uscles moving bones is a big part of what volleyball is all about! It is the impact with the moving bones that transfers momentum to the ball, causing it to move. When a muscle cell receives an electrical impulse from the nervous system, it uses energy harvested by its mitochondria to contract. Thus, just to lift one’s arm into position to try to hit the volleyball is a very complex motion. All the bones in the arm must be moved into position, each requiring at least one, perhaps several muscles to move it. The cells in each of those muscles must receive a “message” from the brain to contract. Another area of the brain must coordinate all the separate electrical messages so that all the muscles work together. Since muscles can only contract and pull, and cannot push, if the bones need to be slightly repositioned, that requires a whole group of “antagonistic” muscles to move the bones in the opposite direction.

Skeletal and Muscular Systems

Bone tissue is made up of repeated “circular” units like this one, all packed next to each other. Each of these units is called an Haversian system. The concentric layers that make up an Haversian system are made of collagen protein (the same as is in many of our other tissues, and vitamin C is needed to make it), with the difference that in bone tissue, there is a bunch of calcium phosphate embedded in the collagen to make the bone hard. That’s why we need so much calcium for strong bones, and that’s also why drinking too many soft drinks containing phosphoric acid (phosphate) can actually leach calcium out of a person’s bones. The somewhat crescent-shaped black “spots” in this photo contain the actual bone cells, called osteocytes.

All the bones, together, make up our skeleton. The skeleton provides strength and shape/structure to the body, serves as attachment places for the muscles so we can move, and helps to protect delicate internal organs (consider the differences among the levels of protection the skeleton gives to the brain, the heart and lungs, and the digestive tract). By the way, contrary to a widely-circulated “urban legend,” all humans, both male and female, have 12 pairs of ribs. Many people are required to learn the names of the bones in junior or senior high school biology classes. If you don’t know all the names or need a review, the Biol. 105 Web page mentioned below has a diagram and a list of bones — learn them.

The muscles that move our bones are sometimes referred to as “skeletal muscles.” They are also referred to as “striated muscles” because of the way they look when viewed under a microscope. Muscle cells, also called muscle fibers, contain many mitochondria to harvest the energy they need to function. They also contain large amounts of two special proteins: actin and myosin, and it is the actin and myosin sliding past each other in a muscle cell that causes that cell to contract. In skeletal muscles, the actin molecules and the myosin molecules are very neatly organized and lined up making the areas with and without myosin readily distinguishable from each other. Thus the muscle cell appears “banded” with alternating “light” and “dark” bands or striations. In Dr. Fankhauser’s photograph, the “stripe” running across the middle of the picture is a portion of a skeletal muscle cell. Within that cell, the dark vertical bands are the areas where the myosin fibers are lined up, and the whitish vertical bands are the spaces between the ends of the myosin.

We have two other types of muscle tissue in our bodies. These are known as smooth and cardiac muscle. Smooth muscle is found in association with our internal organs; for example, the muscles that move the food along the digestive tract (and are also the source of the “rumbling” of an empty stomach when someone is hungry). Smooth muscle does not have the visible striations that skeletal muscle does; it appears to be “smooth” when viewed under a microscope. Cardiac muscle is only found one place in the body – in the heart, and it shares some characteristics of both striated and smooth muscles. Cardiac muscle does have some striations, but not as many as skeletal muscle tissue.

On Thanksgiving, when people sit down to eat the cooked muscles of a turkey, one of the first questions that is often asked is, “Do you want light meat or dark meat?” Biologically, we would rephrase this question as, “Do you want red muscle tissue or white muscle tissue?” The muscles being eaten are all skeletal muscles, but depending on the function of a muscle, it may or may not contain an oxygen-storage chemical called myoglobin. Muscles which contain myoglobin are typically those that are used continuously for long periods of time (such as muscles used in maintaining posture), thus need to have more oxygen available for their use, and due to the presence of the myoglobin, these muscles appear more reddish in color. Muscles which lack myoglobin are typically those that are used less frequently and for only short periods of time, thus don’t usually need to have a supply of “extra” oxygen stored up, and these appear more whitish in color. The presence or absence of myoglobin in a muscle is under genetic control, so a muscle cannot just switch from one to the other. For example, since turkeys and chickens don’t fly very much, their flight muscles are white, but pheasants, which fly a lot, have red flight muscles. In turkeys and chickens, the frequently-used leg muscles contain myoglobin and are red. Humans also contain some red and some white muscle tissue.

As mentioned above, muscles can only contract, only pull; muscles cannot push. They’re either contracted and pulling or else they’re relaxed. Thus, our skeletal muscles come in sets called “antagonistic pairs” which typically have opposite functions. The example of this with which must people are probably the most familiar are the muscles in the upper arm. The biceps (officially, biceps brachii) on the “top” side pull on the lower arm bones and bend the elbow joint, while the triceps, on the “bottom” side of the upper arm, pulls the lower arm bones the opposite direction to straighten out the elbow joint. Notice, by the way, the proper way to refer to what’s going on here: muscles, themselves, do not “bend,” but rather, muscles bend a joint. Muscles such as the biceps brachii, which decrease the angle of a joint, are called flexors, while muscles such as the triceps, which increase the angle of (straighten) a joint, are called extensors.

