Module 3 - Muscle Architecture & Mechanical Properties Flashcards
What are the 3 layers of Skeletal Muscle?
- Epimysium: outer part
- Perimysium: Middle part
- Endomysium: inner part
How does Connective Tissue play more than a supportive role in muscle function?
- Muscle fiber tendon force transmission
What muscle fibers are intimately associated with connective tissue?
- Endomysium
How do muscles contribute to the movement?
- Production of movement
- Maintain a stable posture
- Stabilizing Joints
Muscles contribute to movement, what else do they do?
- Support and protect internal organs
- Help in maintenance of body temperature
What are the 10 factors influencing muscular tension?
- 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
What is usually the angle of muscle fiber arrangement relative to the axis of force generation?
- 0-30 degrees at rest
What are the three main muscle fiber architecture types?
- Fusiform (parallel)
- Unipennate
- Multipennate
What is the physiological cross-sectional area of a muscle?
- 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
What is the equation for physiological cross-sectional area?
- Muscle Mass (g) * cos(0) / Muscle Density (g/cm3) * Fiber Length (cm)
What muscle architecture type has an anatomical cross-section area that equals the physiological cross-sectional area?
- Fusiform Muscles: parallel
What is larger for pennated muscles, Anatomical or Physiological Cross-sectional area?
- Physiological
What does a muscle with a larger PCSA have to one with a small one?
- Greater number of fibers in parallel
What will generate more power if they have the same anatomical cross-sectional area, a pennated muscle or fusiform muscle?
- Pennated Muscle
What will generate more power if they have the same anatomical cross-sectional area, a pennated muscle or fusiform muscle?
- Pennated Muscle
What is the effect of fiber angulation?
- 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
What determines the muscle fiber length?
- Number of Sarcomeres in series
- Muscle fiber excursion
Can Sarcomeres change length?
- Yes
How much can muscles shorten from resting length?
- 50-70%
What muscles fibers are generally shorter, pennate or fusiform?
- Pennate Muscles
What muscle fibers have smaller excursions?
- Pennate Muscle fibers
What is the typical length of muscle fibers compared to muscle length?
- Typically 20-60%
Describe what happens when a muscle begins to shorten
Muscle is Activated
- External Moment smaller than muscle moment
Describe what happens when muscle maintains constant length
Muscle is Activated
- External moment equals muscle moment
Describe what happens while a muscle is lengthening
Muscle is Activated
- External moment is larger than muscle movement
What is Active Tension?
- Force created between actin and myosin filaments in sarcomeres of activated motor units
- Unique property of muscle (compared to tendons, ligaments, and bones)
What is Passive Tension?
- Forces created by the elongation of the titin molecule or connective tissue components of muscle
What is the standard for modeling muscle properties?
- 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
What is Hill’s Model?
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
What is the contractile component of Hill’s model?
- Actin-Myosin cross-bridge
What is the Series Elastic Component of Hill’s Model?
- Titin Molecule
- Tendons
- Flexibility of the actin-myosin component (if active)
What is the Parallel elastic component of Hill’s Model?
- Fascia Layer of the Muscle (endo, peri, epimysium)
What is the Role of the Parallel Elastic Component in Hill’s Model?
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
