chapter 9 questions

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what is the minimum voltage needed to generate active force in the skeletal muscle?

threshold voltage

Both actin and myosin are found in the

A band

the myosin filaments are located in the

A band

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge attachment?

ATP binds to the myosin head the binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next powerstroke.

During muscle contraction, myosin cross bridges attach to which active site?

Actin filaments

The cross bridge cycle begins when

Ca2+ from the sarcoplasmic reticulum binds to troponin

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. The sarcoplasmic reticulum contains Ca2+ ATPase that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to it's resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.

contain abundant amounts of glycogen

Fast (oxidative or glycolytic), fatigable fibers

A neurotransmitter released at motor end plate by the axon terminals

acetylcholine

the_____contains ony the actin filaments.

I band

A relatively high percentage are found in successful marathon runners

Slow (oxidative), fatigue-resistant fibers

Red fibers, the smallest of the fiber types.

Slow (oxidative), fatigue-resistant fibers

abundant in muscles used to maintain posture

Slow (oxidative), fatigue-resistant fibers

depends on oxygen delivery and aerobic mechanisms

Slow (oxidative), fatigue-resistant fibers

When a sarcomete contracts and thin filaments move over thin filaments you would expect to see

The I bands to appear smaller

As the stimulus voltage increased in this activity, which of the following occurred?

The muscle force generated increased

Which of the following is proportional to the amount of tension produced by a skeletal muscle?

The number of motor units activated

Which of the following describes the relaxation phase?

The sarcomeres are increasing in length, and the force generated decreases.

The mechanism of contraction in smooth muscle is different from skeletal muscle in that

The site of calcium binding site differs

what is the role of tropomyosin in skeletal muscles?

Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules

A sacromere is the distance between two

Z discs

Most skeletal muscles contain ________.

a mixture of fiber types

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 as soon as a myosin head forms a cross bridge with actin, the power stroke begins.

Although all the anatomical parts of muscle work together to give it it's characteristics, which of the following proteins listed below would be most associated with the characteristics of excitability?

acetylcholine receptors in the motor end plate

Breaks down ACh into its building blocks, rendering it ineffective.

acetylcholinesterase

Activates synaptic vesicles in axon terminals to fuse with plasma membrane of axon terminal

calcium ions

The final chemical messenger and "trigger" for muscle contraction. It binds to troponin

calcium ions

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 sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.

What specific event triggers the uncovering of the myosin binding site on actin?

calcium ions bind to troponin and change it's shape the shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.

Which of the following occurs during the latent period of muscle contraction?

calcium is releases from the sarcoplasmic reticulum

Sarcomeres are functional units of

cardiac and skeletal muscles only

The ability of muscle to shorten forcibly when adequately stimulated is known as and sets muscle apart from other tissue types.

contractibility

An anaerobic metabolic pathway that results in the production of two net ATPs per glucose plus two pyruvic acid molecules is

direct phosphorylation of ADP by creatine phosphate the rapid ATP-synthesizing pathway only lasts for about 15 seconds

which of the following surrounds an individual muscle cell?

endomysium

which of the following properties is most directly associated with changes to a muscle cell's membrane potential (the voltage across the plasma membrane)?

excitability

Exhaustion of glycogen storage within muscle fiber would have the biggest effect on

fast glycolytic fibers

Addition to more myoglobin to a muscle fiver would have the largest effect on

fast oxidative and slow oxidative fibers

skeletal muscles are composed of hundreds of thousands of individual cells called

fibers

It diffuses across the cell membrane resulting in depolarization.

sodium ions

Which of the following statements is not true regarding ATP production in muscles during periods of prolonged energy use, such as exercise?

in the absence of oxygen, creatine phosphate can drive aerobic respiration pathways for a few minutes

When muscle tension develops but the load is not moved

isometric contraction

When the muscle tension developed overcomes the load and muscle shortening occurs

isotonic contraction

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

No force is generated during which of the following?

latent period

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, Self-defense power stroke, sliding of myofilaments

Each neuron shown in this figure innervates a group of muscle fibers. What is the term for a group of muscle fibers innervated by a single neuron?

motor unit

how a smooth muscle increase in muscle force is produced

multiple motor unit summation

determined by alternating motor units of a muscle organ even when the muscle is at rest

muscle tone

The thicker filaments are the

myosin filaments

If a muscle fiber were to suddenly and permanently stop producing ATP the fiber would no longer be able to actively transport calcium out of the cytoplasm (sarcoplasm) and the intracellular calcium concentration would rise. Which of the following would you expect to happen?

