Module 3 - Muscle Architecture & Mechanical Properties

Question 1

What are the 3 layers of Skeletal Muscle?

Answer 1

• Epimysium: outer part
• Perimysium: Middle part
• Endomysium: inner part

Question 2

How does Connective Tissue play more than a supportive role in muscle function?

Answer 2

• Muscle fiber tendon force transmission

Question 3

What muscle fibers are intimately associated with connective tissue?

Answer 3

• Endomysium

Question 4

How do muscles contribute to the movement?

Answer 4

• Production of movement
• Maintain a stable posture
• Stabilizing Joints

Question 5

Muscles contribute to movement, what else do they do?

Answer 5

• Support and protect internal organs
• Help in maintenance of body temperature

Question 6

What are the 10 factors influencing muscular tension?

Answer 6

• Physiological Cross-sectional area
• Pennation Angle
• Muscle Fiber Type
• Force-Length Relationship
• Force-Velocity Relationship
• Recruitment, Frequency, Synchronization
• Elastic Energy Storage
• Electromechanical Delay
• Muscle Temperature
• Mechanical Links to other muscles

Question 7

What is usually the angle of muscle fiber arrangement relative to the axis of force generation?

Answer 7

• 0-30 degrees at rest

Question 8

What are the three main muscle fiber architecture types?

Answer 8

• Fusiform (parallel)
• Unipennate
• Multipennate

Question 9

What is the physiological cross-sectional area of a muscle?

Answer 9

• Sum of the cross-sectional areas of all muscle fibers within a muscle
• Directly proportional to the maximum tetanic tension generated
• Likely different from anatomical cross-sectional area
• Mass gives little information that is relevant to function

Question 10

What is the equation for physiological cross-sectional area?

Answer 10

• Muscle Mass (g) * cos(0) / Muscle Density (g/cm3) * Fiber Length (cm)

Question 11

What muscle architecture type has an anatomical cross-section area that equals the physiological cross-sectional area?

Answer 11

• Fusiform Muscles: parallel

Question 12

What is larger for pennated muscles, Anatomical or Physiological Cross-sectional area?

Answer 12

• Physiological

Question 13

What does a muscle with a larger PCSA have to one with a small one?

Answer 13

• Greater number of fibers in parallel

Question 14

What will generate more power if they have the same anatomical cross-sectional area, a pennated muscle or fusiform muscle?

Answer 14

• Pennated Muscle

Question 15

What will generate more power if they have the same anatomical cross-sectional area, a pennated muscle or fusiform muscle?

Answer 15

• Pennated Muscle

Question 16

What is the effect of fiber angulation?

Answer 16

• Line of action of pennate muscle is non-parallel to its fibers
• Loss of force relative to muscle with same mass/fiber length
• Largely compensated for space-saving capacity: Fiber Packing

Question 17

What determines the muscle fiber length?

Answer 17

• Number of Sarcomeres in series
• Muscle fiber excursion

Question 18

Can Sarcomeres change length?

Answer 18

• Yes

Question 19

How much can muscles shorten from resting length?

Answer 19

• 50-70%

Question 20

What muscles fibers are generally shorter, pennate or fusiform?

Answer 20

• Pennate Muscles

Question 21

What muscle fibers have smaller excursions?

Answer 21

• Pennate Muscle fibers

Question 22

What is the typical length of muscle fibers compared to muscle length?

Answer 22

• Typically 20-60%

Question 23

Describe what happens when a muscle begins to shorten

Answer 23

Muscle is Activated
- External Moment smaller than muscle moment

Question 24

Describe what happens when muscle maintains constant length

Answer 24

Muscle is Activated
- External moment equals muscle moment

Question 25

Describe what happens while a muscle is lengthening

Answer 25

Muscle is Activated
- External moment is larger than muscle movement

Question 26

What is Active Tension?

Answer 26

• Force created between actin and myosin filaments in sarcomeres of activated motor units
• Unique property of muscle (compared to tendons, ligaments, and bones)

Question 27

What is Passive Tension?

Answer 27

• Forces created by the elongation of the titin molecule or connective tissue components of muscle

Question 28

What is the standard for modeling muscle properties?

Answer 28

• Includes both passive and active components of muscle tension
• Model allows generalization of mechanical behavior of muscles
• Can make predictions (quantitative hypotheses) of muscle behavior

Question 29

What is Hill’s Model?

Answer 29

Muscle Property Model
- There is no elasticity in the production of active tension
- Net muscle tension results from complex interaction of active and passive sources of tension

Question 30

What is the contractile component of Hill’s model?

Answer 30

• Actin-Myosin cross-bridge

Question 31

What is the Series Elastic Component of Hill’s Model?

Answer 31

• Titin Molecule
• Tendons
• Flexibility of the actin-myosin component (if active)

Question 32

What is the Parallel elastic component of Hill’s Model?

Answer 32

• Fascia Layer of the Muscle (endo, peri, epimysium)

Question 33

What is the Role of the Parallel Elastic Component in Hill’s Model?

Answer 33

Unclear
- Could offer an opposing force and prevent Contractile element from being pulled apart by external forces
- Could play a role in lateral force transmission