MUSCLE CONTRACTION ACTIVITIES
Activity #1: Go to the following website- http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html
Click on the Animation: Action Potentials and Muscle Contraction on the left hand side. Watch the animation and
answer the following questions. (For each of these questions, enter them online so that you may see if you got them
right and record the CORRECT answers on here!)
1
An action potential enters a neuron...
A)
by diffusion.
B)
by the T-tubules.
C)
by the sarcolemma.
D)
by the sarcoplasmic reticulum.
E)
by the actin myofilament.
2
What structures do the calcium ions bind to when muscle contraction is initiated?
A)
the actin myofilament.
B)
the troponin molecule.
C)
the tropomyosin molecule.
D)
the sarcoplasmic reticulum.
E)
the sarcolemma.
3
Cross bridges form between...
A)
troponin and tropomyosin.
B)
calcium and sodium.
C)
the sarcolemma and the sarcoplasmic reticulum.
D)
the T-tubules and the sarcolemma.
E)
the actin filaments and the myosin heads.
4
An action potential introduced at the neuromuscular junction is propagated along the sarcoplasmic reticulum.
A)
True
B)
False
5
In response to an action potential entering the neuron, calcium ions diffuse from the sarcolemma into the
sarcoplasm.
A)
True
B)
False
Activity #2:
Click on the animation “Breakdown of ATP and Cross-Bridge Movement During Muscle Contraction”. Watch the
animation and answer the following questions.
1
During contraction of a muscle, calcium ions bind to...
A)
the actin myofilament.
B)
the troponin molecule.
C)
the tropomyosin molecule.
D)
the sarcoplasmic reticulum.
E)
the sarcolemma.
2
The bond between the actin and myosin head is broken when...
A)
an ATP molecule binds to the myosin head.
B)
an ATP molecule binds to the actin molecule.
C)
an ATP molecule breaks down on the myosin head.
D)
an ATP molecule breaks down on the actin molecule.
E)
ADP and phosphate bind to the myosin head.
3
Energy is released when...
A)
ADP is broken down into ATP and phosphate.
B)
ATP is broken down into ADP and phosphate.
C)
ADP and phosphate combine to form ATP.
D)
ATP and phosphate combine to form ADP.
E)
AMP and two phosphates combine to form ATP.
4
The sequence of cross bridge formation and myofilament movement will be repeated as long as calcium ions are
present.
A)
True
B)
False
5
When cross bridges form and the muscle fibers contract, the actin myofilament slides past the myosin
myofilament.
A)
True
B)
False
Activity #3: Click on the animation: Function of the Neuromuscular Junction. Watch the animation and answer the
following questions.
1
An action potential arriving at the presynaptic terminal causes...
A)
voltage-gated sodium ion channels to open, and sodium ions to diffuse into the cell.
B)
voltage-gated sodium ion channels to open, and sodium ions to diffuse out of the cell.
C)
voltage-gated calcium ion channels to open, and calcium ions to diffuse into the cell.
D)
acetylcholine to diffuse into the cell.
E)
ligand-gated sodium channels to open, and sodium ions to diffuse out of the cell.
2
In the neuromuscular junction, acetylcholine...
A)
diffuses across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic muscle fiber.
B)
is actively transported across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic
muscle fiber.
C)
diffuses across the synaptic cleft and causes calcium ions to diffuse into the postsynaptic muscle fiber.
D)
diffuses across the synaptic cleft and causes sodium ions to diffuse out of the postsynaptic muscle fiber.
E)
is actively transported across the synaptic cleft and causes calcium ions to diffuse into the postsynaptic
muscle fiber.
3
The neurotransmitter in the neuromuscular junction...
A)
causes ligand gated calcium channels in the muscle fiber to increase their permeability to calcium, which
depolarizes the postsynaptic membrane.
B)
causes ligand gated sodium channels in the muscle fiber to increase their permeability to sodium, which
depolarizes the postsynaptic membrane.
C)
increases the calcium ion permeability of the presynaptic membrane.
D)
increases the sodium ion permeability of the presynaptic membrane.
E)
depolarizes the presynaptic membrane by increasing the permeability of sodium ions.
4
Acetylcholine is broken down into acetic acid and cholinesterase by choline.
A)
True
B)
False
5
Once threshold is reached on the postsynaptic membrane, an action potential is generated and propagated over
the muscle cell membrane.
A)
True
B)
False
Activity #4: Click on the animation “Myofilament Contraction”. Watch the animation and answer the following
questions.
Each actin filament is composed of
A)
a single strand of actin molecules.
B)
two strands of actin molecules wrapped together.
C)
three strands of actin molecules wrapped together.
D)
four strands of actin molecules wrapped together.
E)
hundreds of strands of actin molecules wrapped together.
2
As actin and myosin filaments slide past each other during muscle contraction,
A)
actin filaments shorten, while myosin filaments do not.
B)
myosin filaments shorten, while actin filaments do not.
C)
either actin or myosin filaments shorten, but not both at the same time.
D)
both actin and myosin filaments shorten.
E)
neither actin nor myosin filaments shorten.
3
Which of the following statements about the "heads" of the myosin molecules is TRUE?
A)
they form permanent links with actin filaments
B)
they can attach to different sites on the actin filament
C)
they straighten the myosin filaments
D)
they allow the myosin filaments to wrap around each other
E)
none of the above
4
Each myosin protein has a globular head that extends outward from the myosin filament.
A)
True
B)
False
5
Unflexing of the myosin head requires ATP.
A)
True
B)
False
Activity #5: Watch the animation “Sarcomere Contraction”. Answer the following questions.
Muscle contraction is caused by
A)
actin filaments sliding past each other.
B)
myelin filaments sliding past each other.
C)
myosin filaments sliding past each other.
D)
actin filaments sliding past myelin filaments.
E)
actin filaments sliding past myosin filaments.
2
Which of the following statements about H zones and I bands is TRUE?
A)
the H zones contain only myosin, while the I bands contain only actin
B)
the H zones contain only actin, while the I bands contain only myosin
C)
the H zones contain only myosin, while the I bands contain both actin and myosin
D)
the H zones contain both actin and myosin, while the I bands contain only actin
E)
the H zones and the I bands each contain both actin and myosin
3
During muscle contraction
A)
the A band remains the same and the I band narrows.
B)
the I band remains the same and the A band narrows.
C)
both the A band and I band remain the same.
D)
both the A band and I band narrow.
E)
both the A band and I band become wider.
4
In a contracting muscle the Z lines come closer together.
A)
True
B)
False
5
In a relaxed muscle, the H zone is at its narrowest width.
A)
True
B)
False
Conclusion Questions:
1. In your own words, explain what happens at the neuromuscular junction in order to initiate muscle contraction.
2. In your own words, give a summary of what is happening in the sarcomere during muscle contraction.
3. In your own words, explain what is happening during the full process of muscle contraction between actin,
myosin, ATP, Ca2+, troponin/tropomyosin etc.