Mechanical Station 2.2 LAB
Mechanical Systems in Health Fields
Levers and Muscle Contraction
http://es.wikipedia.org/wiki/Sistema_muscular
- Lab Goal: The goal of this station is to practice moving antagonistic (an-TAG-uhn-is-tic)muscles and to measure different lengths of muscles around a fulcrum (or pivot point) as the mechanical advantage of movement changes.
- Lab Materials Required: Carolina model“Investigating the Interactions of Muscles and Bones Kit” and string (provided)
- Objectives for Experiment:
- Identify what happens to a muscle’s length when it contracts, as well as what happens to its antagonistic muscle’s length at the same time.
- Identify which of the two main muscles in the upper arm is responsible for different movements of the arm.
- Use differing lengths of “muscle” on the model arm to identify changes in mechanical advantage.
- Correctly define the terms in bold from the introduction.
- Correctly answer application questions relating to the lab experiment.
- Prerequisite knowledge: 6th-8th grade reading level. All instructions provided
- Applied Health Terminology: Like many professions, the medical field has its own vocabulary. We have created flashcards to help you learn some of the vocabulary related to joints and movement that was used in this lesson. You can find these flashcards on the computer at the site below.
- Instructions to site:
- Click on the link below.
- https://quizlet.com/84853923/mechanical-station-22-levers-and-muscle-contraction-flash-cards/
- Then click on the “Flashcards” button in the upper left corner of the screen.
- For each card, say the word out loud and try to say what you think the definition is.
- Flip the card by clicking on it and say the definition listed out loud.
- Evaluation: Your lab performance will be evaluated by the criteria (standards) you will find in this project’s rubric. A rubric is simply a table that states how you will be evaluated. Your coach will use this table to report your performance.
Process Summary: At this station you will…
- Review the medical vocabulary and read instructions on how to perform an experiment with antagonistic muscles.
- Experiment with contracting each antagonistic muscle of the upper arm to see the effects on movement and muscle length.
- Follow instructions on how to use weights and changing muscle lengths to calculate forces and mechanical advantage.
- Identify how changing the insertion point of a muscle effects mechanical advantage and record the data in a table.
- Graph the collected data.
- Identify another part of the body that uses a pair of antagonistic muscles.
- Explain the benefit of the human arm’s poor mechanical advantage.
CLICK HERE TO GO TO THE RUBRIC
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INTRODUCTION
How do different muscles make us move?
Interesting Facts to Know
Muscle Structure
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While bones give our body a solid inner frame, muscles give our body shape, protect the skeleton, and allow us to actually move our bones! A muscle causes movement through contraction. You probably know how this feels because when you contract a muscle, it suddenly shortens, looks bigger and becomes hard (or tense). |
There are actually three different types of muscles in our bodies.
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Cardiac (CAR-dee-ac) muscle is only found in the heart, and allows your heart to pump blood through the body. Smooth muscle is found in organs such as the intestines which allow things to move through the digestive tract. Both cardiac and smooth muscles are known as involuntary, meaning we do not decide when to make them contract. Skeletal muscle is the type you are probably most familiar with. This is the voluntary muscle attached to our bones that we decide to contract on our own. |
Muscles are not one big solid piece. Skeletal muscles are actually made up of many bundles of much smaller long muscle fibers (kind of like thick strands of string). Each muscle fiber is a single muscle cell. Then inside the muscle fibers there are even smaller fibers called myofibrils (my-o-FIBE-rils). Myofibrils are made up of rectangular areas called sarcomeres (SAR-co-meers) that are lined up end to end. Sarcomeres are considered the smallest useful part of a muscle. But sarcomeres have even smaller thick and thin strands inside them called myofilaments! So muscles actually have many tiny parts inside of each other!
During a contraction, the entire muscle appears to get shorter and thicker. The reason for this is actually that the myofilaments inside the sarcomere are pulling themselves past each other until they fully overlap. So it makes sense that the muscle gets thicker and harder, because millions of myofilaments in the sarcomeres are sliding past each other, leaving less space between sarcomeres and
less space between myofilaments! Watch the video below (most of what we have talked about is covered, but don’t worry if there any words you don’t know):
https://www.youtube.com/watch?v=EdHzKYDxrKc
As you can see, skeletal muscles are very complex structures. Your body has more than 400 of these muscles, and they make up between 40 and 45% of your total body weight!
Bones and Muscles Together Create Movement
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The skeleton, skeletal muscles and the tissues that connect them all make up the musculoskeletal (mus-cue-low-SKEL-it-uhl) system. While bones meet other bones in joints and are held together by ligaments, muscles are attached to bones by tendons. Each muscle is connected to at least two different bones which meet at a joint. A single muscle may have multiple tendons that attach to the same bone.
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Each muscle has at least two places where they attach to bones called an attachment point. The attachment point that is closer to the center of the body and which is connected to the more stationary (less movable) bone is called the origin (OR-i-jin). The attachment point that is farther from the center of the body and which is connected to the more movable bone is called the insertion (in-SUR-shun). When a skeletal muscle contracts and gets shorter, this pulls the insertion and the bone it is attached to closer to the origin. This is what allows the muscle to move the bones of a joint. |
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For example, when the biceps brachii (BY-seps- BREAK-e-i) or biceps muscle contracts, it pulls the insertion on the forearm bones toward the two origins on the shoulder. This causes bending of the elbow, called flexion. The biceps is therefore called a flexor muscle. (Note: Notice that we use the word “biceps” for a single muscle. Even though “bicep” is commonly used, it is incorrect).