myosin would be able to bind to the exposed binding sites on thin filaments but it would not be able to detach

The motor neuron and muscle fiber intersect at what is called

neuromuscular junction

Where the axon of a motor neuron connects with the muscle fibers

neuromuscular junction

Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped

no muscle tension could be generated

A twitch is

one contractile response to a single action potential

The term motor unit refers to

one motor neuron and all of the skeletal muscle fibers it innervates

troponin, a major protein in thin filament, is globular protein with three polypeptide subunits. Which of the following is not a function of the troponin?

one subunit binds to potassium ions

When a muscle is unable to respond to stimuli temporarily, it is in which of the following periods?

refractory

Which of the following can trigger a muscle twitch?

release of acetylcholine or electrical stimulation

it diffused across the cell membrane resulting in depolarization

sodium ions

which of the following is NOT a normal function of muscle tissue?

secreting hormones

which type of muscle requires somatic (voluntary) nervous stimulation for activation?

skeletal in order to contract muscle fibers must be voluntarily stimulated by motor neurons of the somatic nervous system

which of the following are correctly paired?

skeletal muscle, voluntary control

Reduction in blood flow to a muscle fiver would gave the greatest effect on

slow oxidative fibers

Which muscle cells have the greatest ability to regenerate?

smooth

Oxygen starved tissues can release chemical signals into the blood that can change the diameter of nearby blood vessels delivering oxygen and nutrients to the tissues. In doing so the blood vessels will respond through vasodilation (widening of the vessel). Which muscle type is responsible for this vasodilation?

smooth muscle

myoglobin

stores oxygen in muscle cells

creatine phosphate functions in the muscle cell by

storing energy that will be transferred to ADP to resynthesize ATP

unlike skeletal muscle, smooth muscle may spontaneously contract when it is stretched. What feature of smooth muscle allows it to stretched without immediately resulting in a strong contraction?

stress-relaxation response Stretching of smooth muscle provokes contraction; however, the increased tension persists only briefly, and soon the muscle adapts to it's new length and relaxes, while still retaining the ability to contract on demand. The stress-relaxation response of smooth muscle allows a hollow organ to fill or expand slowly to accommodate greater volume without promoting strong contractions that would expel it's contents.

skeletal muscles are connected to bones by

tendons

continued sustained smooth contraction due to rapid stimulation

tetanus

A motor unit is defined as

the axon terminals of a single motor neuron and all of the muscle fibers that it stimulates

How does the myosin head obtain the energy required to activation?

the energy comes from the hydrolysis of ATP myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activated the myosin head.

What structure is the functional unit of contraction in a skeletal muscle fiber?

the sarcomere a sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.

Smooth muscle is characterized by all of the following except

there are more thick filaments than thin filaments

Although all the anatomical parts of muscle work together to give it it's characteristics, which if the following proteins listed below would be most associated with the characteristics of contractibility?

thick (myosin) filaments

Which type of muscle is found in the body wall of hollow organs?

unitary smooth muscle

which of the following is/are mechanism(s) to end neural transmission at the neuromuscular junction?

•ACH is broken down into acetic acid and choline by the enzyme acetylcholinesterase •ACH diffused away from the synaptic cleft

The conversion of an action potential (AP) generated by a motor neuron to contraction of skeletal muscle fiber is called excitation-contraction coupling. This activity will test your understanding of the sequence of events that occur during excutation-coupling.

•AP propagates along sarcolemma •AP travels down T tubules to triads •voltage-sensitive proteins open Ca2+ channels •sarcoplasmic reticulum releases Ca2+ •Ca2+ levels in sarcoplasm increase

identify the correct sequence of the following events

•Ca++ binds to troponin •troponin removes tropomyosin from G actin • myosin binds to actin • myosin generates a power stroke • the sarcomete shortens • ATP recharges the myosin head

The site where a motor neuron excites a skeletal muscle fiber is called the neuromuscular junction. This activity will test your understanding of the sequence of events that occur at the neuromuscular junction.

•Ca2+ enters the axon terminal •synaptic vesicles release ACH Ach binds to act receptions •ligand-gated cation channels open •Na+ enters cation channels open •membrane potential is less negative


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