chapter 20

Question 1

In striated muscle, a web of accessory proteins at each end of a sarcomere that anchors the proteins titin and nebulin and the actin thin filaments. Also called Z line, Z band.

Answer 1

Z disc

Question 2

See external work, internal work, physiological work.

Answer 2

work

Question 3

A giant elastic protein molecule that in a striated muscle spans an entire half-sarcomere from Z disc to M line.

Answer 3

titin

Question 4

Summed twitches of skeletal muscles produced by trains of motor action potentials. Fused tetanus is a smooth rise in tension produced by a high-frequency train of action potentials. Unfused tetanus is produced by a lower-frequency train of action potentials and shows some relaxation of each twitch between action potentials.

Answer 4

tetanus

Question 5

(1) In excitable cells, the addition of graded subthreshold potentials (electrical events). (2) In muscle fibers, the addition of twitches (mechanical events) produced by high frequencies of action potentials.

Answer 5

summation

Question 6

The contractile unit of striated muscle that consists of contractile, regulatory, and cytoskeletal proteins. Many sarcomeres in series, delineated by Z discs, constitute a myofibril.

Answer 6

sarcomere

Question 7

The cell membrane of a muscle fiber.

Answer 7

sarcolemma

Question 8

A pattern of innervation in which a single muscle fiber receives synaptic contacts from more than one motor neuron.

Answer 8

polyneuronal innervation

Question 9

In a sarcomere, a large inelastic protein that extends along the thin filament from the Z disc to the margin of the H zone.

Answer 9

nebulin

Question 10

A molecular motor found in many types of cells that converts chemical energy of ATP into mechanical energy of motion. In muscle cells, it functions as a contractile protein. Myosin monomers polymerize to form thick myofilaments.

Answer 10

myosin

Question 11

A group of muscle cells (muscle fibers) and associated tissues. It may be smooth, skeletal, or cardiac.

Answer 11

muscle

Question 12

A pattern of innervation in which a single axon branches near its end to make many synaptic contacts along the length of a muscle fiber.

Answer 12

multiterminal innervation

Question 13

motor unit

A motor neuron and all the muscle fibers it innervates

Answer 13

motor unit

Question 14

In muscle fibers, a web of accessory proteins at the center of a sarcomere that anchors the thick filaments and titin.

Answer 14

M line

Question 15

The force against which a contracting muscle exerts an opposing force, the latter being referred to as muscle tension.

Answer 15

load

Question 16

latch state
A characteristic state of smooth muscle in which dephosphorylated myosin heads remain attached to actin and maintain tension for long periods of time.

Answer 16

latch state

Question 17

In striated muscle, a region at the center of a sarcomere that contains only thick filaments; shortens during contraction. Also called H band.

Answer 17

H zone

Question 18

The condition in which a muscle is activated to produce force. In a skeletal muscle, contraction can be shortening (isotonic), isometric (remaining the same length), or lengthening (isotonic).

Answer 18

contraction

Question 19

One of the contractile proteins of muscle cells. Globular G-actin monomers polymerize to form the filamentous F-actin of the thin myofilaments. Actin also contributes to motility in many other kinds of cells.

Answer 19

actin

Question 20

Slow oxidative fibers in skeletal muscle are used

Answer 20

constantly, for postural activities such as standing and sitting.

Question 21

In the absence of _______, muscle can contract but cannot relax.

Answer 21

atp

Question 22

Which of the following factors would increase the stimulation frequency at which a muscle shifts from twitch to tetanic contractions?

a. Lactate dehydrogenase with faster kinetics
b. Voltage-gated sodium channels with faster kinetics
c. A larger volume fraction of mitochondria
d. A larger volume fraction of myofibrils
e. A larger number of SR Ca2+-ATPase proteins

Answer 22

e

Question 23

A hypothetical skeletal muscle cell with no t-tubules would probably

Answer 23

contract and relax more slowly during twitch contractions.

Question 24

Which of the following statements about slow oxidative and fast glycolytic muscle fibers is false?

a. They have isoforms of many muscle proteins that have different properties.
b. Their thick and thin filaments are arranged differently.
c. They have differing numbers of organelles such as mitochondria and sarcoplasmic reticulum.
d. They have different amounts of metabolic enzymes such as hexokinase or citrate synthase.
e. They have different amounts of certain EC-coupling proteins, such as SR Ca2+-ATPase.

