WEEK 7 (Skeletal muscle mechanics)

Question 1

Describe the role of connective tissue in fibers

Answer 1

• Each muscle is sheathed by connective tissue that penetrates from the surface into the muscle to ENVELOP each individual fiber and divide the muscle into BUNDLES
• connective tissue extends beyond the ends of the muscle to form TOUGH, COLLAGENOUS TENDONS that attach the muscle to bones

Question 2

Sarcomeres are not attached to bone, what is instead?

Answer 2

Tendons

Tension generated by these contractile elements must be transmitted to the bone via tendon before the bone can be moved

Question 3

What is another name for tendons?

Answer 3

Series-elastic component

Question 4

A _______ is typically attached to at least two bones across a joint by means of tendons that extend from each end of the muscle

Answer 4

muscle

Question 5

Define the ‘Origin’ and ‘Insertion’

Answer 5

Origin is the end of the muscle attached to the more stationary part of the skeleton

Insertion is the end attached to the skeletal part that moves

Question 6

Since muscle contraction can only pull and not push bone, what happens?

Answer 6

Two different antagonistic muscles or muscle groups are situated to pull on opposite sides of the joint

Question 7

What are the differences between Isotonic contraction, Isokinetic contraction & Isometric contraction?

Answer 7

Isotonic contraction = the load remains constant as the muscle changes length

Isokinetic contraction = the velocity of shortening remains constant as the muscle changes length

Isometric contraction = the muscle is prevented from shortening so tension develops at constant muscle length

Question 8

What are the stages of muscle contraction?

Answer 8

1) Muscle excitation turns on the tension-generating contractile process
2) Cross bridges start cycling
3) Filament sliding shortens the sarcomeres which stretches the series-elastic components to exert forces on the bones at the sites of the muscle’s origin and insertion

Question 9

What happens in Isotonic contraction?

Answer 9

• weight of object does not change as it is lifted
• the angle of the joint changes while the object is being lifted so MUSCLE TENSION must change to counterbalance the load. Thus, muscle tension does not remain constant throughout the period of shortening
• CONCENTRIC: muscle length SHORTENS during contraction
• ECCENTRIC: muscle length INCREASES during contraction

Question 10

What happens in Isokinetic contraction?

Answer 10

• occur when muscle fibers shorten at a constant velocity or speed
• angular speed is constant during contraction
• more rapid development of muscle strength

Question 11

What happens in Isometric contraction?

Answer 11

• no change in muscle length
• takes place when the tension developed in the muscle is less than needed to move the load

Question 12

What is the difference between concentric and eccentric contractions?

Answer 12

CONCENTRIC CONTRACTIONS = muscle shortens

ECCENTRIC CONTRACTIONS = muscle lengthens

Question 13

What are Sphincters?

Answer 13

• muscles not attached to bone at all and prevent movement
• voluntarily controlled rings of skeletal muscle that when contracted, close an opening which guides movement of material through the opening

Question 14

Describe the load-velocity relationship for concentric contractions

Answer 14

The speed of shortening is maximal when there is no external load, and falls to zero when the load cannot be overcome by maximal tension. Load and velocity for shortening are INVERSELY related for concentric contractions.

Question 15

How is the relationship between load and shortening velocity a fundamental property of muscle?

Answer 15

Since the power stroke slows when the myosin head tilts against a greater load

Question 16

Describe the load-velocity relationship for eccentric contractions

Answer 16

Load and velocity for lengthening are DIRECTLY related for eccentric contractions. An external force (load) greater than a muscle’s maximal contraction force causes the muscle to lengthen, with the velocity of lengthening being directly dependent on the load.

Question 17

Define Work and Force

Answer 17

Work is force multiplied by distance

Force is the muscle tension required to overcome the load

Question 18

Most skeletal muscles are attached to bones across joints, forming lever systems. What is a lever?

Answer 18

A lever is a rigid structure capable of moving around a pivot point known as a FULCRUM

Question 19

What is the Power arm?

Answer 19

The portion of a lever between the fulcrum and the point where a force is applied by the muscle

Question 20

What is the Load arm?

Answer 20

The portion between the fulcrum and the force exerted by a load

Question 21

What are the two primary factors that can be adjusted to accomplish gradation of whole muscle tension?

Answer 21

• number of muscle fibers contracting within a muscle
• tension developed by each contracting fiber

Question 22

A single action potential in a muscle fiber produces a brief, weak contraction called a __________

Answer 22

twitch

Question 23

Why can larger muscles consisting of more muscle fibers generate more tension than smaller muscles with fewer fibers?

Answer 23

Since the greater the number of fibers contracting, the greater the total muscle tension.

Question 24

What are the properties of motor neurons & muscle fibers?

Answer 24

• One motor neuron innervates a number of muscle fibers but each muscle fiber is supplied by only one motor neuron
• Muscle fibers that compose a motor unit are dispersed throughout the whole muscle so their simultaneous contraction results in an evenly distributed, although weak, contraction of the whole muscle

Question 25

What is a motor unit?

Answer 25

One motor neuron plus all the muscle fibers it innervates

Question 26

What is motor unit recruitment?

Answer 26

For stronger and stronger contractions, more and more motor units are recruited, or stimulated to contract simultaneously

Question 27

What can influence the extent to which tension can be developed?

Answer 27

• Frequency of stimulation
• Length of the fiber at the onset of contraction
• Extent of fatigue
• Thickness of the fiber

Question 28

What is Twitch summation?

Answer 28

A process when two twitches from two action potentials add together, or sum, to produce greater tension in the fiber than that produce by a single action potential

Question 29

What is Tetanus?

Answer 29

Produced when the muscle fiber is stimulated so rapidly that it does not have a chance to relax at all between stimuli. It is a smooth, sustained contraction of maximal strength.