Chapter 12: Muscle Physiology Flashcards
A skeletal muscle is composed of a number of ________, each composed of many muscle fibers bundled by connective tissue.
fascicles
What structure composed of connective tissue transmits force from contracting skeletal muscle to bone?
tendon
What is the saclike membranous network that surrounds each myofibril called?
sarcoplasmic reticulum
The fundamental repeating unit of the myofibril called a ________ gives skeletal muscle its striated appearance, and is bordered by ________.
sarcomere : Z lines
What is the region of the striated muscleʹs banding patterns that contains only the connections between the tails of myosin molecules?
M line
The contractile portion of the thin filament is composed of what protein?
actin
What is the protein component of the thin filament that binds to calcium thereby initiating skeletal muscle contraction?
troponin
Which of the following is a structural protein that extends along each thick filament from M line to Z line.
Titin
The shortening of a skeletal muscle fiber during contraction involves which of the following?
the sarcomeres shortening
During skeletal muscle contraction, as the muscle shortens, the thick and thin filaments _______
slide past one another
When a skeletal muscle is passively stretched, that cell has a tendency to spring back once the force that was stretching the muscle is removed due to ________.
titin acting as a spring using the energy stored by the stretching
The repeated, oscillating interaction between actin and myosin that results in the generation of force by a skeletal muscle cell is called what?
crossbridge cycling
What converts the myosin head into the high-energy state?
the hydrolysis of ATP
The release of an inorganic phosphate from the myosin molecule directly results in which of the following?
power stroke
In order for crossbridge cycling to occur, the actin-myosin complex must be broken by which of the following?
binding of ATP to myosin
The sequence of events that links the action potential to changes in skeletal muscle force development is called what?
excitation-contraction coupling
During skeletal muscle contraction, multiple crossbridge cycles are occurring between the same thick and thin filament. Which of the following best describes this process?
Crossbridge cycling is asynchronous between a certain thick and thin filament.
Contraction of skeletal muscle fibers is stimulated by what type of neuron?
motor neurons
Which of the following is NOT a specialization observed at the neuromuscular junction?
Each muscle fiber is innervated by multiple motor neurons.
Increases in the amount of cytoplasmic calcium required to initiate a muscle contraction are mediated by the coupling between a ________ on the T tubule and a ________ on the membrane of the sarcoplasmic reticulum.
dihydropyridine receptor : ryanodine receptor
Which of the following is the voltage sensor that initiates an increase in cytoplasmic calcium in response to an action potential?
dihydropyridine receptor
The binding of calcium to troponin will directly cause which of the following?
the movement of tropomyosin, thereby exposing the myosin-binding site on the actin
molecule
What portion of a sarcomere shows up as light striations when viewed under a microscope?
I band
Which of the following best describes the function of transverse (t) tubules and the sarcoplasmic reticulum in skeletal muscle contraction?
Action potentials in T tubules are detected by DHP receptors, which are coupled to ryanodine receptors in the sarcoplasmic reticulum and open channels for calcium.
During the cross-bridge cycle, ATP binding to myosin causes which of the following?
the myosin head to detach from actin
What is the function of T tubules?
They conduct action potentials from the sarcolemma to the interior of the muscle cell.
What is a motor unit?
a motor neuron and all the muscle fibers it innervates
In order to allow discrete contractile events to occur, calcium is rapidly removed from the cytoplasm via ________.
calcium pumps (active transport of calcium)
Which of the following is NOT part of the process whereby skeletal muscles relax?
Sarcolemmal calcium channels open to allow the efflux of calcium.
