Bones and Muscles
Whenever you run, sit, walk, or even stand, your bones and muscles are working together in the activity. Bones are similar to the framework of a building; they provide the shape and protection. Our bones also produce our much-needed supply of daily blood cells about 200 billion a day! They are the holding places for minerals and other key substances the body needs.
Many muscles are attached to bones and they pull the bones for movement. Other muscles provide much-needed functions for daily life. Even when you are just sitting still, your muscles are at work. They are allowing you to breath, swallow, smile, and even move your eyes. And it is a muscle that powers your entire body -- the heart muscle. Working nonstop through a person's life, this vital muscle beats an average of seventy times per minute.
Bones, Bones, Bones
An adult body has about 206 bones. The number varies from person to person because of differences in the number of small bones. Some bones are responsible for movement, including bones in the hands, feet, and limbs. Other bones primarily give protection to the internal structures, such as the skull protecting the brain and the ribs shielding the heart, lungs, and liver.
When looking at animal bones or at a skeleton, bones may appear to be static and dead, but in the body they are actually full of activity. Bones grow and change along with the person. They are made of living and nonliving materials: About 70 percent of an adult's bones are composed of minerals. The remaining part is bone tissue, a group of similar cells with a common function. Bone tissue is constantly building new bone. In fact, about every seven years your bone tissue makes essentially a whole new skeleton.
Wherever two bones meet there is a joint. In some places, such as the bones in the skull, the joints are locked together and do not move. Most joints are movable, though, and are coated with a fluid that acts as a lubricant. Ligaments are a tough connective tissue that links bones together at the joints. Ligaments prevent the bones at the joints from becoming dislocated. Cartilage is another connective tissue found at the end of the bones and in the joints. This is a smooth and flexible tissue that lets one bone slide smoothly over another.
Hard and Spongy
Almost every bone in the body is made of the same materials: The outside of the bone is the hard layer that is strong. It is made of living cells and is called compact or hard bone. Holes and channels run through the compact bone, carrying blood vessels and nerves to its inner parts. Inside this layer is cancellous bone or spongy bone. Cancellous bone has cells with large spaces in between them like a honeycomb. The spaces in this network are filled with a jellylike red-and-yellow bone marrow. Red bone marrow, found mainly at the ends of bones, makes most of our body's blood cells. Red bone marrow also produces white blood cells, which help fight infection, and platelets, which help blood clot. Yellow bone marrow stores fat and releases it when it is needed somewhere in the body.
Bones contain large amounts of a protein called collagen as well as minerals, including calcium and phosphorous. Collagen gives bones their elasticity. Calcium is what gives bones their strength. Extra minerals are stored in the bone, and the bones release them when they are needed by other parts of the body. The amount of minerals that a person eats affects how many minerals the bones contain and store.
As a person gets older, the amount of new bone created slows down and bones break down at a faster rate than they are being made. Women especially may lose the stored calcium in their bodies that helps keep their bones strong and healthy. This causes the bones to become weak, which can lead to breaks. The disease osteoporosis occurs most often among older people. In osteoporosis bone tissue becomes brittle and thin. Bones break easily, and the spine can begin to collapse. Building up adequate stores of calcium in the bones as a young adult is one important way people can prevent or delay the development of this disease.
Muscular Strength
Bones are moved by muscles attached to them. These muscles are fastened to bones by a thin, tough tissue called tendons, which also link muscles to other muscles.
Muscles come in all shapes and sizes. The human body has about 650 muscles, which make up about 40 percent of a person's body weight. Muscles are classified as voluntary or involuntary. Voluntary muscles are those you can control at will, such as moving your arm. Involuntary muscles act automatically, such as your stomach muscles digesting food. Some muscles fit into both categories, such as the muscle used in blinking your eyes.
Muscles are made of stacks of long, thin cells called muscle fibers. Each muscle fiber is a single cell and contains at least one nucleus. The nucleus (plural: nuclei) is an enclosed structure that contains the cell's genetic material and controls its growth and reproduction. There are three types of muscle fibers: skeletal, smooth, and cardiac. Skeletal muscle fibers are attached to bone and are voluntary muscles. They are the most abundant and largest of the three, with some fibers running more than a foot long. Each skeletal muscle fiber has several nuclei. Smooth muscle fibers are involuntary, as in the stomach and intestines. They are smaller than the skeletal muscles and are narrow at the ends, with one nucleus in each cell. Cardiac muscles are found only in the heart. These muscles have fibers that are tightly packed together and have branches. A cardiac muscle cell usually has a single nucleus.
When muscles go into action they work in terms of contractions and relaxations. Muscles can only pull bones because they can only contract, or get shorter. They cannot push bones back into their original position. Because of this, muscles work in pairs. When one muscle contracts it can bend a limb; then when that muscle is finished contracting, its partner muscle contracts to extend or straighten the limb. Whenever you bend your arm, for example, the bicep muscle in the front of the upper arm contracts. When the arm straightens, the bicep relaxes and the tricep muscle at the back of the upper arm contracts.
