chapter 9
Which of these would not lead to increased oxygen consumption?
lactic acidosis
The increase in muscle tension that is produced by increasing the number of active motor units is called
recruitment
The narrow space between the synaptic terminal and the muscle fiber is the
synaptic cleft.
Within a resting skeletal muscle fiber, where is the greatest concentration of Ca2+? (Module 9.3C)
terminal cisternae of the sarcoplasmic reticulum
Identify three sources of stored energy utilized by muscle fibers. (Module 9.12B)
ATP, creatine phosphate, and glycogen
Which of the following statements is/are not true regarding human muscles?
Fast fibers are high in myoglobin.
What happens to the lactate produced by skeletal muscle during peak activity? (Module 9.13C)
Most of the lactate diffuses into the bloodstream and enters the liver where it is converted to pyruvate.
When do muscle fibers produce lactate? (Module 9.12C)
Muscle fibers produce lactate when there is a lack of oxygen.
Tetanus is most likely to result from which condition?
a deep puncture wound, such as that from a nail
Which of the following muscles would contract more forcefully?
a muscle receiving 20 to 25 action potentials per second
Individual muscle cells are surrounded by what connective tissue?
endomysium
The dense layer of connective tissue that surrounds an entire skeletal muscle is the
epimysium
Muscle fibers differ from "typical cells" in that muscle fibers
have many nuclei.
Each skeletal muscle fiber contains ________ myofibrils.
hundreds to thousands
Muscular force can be adjusted to match increased loads by
increasing the frequency of action potentials in motor neurons.
Aerobic metabolism normally provides ________ percent of the ATP demands of a resting muscle cell.
95
The region of the sarcomere containing the thick and thin filaments is the
A band.
Define motor unit. (Module 9.10B)
A motor unit is a motor neuron and all the muscle fibers that it controls.
Define tendon and aponeurosis. (Module 9.2A)
A tendon is a bundle of collagen fibers that connects a skeletal muscle to a bone, whereas an aponeurosis is a broad collagenous sheet that connects skeletal muscle to a broad area on one or more bones.
A two-second duration of isometric tetanic contraction is supported by which energy source alone?
ATP
What event initiates the contraction cycle?
Calcium ions arrive within the zone of overlap.
Compare concentric and eccentric contractions. (Module 9.11B)
Concentric contractions occur when the muscle tension exceeds the load, and the muscle shortens. Eccentric contractions occur when the muscle tension is less than the load, and the muscle elongates.
Which of the following is correct regarding muscle fatigue and recovery?
During the recovery period, lactate can be recycled back to pyruvate.
Compare F-actin with G-actin. (Module 9.4A)
F actin is a twisted strand made up of two rows of G actin subunits where myosin heads can bind.
The region of the sarcomere that always contains only thin filaments is the
I band.
How would the loss of acetylcholinesterase from the motor end plate affect skeletal muscle?
It would cause spastic paralysis (muscles are contracted and unable to relax).
Which of the following is not true of the muscular system?
It depends upon the cardiovascular system to provide the hemoglobin stored in slow muscle fibers.
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.
How would a drug that blocks acetylcholine receptors at the motor end plate affect skeletal muscle?
It would cause flaccid paralysis (muscles are relaxed and unable to contract).
Define muscle hypertrophy and muscle atrophy. (Module 9.15A)
Muscle hypertrophy is an increase in the size of the muscle cells and muscle atrophy is a decrease in the size of the muscle cells.
When a skeletal muscle fiber contracts, which of the following does not occur?
Myosin and actin filaments decrease in length.
Name the three types of muscle tissue, identify where they are found, and list their functions. (Module 9.1A)
Skeletal muscle is directly or indirectly attached to bones and enables movement of the body. Cardiac muscle forms the heart and propels blood. Smooth muscle is found throughout the body and moves substances through hollow tubes, such as in the digestive tract and regulates the diameter of blood vessels.
The endomysium __________.
Surrounds individual muscle fibers
Which is true regarding events that occur at neuromuscular junctions?
