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SKELETAL MUSCLE NOTES
Terms
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epi = upon
peri = around
endo = within or inner
mys = muscle
sarco = flesh
lemma = husk
fasci = bundle
Structure of skeletal muscle fiber
A sarcomere
Twizzler analogy
Many packages of
Twizzlers =
Fascicle
Twizzler analogy 2
1 package of
Twizzlers =
Muscle fiber
The packaging =
Sarcolemma
Twizzler analogy 3
1 bundle of twizzlers =
myofibril
Twizzler analogy 4
1 Twizzler strand =
Filament
Terms associated with skeletal
muscles
• Tendon- Attaches
muscle to bone
• Ligament- Attaches
bone to bone
• Origin- The
location where the
muscle is
attached to the
relatively
immovable end of
the bone
Insertion- end of the
muscle that is
attached to the
movable bone
• Prime mover- the
muscle that provides
most of the
movement
• Synergist- muscle
that assists the prime
mover
• Antagonist- the
muscle that opposes
the action of the
prime mover
Muscle Contraction
Neuromuscular Junction
Neuromuscular junction animation
• animation
Sliding Filament theory
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Boat = Myosin (thick filament)
Oar = Myosin side arm
Water = Actin (thin filament)
Life ring = Calcium
Resting
1. ATP is bound to myosin side arm.
2. ATP cleaves into ADP + P (high energy)
Step 1 Action potential
1. A nerve action potential releases acetylcholine
into the synaptic cleft opening the Na+
channels.
2. Action potential spreads across sarcolemma
releasing Ca into sarcoplasma
Step 2 Myosin-actin binding
1. Ca binds to troponin
2. A shape change in troponin moves
tropomyocin out of the way of actin binding site
3. Actin and myosin bind using energy from
cleaved ATP.
Step 3 Power Stroke
1. Side arm pivots so myosin and actin slide by
each other shortening the sarcomere.
2. ADP and P released (low energy)
Step 4 ATP binding and actinmyosin release
1. A different ATP molecule binds to active site.
2. Actin released
Step 5 ATP cleavage
1. Return to high energy state
2. Cycle will repeat if Ca still available.
A few thoughts
• The boat (myosin) does not move far in
one cycle, a muscle contraction requires
many cycles
• What happens if ATP is not available?
• Muscle stays contracted- cramps
• Why does rigor mortis occur?
• ATP is not available to control Ca release
so contractions are continuous 6-8 hours
after death. Body relaxes 16-24 hours as
enzymes break down contractile structures
Sarcomere summary
Final animation
• animation 2
• Watch “Distonia: movie
Muscles of the Head
Anterior torso muscles
Posterior torso muscles
Anterior shoulder and arm
Anterior
forearm
Anterior
thigh
Lateral thigh
Posterior
thigh