All the energy that muscles use is created when muscle cells process the carbohydrates, fats, and proteins in foods. Healthy muscles burn nutrients efficiently. The amount a person exercises and his or her general health will make muscles work better and become less fatigued. Muscle fatigue occurs when the muscle stops contracting. When muscle cells run out of oxygen, they reach a point where the muscles have a reduced ability to contract. When a person builds his or her muscles, the muscle fibers grow. This increases the blood flow in the fibers, increasing their ability to contract.
Bone Loss: How does the loss of calcium affect bone strength?
Purpose/Hypothesis
Your bones are lightweight and incredibly strong. Bones get their strength from a hard outer shell that contains the mineral calcium carbonate. The calcium keeps the bone stiff and rigid. A strong acid can chemically react with the bones and remove much of the calcium carbonate.
In this experiment you will determine how the loss of calcium carbonate affects the strength of bones. You will use vinegar as the acid. The vinegar will react with three bones for varying lengths of time. The longer the vinegar reacts with the bone, the more calcium the vinegar will remove from the bone. How much you can bend the bone will allow you determine the bone's strength.
Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of bones and the mineral calcium. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
- the topic of the experiment
- the variable you will change
- the variable you will measure
- what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: "The more calcium a bone loses, the weaker the bone will be and the more it will bend."
In this case, the variable you will change is the amount of time the bones react with the vinegar or acid. The variable you will measure is the bone's strength or how much the bone bends.
Conducting a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control and the experimental bones, and that is the solution that immerses the bones. For the control, you will soak a bone in plain water, which does not react with the bone. At the end of the experiment you will compare the water-soaked bone with each of the vinegar-soaked bones.
For your experiment you will select four bones of the same type that are of equal thickness and general appearance. You will soak three of the bones in vinegar and one of the bones in water. Every four days you will remove each of the vinegar-soaked bones and test its strength. To compare the bones again at the end of the experiment, you will wrap each of the bones after the allotted period of time. If you leave them in the open air, the bone will react with the carbon dioxide in the air and harden again.
What Are the Variables?
Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
- the type of bone you use
- the thickness of the bone
- the cleanliness of the bone
- the solution the bone is soaked in
- residue in the jars
- the environment of the bones when they are not soaking
In other words, the variables in this experiment are everything that might affect the vinegar reacting with the bone. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on bone strength.
Level of Difficulty
Easy/Moderate.
Materials Needed
- four similar chicken bones (drumsticks from chicken wings work well)
- vinegar, white
- four glass jars with lids, large enough to hold a bone
- marking pen
- masking tape
- plastic wrap
Approximate Budget
$5.
Timetable
20 minutes initial setup time; another 30 minutes spread out over the next 12 days.
How to Experiment Safely
Vinegar is an acid. Be careful about getting any of the vinegar in your eyes. Do not eat any of the vinegar-soaked bones. Throw them out after the experiment is complete.
- Clean the four bones thoroughly, scrubbing them with water.
- Place a piece of masking tape on each jar and label the first jar "Control," the second jar "4 Days," the third "8 Days," and the last "12 Days."
- In the control jar, cover the bone with water. In the other three jars, cover the bones with vinegar. Set the jars aside.
- After four days, open the "4 Day" jar and rinse off the bone with water. Test the strength of the bone by trying to bend it. While the bone is still wet, wrap it in plastic wrap thoroughly. Rinse the jar clean and place the wrapped bone back in the jar, screw on the lid and set it aside.
- Repeat Step 4 after another four days for the bone in the "8 Day" jar. Repeat again four days later for the "12 Day" jar, except do not place the bone in plastic wrap.
- Unwrap the other bones and examine how far each bone bends. Rinse the control bone with water and compare the strength of the three bones to the control.
- Create a graph of the results, using an estimate of the degree the bones
bend for the y-axis, and the number of days of calcium loss on the x-axis.
Summary of Results - Examine your graph of the data. How did the control bone compare to the bone with the greatest calcium loss? What do the bones feel like? Do they feel different from each other? Think about how the loss of calcium in bones would affect a person. What can this experiment teach you about osteoporosis in older people?
Troubleshooter's Guide
Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem.
Problem: The bones all have the same strength, even after twelve days.
Possible cause: The bones you used may be too thick. Try repeating the experiment, increasing the amount of soaking time by doubling the days. You could also repeat the experiment using bones that are thinner.
Change the Variables
You can vary this experiment by changing the thickness or type of bone you use. Do you get the same results with a turkey bone as a chicken bone? You could also try leaving the bones out in the air for several days after they have finished soaking in vinegar and compare the results. You could also try comparing the same type bone from a young animal and an old animal. You may have to talk with your local butcher for help in selecting the bones.