The binding of acetylcholine molecules to the receptors alters the membrane's permeability.
Describe the connective tissue layers associated with skeletal muscle tissue. (Module 9.2B)
The epimysium surrounds the entire muscle; the perimysium divides the skeletal muscle into fascicles; the endomysium surrounds individual muscle fibers.
Describe the relationship between the number of fibers in a motor unit and the precision of body movements. (Module 9.10C)
The finer and more precise the movement, the fewer the number of muscle fibers in the motor unit.
Explain the relationship between load and speed of muscle contraction. (Module 9.11A)
The greater the load on a muscle, the longer it takes for the muscle to shorten, and the less it shortens.
What would happen if there were no AChE in the synaptic cleft? (Module 9.6C)
The motor end plate would be continuously stimulated and continuous muscle contraction would occur.
Describe the neuromuscular junction. (Module 9.6A)
The neuromuscular junction is where the axon terminals of a motor neuron interact with the skeletal muscle fiber midway along the fiber's length.
What special terms are used to describe the plasma membrane and cytoplasm of a skeletal muscle fiber? (Module 9.2C)
The plasma membrane is called the sarcolemma and the cytoplasm is called the sarcoplasm.
Explain why the propagation of action potentials along electrically excitable membranes occurs in only one direction. (Module 9.5D)
The refractory period prevents it from propagating back in the direction from which it began.
Which occurs during an eccentric contraction?
The tension developed is less than the load, causing the muscle to lengthen while it is contracted.
Which of the following statements is not true about action potentials?
They can travel in two directions.
Define transverse tubules. (Module 9.3B)
Transverse tubules are tubular extensions of the sarcolemma that extend deep into the sarcoplasm contacting the terminal cisternae of the sarcoplasmic reticulum.
Triggering of the muscle action potential occurs after
acetylcholine binds to chemically gated channels in the motor end plate membrane.
A resting muscle generates most of its ATP by
aerobic metabolism of fatty acids.
Decreased blood flow to a muscle could result in all of the following except
an increase in intracellular glycogen.
When comparing slow fibers to fast fibers, slow fibers
appear dark red.
Muscle tissue, one of the four basic tissue groups, consists chiefly of cells that are highly specialized for
contraction.
Which of the following is not a recognized function of skeletal muscle?
controlled involuntarily
During the ________ phase of action potential development, voltage-gated sodium channels are open.
depolarization
Na+ and K+ both use ________ to passively diffuse across the plasma membrane.
leak channels
When acetylcholine binds to receptors at the motor end plate, the end plate membrane becomes
more permeable to sodium ions.
Receptors for acetylcholine are located on the
motor end plate
A single motor neuron together with all the muscle fibers it innervates is called a(n)
motor unit.
Neurons and ________ have electrically excitable membranes that propagate action potentials.
muscle cells
Name the protein that make up a thick filament. (Module 9.4B)
myosin and titin
Cross-bridges are portions of
myosin molecules.
Rigor mortis __________.
occurs as the sarcoplasmic reticulum deteriorates, releasing calcium ions
Of the following clinical conditions affecting skeletal muscle, which is caused by a virus?
polio
After death, muscle fibers run out of ATP and calcium begins to leak from the sarcoplasmic reticulum into the sarcoplasm. This results in a condition known as
rigor mortis.
The type of muscle fiber that is most resistant to fatigue is the ________ fiber.
slow
Which type of muscle fiber predominates in the leg muscles of endurance athletes, such as long-distance runners? (Module 9.14C)`
slow fibers
Membrane potential is
the electrical gradient of a cell.
At rest, active sites on the actin are blocked by
tropomyosin molecules.
When calcium ion binds to troponin,
tropomyosin moves into the groove between the helical actin strands.
When does a muscle contraction begin?
when stored calcium ions are released from the sarcoplasmic reticulum into the sarcoplasm through gated calcium channels
Which of the following best describes the term "Z line"?
where thin filaments are anchored
