Download I DO: Muscle Cells

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Day One: Introduction
DO NOW
Directions: The ancient Greek warrior, Achilles, was nearly immortal after being dipped in the River Styx as a child.
However, he was held by his heel, and this left his heel as the only weak point of his body. Indeed, it was an arrow to
this heel that finally brought his life to an end, and this area of the human body has been named the Achilles tendon.
Why do you think the Achilles tendon is such an important part of the body?
Without a working tendon, no muscles attached to the bone can function.
Mr. Shah’s 7th Grade Science Class | Page 1
TALK LIKE A SCIENTIST
Muscle:
Tendon:
Fiber-like cells which contract
to move skeletal bones
Ends of muscles which connect
muscles to bones
I DO: Muscle Cells
Directions: Use the diagram above to answer the questions below about muscle cells.
1. Based on its location, what is the function of the endomysium? It contains the skeletal muscle fibers.
2. Based on its location, what is the function of the perimysium? It contains the muscle fascicles.
3. Based on its location, what is the function of the epimysium? It envelopes the muscle.
4. Based on its location, what is the function of a tendon? It connects the muscle to a bone.
5. Why are there blood vessels near the muscle? It provides muscle cells with oxygen.
6. Why are there nerves near the muscle? It transmits motor signals to the muscle cells.
Mr. Shah’s 7th Grade Science Class | Page 2
WE DO: Actin and Myosin
Muscles can be subdivided into units called sarcomeres, groups of muscle fascicles that have different types of fibers
which can move alongside one another in order to expand and contract the muscle as a whole. These are made up of
thin filaments called actin, which are attached to the ends of the sarcomeres, which move together over thick filaments
called myosin. When the actin move closer together over the myosin, the muscle is contracted.
This takes a lot of energy, so the muscle cells are filled with tons of mitochondria, ready to break down glucose in
cellular respiration and produce energy in the form of ATP. Normally, this leaves behind a molecule called pyruvate.
However, while exercising, when there isn’t enough oxygen going to our cells, the pyruvate ferments into lactic acid, a
chemical which, when built up, causes our muscles to feel pained and fatigued.
Directions: List three things your body does while exercising to increase the amount of oxygen going to your blood
cells and prevent lactic acid fermentation from happening:

Increased breathing rate to inhale more oxygen

Increased blood flow to pump oxygen to body cells via blood

Increased sweat to balance body temperature against increased heart rate
Mr. Shah’s 7th Grade Science Class | Page 3
YOU DO: Contractions
Directions: Organize information about the types of muscle contractions in the table below.
Contraction
Description
Example
Isometric
Joint angle and muscle length do not
change during contraction, so that
contraction takes place in a static
position.
Pushing a stalled car
Isotonic
Joint angle and muscle length change
during contraction, so that contraction
is dynamic.
Pumping a bike tire
Concentric
Muscles shorten while generating force
due to the force of the muscles being
greater than the force being exerted
upon.
Lifting a rowing oar
Eccentric
Muscles elongate while under tension
due to an opposing force greater than
the force of the muscles.
Setting down a bag
Mr. Shah’s 7th Grade Science Class | Page 4
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EXIT TICKET
Directions: What chemical might be found in position X?
A. Glucose
B. Lactic Acid
C. Actin
D. Myosin
Directions: What kind of muscle contraction is being shown in the image above?
A. Isometric
B. Isovelocity
C. Concentric
D. Eccentric
Mr. Shah’s 7th Grade Science Class | Page 5