Ch. 9 Test Review-- A&P
The region of the sarcomere containing the thick and thin filaments is the
A band
When a skeletal muscle fiber contracts, which of the following does not occur?
Myosin and actin filaments decrease in length.
What special terms are used to describe the plasma membrane and cytoplasm of a skeletal muscle fiber?
The plasma membrane is called the sarcolemma and the cytoplasm is called the sarcoplasm
concentric contraction
The muscle shortens as the tension remains constant in a concentric contraction
Describe the neuromuscular junction
The neuromuscular junction is where the axon terminals of a motor neuron interact with the skeletal muscle fiber midway along the fiber's length
Muscle fibers differ from "typical cells" in that muscle fibers
have many nuclei
Skeletal muscle fibers are formed from embryonic cells called
myoblasts
Determine the correct structural hierarchy of skeletal muscles from microscopic to gross levels.
myofibril - fiber - fascicle - muscle
________ are stem cells located between the endomysium and sarcolemma that function in the repair of damaged muscle tissue.
myosatellite cells
Cross-bridges are portions of
myosin molecules
isometric contraction
the individual muscle fibers shorten as connective tissues stretch.
transverse tubules
tubular extensions of the sarcolemma that extend deep into the sarcoplasm contacting the terminal cisternae of the sarcoplasmic reticulum
If a second stimulus arrives before the relaxation phase has ended, a second, more powerful contraction occurs. This is called
wave summation
Which of the following best describes the term "Z line"?
where thin filaments are anchored
A two-second duration of isometric tetanic contraction is supported by which energy source alone?
ATP
What causes calcium to be released from the sarcoplasmic reticulum?
Calcium is released when an action potential reaches the triad
Compare concentric and eccentric contractions
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
relaxation phase
During this period, calcium levels are falling, active sites are being covered by tropomyosin, and the number of active cross-bridges is declining as they detach.
The area in the center of the A band that contains no thin filaments is the
H band
Compare incomplete tetanus with wave summation.
In incomplete tetanus, the muscle is producing near-peak tension during rapid cycles of contraction and relaxation. Wave summation refers to the addition of one twitch to another
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
In a sarcomere, thick filaments are linked laterally by proteins of the
M line
Which statement about the microscopic anatomy of skeletal muscle fibers is not true?
Multiple myofibrils link end-to-end along length of the muscle cell
Describe the relationship between the number of fibers in a motor unit and the precision of body movements
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
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?
The motor end plate would be continuously stimulated and continuous muscle contraction would occur
isometric contraction
The muscle does not change length during an isometric contraction.
resting phase
The resting phase occurs prior to the stimulus.
Which occurs in a muscle at moderate levels of activity?
The skeletal muscle relies primarily on the aerobic metabolism of pyruvate to generate ATP
complete tetanus
This condition occurs when a higher stimulation frequency eliminates the relaxation phase.
incomplete tetanus
This condition occurs when a muscle produces almost peak tension during rapid cycles of contraction and relaxation.
treppe
This phenomenon occurs when a skeletal muscle fiber is stimulated immediately after the relaxation phase has ended, and a subsequent contraction develops a slightly higher maximum tension than did the previous contraction, resulting in increasing peak tensions that continue over the first 30-50 stimulations
Can a skeletal muscle contract without shortening? Why or why not?
Yes, because muscles can still contract during an isometric contraction when the muscle tension is equal to the load
Which of the following muscles would contract more forcefully?
a muscle receiving 20 to 25 action potentials per second
The skeletal muscle complex known as the triad consists of
a transverse tubule and two terminal cisternae
The cytoplasm of the neuromuscular synaptic terminal contains vesicles filled with molecules of the neurotransmitter
acetylcholine
Triggering of the muscle action potential occurs after
acetylcholine binds to chemically gated channels in the motor end plate membrane.
Which phase of the contraction cycle directly requires that calcium ions bind to troponin?
active-site exposure
Which process can, by itself, power the greatest number of twitches, based on the energy sources available in a typical muscle fiber?
aerobic metabolism of glycogen
Motor units are activated on a rotating basis to reduce fatigue. What is this mechanism called?
asynchronous motor unit summation
Which process employs exocytosis?
chemical synapse
During which phase of a muscle twitch do cross-bridge interactions occur?
contraction phase
Which of the following is not a recognized function of skeletal muscle?
controlled involuntarily
Physical evidence that supports the sliding filament theory of muscle contraction includes
decreased width of the H band during contraction
Which type of contraction results in elongation of the muscle?
eccentric contraction
The dense layer of connective tissue that surrounds an entire skeletal muscle is the
epimysium
Mature skeletal muscle fibers:
individually contain hundreds of nuclei just internal to the plasma membrane.
The type of contraction in which the muscle fibers do not shorten is called
isometric
Why is the zone of overlap an important region of the sarcomere?
it is where the myosin heads can interact with the thin filaments
A single motor neuron together with all the muscle fibers it innervates is called
motor unit
Nerves and blood vessels that service the muscle fibers are located in the connective tissues of the
perimysium
The advantage of having many nuclei in a skeletal muscle fiber is the ability to
produce large amounts of the muscle proteins needed for muscle contraction
The increase in muscle tension that is produced by increasing the number of active motor units is called
recruitment
The plasma membrane of skeletal muscle is called the
sarcolemma
the repeating contractile unit of a skeletal muscle fiber is the
sarcomere
At each end of the muscle, the collagen fibers of the epimysium, and each perimysium and endomysium, come together to form a
tendon
In neuromuscular junctions (NMJs):
the cytoplasm of the synaptic terminal contains vesicles filled with molecules of acetylcholine
Which of the following proteins is not found as a part of thin filaments?
titin
The action potential is conducted into a skeletal muscle fiber by
transverse tubules
At rest, active sites on the actin are blocked by
tropomyosin molecules
Which thin filament-associated protein binds two calcium ions?
troponin
At rest, the tropomyosin molecule is held in place by
troponin molecules
