Mechanics of Muscle Contractions

Question 0

What are the periods of a muscle twitch?

Answer 0

Latent period
Period of contraction
Period of relaxation

Question 1

What is a muscle twitch?

Answer 1

A mechanical response to a single stimulation

Question 2

Describe the latent period in a muscle twitch

Answer 2

• time between stimulus and initiation of a contraction (2-4 seconds)
• when the process associated with EC coupling occur

Question 3

EC coupling occurs during what period of the muscle twitch?

Answer 3

the latent period

Question 4

Describe the period of contraction

Answer 4

When actin and myosin interact so the muscle actively develops tension

Question 5

During the period of contraction, if tension > load resistance, what type of contraction do you have?

Answer 5

isotonic

Question 6

During the period of contraction, if tension < load resistance, what type of contraction do you have?

Answer 6

isometric contraction

Question 7

Describe the period of relaxation in a skeletal muscle twitch

Answer 7

[Ca2+]_i returns to normal and tension diminishes

Question 8

What does twitch duration depend on? What are factors influcing twitch duration?

Answer 8

Depends on Muscle type!

Factors including twitch duration include:
1) rates of hydrolysis of ATP by myosin produces different rates of contraction
2) differences in rate of Ca2+ uptake into SR
2)

Question 9

Does fast twitch skeletal muscle fibers have a short or long twitch duration?

Answer 9

Short twitch duration

Question 10

Do slow twitch fibers have fast or long twitch durations?

Answer 10

long twitch durations

Question 11

How do the rates of Ca pumps in fast twitch fibers compare to slow twitch fibers?

Answer 11

Fast twitch fibers have faster Ca2+ uptake than slow twitch fibers, resulting in quicker Ca uptake and faster relaxation

Question 12

What is summation in regards to skeletal muscle?

Answer 12

The adding of force to the first action potential if a subsequent action potential occurs before an activated muscle has time to fully relax

Question 13

What is tetanus in regards to skeletal muscle contraction?

Answer 13

when action potentials occur repeatedly and rapidly creating a sustained contraction

Question 14

What is tetanus fusion frequency?

Answer 14

the rate at which the action potentials occur so rapidly that no relaxation occur creating smooth or fused rise in tension to a pleateau

Question 15

Applying the tetanic fusion frequency to stimulate the muscle results is what size tension?

Answer 15

The maximum tension that the muscle can produce.

Question 16

What is the relationship between the tension the muscle can produce during tetanus and during a single twitch?

Answer 16

The tension produced during the plateau of a fused tetanus is 3 to 8 times that of a single twitch

Question 17

What three factors influence the development of tension in a skeletal muscle?

Answer 17

Internal Ca2+ concentration
Series elastic elements
Muscle length

Question 18

How does internal Ca2+ concentration influence the development of tension?

Answer 18

The Ca2+ released from a single action potential is nearly saturating. However, Ca2+ uptake begins as soon as the muscle is stimulated, so the elevated Ca2+ concentration is brief compared to the development of tension.

Question 19

What is needed to maintain saturating levels of Ca2+?

Answer 19

multiple stimuli

Question 20

What are series elastic elements?

Answer 20

structures in a muscle that are stretched when the muscle actively contractions. Exact structures unknown.

Question 21

What is the effect of series elastic elements on twitch tension?

Answer 21

Much of the tension in a twitch tension must be used to stretch the series elastic elements before tension is transmitted to the load. Therefore, less than the full tension is transmitted to the load.

Question 22

How does tetanus affect the series elastic elements?

Answer 22

because of the tetanic contraction, the series elastic elements remain stretched and more internal tension is applied to the load

Question 23

What is a motor unit?

Answer 23

a motor neuron and all the muscle fibers it innervates

Question 24

Are all the muscle fibers in a motor unit the same or of different types?

Answer 24

same type!

Question 25

How many muscle fibers do large and small motor units innervate? What it it’s effect on movement? What type of fibers are usually in each?

Answer 25

Large motor units = a large diameter axons with many fast, glycolytic muscle fibers and the movement is course

Small motor units = a small diameter axon with few slow, oxidative fibers and the movement is delicate

Question 26

What influences the degree of contraction for skeletal muscle?

Answer 26

simultaneous activity of motor units.

Question 27

More motor units lead to lesser or greater tension?

Answer 27

greater tension

Question 28

Which motor units are recruited first: small or large?

Answer 28

small

Question 29

What does the amount of tension developed by an individual skeletal muscle motor unit devepend on?

Answer 29

The rate of stimulation. If it’s high enough, the twitches will sum, resulting in tetanus of the fibers.

Question 30

If you want to increase the force of a skeletal muscle, what can you do?

Answer 30

Increase the number of motor neurons activated or increase the rate of action potentials

Question 31

In skeletal muscle, when calcium floods out of the SR, which part of skeletal muscle (i.e. band) does it flood out to?

Answer 31

the AI band