Chapter 12 concept questions

Question 1

Identify as many pairs of antagonistic muscle groups in the body as you can. If you cannot name them, point out the probable location of the flexor and extensor of each group.

Answer 1

Biceps/triceps,
hamstring (flexor)/quadriceps (extensor),
Tibialis anterior(flexor)/gastrocnemius (extensor)

Question 2

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

Answer 2

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

Question 3

What is the function of t-tubules?

Answer 3

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

Question 4

Why are skeletal muscles described as striated?

Answer 4

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

Question 5

What are the three anatomical elements of a neuromuscular junction?

Answer 5

A neuromuscular junction consists of axon terminals form one somatic motor neuron, the synaptic cleft, and the motor end plate on the muscle fiber.

Question 6

What is the chemical signal at a neuromuscular junction?

Answer 6

The chemical signal at a neuromuscular junction is acetylcholine.

Question 7

Each myosin molecule has binding sites for what molecules?

Answer 7

Each myosin molecule has binding sites for ATP and actin.

Question 8

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

Answer 8

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

Question 8

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

Answer 8

Enzymes that hydrolyze ATP are ATPases

Question 9

Name an elastic fiber in the sarcomere that aids relaxation.

Answer 9

Titin is an elastic fiber in the sarcomere

Question 10

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

Answer 10

The cross bridges do not all unlink at one time, so while some myosin heads are free and swiveling, others are still tightly bound.

Question 11

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

Answer 11

The release of myosin heads from actin requires ATP binding. Energy from ATP is required for the power stroke. Relaxation does not directly require ATP, but relaxation cannot occur unless Ca2+ is pumped back into the sarcoplasmic reticulum using a Ca2+-ATPase.

Question 12

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

Answer 12

The events of the latent period include creation of the muscle action potential, release of Ca2+ from the sarcoplasmic reticulum, and diffusion of Ca2+ to the contractile filaments.

Question 13

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

Answer 13

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

Question 14

The reactions in figure 12.12 show that creatine kinase catalyzes the creatine-phosphocreatine reaction in both directions. what then determines the direction that the reaction goes at any given moment?

Answer 14

Because creatine kinase catalyzes the reaction in both directions, the relative concentrations of the reactants and products determine the direction of the reaction. The reaction ones the law of mass action and goes to equilibrium.

Question 15

If K+ concentration increases in the extracellular fluid surrounidng a cell but does not change significantly in the cell’s cytoplasm, the cell membrane __________ (depolarizes/hyperpolarizes) and becomes ___________ (more/less) negative.

Answer 15

Increasing extracellular K+ causes the cell to depolarize and become less negative.

Question 15

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

Answer 15

tenstion

Question 16

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

Answer 16

strength of the graded potential.

Question 17

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

Answer 17

marathon runner.. duh

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

Multi-unit smooth muscle increases force by recruiting additional muscle fibers; single-unit smooth muscle increases force by increasing Ca2+ entry.

Question 22

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?

Answer 22

Contraction of the circular layer decrease the diameter of a tube. Contraction of the longitudinal layer shortens the tube.

Question 23

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

Answer 23

Dense bodies are analogous to Z disks.

Question 24

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

Answer 24

Smooth muscle myosin is longer and has heads the entire length of the filament.

Question 25

Compare the following aspects of skeletal muscle and smooth muscle contraction:
a)signal for crossbridge activation
b)source(s) of calcium for the Ca2+ signal
c)signal that releases Ca2+ from the sarcoplasmic reticulum

Answer 25

a) skeletal muscle: Ca2+ binds to troponin.
Smooth msucle: myosin phorylated.
b) skeletal muscles: all Ca2+ comes form the sarcoplasmic reticulum.
Smooth muscle: Ca2+ from both SR and ECF.
c) Skeletal muscle: depolarization signal.
Smooth muscle: IP3 signal.

Question 26

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

Answer 26

without ECF Ca2+, contraction decreases because smooth muscle depends on ECF Ca2+ for contraction.

Question 27

Compare Ca2+ release channels in skeletal and smooth muscle sarcoplasmic reticulum.

Answer 27

Skeletal muscle Ca2+-release(RyR) channels are mechanically linked to DHP receptors. Smooth muscle also has Ca2+-release channels that are activated by IP3.

Question 28

How do pacemaker potentials differ from slow wave potentials?

Answer 28

Pacemaker potentials always reach threshold and create regular rhythms of contraction. slow wave potentials are variable in magnitude and may not reach threshold each time.

Question 29

When tetrodotoxin (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?

Answer 29

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

Question 30

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

Answer 30

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

Question 30

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

Answer 30

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

Question 31

What causes relaxation in skeletal muscle?

Answer 31

Relaxation in skeletal muscle occurs when troponin releases Ca2+ and tropomyosin moves back to block actin’s binding site for myosin.