Answer 24

b

Question 25

On the plateau of the length–tension curve,

Answer 25

all myosin heads are in proximity to actin.

Question 26

Which of the following factors best explains why vertebrates evolved to have FG muscle fibers that are larger than SO fibers?

a. SO fibers rely on aerobic metabolism, whereas FG fibers rely on anaerobic metabolism.
b. SO fibers can oxidize a variety of fuels, whereas FG fibers primarily oxidize glucose/glycogen.
c. FG fibers must be larger to generate larger action potentials and greater force.
d. FG fibers must be larger to exchange glucose across the sarcolemma more quickly.
e. SO fibers must be smaller in order to exchange Ca2+ across the sarcolemma more rapidly.

Answer 26

A

Question 27

Lactate produced by muscle cells

Answer 27

can be exported into the bloodstream and used by other cells.

Question 28

Muscles of the larynx that help mammals to produce complex sounds can contract and relax at much higher frequencies than the muscles of the limbs, but they produce relatively low force as they act on the vocal cords. Based on these characteristics, one would predict that laryngeal muscles have

Answer 28

high levels of parvalbumin.

Question 29

Which of the following statements about skeletal muscle is true?

a. Proteins in thick filaments pull on thin filaments, while intermediate filaments hold sarcomeres together.
b. Proteins in thin filaments pull on intermediate filaments, while thick filaments hold sarcomeres together.
c. Proteins in thin filaments pull on thick filaments, while intermediate filaments hold sarcomeres together.
d. Proteins in intermediate filaments pull on thin filaments, while thick filaments hold sarcomeres together.
e. Proteins in thick filaments pull on intermediate filaments, while thin filaments hold sarcomeres together.

Answer 29

A

Question 30

Muscle A has a volume of 200 cm3, a length of 10 cm, and a cross-sectional area of 20 cm2. Muscle B has a volume of 100 cm3, a length of 5 cm, and a cross-sectional area of 20 cm2. Which of the following statements about the muscles is true?

a. Both muscles can produce the same power, but they can shorten at different speeds.
b. Both muscles can shorten at the same speed, but they can produce different amounts of power.
c. Both muscles can exert the same force and can produce the same amount of power.
d. Both muscles can exert the same force, but one can shorten more quickly than the other.
e. The two muscles can exert different forces and shorten at different speeds.

Answer 30

D

Question 31

In smooth muscle, calcium must bind to _______ to initiate contraction.

Answer 31

calmodulin

Question 32

Why is the latent period of an isotonic twitch different from that of an isometric twitch?

Answer 32

An isotonic twitch does not begin until the muscle develops enough force to lift the load.

Question 33

The power stroke of the myosin head occurs in conjunction with what other event of the cross-bridge cycle?

Answer 33

Release of inorganic phosphate from the myosin head

Question 34

During an isometric tetanic contraction,

Answer 34

the sarcomeres generate force and stretch the elastic component of the muscle, but they cannot move the load.

Question 35

In a vertebrate skeletal muscle cell, depolarization of the t-tubule membrane causes dihydropyridine receptors to

Answer 35

change conformation and interact with ryanodine receptors.

Question 36

If a muscle contains 10,000 sarcomeres in a series (i.e., end-to-end along its length), each sarcomere is ~2.5 μm in length, and each sarcomere can shorten by 2.5 μm/s, how fast can the muscle shorten?

Answer 36

2.5 cm/s

Question 37

Which of the following cannot modulate force production in smooth muscle?

a. Ca2+
b. Inhibition of myosin light chain kinase.
c. Inhibition of myosin light chain phosphatase.
d. Binding of Ca2+ to troponin C
e. Hormonal stimuli

Answer 37

d

Question 38

Compared to a typical avian leg muscle, hummingbird flight muscle

Answer 38

has an exceptionally high volume fraction of mitochondria.

Question 39

Calcium enters the cytoplasm of a smooth muscle cell by

Answer 39

diffusion from the extracellular space and the sarcoplasmic reticulum.