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 Using the numbers 1-8, put the following steps
for muscle contraction in the correct order.
____ Cross-bridge forms between actin and myosin
____ Motor neuron receives an impulse
____ Acetylcholine attaches to receptor on muscle fiber
____ Muscle contracts!
____ Calcium ions attach to actin and open binding site
____ Myosin pulls actin which shortens the sarcomere
____ Calcium ions are released into myofibrils
____ Motor neuron releases acetylcholine
Sliding Filament Model
 Create a model of muscle contraction
 The model must show all stages of actin-myosin
binding
 You must label every stage and write a description

Think beyond a poster – possible ideas could include a series
of photographs, short video, 3D models
 You may work by yourself or with 1 or 2 partner(s)
 Due Friday
Slow Twitch Fibers
 Slow twitch fibers are a type of muscle fiber that are
used during sustained activities. They are more
efficient at using oxygen to generate more fuel. They
fire slowly and therefore fatigue slowly. If you do
exercises like running or cardio, you will work on
slow-twitch fibers. Slow twitch fibers get better and
better at working over long periods of time and will
become less prone to fatigue.
 What are slow-twitch fibers?
 What types of activities use slow-twitch fibers? Give
at least 3 specific examples.
 If you work out slow-twitch fibers, what benefits
would you see during exercise?
 What types of athletes do you think have the most
slow-twitch fibers?
Fast Twitch Fibers
 Fast twitch fibers are a type of muscle fiber that are
used for short-term activities. They use anaerobic
metabolism to create fuel so they generate short
bursts of strength or speed and fire rapidly. If you do
short-term, high-stress exercises then you work on
fast-twitch fibers. Things like sprinting & jumping
use fast-twitch fibers. These fibers are in charge of
strength and power. They can get stronger and will
be able to do more the more your work on them.
 What are fast-twitch fibers?
 What types of activities use fast-twitch fibers? Give
at least 3 specific examples.
 If you work out fast-twitch fibers, what benefits
would you see during exercise?
 What types of athletes do you think have the most
fast-twitch fibers?
Muscle Fatigue
 When you use your muscles for a long time, they get
tired. Your muscles start by using glucose (sugar)
and oxygen in order to get energy. They get their
oxygen from a special type of blood called
myoglobin. Myoglobin only works in muscles and
makes it so more oxygen is available to the muscles.
 When muscles run out of oxygen, they switch to
anaerobic metabolism which makes less energy and
produces this stuff called lactic acid. As the lactic
acid builds up, your muscles are not able to work as
well and they get pooped out!
 What role do glucose and oxygen play in muscle
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action?
What is myoglobin?
How does myoglobin work hand in hand with
muscles?
What is anaerobic metabolism?
Why does your body produce lactic acid and what
happens when you get too much of it?
How do you get buff?
 When you build up muscles, your muscles are adding
more Actin and Myosin. You don’t gain more muscles or
muscle fibers, you gain more protein fibers. These
protein fibers (actin and myosin) make the muscles
bigger and stronger.
 If someone has huge muscles, does that mean they have
more muscles than the average person?
 If you work out a lot are you making more muscle fibers?
 What are the two examples of protein fibers that make up
muscles?
 When your muscles get larger, what are you gaining more
of?
If you don’t use it, you lose it!
 If you don’t use muscles for an extended period of time, then
you will lose them. Your bicep won’t actually DISAPPEAR,
but you will lose the protein fibers that make up the muscle.
Once you lose this actin and myosin, the muscle becomes
weaker and eventually turns into fat. The process of muscle
degradation (loss) is called muscle atrophy.
 What happens if you were to stop using your muscles?
 What disappears when you stop working out your muscles?
 What do your muscles turn into?
 What does degradation mean?
 What is muscle atrophy?
Name the muscles – try without your notes!