Chapter 9

Which of the following is most directly required to initiate the coupling of myosin to actin?

Ca++

Which step precedes all of the other listed steps?

ACh is released by the motor neuron.

Which statement best describes the importance of calcium in skeletal muscle contraction?

Calcium released from the sarcoplasmic reticulum binds to troponin to initiate muscle contraction.

Which of the following is true about smooth muscle?

Certain smooth muscle cells can actually divide to increase their numbers.

Mrs. As Which statement best describes what might happen if a child with malignant hyperthermia is given the wrong anesthetic and the sarcoplasmic reticulum releases all its calcium?

Continuous cross bridge cycling causes the muscle to contract too much.

What cell organelle plays a role in the process of regulating intracellular calcium ions for muscle contraction?

Endoplasmic reticulum

A motor neuron and all the muscle cells that it stimulates are referred to as a motor end plate.

False

During isometric contraction, the energy used appears as movement.

False

Of the following items listed below, which is the best description for why skeletal muscle stores glycogen?

Skeletal muscle is a heavy consumer of energy.

If troponin is a component of both cardiac and skeletal muscle, why is an elevated plasma troponin level useful in diagnosing myocardial damage?

The subunits of the troponin in cardiac muscle are unique to heart muscle.

The effect of a neurotransmitter on the muscle cell membrane is to modify its ion permeability properties temporarily.

True

Muscle tone is

a state of sustained partial contraction

After nervous stimulation stops, what prevents ACh in the synaptic cleft from continuing to stimulate contraction?

acetylcholinesterase breaks apart the ACh

The sliding filament model of contraction involves ________.

actin and myosin sliding past each other and partially overlapping

Sarcomeres are functional units of ________ muscle.

cardiac and skeletal only

In an isotonic contraction, the muscle ________.

changes in length and moves the "load"

The sliding filament model of contraction states that

during contraction, the thin filaments slide past the thick filaments so that actin and myosin filaments overlap.

A muscle that is lengthening while it produces tension is performing a(n) __________ contraction.

eccentric

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

elastic (titin) filaments

What is the functional role of the T tubules?

enhance cellular communication during muscle contraction

Which of the following is the correct order for the phases of a muscle twitch?

latent, contraction, relaxation

Cross bridge formation between myosin heads and actin molecules is caused by the elevation of calcium ion concentration in the cytosol. During rigor mortis, this elevation of calcium ion concentration in the cytosol is permanent because ________.

mitochondria stop producing ATP molecules required by the sarcoplasmic reticulum's calcium ion pumps

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

During development embryonic cells will fuse to form muscle fibers. This will result in ________.

multinucleated muscle fibers that can extend as long as 30 centimeters

Which term best identifies a muscle cell?

muscle fiber

Rigor mortis occurs because

no ATP is available to release attached actin and myosin molecules

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

no muscle tension could be generated

Approximately 80% of a muscle fiber's volume are the myofibrils. This characteristic reflects muscles ability to ________.

produce movement through contractile force

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

refractory period

What structure in skeletal muscle cells functions in calcium storage?

sarcoplasmic reticulum

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

Of the following muscle types, which has the longest muscle cells and has obvious stripes called striations?

skeletal muscle

Addition of more mitochondria to a muscle fiber will have the greatest effect on ________.

slow oxidative fibers

Which muscle fiber type is best suited for endurance activities, such as long-distance jogging?

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

When a sarcomere contracts and thin filaments move over thick filaments you would expect to see ________.

the I bands to appear smaller

What is the most distinguishing characteristic of muscle tissue?

the ability to transform chemical energy into mechanical energy to move the body

The force of a muscle contraction is NOT affected by __________.

the amount of ATP stored in the muscle cells

Based on what you know of the relationship between the thick and the thin filaments, what would happen if a disorder existed that caused a person to produce no tropomyosin?

the muscles would never be able to relax

The contractile, or functional, unit of a muscle fiber is __________.

the sarcomere

Which muscle cell structure stores calcium ions that are used to trigger the contraction?

the sarcoplasmic reticulum

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

the site of calcium binding site differs

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 contractility?

thick (myosin) filaments

The interaction between which protein and ion initiates muscle coupling?

troponin; calcium ions

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

unitary smooth muscle

Myasthenia gravis is a disease that is believed to be caused by autoimmune disorder, resulting in the loss of ACh receptors at the motor end plate of muscle fibers. Which of the following is likely to be a symptom of myasthenia gravis?

weakness of muscle

What level of structural organization does the actin and myosin in a sarcomere of a muscle fiber represent?

Molecular

What part of the sarcolemma contains acetylcholine receptors?

Motor end plate

The oxygen-binding protein found in muscle cells is ________.

Myoglobin

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 contraction in which the muscle does not shorten but its tension increases is called isometric contraction.

True

A skeletal muscle contracts with varying force and length of time in response to the body's needs at the time.

True

Although there are no sarcomeres, smooth muscle still possesses thick and thin filaments.

True

An increase in the calcium ion level in the sarcoplasm starts the sliding of the thin filaments. When the level of calcium ions declines, sliding stops.

True

Cardiac muscle has a limited regenerative capacity.

True

Cells of unitary smooth muscle are found in the longitudinal and circular muscle layers of the intestine.

True

Excitability is the ability of a cell to receive and respond to stimulus by changing its membrane potential.

True

Isometric contractions are important contractions that allow humans to hold their posture over time.

True

Peristalsis is characteristic of smooth muscle.

True

Smooth muscles relax when intracellular Ca2+ levels drop but may not cease contractions.

True