Muscle Structure and Function

Question 1

What is the sarcomere?

Answer 1

The fundamental unit within muscle fiber.

Question 2

What are the contractile proteins of a muscle? What is there function?

Answer 2

1. Actin
2. Myosin

Shorten muscle fiber and generate active force.

Question 3

What are the non-contractile proteins of a muscle? What do they do?

Answer 3

1. Titin
2. Desmin

Support the structure of the muscle fiber.

Question 4

What is the components of extracellular connective tissue in muscle?

Answer 4

Collagen and elastin

Question 5

What is the difference between a muscle belly, a muscle fascicle, and a muscle fiber?

Answer 5

Muscle belly = a bunch of fascicles put together.

Fascicles = a bunch of fibers put together

Muscle fiber = a bunch of myofibrils

Question 6

Describe a fusiform muscle.

Answer 6

• Have parallel fibers attach to central tendon
• Typically longer
• Have a greater ROM potential

Question 7

Describe a pennate muscle.

Answer 7

• Has oblique fibers that approach central tendon
• Typically are shorter
• Have more numerous fibers per given area = greater strength/greater force production
• Smallar ROM

Question 8

What is force coupling?

Answer 8

• Another example of a synergist
• Formed when 2 or more muscles simultaneously produce force in different linear directions but produce torque in the same direction.

Example: Anterior tilt of pelvis

Question 9

Describe the qualities of a concentric contraction.

Answer 9

• Typically a “shortening” muscle contraction.
• The movement usually occurs against gravity.
• Typically an acceleration activity.

Question 10

Describe the qualities of a eccentric contraction.

Answer 10

• Typically a “lengthening” muscle contraction.
• Movement usually occurs with gravity.
• Typically a deceleration activity.

Question 11

Describe an isometric contraction.

Answer 11

• Allows contraction of the muscle without movement through full ROM.
• Usually for post-op rehabilitation.

Question 12

Describe an isokinetic contraction.

Answer 12

• Allows the ability to adjust resistance throughout ROM of the muscle to account for stronger/weaker areas.

Question 13

What type of contraction causes more overall muscle damage?

Answer 13

Eccentric Contractions

Question 14

What is tension? Where does active tension come from? And what builds passive tension?

Answer 14

Tension = force built up within a muscle

• Active tension comes from contractile units
• Passive tension is built by stretching

Question 15

What is total tension?

Answer 15

Combination of active and passive tension.

Question 16

What is tone?

Answer 16

Slight tension in muscle at all times; state of readiness.

Question 17

Describe passive length tension.

Answer 17

• When a muscle is stretched, spring-like resistance (stiffness) is generated within the muscle.
• Passive tension is attributed to elastic forces produced by non-contractile elements.

Question 18

What does the passive length tension curve tell you?

Answer 18

• Passive tension is created after the critical length is reached.
• The tension is increased as the tissue is stretched.
• High tension results in rupture or failure.

Question 19

Describe active-length tension.

Answer 19

• Muscle is generating active force.
• Ideal resting length = length that allows the greatest number of crossbridges
• Potential crossbridges decrease as the muscle is stretched or shortened from resting length. So less active force can be generated.
• Peak of curve = ideal resting length. Place where the most force can be produced.

Question 20

What does the length-tension relationship tell you?

Answer 20

• Muscle length is a factor that determines the amount of tension present.
• Muscle can produce greater force if put on stretch prior to contracting.

Question 21

In the length tension relationship, what is the difference for muscles that span 1 or 2 or more joints?

Answer 21

Muscles spanning 1 joint = usually have sufficient excursion to allow joint to move through the entire ROM.

Muscles spanning 2 or more joints = may not have sufficient excursion to allow joint to move through combined range of all joints it crosses.

Question 22

In the length tension relationship, what is the amount of passive tension dependent on?

Answer 22

• Dependent on stiffness of the muscle.

**High levels of passive tension in muscles that cross multiple joints.

Example = during wrist extension, fingers flex

Question 23

What is passive insufficiency?

Answer 23

When a multi-joint muscle is of insufficient length to permit full ROM.

Question 24

What is tenodesis grasp?

Answer 24

Passive movement of tendons in response to passive insufficiency.

Question 25

What is active insufficiency?

Answer 25

• Point at which a 2-joint muscle reaches a point where it cannot shorten any farther.
• The muscle has “insufficient power” to contract further.
• Multi - muscle has diminished ability to produce force.

Question 26

Describe types of isometric muscle forces.

Answer 26

Max isometric force = used as indicator of peak strength.

Internal torque can be measured by isometric contraction at several joint angles; max effort against known external force.

Force output highly dependent on muscle length.

Question 27

Describe the force-velocity curve.

Answer 27

• the velocity of the shortening of a muscle concentrically contracting is inversely related to the external load. (increase load = decrease speed)
• The velocity of the lengthening of an eccentrically contracting muscle is proportional to the external load. (increase load = increase speed)

Question 28

What does the force-time relationship tell you?

Answer 28

• The force generated by a muscle is proportional to the contraction time.
• The greater the contraction time the greater the force up to maximum contraction.

Question 29

What is the purpose of stretching.

Answer 29

• To lengthen the resting length of a muscle.

- Should be performed on relaxed muscles.