Quiz 4 Flashcards
What is the end-plate potential?
Occurs at motor end plate of sarcolemma (muscle cell) that always causes AP.
Each muscle action potential generates a _____ _______.
Single twitch
What is excitation -contraction coupling?
The sequence of muscle action potentials and Ca2+ release that initiates contraction
What are t-tubules? What do they do?
Inward extensions of sarcolemma that propagated sarcolemmal action potentials.
What is the sarcoplasmic reticulum?
Similar to endoplasmic reticulum, sequesters Ca2+ in a muscle cell.
What happens after an action potential has propagated a long a t-tubule?
The action potential activated DHP receptor that mechanically opens the ryanodine receptor in the sarcoplasmic reticulum to release Ca2+.
What is the contraction cycle?
Ca2+ binds to troponin –> moves tropomyosin –> exposes entire binding site on actin –> sliding filaments allow muscle to shorten
What are the steps of the contraction cycle?
- Myosin in resting “cocked” state
- Power stroke activated by Ca2+
- Enters rigor state
- Myosin releases actin
What happens when myosin is in the “cocked” phase?
-Bound to ADP and Phosphate
-Weakly bound to actin
What happens in the power stroke phase?
-Myosin bound strongly to actin
-Phosphate released
-Myosin head swivels toward M line
What happens in the Rigor state?
-Myosin releases ADP
-Myosin strongly bound to actin (stuck until another ATP can come & release myosin)
What causes Myosin to release actin?
ATP binds to myosin
What moves Myosin back to the “cocked” position?
ATP hydrolysis
What terminates the contraction cycle?
Calcium pumped back into SR by Ca2+ ATPase
What are the types of skeletal muscle fibers?
- Type 1 (slow oxidative)
- Type 2a (fast oxidative-glycolytic)
- Type 2b/x (Fast glycolytic)
What are the characteristics of Type 1 skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:
Speed: Slowest
Myosin ATPase activity: slow
Diameter: small
Endurance: fatigue resistance
What are the characteristics of Type 1 skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:
Metabolism: Aerobic (uses O2)
Capillary Density: High
Mitochondria: Many
Myoglobin content: High
What are the characteristics of Type 2a skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:
Speed: Intermediate
Myosin ATPase activity: Fast
Diameter: Medium
Endurance: Fatigue Resistence
What are the characteristics of Type 2b/x skeletal muscle fibers?
Speed:
Myosin ATPase activity:
Diameter:
Endurance:
Speed: Fastest
Myosin ATPase activity: Fast
Diameter: Large
Endurance: Easily fatigued
What are the characteristics of Type 2a skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:
Metabolism: Intermediate
Capillary Density: Medium
Mitochondria: Moderate
Myoglobin content: Moderate
What are the characteristics of Type 2b/x skeletal muscle fibers?
Metabolism:
Capillary Density:
Mitochondria:
Myoglobin content:
Metabolism: Anaerobic (uses glycolysis & fermentation)
Capillary Density: Low
Mitochondria: Few
Myoglobin content: Low
What type of muscle fibers mostly make up postural muscles?
Type 1
What type of muscle fibers mostly make up short bursts?
Type 2
What are the factors influencing force production?
-Fiber length
-Summation
-Motor Units
How does summation increase force?
Increased stimulus frequency causes insufficient time to pump Ca2+ back into SR between twitches. The continuing contraction allows more force to be produced.
What is tetanus?
State of maximal contraction
What is unfused tetanus?
Relaxes slightly between stimuli
What is fused tetanus?
Sustained maximal tension
What is a motor unit?
Somatic motor neuron and all the muscle fibers it innervates.
What are the characteristics of motor units?
-all muscle fibers in motor units are same type & twitch together
-each muscle fiber only innervated by 1 motor unit
A muscle unit with few fibers produces what kind of movement?
Fine movements, slow twitch
A muscle unit with 1000s of fibers produces what kind of movement?
Big movements, fast twitch
How do muscles vary force?
-Motor unit recruitment
-Frequency coding
Which muscles are recruited first and why?
Small, slow-twitch muscle units are recruited first while large, fast twitch units are held in reserve because you can wait until you need a lot of force since they are easily fatigued.
How does frequency coding vary muscle force?
Increase in AP frequency leads to summation which increase the muscle force.
What is hypertrophy?
Resistance exercise can lead to muscle fibers thickening & getting bigger
What is atrophy?
Disuse of muscles can lead to the muscle fibers getting thinner & shrinking
