Muscular Physiology Flashcards
Explain the steps involved in a voluntary muscle contraction
Contraction of Muscle (Cross-Bridge Cycling)
- Release of Calcium
– Ca+ is released from SR – Ca+ binds to a Troponin
molecule.
– Ca+ /Troponin complex then attaches to Tropomyosin that is covering a binding site on the Actin filament
– When the Ca+ /Troponin attaches to the Tropomysoin, a binding site is uncovered and a cross-bridge can then attach
Relaxation of Muscle Fibers
- Sarcoplasmic Reticulum needs to re-absorb the calcium for the cross-bridges to release from the actin for the muscle to relax
Identify and explain the three (3) different muscle fiber types
Slow-Twitch (Type I) Muscle Fibers:
Characteristics:
- Contract Slowly: Slow-twitch fibers contract more slowly compared to other types.
- Endurance: They are highly resistant to fatigue, making them well-suited for prolonged, low-intensity activities.
- Aerobic Metabolism: These fibers primarily rely on aerobic metabolism (oxidative phosphorylation) to produce energy, utilizing oxygen efficiently.
- Red Color: Slow-twitch fibers have a higher concentration of myoglobin and blood vessels, giving them a reddish appearance.
Function:
- Suited for activities like long-distance running, cycling, or other endurance-based exercises.
- Provide sustained muscle contractions without rapid fatigue.
Fast-Twitch Oxidative (Type IIA) Muscle Fibers:
Characteristics:
- Intermediate Speed: Contract at a moderate speed compared to slow-twitch and fast-twitch glycolytic fibers.
- Moderate Fatigue Resistance: More fatigue-resistant than fast-twitch glycolytic fibers but less than slow-twitch fibers.
- Aerobic and Anaerobic Metabolism: - Can utilize both aerobic and anaerobic metabolic pathways for energy production.
- Pink Color: Have a moderate myoglobin content, giving them a pinkish appearance.
Function:
- Suitable for activities that involve a combination of endurance and strength, such as middle-distance running or swimming.
Fast-Twitch Glycolytic (Type IIB or IIX) Muscle Fibers:
Characteristics:
- Contract Quickly: Fast-twitch glycolytic fibers contract rapidly, generating high force.
- Fatigue Quickly: These fibers fatigue relatively quickly compared to slow-twitch and fast-twitch oxidative fibers.
- Anaerobic Metabolism: Primarily rely on anaerobic metabolism (glycolysis) for energy production.
- White Color: Have a lower myoglobin content, giving them a whitish appearance.
Function:
- Suited for short bursts of intense activity, such as sprinting, weightlifting, or activities requiring rapid and powerful muscle contractions.
- Contribute to explosive strength and power.
Explain why muscle has the greatest strength potential around mid- length (length-tension relationship). Relate this to a practical strength example.
Length Tension Relationship:
Fewer myosin cross-bridges attached to actin when muscle is shortened AND lengthened. Most myosin/actin cross-bridges at mid-length.
Practical Strength Example:
Consider a bicep curl as a practical example. When your elbow is fully extended, and the bicep muscle is at its longest length, the force-generating capacity is reduced. This is because there is limited overlap between the actin and myosin filaments.
As you bend your elbow to bring the forearm towards your shoulder (shortening the bicep muscle), you reach a mid-length position where the overlap between actin and myosin is optimal. At this point, your bicep muscle can generate the maximum force.
*The more hands on the rope (aka: cross-bridges attached), the stronger you can pull
Using an example, describe the “Stretch Shortening Cycle” and explain how it increases force production (be sure to include active and passive structures).
Active and Passive Structures: Both active structures (muscles) and passive structures (tendons and elastic components) contribute to force production during the SSC. The muscles actively contract, while the elastic elements passively release stored energy.
In summary, the Stretch Shortening Cycle is a mechanism that utilizes the elastic properties of muscles and tendons, along with the stretch reflex, to enhance force production during dynamic movements. This cycle is particularly important in activities that require rapid and explosive actions, such as jumping or sprinting.
Explain why when contraction speed increases, the amount of force the muscle can produce/sustain decreases?
In practical terms, this force-velocity relationship has implications for activities that involve different contraction speeds. For instance, in resistance training, lifting a heavy load at a slow speed maximizes force production, while lifting a lighter load at a faster speed emphasizes power. Athletes and fitness enthusiasts often incorporate a variety of training speeds to target different aspects of muscle function and performance.
Different factors include:
- Cross-Bridge Cycling
- Type of Muscle Fiber:
Muscle sustain force through its ____
properties
passive and active
Passive
– Consists of ______
Connective
Tissue
Active
– The actual ______
Muscle Fibers
Each muscle fiber may contain ______
1000’s of myofibrils
Myofibril is a long chain of _______(striated appearance)
“Sarcomere’s”
The shortening of muscle fibers (sarcomere’s): ______ is required
ATP
Sarcoplasmic Reticulum needs to ________ the calcium for the cross-bridges to release from the actin for the muscle to relax
re-absorb
Faster the contraction,
the lower the muscles maximum force capacity
– _____ cross-bridge cycling means _______
Fast,
fewer cross-bridges attached at any given moment