When the triceps brachii (TRY-seps BREAK-e-i) or triceps muscle contracts, it also pulls the insertion on the forearm toward the three origins on the shoulder. But this causes the straightening of the elbow, called extension. The triceps is therefore called an extensor muscle. |
Did you notice that the biceps and triceps work opposite of each other? There are many muscles in the body that have opposite functions and these pairs of muscles are called antagonists (an-TAG-uhn-ists). When one antagonistic muscle contracts, the other always relaxes. Then again there are other muscles in the body that actually help to create the same movement as another muscle nearby. These pairs of muscles are called synergists (SIN-er-jists). Synergistic muscles always contract and relax at the same time.
Levers, Effort and Resistance of Movement
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A lever is a type of simple machine that changes the direction or amount of force required to perform a task. Levers have 4 parts: a stiff bar called the lever arm, a pivot point or fulcrum, an object that is moved by the levercalled the load, and a certain force applied to the lever called the effort force. The load also puts a force on the lever called the resistance force (usually equal to the weight of the object). The effort force must be able to overcome the resistance force in order to move the object. |
There are actually three different types of levers, depending on where the fulcrum and forces are placed along the bar. The distance from the effort force to the fulcrum is called the effort arm. The distance from the resistance force to the fulcrum is called the resistance arm. Changing these distances actually changes how much effort you need to put in to move the object! If we add these distances to our picture above, it would look like the following:
In a first-class lever, the two forces are on opposite ends of the lever arm, and the fulcrum is between them. This is like the lever shown in the picture above. A good example of a first-class lever is a see-saw. Imagine you are on the ground on one end of the see-saw, and your friend uses their arm to push down on the opposite end. Your friend is supplying the effort force in order to overcome the resistance force of your weight. But they must push down hard enough so that their effort force can overcome your weight and move you up into the air.
In a second-class lever, the fulcrum is at one end of the lever arm, the effort force is at the opposite end, and the resistance force is between them. An example of a second-class lever would be a wheelbarrow. The fulcrum is the wheel, and you pulling up on the handles would be the effort force. The resistance force that you are trying to overcome would be the load in the bucket of the wheelbarrow:
Finally, in a third-class lever, the fulcrum is at one end of the bar, the resistance force is at the opposite end, and the effort force is between them. An example of a third-class lever would be using your biceps muscle to bend your elbow and raise your forearm! In this case, the elbow joint is the fulcrum. The resistance force is the weight of your hand and forearm. The insertion of your biceps on the forearm is where effort force is applied. Since the insertion is actually in front of the elbow joint, this means the effort force is in the middle.
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Mechanical Advantage
Levers are useful because they allow us to move an object or weight. Some levers, such as the see-saw example of a first-class lever, make it easier to move the weight. In other words, less effort force is required to overcome the resistance force. This is because the lever actually multiplies the effort force. But there is a problem with these types of levers: the distance that the object can be moved (also called range of motion), is smaller because the fulcrum is in the middle.
Second and third-class levers have a greater range of motion because the fulcrum is at the end, but they do not make it as easy to move the weight. Third-class levers have the greatest range of motion, but require the greatest effort force to overcome the resistance force:
Whether a lever makes it easier to move an object (requires less effort), or harder to move an object (requires more effort) is determined by the mechanical advantage. This number tells you how much the machine either multiplies or lessens the effort force applied to the lever. Mechanical advantage can be calculated as follows:
What this equation doesn’t show you is that the amount of effort force required to move an object changes when we change the length of the effort arm. (Remember, the effort arm is the distance from the effort force to the fulcrum.)The effort force needed actually gets smaller if we make the effort arm longer!
We can figure out whether a lever makes it easier or harder to move an object by looking at the mechanical advantage (we will call this MA from now on).
If the MA is greater than 1, then the lever makes it easier to move the object by multiplying the effort force. First-class levers (like the see-saw) always have an MA greater than 1.
If the MA is less than 1, then the lever actually makes it harder to move the object by lessening the effort force. Third-class levers (like the biceps raising the forearm) always have an MA of less than 1.
Since using the biceps muscle to bend the elbow is a third-class lever, that means it actually requires more force from the biceps to raise the hand and forearm than they actually weigh! This may seem strange, but the reason for this is that we trade putting in more effort for a greater range of motion.
Process Summary: In this Lab you will:
- Identify what happens to a muscle’s length when it contracts, as well as what happens to its antagonistic muscle’s length at the same time.
- Identify which of the two main muscles in the upper arm is responsible for different movements of the arm.
- Use differing lengths of “muscle” on the model arm to identify changes in mechanical advantage.
- Correctly define the terms in bold from the introduction.
- Correctly answer application questions relating to the lab experiment.
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Links to Station 2.2 Modules
Lab Intro | Lab Presentation and Practice | Communications Intro| Communications Presentation and Practice| Math