Malignant hyperthermia is a potentially fatal genetic disorder. When given inhaled anesthetics, patients with malignant hyperthermia can experience elevated body temperatures, skeletal muscle rigidity, and lactic acidosis. Which of the following molecular changes could account for these clinical manifestations?
Prolonged opening to ryanodine receptors
In order to allow discrete contractile events to occur, calcium is rapidly removed from the cytoplasm via ________.
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 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
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 an accurate description of specific muscle fiber types?
Slow oxidative fibers have a low resistance to fatigue.
Which of the following is true of ALL muscle types?
contract by using the sliding filament mechanism and cross-bridge cycling
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
Which of the following best describes the relationship between motor neuron size, motor unit size, and order of recruitment?
small motor neurons : small motor unit : first to be recruited
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
The shortening of a skeletal muscle fiber during contraction involves ________.
the sarcomeres shortening
Which of the following is the correct sequence of events in skeletal muscle excitation-contraction coupling?
action potential generated at the motor endplate → action potential propagation down the transverse tubules → opening of voltage-gated L-type Ca2+ channels (dihydropyridine receptors) → opening of ryanodine receptors → increase in intracellular Ca2+ → binding of Ca2+ to troponin → movement of tropomyosin → binding of myosin to actin → crossbridge cycling
Which of the following would enhance neuromuscular transmission?
inhibiting the Ca2+ reuptake mechanism in the presynaptic terminal
Which of the following treatments would alleviate the symptoms of myasthenia gravis, an autoimmune disease in which antibodies block nicotinic acetylcholine receptors at the neuromuscular junction?
Give the patient a drug that blocks acetylcholinesterases. Examples of acetylcholinesterase inhibitors include physostigmine and even nerve gas agents.
Normalized for any variability in skeletal muscle length, the speed of contraction of a skeletal muscle fiber is dependent upon ________.
the rate of myosin ATPase activity
For individuals with an inherited disorder called hyperkalemic periodic paralysis, an increase in serum K+ concentration could result in spontaneous skeletal muscle contractions followed by prolonged weakness. Use your knowledge of the ionic basis for the skeletal muscle action potential and decide which of the following genetic disorders could explain this disease. (hint: high extracellular K+ can cause a depolarization of the membrane
A mutation in the voltage-gated sodium channel that prevents the normal inactivation of this channel. Thus, the channel stays open longer.
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.
Regarding the hierarchical structure of a muscle cell, which of the following is in the correct sequence (from largest to smallest)?
fascicle fiber myofibril filament
As the muscle shortens with contraction, the length of the I band remains constant as the length of the A band decreases.
While visiting Taiwan, a person is bitten by a krait snake. The venom from a krait snake contains α-bungarotoxin, which blocks the nicotinic acetylcholine receptor. Which of the following effects might this person exhibit?
The ________ is the voltage sensor that initiates an increase in cytoplasmic calcium in response to an action potential.
Which of the following statements about graded potentials generated on the muscle fiber at the neuromuscular junction is FALSE?
They are a result of acetylcholine binding to muscarinic acetylcholine receptors
The repolarization phase of action potentials in muscle fibers is due primarily to ________.
potassium flow out of the cell
In resting muscle (no action potential), there is a large chloride conductance. The equilibrium potential for chloride in muscle is the same as the resting membrane potential. Which of the following best describes the effect of inhibiting chloride channels in muscle?
The muscle becomes easily excitable (easily reaches the threshold for firing an action potential).
Which of the following best describes an isotonic contraction?
When the contractile elements shorten, they create enough force to move the load.
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
A person suddenly develops an elevated body temperature, skeletal muscle rigidity, and lactic acidosis. Which of the following molecular changes could account for these clinical manifestations?
increased activity of dihydropyridine receptors
Which of the following is NOT part of the process whereby skeletal muscles relax?
Sarcolemmal calcium channels open to allow the efflux of calcium
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
Which of the following is a property of isometric skeletal muscle contraction?
load > force generated by muscle
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
The increase in the intracellular concentration of what important chemical triggers crossbridge cycling to occur?
