BSC 109 TEST 1: Chapter 6

In the absence of ATP, a contracted muscle can't relax.

True

Following intense exercise, the human body attempts to overcome oxygen debt by

taking deep breaths

When a sarcomere contracts

the actin and myosin filaments do not change in length.

During the course of muscle contraction the potential energy stored in ATP is transferred to potential energy stored in _____.

the myosin head

When ATP attaches to a myosin head,

the myosin head detaches from actin.

When a muscle relaxes, ATP is required. The reason for this is that

the myosin heads can detach from the actin only when a molecule of ATP binds to the head

Of these events, the first to occur when a motor neuron stops sending an impulse to a muscle is

the pumping of calcium ions out of the cytoplasm and back into the sarcoplasmic reticulum

A single muscle cell is referred to as a _____.

muscle fiber

In skeletal muscle, potassium ions are stored in the sarcoplasmic reticulum.

False

Which of the following happens during muscle contraction?

Sarcomeres shorten.

Which of the following structures is not contained within a muscle fiber?

Tendon

Which of the following events is the direct result of an action potential in the membrane of a muscle cell?

The muscle cell's endoplasmic reticulum (ER) releases calcium ions.

In the lower leg, the gastrocnemius muscle bends the foot away from the knee, as in pointing one's toes. The tibialis anterior muscle flexes the foot toward the knee. These two muscles are

antagonistic

A muscle cell contains bundles of long

myofibrils

In a muscle cell, __________ contain __________.

myofibrils; actin and myosin filaments

The thick filaments of sarcomeres are composed of _____.

myosin

Which term describes the subunits of a myofibril?

sacromere

Skeletal muscle groups that work together to create the same movement are referred to as

synergistic

Which of the following choices arranges the structures (1) muscle fiber, (2) fascicle, (3) myofibril, and (4) muscle from largest (most inclusive) to smallest?

4-2-1-3

What is the first and most direct energy source for muscle contraction?

ATP

Which one of the following statements is TRUE regarding the structure of a muscle?

All muscle cells in a muscle have the same origin and insertion.

Which one of the following statements correctly describes activities of muscles?

All muscles shorten when they contract.

Muscles that oppose each other and produce opposite movements are described as

Antagonistic

In comparing smooth and cardiac muscle, which one of the following best describes the differences between the two muscle types?

Cardiac muscle requires periods of relaxation, whereas smooth muscle is always in a state of partial contraction.

The thin filaments of sarcomeres are composed of

actin

Calcium ions

bind to the protein that blocks the myosin-binding sites on actin

The release of _____ ions from the sarcoplasmic reticulum is required for skeletal muscle contraction.

calcium

Intercalated discs

contain gap junctions that allow the signal to spread quickly through cardiac muscle cells

Once a muscle cell has depleted its small supply of ready-made ATP, what will it use next for energy?

creatine phosphate

Tetanic contractions result from

frequent stimulation, preventing a muscle from relaxing

During a marathon, runners' muscles use up their stored ATP very early in the race. Which of the following energy sources is used first for producing more ATP?

glycogen

When a skeletal muscle contracts, the __________ is pulled toward the __________.

insertion; origin

Which one of the following activities would fast-twitch fibers be most useful for?

lifting weights

All of the following are functions of the muscular system, EXCEPT

maintenance of body calcium stores

When an electrical impulse traveling along a motor neuron arrives at a neuromuscular junction

there is an increase in the secretion of acetylcholine at the neuromuscular junction

Myosin heads bind to _____, which they then pull and cause to slide toward the center of the sarcomere.

thin filaments

Which one of the following is an example of an isometric contraction?

tightening of abdominal muscles while sitting

Isometric contractions usually result in no movement of the skeleton or objects

true

True or false. Muscle fibers are among the largest cells in the body and are actually fusions of hundreds of individual cells

true

The all-or-none principle states that

when a muscle cell is stimulated, it responds with a complete cycle of contraction and relaxation