Chapter 9: Muscular Physiology

___ stimuli have no additional effects on force production than a maximal stimuli.

supra-maximal

Which of the following is associated with the relaxation phase?

1. Myosin releases thin filaments. 2. Muscle tension declines. 3. Calcium levels in the cytoplasm fall.

When a muscle fiber relaxes, ATP is used:

1. To maintain the normal concentrations of Na+ and K+ across the sarcolemma. 2. To detach the myosin head from actin. 3. To transport of Ca2+ into the sarcoplasmic reticulum

When does the sarcoplasmic reticulum release calcium?

Calcium is released when the muscle fiber is depolarized or excited.

A sarcomere is formed from the arrangement of ___ and ___ myofilaments.

actin, myosin

An ___ potential is a propagated change in the membrane potential of a cell such as a neuron.

action

In isotonic contractions, the length of the muscle ___ and the tension ___.

changes; remains constant

The muscle shortens and generates force during the ___ phase of a muscle twitch.

contraction

The power stroke occurs during the ___ phase of the muscle twitch.

contraction

The cocking of the myosin head into a high energy position occurs because of:

energy released by hydrolysis of ATP.

The first stage of anaerobic and aerobic respiration is ___.

glycolysis

Whole muscles respond to a stimuli in a ___ fashion.

graded

Which of the following would increase twitch strength in a muscle fiber?

high stimulus frequency

As the strength of the stimulus event increases, the frequency of the action potentials generated ___.

increases

Each ___ includes a Z disk and extends from each side of the Z disk to the ends of the myosin myofilament.

isotropic band of I band

The sarcoplasm of a muscle fiber is:

its cytoplasm

Calcium ion imbalances that occur as ATP levels drop lead to ___ fatigue.

muscular

Each ___ is a threadlike structure, approx 1-3 micrometers in diameter, that extends from one end of the muscle fiber to the other.

myofibril

The energized ___ attach to the exposed myosin binding site on G-actin forming a cross-bridge.

myosin heads

During the ___, the myosin head returns to its original position after the cross-bridge has been released.

recovery stroke

Within one muscle, multiple motor unit ___ involves using more motor units to increase the force of contraction.

recruitment

Tropomyosin moves back to cover the active sites on actin during the ___ phase of the muscle twitch.

relaxation

The plasma membrane of a muscle fiber is called the ___.

sarcolemma

The basic structural and functional unit of a skeletal muscle fiber is called the ___; smallest unit of skeletal muscle that is capable of contracting.

sarcomere

The type of muscle that constitutes about 40% of the body's weight, is responsible for locomotion, facial expressions, posture, respiratory functions, and many other body movements is...

skeletal muscle

The ___ myofilament is composed of actin.

thin actin

Sum of active and passive tension is called ___.

total tension

Which of the following ion channels are classified as ligand-gated channels?

1. A channel that requires the binding of a neurotransmitter in order to operate. 2. The sodium channels that acetylcholine molecules bind to in the postsynaptic sarcolemma.

List the actions that occur during the process known as cross-bridge cycling.

1. Power stroke 2. Cross-bridge release 3. Cross-bridge formation 4. Recovery stroke

Describe the epimysium.

Layer of dense collagenous connective tissue that surrounds a muscle.

The boundaries of the sarcomere are defined by the ___.

Z disks

Multiple wave summation leads to a state of fluttering contraction called:

incomplete tetanus

The actin and myosin ___ form highly ordered units called sarcomeres which are joined end to form the ___.

myofilaments; myofibrils

The nerve fiber innervates the muscle fiber at the:

neuromuscular junction

When considering permeability to sodium and potassium, neuronal plasma membranes have a higher permeability to potassium.

potassium

Movement of the myosin molecule while the cross-bridge is attached is called the ___.

power stroke

A ___ is not strong enough to cause an action potential in any of the axons in a nerve and therefore does not cause a contraction.

sub-threshold stimulus

Describe troponin.

1. It is a globular protein composed of 3 subunites. 2. It has a binding site for calcium ions. 3. It is bound to both actin and tropomyosin.

Sarcomere lengthening involves:

1. the recoil of the elastic elements of the cell 2. an external force applied to a muscle by other muscles or by gravity

Which of the following ion channels directly generate the phenomenon known as the action potential in a motor neuron?

1. voltage gated potassium channel 2. voltage gated sodium channel

The resting membrane potential of most neurons and muscle fibers is between:

70 and -90 mV

Perimysium:

a thick connective tissue layer around each fasciculus.

The ___ ___ in a muscle fiber stores calcium in between contractions.

sarcoplasmic reticulum

Stimuli which get progressively ___ and produce action potentials in axons of additional motor units are called sub-maximal stimuli.

stronger

Sustained contraction due to such a high frequency of action potentials that a relaxation phase does not occur between stimuli is referred to as ___.

tetanus

The role of the transverse tubules is to:

transmit the signal to contract deep into the muscle fiber

True of isometric contractions but not isotonic contractions

1. Tension generated in the muscle is less than the load applied to the muscle. 2. Tension is generated in the muscle. 3. The length of the muscle does not change.