Below are steps of neuromuscular transmission. Choose the correct order.
1. Acetylcholine binds to postsynaptic receptors.
2. Acetylcholine is released from the presynaptic terminal by exocytosis.
3. A graded depolarization is produced in the postsynaptic membrane.
4. Voltage-gated Na+ channels open and an action potential is produced on the muscle cell membrane.
5. Nicotinic acetylcholine receptors open and conduct Na+
6. Voltage-dependent Ca2+ channels on the plasma membrane open.
7. An action potential arrives at the axon terminal.
What is the function of T tubules?
They conduct action potentials from the sarcolemma to the interior of the muscle cell.
Which of the following is a property of isotonic skeletal muscle contraction?
load is less than the force generated by the muscle
The tension produced in skeletal muscle during isometric contractions 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.
The fundamental repeating unit of the myofibril called a ________ gives skeletal muscle its striated appearance, and is bordered by ________.
sarcomere : Z lines
On an episode of CSI-NY, a killer extracts the venom from krait snakes and uses it as a poison. The venom of a krait snake contains α-bungarotoxin, which blocks the nicotinic acetylcholine receptor. The victim that was given the poison most likely died from which of the following
paralysis of the diaphragm
The primary source of calcium that drives skeletal muscle contraction is the sarcoplasmic reticulum.
During isotonic contraction of a skeletal-muscle fiber the
Both sarcomeres shorten and I bands shorten are correct
Which of the following statements regarding the shortening of a skeletal-muscle fiber is not true? When a skeletal-muscle fiber shortens, the
Binding of ________ to myosin permits cross-bridge _____________ between actin and myosin
ATP is necessary for each of the following mechanisms or functions in skeletal muscle except
Release of Ca2+ from the sarcoplasmic reticulum
Rigor mortis occurs in a dead person because
ATP, which is necessary for the detachment of cross bridges, is not being formed
The removal of calcium ions from the cytosol of skeletal muscle causes
The myosin binding sites on actin to be covered by tropomyosin
Which of the following statements is true regarding skeletal-muscle contraction?
Binding of myosin to actin cannot take place in the absence of calcium ion
The transverse tubules in a skeletal-muscle fiber
Provide a means of transmitting an action potential in the muscle plasma membrane to central portions of the fiber
An action potential in the motor end plate rapidly spreads to the central portions of a muscle cell by means of the
Which of the following statements regarding the motor end plate of a skeletal-muscle fiber is true?
Acetylcholinesterase in the end plate membrane catalyzes the breakdown of acetylcholine
Myasthenia gravis is an autoimmune disease - that is, a disease in which one's immune system gradually attacks a part of one's own body, in this case the receptors for acetylcholine at the neuromuscular junction. Which of the following drugs might be useful in treating this disease?
A drug that inhibits acetylcholinesterase
Which of the following statements regarding skeletal-muscle contraction is true?
Both the tension developed during the contraction of a muscle fiber is dependent upon the initial length of the fiber and there is a positive correlation between the frequency of action potentials in a single muscle fiber and the tension it can develop: the greater the frequency, the greater the tension, up to a plateau are true
The optimal length of a skeletal muscle is
Both the length at which the muscle can generate its maximal tetanic tension and approximately the same as its resting length are correct
The first means by which ATP is produced at the onset of contractile activity in a skeletal muscle is
Transfer of energy and phosphate from creatine phosphate to ADP
When a muscle has been contracting for an extended period of time (more than a few minutes), the primary source of ATP is
Which of the following statements regarding myosin in skeletal muscle is/are true?
Myosin is an ATPase
Which of the following is not true regarding the comparison of type I (slow oxidative) and type II b (fast-glycolytic) skeletal-muscle fibers?
Type I fibers fatigue more readily
Which of the following statements about different kinds of skeletal-muscle fibers is true?
Fast-glycolytic fibers can generate greater tension than can slow-oxidative fibers
Fast-glycolytic muscle fibers differ from slow-oxidative fibers in that
The former can generate greater maximal tension than the latter
Which of the following is not a determinant of whole-muscle tension?
