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Determine the correct structural hierarchy of skeletal muscles, from microscopic to gross levels.
myofibril - fiber - fascicle - muscle
Mature skeletal muscle fibers
individually contain hundreds of nuclei just internal to the plasma membrane.
How is the H band distinguished from the other prominent structural features of the sarcomere?
It is a lighter region that contains thick filaments, but no thin filaments.
When does a muscle contraction begin?
when stored calcium ions are released into the sarcoplasm through gated calcium channels
The complex of a transverse tubule and two adjacent terminal cisternae is known as a ________.
Which of the following is a recognized
function of skeletal muscle? maintain posture
guard body entrances and exits
maintain body temperatur
all of the above
The bundle of collagen fibers at the end of a skeletal muscle that attaches the muscle to bone is called a(n)
The structural theory that explains how a muscle fiber contracts is called the
sliding filament theory
Which of the following best describes the sarcoplasmic reticulum?
storage and release site for calcium ions
Determine during which phase of the contraction cycle the calcium ions bind to troponin.
Which statement about the microscopic
anatomy of skeletal muscle fibers is true? Cross striations result from the lateral alignment of thick and thin filaments.
Tubular extensions of the sarcolemma penetrate the fiber transversely.
Muscle fibers are continuous from tendon to tendon.
Each fiber has many nuclei.
All are true.
Interactions between actin and myosin filaments of the sarcomere are responsible for
The cytoplasm of the neuromuscular synaptic terminal contains vesicles filled with molecules of the neurotransmitter
Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?
Acetylcholine is degraded by acetylcholinesterase.
The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?
Acetylcholine is released by axon terminals of the motor neuron.
Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.
extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fibe
Calcium entry into the axon terminal triggers which of the following events?
Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels
Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?
The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?
A myosin head bound to actin
Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?
Calcium ions are stored in the sarcoplasmic reticulum.
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?
ATP binds to the myosin head
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of ATP.
What specific event triggers the uncovering of the myosin binding site on actin?
Calcium ions bind to troponin and change its shape.
When does cross bridge cycling end?
Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.
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