A&P Chapter 9

A sarcomere is the distance between two ________.

Z discs

The ________ contains only the actin filaments.

I band

The thicker filaments are the ________ filaments

Myosin

Both actin and myosin are found in the ________.

A band

The myosin filaments are located in the ________.

A band

Serves as the actual "trigger" for muscle contraction by removing the inhibition of the troponin molecules

Calcium ions

A neurotransmitter released at motor end plates by the axon terminals.

Acetylcholine

Diffusion across the cell membrane results in depolarization.

Sodium-potassium ions

Activate synaptic vesicles in axon terminals.

Calcium ions

Used to convert ADP to ATP by transfer of a high-energy phosphate group. A reserve high-energy compound.

Creatine phosphate

Destroys ACh.

Acetylcholinesterase

Once a motor neuron has fired, all the muscle fibers in a muscle contract.

false

The thin filaments (actin) contain a polypeptide subunit G actin that bears active sites for myosin attachment.

true

The force of muscle contraction is controlled by multiple motor unit summation or recruitment.

true

Eccentric contractions are more forceful than concentric contractions.

true

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

false

Peristalsis is characteristic of smooth muscle.

true

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

true

During isotonic contraction, the heavier the load, the faster the velocity of contraction.

false

During isometric contraction, the energy used appears as movement.

false

One of the important functions of skeletal muscle contraction is production of heat.

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

Muscle contraction will always promote movement of body parts regardless of how they are attached.

false

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

true

Muscle tone is the small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units.

true

Single-unit smooth muscle is found in the intestines.

true

A resting potential is caused by a difference in the concentration of certain ions inside and outside the cell.

true

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

true

When a muscle fiber contracts, the I bands diminish in size, the H zones disappear, and the A bands move closer together but do not diminish in length.

true

Contractures are a result of a total lack of ATP

true

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

true

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.

Which muscle cells have the greatest ability to regenerate?

smooth

Most skeletal muscles contain ________.

a mixture of fiber types

Fatigued muscle cells that recover rapidly are the products of ________.

intense exercise of short duration

The strongest muscle contractions are normally achieved by ________.

increasing the stimulation up to the maximal stimulus

Which of the following would be recruited later in muscle stimulation when contractile strength increases?

motor units with larger, less excitable neurons

Which of the following is not a usual result of resistance exercise?

ncrease in the number of muscle cells

Excitation-contraction coupling requires which of the following substances?

Ca2+ and ATP

Which of the following is a factor that affects the velocity and duration of muscle
contraction?

load on the fiber

Myoglobin ________.

stores oxygen in muscle cells

What structure in skeletal muscle cells functions in calcium storage?

sarcoplasmic reticulum

What does oxygen deficit represent?

the difference between the amount of oxygen needed for totally aerobic muscle activity and the amount actually used

Immediately following the arrival of the stimulus at a skeletal muscle cell there is a short period called the ________ period during which the events of excitation-contraction coupling occur.

latent

Creatine phosphate functions in the muscle cell by ________.

storing energy that will be transferred to ADP to resynthesize ATP

What controls the force of muscle contraction?

multimotor unit summation

The major function of the sarcoplasmic reticulum in muscle contraction is to ________.

regulate intracellular calcium concentration

What produces the striations of a skeletal muscle cell?

the arrangement of myofilaments

Which of the following are composed of myosin?

thick filaments

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

actin filaments

Which of the following surrounds the individual muscle cell?

endomysium

Smooth muscles that act like skeletal muscles but are controlled by autonomic nerves and hormones are ________.

multiunit muscles

Rigor mortis occurs because ________.

no ATP is available to release attached actin and myosin molecules

Which of the choices below does not describe how recovery oxygen uptake (oxygen deficit) restores metabolic conditions?

increases the level of lactic acid in the muscle

The term aponeurosis refers to ________.

a sheetlike indirect attachment to a skeletal element

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

myoglobin

The contractile units of skeletal muscles are ________.

myofibrils

Which of the following is not a way muscle contractions can be graded?

changing the type of muscle fibers involved in the contraction

What is the functional unit of a skeletal muscle called?

a sarcomere

What is the functional role of the T tubules?

enhance cellular communication during muscle contraction

What is the role of calcium ions in muscle contraction?

bind to regulatory sites on troponin to remove contraction inhibition

The warm-up period required of athletes in order to bring their muscles to peak performance is called ________.

treppe

The main effect of the warm-up period of athletes, as the muscle contractions increase in strength, is to ________.

enhance the availability of calcium and the efficiency of enzyme systems

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

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

refractory period

In an isotonic contraction, the muscle ________.

changes in length and moves the "load"

The muscle cell membrane is called the ________.

sarcolemma

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, ATP-driven power stroke, sliding of myofilaments

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

the site of calcium regulation differs

Which of the following describes the cells of single-unit visceral muscle?

They exhibit spontaneous action potentials.

Which of the following is not a role of ionic calcium in muscle contraction?

activates epinephrine released from adrenal gland

Which of the following is true about smooth muscle contraction?

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

Smooth muscle is characterized by all of the following except ________.

there are more thick filaments than thin filaments

Muscle tissue has all of the following properties except ________.

secretion

The giant protein titin maintains the organization of the ________ assisting in muscle stretching.

A band

Which of the following statements is true?

Striated muscle cells are long and cylindrical with many nuclei.

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

glycolysis

Muscle tone is ________.

a state of sustained partial contraction

The sliding filament model of contraction involves ________.

actin and myosin sliding past each other and partially overlapping

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

acetylcholinesterase destroying the ACh

Which of the following statements is most accurate?

Muscle tension remains relatively constant during isotonic contraction.

What is the most distinguishing characteristic of muscle tissue?

the ability to transform chemical energy into mechanical energy

Three discrete types of muscle fibers are identified on the basis of their size, speed, and endurance. Which of the following athletic endeavors best represents the use of red fibers?

a long, relaxing swim

Of the following muscle types, which has only one nucleus, no sarcomeres, and rare gap junctions?

multiunit smooth muscle

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

no muscle tension could be generated

What part of the sarcolemma contains acetylcholine receptors?

motor end plate

Which of the following statements is false or incorrect?

Cardiac muscle fibers depend mostly on anaerobic cellular respiration to generate ATP.