9/24 Excitation-Contraction Coupling Flashcards
what is the Excitation-Contraction Coupling?
the process by which an electrical stimulus triggers the release of Ca by the sarcoplasmic reticulum, initiating the mechanism of muscle contraction by sarcomere shortening
Axon
Acetylcholine and genetic expression
Acetylcholinesterase breaks down Ach into choline and acetyl
Neuromuscular Junction
-subneural clefts
Calcium and Exocytosis
- Voltage-gated Ca channels open
- 300,000 vesicles stored per end plate
- 125 vesicles released per AP
Synaptic Cleft
ACh is what kind of gated channel?
ligand gated channel
Action Potential Transmission
Calcium Release from SR
- Dihydropyridine (DHP) Receptors = along T-tubule
- Ryanodine (RyR) Receptors = on sarcoplasmic reticulum
Calcium Sequestration in SR
- ATP-dependent Ca pump moves Ca into SR
- Calsequestrin binds Ca allowing 40x more Ca to be stored
Sarcomere
Cross-Bridge
2 light chains and 2 heavy chains
Tropomyosin and Troponin Complex
- Troponin I • Strong affinity for actin
- Troponin C • Strong affinity for Ca
- Troponin T • Strong affinity for tropomyosin
Calcium and Contraction
Walk-Along/Ratchet Theory
• ATPase enzyme on myosin head cleaves ATP to ADP + P
Myosin Head Cocking
Power Stroke
Length-Tension Curve
1.8-2.2um sarcomere length produces the strongest tension
Force Generation
- Motor unit = all muscles innervated by a single nerve fiber
- Small, more precise muscles have more nerve fibers than larger muscles
- ~ 80-100 muscle fibers per motor unit
Tetany = Tetany is a disorder of increased neuronal excitability usually associated with hypocalcemia.
• Summation = adding together of individual twitch contractions to increase the intensity of overall muscle contraction
• Increase number of motor units contracting simultaneously
• Increase frequency of contraction
Rigor Mortis
- State of constant contracture
- Lasts 15-25 hours
ATP Regeneration
phosphocreatine
8-10 seconds
Glycolysis
1.3-1.6 minutes
Oxidative Metabolism, which is Nutrient Dependent
Fiber Types
Time to Fatigue
Training
- Strength determined by muscle size
- Endurance depends on glycogen stored prior to exercise (high-carb diet)
- Hypertrophy increases diameter, not number of fibers
- Increased myofibrils
- 120% increased mito enzymes
- 60-80% more components of phosphagen systems
- 50% increased glycogen