What enzyme catalyzes the reaction that creates creatine phosphate?
creatine kinase
Since the creatine phosphorylation reaction is substrate driven, an increase in the concentration of creatine within a skeletal muscle fiber will directly have what effect?
increase creatine phosphate concentration
During intense (heavy) exercise, the ability of oxidative phosphorylation to provide enough ATP for force generation by the skeletal muscle is ________, thereby causing the muscle fiber to derive energy from ________.
diminished : substrate-level phosphorylation
As the intensity of exercise increases, the muscles switch from oxidative to substrate-level phosphorylation, resulting in the increased generation of which of the following?
lactic acid
When an action potential is generated within a motor neuron, ________.
every muscle cell of the motor unit is stimulated to contract
Which is the longest phase of a twitch?
relaxation
Which of the following is NOT part of the explanation for the all-or-nothing property of an isometric twitch contraction of skeletal muscle?
equivalent activation of calmodulin stimulating myosin light-chain kinase activity
Which of the following is a property of isometric skeletal muscle contraction?
load is greater than the force generated by the muscle
Which of the following is a property of isotonic skeletal muscle contraction?
load is less than the force generated by the muscle
Which of the following statements about excitation-contraction coupling in skeletal muscle is FALSE?
An action potential in the sarcolemma stimulates the opening of voltage-gated calcium channels in the plasma membrane and the sarcoplasmic reticulum.
Which of the following statements about end-plate potentials is FALSE?
They are a result of acetylcholine binding to muscarinic cholinergic receptors.
Which of the following best describes an isotonic contraction?
When the contractile elements shorten, they create enough force to move the load.
The speed with which the skeletal muscle generates force is determined primarily by _______
the type of myosin present
Which of the following is the property of skeletal muscle whereby an increase in the frequency of action potentials enhances the force developed by the muscle cell?
Summation
The tension produced during skeletal muscle contraction can be increased by all of the following except one. Which one is it?
increasing the load on the muscle
Which of the following statements about summation and tetanus is FALSE?
The maximum tension developed during summation and tetanus is treppe.
Once a skeletal muscle cell begins to shorten during an isotonic twitch contraction, ________.
the amount of force generated by the muscle will remain constant
Which of the following conditions will result in a skeletal muscle that produces a greater amount of force?
more sarcomeres in parallel
Which of the following is NOT an accurate description of specific muscle fiber types?
Slow oxidative fibers are quick to fatigue.
As skeletal muscle is further stretched beyond the length where optimum force is developed, ______
the thin filaments are pulled away from one another, thereby reducing their ability to interact with myosin
As the sarcomere length of skeletal muscle is reduced beyond the length where optimum force is developed, ______
the thin filaments overlap one another, thereby reducing their ability to interact with myosin
In the body, the sarcomere length of skeletal muscle cells is usually ________.
near optimal
Which of the following does NOT influence the force generated by an individual muscle fiber?
recruitment
What is an increase in the number of active motor units that would increase the force developed by a skeletal muscle called?
Recruitment
Contraction of motor units in a(n) ________ manner allows a muscle to maintain a level of force for a duration of time without fatiguing.
asynchronous
Which of the following best describes the relationship between motor neuron size, motor unit size, and order of recruitment?
large motor neurons : large motor unit : last to be recruited
A muscle is stimulated at a frequency that allows the muscle to relax completely between contractions. However, the amount of tension increases with each contraction. What is this called?
treppe
The mechanism responsible for the size principle involves ________.
smaller motor neurons that contain the least number of muscle cells and reach threshold
easier than larger neurons
Which of the following is NOT a property of glycolytic fibers as compared to oxidative fibers?
poor ability to produce ATP in the absence of oxygen
What molecule present primarily within oxidative skeletal muscle cells acts as an oxygen buffer due to its ability to bind oxygen?
Myoglobin
What causes some muscle fibers to appear red?
presence of myoglobin
What is the site where a muscle attaches to a stationary bone called?
origin
What connects muscles to bone?
tendons
Relative to the triceps muscle, the biceps is its ________.
antagonist
What type of receptor detects muscle length?
muscle spindle
What is an annulospiral ending?
sensory endings in the muscle spindle that detect muscle length
What type of efferent neuron innervates intrafusal muscle fibers?
gamma motor neurons
Which of the following statements is TRUE regarding activation of alpha and gamma motor neurons?
