starters, I am not expecting you to learn quite as much about these muscle types as is
described in your book. Especially when it comes to smooth muscle. So, take a
look at the important points I list here on each of these muscle types, and then make sure
you understand these points in your book.
General Characteristics of Both Cardiac & Smooth Muscle
(that makes them different from skeletal muscle)
- Calcium ions enter the muscle fiber sarcoplasm, at least in part, from the extracellular
fluid (not just the SR).
- Smooth & cardiac muscle fibers are connected to each other electrically, so that
excitation of one muscle fiber may be enough to activate the next muscle fiber
(without necessarily getting the nervous system involved in activating each and every
separate muscle fiber like it has to do in skeletal muscle motor units).
- Less force production than skeletal muscle (a slightly different myosin exists in these
- Only one myonucleus per muscle fiber.
General Characteristics of All Muscle Tissue Types (cardiac,
smooth, & skeletal)
- Contain sarcomeres of actin and myosin (that shorten by sliding filaments) organized
- Use calcium to regulate when contractions occur
- Have an electrically-excitable sarcolemma
|Cells are connected to each other by intercalated
disks (and this is also a location for electrical coupling between cells).
The cells can communicate so well through these disks that when one muscle fiber is
excited, its excitation spreads across huge regions of the heart and excites other muscle
fibers. In this way, large regions of cardiac muscle tissue work together, and these
regions are called syncytia (while the singular form of this word is syncytium).
|Has an extensive t-tubule system
|Less organized, thin myofibrils
|Typically found to occur in sheets
(your book calls this "visceral smooth muscle," but don't worry about this title
or "multiunit smooth muscle" either).
|Sheets of smooth muscle tend to run
both longitudinally and circularly wherever they are found... this allows for peristalsis
(a patterned movement of a tube, like of our esophagus when we swallow), mainly because
the muscle fibers are electrically communicative (your book says that they can
"transmit impulses from cell to cell").
|No troponin, so these muscle fibers use
a different calcium-receiving molecule called calmodulin. You'll
see this molecule name come up again when we do the endocrine system next semester.
|Very slow at contraction (much slower
than slow skeletal muscle fibers). Also, very resistant to fatigue.
Here's a histology site that I'm not sure if I gave you
before. Go here and click on muscle and then check out some different views of
cardiac, skeletal, and smooth muscle.