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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 ________.

Calcium pumps

As the intensity of exercise increases, the muscles switch from oxidative to substrate-level phosphorylation, resulting in the increased generation of ________.

Lactic acid

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 muscle types has the slowest contraction time?

smooth muscle

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

the sarcomeres shortening

dihydropyridine receptor : ryanodine receptor

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.

Contraction of skeletal muscle fibers is stimulated by ________.

Motor neurons

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

The myosin head is converted into the high-energy state by ________.

the hydrolysis of ATP

As the muscle shortens with contraction, the length of the I band remains constant as the length of the A band decreases.

False

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?

Paralysis

The ________ is the voltage sensor that initiates an increase in cytoplasmic calcium in response to an action potential.

dihydropyridine receptor

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

Where are gap junctions commonly found

both single-unit smooth muscle and cardiac muscle

A cross-section of a myofibril in the I band would show ____________.

actin filaments only

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

What converts the myosin head into the high-energy state?

hydrolysis of ATP

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?

Ca2

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.

7621534

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

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.

In smooth muscle, calcium triggers contraction by binding to what protein?

calmodulin

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.

true

Which of the following ions binds to calmodulin to ultimately activate a protein kinase?

calcium

A myofibril is

Both composed of filaments and composed of proteins

Thick filaments in skeletal muscle are composed of

Myosin

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

Myofilaments shorten

In skeletal muscle, calcium facilitates contraction by binding to

Troponin

Binding of ________ to myosin permits cross-bridge _____________ between actin and myosin

ATP; detachment

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

Rigor mortis is caused by

Lack of ATP

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

"Motor unit" refers to

A single motor neuron plus all the muscle fibers it innervates

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

Transverse tubules

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

Curare is?

Is a nicotinic acetylcholine antagonist

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

During any isometric twitch in a skeletal muscle,

Load exceeds tension

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

Oxidative phosphorylation

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

Which of the following statements is false

None of the choices are false

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

Multiunit smooth-muscle cells

Have individual innervation of each cell

Some athletes may turn to dietary supplements containing ____ to increase the amount of _____ immediately available within the muscles.

Creatine, ATP

Myasthenia gravis

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.

False

The name given to the unit of repeating pattern in a myofibril is "sarcomere

True

The force-generating sites in a myofibril are the Z lines

False

The energy for muscle contraction is provided by the hydrolysis of ATP.

True

Actin is an ATPase.

False

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.

True

The phenomenon of rigor mortis demonstrates that myosin can bind to actin in the absence of ATP, but the bond cannot then be broken.

True

Binding of myosin to actin cannot take place in the absence of calcium ion.

True

Excitation-contraction coupling refers to the binding of energized myosin to actin.

False

The site of calcium-ion storage in muscle cells is the lateral sacs of the transverse tubules.

False

Curare blocks neuromuscular transmission by preventing the release of neurotransmitter from the motor neuron

True

Organophosphate "nerve gases" induce paralysis by blocking neural stimulation of the neuromuscular junctions, while botulinum toxin produces the same effect by inhibiting acetylcholinesterase.

False

All isotonic contractions begin and end as isometric contractions.

True

Sustained contraction and tension in a skeletal muscle is called tetanus

True

A skeletal muscle generates its greatest twitch tension when it is stretched to twice its resting length.

False

Fast fibers can be distinguished from slow fibers by the rate at which their myosin-ATPases split ATP

True

Characteristics of oxidative fibers include numerous mitochondria, abundant myoglobin and large stores of glycogen.

False

The difference in color between white muscle and red muscle is accounted for by the greater abundance of glycogen in white muscle.

False

The fiber type intermediate between the two extremes of fast glycolytic and slow oxidative is slow glycolytic.

false

Muscles used for delicate, finely controlled movements have smaller motor units than more coarsely controlled muscles.

True

In general, activating a slow-oxidative motor unit in a muscle will generate more tension than activating a fast-glycolytic motor unit.

False

Endurance exercise, such as long-distance swimming, causes a preferential increase in glycolytic enzymes and increased mass of the exercising muscles

False

The larger the diameter of a skeletal-muscle fiber, the greater the tension it can generate

True

Recruitment of different types of motor units in a muscle is the primary means of varying the amount of tension generated in that muscle.

True

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.

False

The calcium-binding protein in smooth muscle is calmodulin

True

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.

True

Action potentials in smooth-muscle are produced by the opening of voltage-sensitive sodium channels

False

Nervous stimulation of skeletal muscle is always excitatory, whereas nervous stimulation of smooth muscle may be excitatory or inhibitory.

True

Smooth-muscle cells may contract in the absence of nervous stimulation

True

Multiunit smooth muscle is characterized by many gap junctions between cells

False

Abundant mitochondria is typical of which type of skeletal-muscle fibers?

Type I

Abundant myoglobin is typical of which type of skeletal-muscle fibers

Type I

A large diameter is typical of which type of skeletal-muscle fibers?

Type II

Fast myosin ATPase activity is typical of which type of skeletal-muscle fibers?

Type II

Recruited first is typical of which type of skeletal-muscle fibers?

Type I

Fatigued first is typical of which type of skeletal-muscle fibers?

Type II

Few mitochondria is typical of which type of skeletal-muscle fibers?

Type II

Little myoglobin is typical of which type of skeletal-muscle fibers?

Type II

Small diameter is typical of which type of skeletal-muscle fibers?

Type I

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