Which of the following accurately describes the structure of a muscle?

1. A skeletal muscle fiber is a single, long, cylindrical cell containing several peripherally located nuclei. 2. A single skeletal muscle fiber can extend from one end of a muscle to the other.

Events of skeletal muscular contraction

1. Action potential reaches presynaptic terminal, allow for the exocytosis of acetylcholine. 2. ACh binds to the postsynaptic membrane stimulating an action potential in the sarcolemma. 3. Action potential tracels along sarcolemma and along transverse tubules. 4. Calcium is released into sarcoplasm and binds to troponin. 5. Active sites exposed to G actin. 6. Myosin binds to actin and pulls actin towards center of sarcomere.

During muscle relaxation, the sarcomeres within the contracted muscle lengthen. How does this occur?

1. An external force such as gravity applied to the muscle. 2. Opposing or antagonistic muscles exert a force pulling the muscle back to its resting position. 3. The recoil of the cytoskeleton and other tissue overcomes the contractile force as calcium levels drop.

The terminal cisternae:

1. Are a part of the sarcoplasmic reticulum. 2. Contains calcium ion channels that open in response to an action potential. enlarged portion of the sarcoplasmic reticulum.

List the steps in contraction of muscle fibers.

1. Binding of ATP to the myosin head. 2. Release of ADP from the myosin head. 3. Hydrolysis of ATP.

Which of the following events occur during the relaxation phase of the muscle twitch?

1. Calcium ions are actively transported back into the sarcoplasmic reticulum. 2. The muscle fibers lengthen passively.

The A band of the sarcomere:

1. Contains both actin and myosin proteins. 2. Extends the length of the myosin myofilaments. 3. Contains the H zone and the M line.

What does the sliding filament theory of muscle contraction predict about myofilaments and sarcomere length?

1. During contraction, the thin myofilaments slide past the thick myofilaments. 2. During contraction, the total length of the sarcomere decreases.

Describe the I band of the sarcomere. The I band:

1. Extends from each side of the Z disk to the ends of the myosin myofilaments. 2. Consists of actin myofilaments on each side of the Z disk.

During a muscle fiber contraction, which of the following decreases in size?

1. H zone 2. I band 3. entire sarcomere

Recruitment increases the amount of force produced by:

1. Increasing the number of muscle fibers contracting. 2. Increasing the number of motor units stimulated.

Steps of the Relaxation of muscle.

1. Nerve signal ceases. 2. AChE breaks ACh down. 3. Active transport pumps in the Sarcoplasmic Reticulum begin to pump calcium back into the cisternae. 4. Calcium releases from troponin. 5. Tropomyosin covers the myosin binding sites.

Aerobic respiration:

1. Produces more ATP per unit of glucose than anaerobic respiration. 2. Produces ATP molecules at a slower rate than anaerobic respiration.

Fast twitch of Type II muscle fibers:

1. Respond rapidly to nervous stimulation. 2. Have a fast form of myosin ATPase, which allows them to break down ATP more rapidly than other muscle fiber types.

Name the events that occur during the lag phase of the muscle twitch.

1. Sodium ions diffuse into the muscle fiber, causing a local depolarization that exceeds threshold and produces an action potential. 2. The troponin-tropomyosin complex changes its position and exposes active sites on the actin myofilaments. 1. Calcium ions diffuse from the sarcoplasmic reticulum into the sarcoplasm. 2. An action potential is propagated to the presynaptic terminal of the motor neuron.

If the elasticity of a muscle were to increase, which of the following would be true?

1. The amount of active tension needed to be generated by the muscle in order to contract would increase. 2. The total amount of passive tension that the muscle would generate would increase. 3. The muscle would have difficulty contracting.

If all of the calcium within a muscle fiber was removed, which of the following could still occur?

1. The heads of the myosin molecules return to their resting position and the recovery stroke occurs. 2. An action potential that was produced at the neuromuscular junction is propagated along the sarcolemma.

Which events of action potential generation cause a depolarization?

1. The membrane reaches threshold. 2. The voltage-gated sodium (Na+) channels open.

Which of the following would be most likely if the excitability of a muscle cell INCREASED?

1. The muscle cell would depolarize more readily. 2. The muscle cell would contract more readily.

If the elasticity of muscle were to decrease, which of the following would not be able to occur?

1. The muscle would not return to its resting length. 2. The muscle would not lengthen.

Once a cell's threshold has been reached:

1. The sodium voltage-gated channels open rapidly. 2. The depolarization phase begins.

What are the characteristics are active tension but not true of passive tension?

