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Chapter 9

Which of the following is correctly paired?
Skeletal muscle: voluntary control
Which muscle characteristic describes the ability of muscle to respond to a stimulus?
One of the important functions of skeletal muscle contraction is production of heat.
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 fiber
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.
Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?
Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?
Calcium release from the sarcoplasmic reticulum initiates the contraction.
A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?
A series of proteins that control calcium release.
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium Ions
What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?
Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
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
What structure is the functional unit of contraction in a skeletal muscle fiber?
The sarcomere
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.
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
arrival of an action potential
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
A myosin head binds to which molecule to form a cross bridge?
What causes the myosin head to disconnect from actin?
binding of ATP
What energizes the power stroke?
hydrolysis of ATP
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine (ACh)
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate.
How is acetylcholine (ACh) removed from the synaptic cleft?
acetylcholinesterase (AChE; an enzyme)
The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?
Terminal cisternae of the sarcoplasmic reticulum
What is the role of calcium in the cross bridge cycle?
Calcium binds to troponin, altering its shape.
What role does tropomyosin play in the cross bridge cycle?
The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.
How does troponin facilitate cross bridge formation?
Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.
What, specifically, is a cross bridge?
myosin binding to actin
Which event causes cross bridge detachment?
ATP binding to the myosin head
Where in the cross bridge cycle does ATP hydrolysis occur?
during the cocking of the myosin head
How/when does the myosin head cock back to store energy for the next cycle?
After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.
BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle?
Myosin heads would remain detached, unable to cock.
During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?
There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.
A patient has no peristalsis in the gastrointestinal tract. Why would this be problematic?
The patient would be unable to expel his or her stool, leading to intestinal obstruction.
Which of the following is true about smooth muscle contraction?
Certain smooth muscle cells can actually divide to increase their numbers.
Peristalsis is characteristic of smooth muscle.
Although there are no sarcomeres, smooth muscle still possesses thick and thin filaments.
Smooth muscles are able to regenerate throughout life
When a geriatric patient is admitted to the rehabilitation unit, an important nursing measure is to prevent the loss of muscle mass. What is the term used for loss of muscle mass, and how can the patient prevent it?
Disuse atrophy, where fibrous connective tissue replaces the muscle tissue that was lost. This can be prevented by regular weight-bearing exercise, unless atrophy is complete.
The nurse encourages the patient to do his own activities of daily living such as bathing, eating, dressing, and toileting activities. How do these activities promote physical conditioning?
The contraction of the muscles in these activities helps maintain the shape, size, and strength of muscles, as well as joint mobility.
Which muscle cells have the greatest ability to regenerate?
Most skeletal muscles contain
mixture of fiber types
The strongest muscle contractions are normally achieved by
increasing the stimulation up to the maximal stimulus
stores oxygen in muscle cells
What structure in skeletal muscle cells functions in calcium storage?
sarcoplasmic reticulum
What does oxygen deficit represent?
the difference between the amount of oxygen needed for totally aerobic muscle activity and the amount actually used
Immediately following the arrival of the stimulus at a skeletal muscle cell there is a short period called the ________ period during which the events of excitation-contraction coupling occur.
Creatine phosphate functions in the muscle cell by
storing energy that will be transferred to ADP to resynthesize ATP
What controls the force of muscle contraction?
multimotor unit summation
The major function of the sarcoplasmic reticulum in muscle contraction is to
regulate intracellular calcium concentration
What produces the striations of a skeletal muscle cell
the arrangement of myofilaments
Which of the following are composed of myosin?
thick fillaments
During muscle contraction, myosin cross bridges attach to which active sites?
actin filaments
Rigor mortis occurs because
no ATP is available to release attached actin and myosin molecules
The oxygen-binding protein found in muscle cells is
What is the functional unit of a skeletal muscle called?
What is the role of calcium ions in muscle contraction?
bind to regulatory sites on troponin to remove contraction inhibition
The warm-up period required of athletes in order to bring their muscles to peak performance is called
The main effect of the warm-up period of athletes, as the muscle contractions increase in strength, is to
enhance the availability of calcium and the efficiency of enzyme systems
During vigorous exercise, there may be insufficient oxygen available to completely break down pyruvic acid for energy. As a result, the pyruvic acid is converted to
lactic acid
When a muscle is unable to respond to stimuli temporarily, it is in which of the following periods
refractory period
In an isotonic contraction, the muscle
changes in length and moves the "load"
The muscle cell membrane is called the
Which of the following is the correct sequence of events for muscle contractions?
motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments
Which of the following statements is true?
Striated muscle cells are long and cylindrical with many nuclei.
An anaerobic metabolic pathway that results in the production of two net ATPs per glucose plus two pyruvic acid molecules is
Muscle tone is
a state of sustained partial contraction
After nervous stimulation stops, what prevents ACh in the synaptic cleft from continuing to stimulate contraction?
acetylcholinesterase destroying the ACh
Three discrete types of muscle fibers are identified on the basis of their size, speed, and endurance. Which of the following athletic endeavors best represents the use of red fibers?
a long, relaxing swim
Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped
no muscle tension could be generated
What part of the sarcolemma contains acetylcholine receptors
motor end plate
The time in which cross bridges are active is called the period of ________.
A smooth, sustained contraction is called
Once a motor neuron has fired, all the muscle fibers in a muscle contract.
The force of muscle contraction is controlled by multiple motor unit summation or recruitment.
During isotonic contraction, the heavier the load, the faster the velocity of contraction.
What is the contractor unit
The H-zone does what
gets smaller and changes in size