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MSK Week 3 > 2.3.4. Muscle Mechanics I/II > Flashcards

2.3.4. Muscle Mechanics I/II Flashcards

1
Q

2 Functions of skeletal muscle

A
  1. Produce Skeletal Muscle movement. Performs physical work and develops force, tension or stress
  2. Maintain posture and body position
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2
Q

What are the two functional elements of skeletal muscle and what are they in charge of?

A
  1. Contractile Element - Consists of a cross bridge system that generates muscle force
  2. Viscous Element/Elastic Element - Element that resists motion. Turns that energy into heat.
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3
Q

Formula for calculating the elastic or viscous functional element force value?

A

F = -K*V

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4
Q

What occurs with an isometric contraction?

A

The ends of the muscle are fixed (holding weight without moving it)

Two platforms: one fixed and one adjustable (but immovable during contraction)

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5
Q

What occurs with an isotonic contraction?

A

Use passive stretch to set initial muscle length and apply a supermaximal electrical stimulus

Muscle shortens until there are just enough cross bridges to barely support the load, then motion stops

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6
Q

What is a muscle twitch?

A

A muscle twitch, or fasciculation, is the tension (force) produced in response to a single muscle AP

Isometric Contraction

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7
Q

How are twitch and tetanus related?

A

Twitch may also be used to describe the force and speed of contraction of a single muscle fiber. Total tension developed increases: can result in fused or unfused tetani

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8
Q

Describe the difference between Fused vs. unfused Tetanus.

A

Unfused: Not “continuous” activation, but a summative result (bumpy graph)

Fused: Fused is a mechanical summation overall (smooth graph)

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9
Q

What is muscle efficiency based on?

A

The ratio of mechanical work output to total metabolic cost (aka O2 consumption)

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10
Q

Work equation

A

Work = F x D (joules)

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11
Q

Power equation

A

Power = work/time (watts)

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12
Q

Stress equation

A

Stress = Force / Area of muscle

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13
Q

Is movement required to generate stress?

A

NO

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14
Q

Voluntary activation of skeletal muscle

A

AP in α-motor neuron propagates to NMJ; AP releases transmitters into synaptic cleft; depolarization of sarcolemma; muscle AP; release of Ca; cross bridges cycle and muscle contracts

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15
Q

How does muscle develop force?

A 
Depends on:
Type
Length
Stimulus 
Number of cells firing
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16
Q

What is the greatest determinant for the development of force?

A

Muscle length

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17
Q

Contractile Element of muscles

A

Cross-bridge systems that generates muscle force

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18
Q

Viscous element

A

Resists motion; acts like a shock absorber

Only produces force while in motion

Dissipates energy (turns it into heat)

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19
Q

Series elastic element

A

Made up of tendon and connective tissue (small part made up of titin)

20
Q

Parallel elastic element

A

Largely made up of titin and connective tissue

21
Q

What does a bigger stimulus mean?

A

More fibers are activated (each individual fiber goes “all out” with each stimulus, large stimuli are just able to activate more than small ones)

22
Q

Place these muscles in increasing order of contraction time:

Gastrocnemius, Soleus, Occular

A

Occular < Gastrocnemius < Soleus

eyeballs don’t need a lot of force, but need to move quick < running and jumping < posture

23
Q

Difference b/w muscle twitches and APs

A

Twitches can be summed

24
Q

Mechanism behind fused tetanus

A

The viscous elements in the muscle don’t allow it to fully relax before the next stimulus arrives (intracellular Ca isn’t completely removed from the cytoplasm either)

25
Q

Is increasing the stimulus our primary means of controlling muscle force?

A

No (generally a fused tetanus has a magnitude of only 3-5 times that of an isolated twitch)

26
Q

Passive muscle strength

A

The muscle as a rubber band (no stimulation, no contraction of the muscle in questions)

Stretch the muscle and measure the force produced

27
Q

How is force generated by passive muscle strength

A

By the muscle trying to get back to its resting length

28
Q

Total Tension

A

= Passive + Active Tension

29
Q

Sliding filament theory

A

Force is generated by making and breaking cross-bridges b/w the thick and thin filaments

Sarcomere shortens by thick and thin filaments sliding past each other

30
Q

Active Tension Force Magnitude

A

Related to the number of cross bridges formed

More cross bridges = greater force (related to thick and thin filament overlap and overlap is related to MUSCLE LENGTH)

31
Q

What is the thick filament made up of?

A

Myosin molecules pointed in opposite directions bound together in center of H-band by myomesin that forms the M-line

32
Q

What is the thin filament up of?

A

Actin, tropomyosin & troponin

Attached to the z-disks

33
Q

Cross Bridge Cycling

A

Thick filaments globular heads form cross bridges with thin filaments; heads rotate inward toward the M-line pulling the thin filaments together; heads release from thin filament (need ATP); heads reset

As long as Ca level is high, the muscle can keep contracting/crawling

34
Q

Too much thick/thin interaction

A

Thin filaments shield one another from thick filaments (decrease in cross bridges and less force)

Thick filaments contact the Z line and resist contraction

Tension falls to zero when initial length is set slightly before the thin filament contacts the Z line

35
Q

Skeletal muscle force is regulated by two things

A 
Motor unti recruitment (primary)
Firing pattern (secondary)
36
Q

Skeletal muscle relaxation

A

Isotonic relaxation followed by isometric relaxation

37
Q

Heart muscle relaxation

A

Isovolumetric

38
Q

Voluntary control of skeletal-muscle force

A

Length changes in skeletal muscle are not significant in force regulation

Restricted by bones and ligaments (the muscle works near the flat peak of the active tension curve)

39
Q

Control of cardiac muscle force

A

Length changes are significant

40
Q

Motor Unit

A

All of the muscle fibers innervated by the motor unit

Muscle fibers are not innervated by more than one motor neuron

41
Q

Small motor unit

A

Quick movement but little force

42
Q

Large motor unit

A

Slower movement but lots of force/strength

43
Q

Types of muscle fibers

A

Slow-oxidative
Fast-oxidative
Fast-glycolytic

44
Q

Type I

A

Slow Oxidative; slow myosin ATPase activity; high oxidative capacity

Fatigue resistance; used continuously

RED

45
Q

Type IIx

A

Fast glycolytic; fast myosin ATPase activity; high glycolytic

Fast fatigue; used intermittently

WHITE

46
Q

Type IIa

A

Fast oxidative; fast myosin ATPase activity; moderate oxidative capacity

Moderately fatigue resistant

47
Q

Muscle organization

A

We have many small motor units and very few large motor units

Largest motor units are recruited last, only during the highest forces

MSK Week 3 (8 decks)

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