Muscle Fiber Physiology

Interactive Lecture

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​Muscle Fiber Physiology

Multiple Choice

What initiates the contraction of a

skeletal muscle fiber?

• Electrical stimulation from a sensory neuron

• Chemical stimulation from a neuro-transmitter

• Stimulation by a somatic motor neuron

• Spontaneous generation of action potentials

Multiple Choice

What is the role of calcium ions (Ca2+) in muscle contraction?

• To generate an electrical current

• To provide energy for contraction

• To trigger the interaction of muscle proteins

• To relax the muscle fiber

Fill in the Blank

The electrical current generated in a muscle fiber during contraction is called an ________.

Fill in the Blank

The basic functional units of muscle fibers that shorten during contraction are called ________.

Multiple Choice

What is the typical range for the resting membrane potential of cells?

• -20 to -40 mV

• -40 to -60 mV

• -60 to -90 mV

• -90 to -120 mV

Multiple Choice

What characterizes neurons and muscle cells in terms of their electrical properties?

• They have a constant positive membrane potential.

• They are electrically excitable.

• They cannot generate electrical currents.

• They have a higher concentration of K+ in the ECF than in the ICF.

Fill in the Blank

In neurons and muscle cells, the concentration of Na+ is higher in the ECF than in the ______.

Open Ended

Explain the sequence of events in muscle contraction.

Multiple Choice

What is the role of acetylcholine (ACh) at the neuromuscular junction?

• To depolarize the motor neuron

• To bind to receptors on the muscle fiber and initiate an action potential

• To provide energy for muscle contraction

• To break down acetylcholinesterase

Fill in the Blank

Every skeletal muscle fiber is innervated by one _______ motor neuron.

Fill in the Blank

The muscle fibers are separated by a fluid-filled ____________.

Reorder

Order these events from beginning to end.

• Action potential travels down axon of somatic motor neuron

• Calcium enters axon terminal

• Acetylcholine (ACh) is released from synaptic vesicles

• ACh binds to ACh receptors on the motor end plate of the sarcolemma

• ACh binding opens Na+ channels end plate potential

1

2

3

4

5

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• 2
• 3
• 4
• 5

Multiple Choice

What is the primary effect of myasthenia gravis on muscle contraction?

• It increases muscle contraction by enhancing ACh release.

• It decreases muscle contraction by blocking ACh receptors.

• It has no effect on muscle contraction.

• It increases muscle contraction by blocking acetyl-cholinesterase.

Multiple Choice

How does Botox affect the neuromuscular junction to prevent muscle contraction?

• It blocks ACh receptors.

• It inhibits the release of ACh from synaptic vesicles.

• It increases the release of ACh.

• It enhances the binding of ACh to its receptors.

Fill in the Blank

If the end plate potential is strong enough to reach a ___________, an action potential is generated.

Reorder

Reorder the following events in depolarization

• Opening of Sodium (Na+) Channels

• Influx of Sodium Ions (Na+)

• Membrane Potential Becomes More Positive

• Propagation of Action Potential

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2

3

4

• 1
• 2
• 3
• 4

Reorder

Reorder the following events in repolarization

• Closing of Sodium (Na+) Channels

• Opening of Potassium (K+) Channels

• Efflux of Potassium Ions (K+)

• Membrane Potential Becomes More Negative

• Restoration of Resting Membrane Potential

1

2

3

4

5

• 1
• 2
• 3
• 4
• 5

Open Ended

Explain what causes the rapid rise in membrane potential during the depolarization phase of an action potential.

Multiple Choice

How many sodium (Na+) and potassium (K+) ions are moved by the sodium-potassium pump, and in which direction?

• 2 Na+ out, 3 K+ in

• 3 Na+ out, 2 K+ in

• 2 Na+ in, 3 K+ out

• 3 Na+ in, 2 K+ out

Multiple Choice

What initiates the release of calcium ions (Ca2+) from the sarcoplasmic reticulum during excitation-contraction coupling?

• The binding of acetylcholine (ACh) to receptors

• The propagation of an action potential along the sarcolemma and down the T-tubules

• The opening of sodium (Na+) channels

• The action of the sodium-potassium pump

Multiple Choice

What is the role of calcium ions (Ca2+) in the

process of muscle contraction?

• To depolarize the sarcolemma

• To bind to troponin and cause a shift in tropomyosin, exposing actin binding sites

• To provide energy for cross-bridge cycling

• To repolarize the muscle fiber

Open Ended

Summarize the steps of the cross-bridge cycle.

Note which steps use ATP in your summary.