muscle tissue,
as well as the process by which muscles contract, allowing us to walk, jump, blink, and breathe.
So we are now ready to learn about all the different muscles in our bodies by name, which
together comprise the muscular system.
There are hundreds of muscles in the body, so we won’t name every single one, but we
will go through some important points, as well as a number of the major muscles and
muscle groups.
First, how can we classify muscles?
Let’s start by grouping them according to function.
We must realize that muscles specifically contract and do not expand, which means that
muscles can only pull, they do not push.
So complex motion requires many muscles working together in interesting ways.
The four functions we will examine are as follows.
First, there are prime movers, or agonists.
These are muscles that have a primary responsibility in producing a particular motion.
Muscles that oppose a particular movement are called antagonists.
This can help provide resistance and produce more delicate motions.
Next there are synergists.
These help the prime movers, either by contributing additional force, or reducing undesirable
movements that could occur as the prime mover contracts.
So we can think of synergists as stabilizers in a certain sense.
And lastly, when synergists immobilize a bone they are called fixators.
This includes muscles that maintain our posture.
So there we have prime movers, antagonists, synergists, and fixators, and interestingly
a particular muscle can exhibit more than one of these roles depending on what kind
of motion it is producing.
Skeletal muscles also have specific names, and they are named according to any of seven
specific criteria.
Let’s be aware of these criteria, even if we don’t go over the name of every single muscle.
First, there is muscle location.
For example, the temporalis is adjacent to the temporal bone.
Next there is muscle shape.
The left trapezius muscles are roughly trapezoidal in shape.
Then, muscle size.
We will see words like maximus, minimus, longus, and brevis, in a number of muscles, and these
mean that the muscle is large, small, long, or short, respectively.
Examples include the gluteus maximus and the gluteus minimus.
Next, the direction of muscle fibers.
Sometimes these run in a particular direction with reference to a particular line, like
the midline of the body, or the axis of a bone.
Rectus means parallel, transversus means perpendicular, and oblique means at some angle.
So the rectus femoris is a muscle whose fibers run parallel to the long axis of the femur.
Next, we can consider the number of origins.
Biceps, triceps, and quadriceps have two, three, and four origins, respectively.
Then we can discuss the location where the muscle attaches to other structures.
Here we list the point or points of origin, followed by the point of insertion, such as
with the sternocleidomastoid muscle, which has origins on the sternum and clavicle, and
inserts on the mastoid process.
And lastly, we can name muscles according to the type of motion they produce, like a
flexor, extensor, or adductor.
With these criteria understood, we should have a reasonable capacity to know something
about the function of a muscle from its name.
Now let’s look at different muscle shapes.
The fascicles of a muscle, which as we recall are bundles of muscle fibers, can arrange
themselves in a variety of ways to produce muscles in a variety of shapes.
If in concentric rings, we can get a circular muscle, like the ones around the eyes and mouth.
If they are spread out over a region but all converge towards a tendon of insertion, that
is a convergent muscle, like the pectorals.
If they taper down to a tendon at two ends, that is called fusiform, like the biceps.
If the fascicles run in a straight line parallel to the long axis of the muscle, that is a
parallel arrangement, like with the sartorius muscle found in the thigh.
And lastly, in a pennate muscle, fascicles are short and run at oblique angles, and they
can be unipennate, where muscle sits on one side of a tendon, bipennate, with muscle on
both sides, resembling a feather, or multipennate, which looks like several feathers inserted
into the same tendon.
These different shapes determine the range of motion that the muscle can produce.
Any skeletal muscle can only contract by about thirty percent, so the muscles with fascicles
that run parallel to its long axis will shorten the most, but sacrifice some power.
The muscles with many fibers at oblique angles will shorten less, but produce more power.
Now it’s time to look at specific muscles as they are arranged in the body.
As most viewers of this tutorial probably have no specific need to memorize hundreds
of muscle names, we will display just a few major ones right now, over the course of a
few images.
Should you feel the need to memorize any of these, feel free to pause the clip in full
screen mode and take a screenshot for later reference, otherwise just try to gain a vague
familiarity.
If you decide to go into a medical field, don’t worry, you will see a lot more of
these later and you can memorize them then.
So here we go.
And with that, we have wrapped up our survey of muscle tissue, the mechanism of muscle
contraction, and the muscular system.
We mentioned that muscle contraction begins at the neuromuscular junction, so what are
neurons all about?
These highly specialized cells are part of the nervous system, so let’s learn about that next.