The Biol. 105 Web page listed below lists the names and locations for many of the “more significant” muscles. You should learn those muscle names and locations.

Background Information

Your Assignment
Research a Disease or Disorder

There will be only one, combined assignment for this week’s topics (skeletal, immune, and excretory systems). Thus even though this will appear on each of those three pages to remind you, you only need to do it once. Pick a disease or disorder that affects humans, and do library and/or Web research to find out more about that disease (see below). Suggestion: get in touch with your classmates via e-mail (addresses available from the Check Grades (and Class E-Mail List) Web page) to find out what each other are doing so everybody doesn't do the same thing. As a suggestion, it seems like AIDS is almost “overdone,” these days – it might be more interesting to pick something a bit more “unusual.” If you’re looking for ideas for “different” sorts of things, a few things that come to mind include Hansen’s disease, androgen insensitivity syndrome, scurvy, kuru, beriberi, hemophilia, malaria, sickle-cell anemia, syphilus, bubonic plague, mononucleosis, human papilloma virus, etc., etc. A couple of Web sites which may be of use include The Merck Manual Online and OMIM Home Page or OMIM Searchable Database (OMIM deals specifically with genetic conditions). The grading criteria for this assignment are given below, and you should also refer to those as you work on the assignment. A total of 30 points is possible.

Grading Criteria

1.   Cause of Disease/Disorder:
2  —  The cause of the disease/disorder was thoroughly researched and accurately and clearly presented 1  —  The cause of the disease/disorder was adequately researched and presented 0  —  Information on the cause of the disease/disorder was sketchy and/or mostly incorrect
2  —  Thorough discussion of pre-existing conditions that increase chances of getting or exacerbate the condition was also included 1  —  At least some mention was made of pre-existing conditions that increase chances of getting or aggravate the condition 0  —  Either no or incorrect information on effects of pre-existing conditions was included
2.   Discovery of Disease/Disorder:
2  —  The history of the discovery/description of this condition was thoroughly researched and accurately and clearly presented 1  —  The history of the discovery/description of this condition was adequately researched and presented 0  —  Information on the discovery of this condition was sketchy and/or mostly incorrect
2  —  This information was presented in a manner that was entertaining and fun to read 1  —  This information was adequately presented 0  —  Presentation of this information was monotonous and lacked interest
3.   Signs, Symptoms, etc.:
2  —  The signs, symptoms, and effects on the body systems were thoroughly researched and accurately and clearly presented 1  —  The signs, symptoms, and effects on the body systems were adequately researched and presented 0  —  Information on the effects of this disease/disorder was sketchy and/or mostly incorrect
2  —  The student clearly demonstrated that (s)he knows the difference between “signs” and “symptoms” 1  —  The delineation between “signs” and “symptoms” was included and was at least partially correct 0  —  “Signs” and “symptoms” were not delineated or were incorrectly distinguished from each other or most manifestations of the condition were assigned to the wrong category
4.   Diagnosis & Treatment:
2  —  The diagnosis and treatment of this condition were thoroughly researched and accurately and clearly presented 1  —  The diagnosis and treatment of this condition were adequately researched and presented 0  —  Information on the diagnosis and treatment of this condition was sketchy and/or mostly incorrect
2  —  Thorough discussion of role and usefulness of diet and/or “alternative” therapies was also included 1  —  Effectiveness of diet and/or “alternative” therapies was at least mentioned and partially discussed 0  —  No mention made of effects/influence of diet and/or “alternative” therapies
5.   Spread & Distribution:
2  —  The prevalence, distribution, and means of acquisition were thoroughly researched and accurately and clearly presented 1  —  The prevalence, distribution, and means of acquisition were adequately researched and presented 0  —  Information on the prevalence, distribution, and means of acquisition was sketchy and/or mostly incorrect
2  —  Discussion of likelihood of contracting and means of prevention was thoroughly presented 1  —  Likelihood of getting and means of prevention were at least mentioned 0  —  No mention made of how to keep from getting this disease/disorder or information presented was incorrect
6.   Misconceptions & Role in History:
2  —  Information on misconceptions associated with this condition and its role in history was thoroughly researched and accurately and clearly presented 1  —  Information on misconceptions associated with this condition and its role in history was adequately researched and presented 0  —  Information on misconceptions and/or the role in history was sketchy and/or mostly incorrect
2  —  This information was presented in a manner that was entertaining and fun to read 1  —  This information was adequately presented 0  —  Presentation of this information was monotonous and lacked interest
7.   Overall:
2  —  The grammar, English usage, punctuation, and spelling were very good 1  —  The grammar, etc. were OK 0  —  The grammar, etc. were poor
2  —  The student, obviously, went beyond the minimum requirements of the assignment 1  —  The student adequately completed the assignment 0  —  The student completed considerably less of the assignment than what was required
2  —  It is evident that the student used much insight, thoughtfulness, and critical thinking when completing this assignment 1  —  The student adequately thought about the assignment – there was, perhaps, a bit of “fuzzy thinking” in a couple places 0  —  The assignment gives the appearance of being “slapped together” just to get it done, with little evidence of thoughtfulness

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Copyright © 2006 by J. Stein Carter. All rights reserved.
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