Chapter 12 - Muscles - Concept Questions

Front 1

Identify as many paris of antagonistic muscle groups in the body as you can.

Back 1

biceps/triceps

hamstring/quads

tibialis anterior/gastrocnemius

Front 2

Why are the ends of the A band the darkest region of the sarcomere when viewed under the light microscope?

Back 2

Ends of the A bands are darkest because they are where the thick and the thin filaments overlap.

Front 3

What is the funciton of t-tubules?

Back 3

T-tubules allow action potentials to travel from the surface of the muscle fiber to its interior.

Front 4

Why arre skeletal muscles described as striated?

Back 4

The banding patter of organized filaments in the sarcomere forms striations in the muscle.

Front 5

What are the three anatomical elements of a neuromuscular junction?

Back 5

1. axon terminals from one somatic motor neuron

2. the synaptic cleft

3. the motor end plate on the muscle fiber

Front 6

What is the chemical signal at a neuromuscular junction?

Back 6

acetylcholine

Front 7

Each myosin molecule has binding sites for what molecules?

Back 7

ATP and actin

Front 8

What is the difference between F-actin and G-actin?

Back 8

F-actin is a polymer filament of actin made from globular G-actin molecules

Front 9

Myosin hydrolyzes ATP to ADP and Pi. Enzymes that hydrolyze ATP are collectively known as _________

Back 9

ATPases

Front 10

Name an elastic fiber in the sarcomere that aids relaxation.

Back 10

Titin

Front 11

In the sliding filament theory of contraction, what prevents the filaments from sliding back to their original position each time a myosin head releases to bind to the next actin binding site?

Back 11

The crossbridges do no all unlink at one time, so while some myosin heads are free and swiveling, others are still tightly bound. (Think of the people pulling the rope and the sail mast).

Front 12

Which part of contraction requires ATP? Does relaxation require ATP?

Back 12

(a) The release of myosin heads from actin requires ATP binding. Energy from ATP is required for the power stroke.

(b) relaxation does not directly require ATP, but, cannot occur unless Ca2+ is pumped back into the SR using a Ca2+-ATPase

Front 13

What events are taking place during the latent period before contraction begins?

Back 13

> creation of the muscle action potential

> release of Ca2+ from the SR

> diffusion of Ca2+ to the contractile filaments

Front 14

According to the convention for naming enzymes, what does the name creatine kinase tell you about this enzyme's function?

Back 14

"Creatine" is the substrate, and "kinase" tells you that this enzyme phosphorylates the substrate.

Front 15

Creatine kinase catalyzes the creatine-phosphocreatine reaction in both directions. What then determines the direction that the reaction goes at any given moment?

Back 15

the relative concentrations of the reactants and products determine the direction of the reaction. The reaction obeys the law of mass action and goes to equilibrium.

Front 16

If K+ concentration increases in the CCF surrounding a cell but does not change significantly in the cell's cytoplasm, the cell membrane _____________ and becomes _________ negative.

Back 16

depolarize; less negative

Front 17

Summation in muscle fibers means that the __________ of the fiber increases with repeated action potentials.

Back 17

tension

Front 18

Temporal summation in neurons means that the _____________ of the neuron increases when two depolarizing stimuli occur close together in time.

Back 18

strength of the graded potential

Front 19

Which type of runner would you expect to have more slow-twitch fibers: a sprinter or a marathoner?

Back 19

A marathoner probably has more slow-twitch fibers and a sprinter probably has more fast-twitch fibers.

Front 20

What is the response of a muscle fiber to an increase in the firing rate of the somatic motor neuron?

Back 20

Increased motor neuron firing rate causes summation in a muscle fiber, which increases the force of contraction.

Front 21

How does the nervous system increase the force of contraction in a muscle composed of many motor neurons?

Back 21

The nervous system increases the force of contraction by recruiting additional motor units.

Front 22

One study found that many world-class athletes have muscle insertions that are farther from the joint than in the average person. Wh would this trait translate into an advantage for a weight lifter?

Back 22

If the muscle insertion point is farther from the joint, the leverage is better and a contraction creates more rotational force.

Front 23

What is the difference in how contraction force is varied in multi-unit and single-unit smooth muscle?

Back 23

(a) Multi-unit smooth muscle: recruiting additional muscle fibers

(b) Single unit smooth muscle: increasing Ca2+ entry

Front 24

When the circular muscle layer of the intestine contracts, what happens to the shape of the tube? When the longitudinal layer contracts, what happens to the shape?

Back 24

(a) diameter decreases

(b) length of tube shortens

Front 25

The dense bodies that anchor smooth muscle actin are analogous to what structure in the sarcomere?

Back 25

Z disks

Front 26

Name two ways smooth muscle myosin differs from skeletal muscle myosin.

Back 26

(a) smooth muscle myosin is longer

(b) smooth muscle myosin has heads the entire length of the filament

Front 27

Name one way actin and its associate proteins differ in skeletal and smooth muscle.

Back 27

smooth muscle actin las troponin

Front 28

Compare the following aspects of skeletal and smooth muscle contractions:

(a) signal from crossbridge activation

(b) sources of calcium for the Ca2+ signal

(c) signal that release Ca2+ from the SR

Back 28

(a)

Skeltal: Ca2+ binds to troponin.

Smooth: myosin phosphorylated.

(b)

Skeletal: all Ca2+ comes from SR

Smooth: Ca2+ comes from SR and ECF

(c)

Skeltal: depolarization signal

Smooth: IP3 signal

Front 29

What happens to contraction if a smooth muscle is placed in a saline bath from which all calcium has been removed?

Back 29

contraction decreases because smooth muscle depends on ECF Ca2+ for contraction

Front 30

Compare Ca2+ release channels in skeletal and smooth muscle SR

Back 30

skeletal: Ca2+-release(RyR) channels are mechanically linked to DHP receptors

smooth: Ca2+-release channels that are activated by IP3

Front 31

How do pacemaker potentials differ from slow wave potentials?

Back 31

pacemaker: always reach threshold and create regular rhythms of contraction

slow wave: variable in magnitude and may not reach threshold each time

Front 32

When TTX, a poison that blocks Na+ channels, is applied to certain types of smooth muscle, it does not alter the spontaneous generation of action potentials. From this observation, what conclusion can you draw about the action potentials of these types of smooth muscle?

Back 32

The depolarization phase of the action potentials must not be due to Na+ entry. In these muscles, depolarization is to to Ca2+ entry.

Front 33

How can a neuron alter the amount of neurotransmitter it releases?

Back 33

Increased frequency of action potentials in the neuron increases neurotransmitter release.

Front 34

Explain how hyperpolarization decreases the likelihood of contraction in smooth muscle.

Back 34

Many Ca2+ channels open with depolarization; therefore, hyperpolarization decreases the likelihood that these channels open. The presence of Ca2+ is necessary for contraction.

Front 35

What causes relaxation in skeletal muscles?

Back 35

troponin releasing Ca2+ and tropomyosin moving back to block actin's binding site for myosin