Proportion of the muscle fibers in each motor unit that are contracting at any given time
Which of the following statements regarding skeletal muscle is true?
A given skeletal-muscle fiber will contract when excitatory nervous stimuli sufficiently exceed inhibitory nervous stimuli at the cell body of the motor neuron that innervates that fiber
The tension in a skeletal muscle can be increased by increasing
The number of motor units stimulated and the rate of stimulation to each motor unit
Which of the following statements regarding whole-muscle contraction is true?
Both the order of recruitment of motor units in a muscle is such that the last units recruited are the first to experience fatigue and motor units whose motor neurons have small-diameter cell bodies contract first, followed by motor units with larger-diameter motor neurons are true
John is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest. Jim is a marathon runner who specializes in long, steady runs. Compared to Jim, John is likely to have
Legs with a larger diameter
Olympic speed (ice) skaters have large, muscular legs that are unusual in that the left leg is generally even larger in diameter than the right. This is an example of
Hypertrophy of fast-glycolytic muscle fibers as a result of exercise
Unlike skeletal muscle,
Smooth muscle does not use troponin-tropomyosin to regulate cross-bridge activity
Which of the following statements regarding contraction in skeletal and smooth muscle is true?
Both in skeletal muscle, calcium ion mediates changes in thin filaments that lead to cross-bridge activity; in smooth muscle, calcium ion mediates changes in thick filaments that lead to cross-bridge activity and in skeletal muscle, calcium ion binds to troponin; in smooth muscle, calcium ion binds to calmodulin are true
Which of the following is not true regarding single-unit smooth-muscle cells? They
Have individual innervation of each cell
Some athletes may turn to dietary supplements containing ____ to increase the amount of _____ immediately available within the muscles.
Both is an autoimmune disease and can be treated with a drug that temporarily inhibits acetylcholinesterase are correct
Skeletal muscles are made up of bundles of muscle fibers held together by sheaths called tendons.
The binding of ATP to myosin causes an allosteric change in myosin's actin-binding site such that the affinity of myosin for actin is decreased.
The phenomenon of rigor mortis demonstrates that myosin can bind to actin in the absence of ATP, but the bond cannot then be broken.
The site of calcium-ion storage in muscle cells is the lateral sacs of the transverse tubules.
Curare blocks neuromuscular transmission by preventing the release of neurotransmitter from the motor neuron
Organophosphate "nerve gases" induce paralysis by blocking neural stimulation of the neuromuscular junctions, while botulinum toxin produces the same effect by inhibiting acetylcholinesterase.
A skeletal muscle generates its greatest twitch tension when it is stretched to twice its resting length.
Fast fibers can be distinguished from slow fibers by the rate at which their myosin-ATPases split ATP
Characteristics of oxidative fibers include numerous mitochondria, abundant myoglobin and large stores of glycogen.
The difference in color between white muscle and red muscle is accounted for by the greater abundance of glycogen in white muscle.
The fiber type intermediate between the two extremes of fast glycolytic and slow oxidative is slow glycolytic.
Muscles used for delicate, finely controlled movements have smaller motor units than more coarsely controlled muscles.
In general, activating a slow-oxidative motor unit in a muscle will generate more tension than activating a fast-glycolytic motor unit.
Endurance exercise, such as long-distance swimming, causes a preferential increase in glycolytic enzymes and increased mass of the exercising muscles
Recruitment of different types of motor units in a muscle is the primary means of varying the amount of tension generated in that muscle.
The shortening velocity of a skeletal muscle fiber increases with decreasing load because the rate at which the cross-bridge cycle can occur increases with decreasing load.
The myosin in smooth-muscle cells differs from that in skeletal muscle in that smooth-muscle myosin requires phosphorylation before it can bind to actin.
Action potentials in smooth-muscle are produced by the opening of voltage-sensitive sodium channels
Nervous stimulation of skeletal muscle is always excitatory, whereas nervous stimulation of smooth muscle may be excitatory or inhibitory.