Our third type of tissue we're going to talk about is muscle tissue or muscular tissue. Muscular tissue is contractile. It provides movement, and that can be both voluntary or involuntary. We think of our muscles that we train to move our bones, like your biceps or your quads or hamstrings, and those are certainly muscle tissue.
But you do have muscle tissue around your blood vessels, around your GI tract, and many other places in the body. It provides motion, helps maintain posture. It also functions in controlling heat. For example, you shiver when you go outside in the cold.
There are three types of muscular tissue. And again, I'm just going to run through these fairly quickly because we do have a whole section later this semester on muscles. But we have skeletal muscle.
This is muscle that's attached to your bones that actually moves your body. So these are the muscles that you think about. And also your diaphragm is made of skeletal muscle for breathing.
A cardiac muscle. Cardiac muscle is found in the heart, not in the blood vessels, in the heart only. And then smooth muscles. Smooth muscles found in blood vessels, GI tract, and a variety of other places in the body. So skeletal muscle, the important thing to know about it is it's voluntary, meaning you can consciously control movement of your skeletal muscle.
It's striated. Striated means striped. If you look here, you can see the striping on this muscle tissue. It's also multinucleotide.
If you look at this muscle fiber, a muscle fiber is a muscle cell. We call them fibers. Notice you have multiple nuclei in it.
So they're multinucleotide as well. Cardiac muscle is involuntary, meaning you cannot consciously control it. but it is also striated. You can see that here in this figure.
You can see the striping. It has branched fibers, so a cell will actually branch off like this, and it has something called intercalated discs. Those are these dark lines here, and you can also see those here.
It's the connections between the cells are called intercalated discs, and they have a special junction in them called a gap. junction. And these are like tunnels, remember, between cells.
And this allows the electrical ions, the ions for the electrical impulse to move from cell to cell very quickly. So it allows your heart muscle to contract in unison. You want all your muscle cells of the heart to contract together so you can actually pump blood out of the heart.
So those are the four main features you should know about cardiac muscle. And then smooth muscle. Smooth muscle is involuntary, meaning you cannot consciously control it, but it is not striated. If you look, the muscle cells have a very different shape here, and this shape allows them, when they contract, to change in size much greater than skeletal or cardiac muscle.
When skeletal or cardiac muscle contracts, it doesn't shorten too much when it contracts, but smooth muscle can shorten quite a bit.