1. The tension develops as a result of the sliding filament theory. 2. As a length of the muscle increases past its optimal range, the tension decreases. 3. The tension is the highest at the muscle's optimal length.

Which of the following is true of isotonic contractions but not isometric contractions?

1. The tension generated in the muscle is equal or greater than the load applied to the muscle. 2. During the contraction, the muscle shortens.

Describe cross bridges and what conditions are needed for their formation.

1. They can only form when calcium is present in the sarcoplasm. 2. They form when myosin binds to its active site on actin. 3. They can only form when the myosin head is "cocked" or energized.

The energy required to produce ATP comes from:

1. anaerobic respiration 2. aerobic respiration 3. creatine phosphate

Steps of the sliding filament theory of contraction.

1. calcium ions are released from the sarcoplasmic reticulum. 2. calcium binds to the troponin complex. 3. tropomyosin moves and exposes the active sites on the actin myofilaments. 4. myosin heads bind to active sites on the actin myofilaments to form cross-bridges. 5. energy stored in the myosin heads is used to move the myosin heads causing the actin to slide past myosin. 6. ATP molecule binds to each of the myosin heads, causing them to detach from actin.

Describe multiple-wave summation:

1. can occur because the relaxation of a muscle fiber is not required before a second action potential can stimulate a second contraction. 2. occurs when the frequency of action potentials to a fiber increases causing a correspoinding increase in fiber contraction. 3. causes a sustained contraction in a muscle fiber.

In the sliding filament theory, ATP is involved in:

1. cooking or energizing the myosin heads 2. the uptake of calcium into the sarcoplasmic reticulum at the end of the contraction 3. breaking the bond between actin and myosin.

Incomplete tetanus:

1. is a form of multiple-wave summation 2. allows muscle fibers to partially relax between the contractions.

Action potential frequency:

1. is the number of action potentials produced per unit of time. 2. is the rate at which a neuron is generating action potential.

When the muscle is no longer actively contracting, ATP is used to:

1. move calcium back into the sarcoplasmic reticulum 2. re-energizing the myosin head 3. break the bond between actin and myosin

Which of the following are types or locations of fatigue?

1. synaptic 2. muscle fiber 3. psychological

When a muscle is at its optimal length,

1. the highest number of cross bridges can be formed based on the physical arrangement of actin and myosin. 2. the force it is capable of producing is greater than at any other length.

Which events of action potential generation cause repolarization of the neuron or muscle cell?

1. voltage-gated sodium channels close. 2. Voltage-gated potassium channels open.

Creatine phosphate is used to store energy that can be used to synthesize ___.

ATP

Which of the following are characteristics of a skeletal muscle fiber?

Cylindrical, multinucleate

Example of the contractility of muscle.

Lifting a textbook.

What is the effect when calcium binds to troponin?

The troponin-tropomyosin complex changes shape and exposes the myosin binding sites.

Fast-twitch muscle fibers can be enlarged by ___ exercise.

anaerobic

When the voltage-gated potassium channels open, a large number of potassium ions ___ the cell, resulting in the ___ phase of the action potential.

exit, depolarize

Increasing recruitment in a muscle, causes the strength of the contraction to ___ by ___.

increase; increasing the number of muscle fibers contracting

During which phase of the muscle twitch does the AP propagate to the presynaptic terminal?

lag phase

The time between the stimulus and the twitch is known as the ___.

latent period or lag phase

The tension applied to the load when muscle stretches but is not stimulated is called ___ tension.

passive

In order for the excitation-contracting coupling to occur, the production of an action potential must occur within the ___ of a muscle fiber.

sarcolemma

The sliding filament theory states that during contraction:

sarcomeres shorten because actin myofilaments slide past the myosin myofilaments

The ___ is a modified form of smooth endoplasmic reticulum located in muscle cells.

sarcoplasmic reticulum

When a cell is said to be "polarized", it means:

that there is a difference in the charge between the cytoplasm and the extracellular fluid surrounding it.

A muscle fiber that has been stimulated at a high frequency produces more force because it accummulates more Ca2+ in the sarcoplasm, and thus:

the number of cross-bridges that form increases.

Myoblast(s) are:

the precursors of muscle fibers

The minimum membrane potential needed to be achieved before the voltage-gated ion channels open, and an action potential begins is called the ___.

threshold

The minimum voltage necessary to generate an action potential is called the ___.

threshold

Tube-like invaginations of the sarcolemma that conduct action potentials toward the center of the muscle fiber are called ___.

transverse tubules.

The molecule that inhibits the binding of myosin to actin by blocking the binding site is ___. The fibrous protein that winds along the groove of the F actin double helix and blocks the myosin-binding sites on the actin filaments is called ___.

tropomyosin

The organelles are located within the presynaptic terminals and contain neurotransmitters are called synaptic ___.

vesicles

The development of action potentials involved the opening of ___ -regulated ion gates.

voltage

End products of aerobic respiration.

water, ATP, CO2