Alpha and gamma motor neurons are activated at the same time.
Which of the following is the correct order of muscle fiber recruitment from first to last?
slow oxidative : fast oxidative : fast glycolytic
Which of the following muscle types has the slowest contraction time?
smooth muscle
Which of the mechanisms listed below does NOT account for the decrease in force development by muscle cells during sustained force development?
The crossbridges can become resistant to ATP.
Which of the following is NOT an adaptation of skeletal muscle that would be observed in response to aerobic training?
an increase in the diameter of the skeletal muscle fibers
Where are gap junctions commonly found?
both single-unit smooth muscle and cardiac muscle
Which of the following is true of ALL muscle types?
contract by using the sliding filament mechanism and cross-bridge cycling
In smooth muscle, calcium triggers contraction by binding to what protein?
calmodulin
Calcium binding to calmodulin causes phosphorylation of what protein in what type of muscle?
myosin in smooth muscle only
Which of the following adaptations does NOT generally occur with aerobic exercise?
an increase in the number of myofibrils per muscle fiber
The interaction between actin and myosin in smooth muscle requires ________.
that the calcium-calmodulin complex activates myosin light-chain kinase, which
phosphorylates myosin light chain thereby allowing myosin to bind with actin
What is the source of variability in the response of smooth muscle cells from different organs to autonomic nervous activity (some relax to sympathetic nervous output while others contract)?
the type of receptor present on the effector organ
Which of the following could cause a pacemaker potential?
spontaneous opening of sodium channels
The continuation of the sarcolemma that penetrates the interior of the muscle fiber and thereby facilitates the release of calcium from the sarcoplasmic reticulum is called what?
transverse tubule
What is the protein component of the thin filament that blocks the myosin-binding site on the actin monomer?
tropomyosin
Troponin is a complex of three proteins that bind to ________, ________, and ________.
tropomyosin, calcium, and actin
Calcium is stored in what region of skeletal muscle cells?
sarcoplasmic reticulum
Another name for a muscle cell is (myofibril / muscle fiber).
muscle fiber
Name the three proteins found in thin filaments.
actin, troponin, and tropomyosin
Following death, rigor mortis occurs due to a lack of (calcium / ATP).
ATP
Receptor types at the motor end plate are (muscarinic / nicotinic) cholinergic receptors.
nicotinic
(Dihyropyridine / Ryanodine) receptors are located on the sarcoplasmic reticulum.
ryanodine
Heavy intensity exercise generates what by-product that contributes to fatigue?
lactic acid
During summation, calcium release is (greater than / less than / equal to) calcium reuptake.
greater than
The time between the occurrence of an action potential in skeletal muscle and the onset of tension is called what?
latent period
List the three mechanisms whereby force of individual skeletal muscle fibers can be altered.
frequency of stimulation (summation), fiber diameter (sarcomeres in parallel), and fiber length
The velocity at which a skeletal muscle contracts is (directly / inversely) related to load.
inversely
Name the two types of sensory endings found in muscle spindles.
annulospiral endings, flower-spray endings
What type of motor neuron innervates intrafusal muscle fibers?
gamma
Name the antagonistic muscle to the triceps.
biceps
Identify the three types of muscle fibers that are found in all skeletal muscles.
slow oxidative, fast oxidative, and fast glycolytic
Postural muscles of the legs and back tend to have a high proportion of this fiber type.
slow oxidative
In smooth muscle, calcium binds to ________, and then activates the enzyme ________.
calmodulin : myosin light-chain kinase
The decreased ability of a muscle to maintain a constant force of contraction during repetitive stimulation is called what?
fatigue
In smooth muscle, the structures analogous to Z lines in skeletal muscle are called ________.
dense bodies
(Single-unit / Multi-unit) smooth muscle contains pacemaker cells.
Single-unit
Cardiac muscle is (smooth / striated).
striated
Intercalated disks contain what type of special junctions?
gap junctions and tight junctions
