27 Questions
What is the overall process that transforms the nerve impulse into muscle contraction?
Excitation-contraction coupling
What is the function of the sarcoplasmic reticulum in muscle contraction?
To store calcium ions
What triggers the opening of the calcium channels on the sarcoplasmic reticulum membrane?
Action potentials in T-tubules cause conformational change in voltage-sensing proteins, known as the DHPR’s
What is the function of the ryanodine receptors (RyRs) in muscle contraction?
To regulate calcium ion release
What is the role of the T tubules in muscle contraction?
To transmit action potentials to the interior of the cell
What is the function of SERCA 1a in muscle contraction?
To remove calcium ions from the myofibrillar fluid
What is the 'Walk Along Theory' of muscle contraction?
A theory that explains the mechanism of muscle contraction
What is the result of the action potential on the sarcolemma?
Fast depolarization of the membrane
What is the condition necessary for muscle contraction to continue?
High calcium ion concentration
What is the energy state of myosin heads when they bind with ATP?
Low energy configuration
What is the immediate result of ATPase activity in the myosin head?
ADP and phosphate ion are kept bound to the head
What is the role of calcium in muscle contraction?
It binds to troponin, exposing myosin-binding sites
What is the result of the power stroke in muscle contraction?
The myosin head moves from a high-energy to a low-energy state
What is the function of the troponin-tropomyosin complex in muscle contraction?
It inhibits myosin-binding sites on the actin filament
What is formed when myosin heads bind to actin filaments?
Cross-bridge
What is the result of the cleavage of ATP by the myosin head?
ADP and phosphate ion are kept bound to the head
What is the source of calcium that binds to troponin?
Sarcoplasmic reticulum
What triggers the power stroke in muscle contraction?
The release of phosphate
Which of the following is NOT true regarding the SERCA 1a (calcium pump)?
More than one above
Part 1 of steps: The AP propogates down the (1). The (2)__ senses membrane depolarization, opening (3)__ on the Sarcoplasmic Reticulum. This (4) opens briefly and releases a pulse of (5)_ ions.
T-tubules, DHPR, RYR channels, RYR's, Calcium
Part 2: Calcium diffuses into the myofilaments and binds to (1)__, Calcium causes (2) to move away from myosin binding sites.
Troponin, tropomyosin
Part 3: Before muscle contraction begins, myosin heads bind with _____. This is the ______ energy configuration. The ATPase activity cleaves ATP to _____ and ____ causing the head to become _______ and in a ________ position.
ATP, low, ADP, inorganic Phosphate, energized, cocked
Part 4: Myosin heads bind to the binding sites creating a __________. The release of the ____ triggers the __________. This goes from a ________ energy state to a _______ energy state. The myosin head bends towards the center of the _______, causing the actin to slide toward the ___ line.
Cross bridge, Inorganic phosphate, power stroke, high, low, sarcomere, M
Part 5: As the power stroke occurs, the ______ is released from the myosin head. The myosin head remains tightly bound to actin, known as the _____ state. The binding of a new ____ causes detachment of the myosin head from the ______ filament.
ADP, rigor, ATP, actin
Match the following terms to their description
Z-disc = Ends of sarcomere Middle of the sarcomere = M-line I band = Only thin filament; light band A band = Thick and thin filament; dark band
What are the three energy sources for muscle contraction?
Phosphocreatine (creatine phosphate), Glycolysis and Oxidative metabolism
A muscle fiber either contracts completely or not at all, describes:
All or None Response
Study Notes
Muscle Contraction
- Excitation-contraction coupling is the process that transforms a nerve impulse into muscle contraction
- Action potentials on the sarcolemma spread from the motor end plate along the length of the fiber and into the cell along the transverse tubules (T tubules)
Excitation-Contraction Coupling
- T tubules are associated with the sarcoplasmic reticulum (SR)
- SR is composed of large chambers called terminal cisternae and long longitudinal tubules that surround the myofibrils
- The action potential causes a conformational change in voltage-sensing proteins (dihydropyridine receptors – DHPRs) on the T tubule
- DHPRs are mechanically coupled to the ryanodine receptors (RyRs) calcium channels on the SR membrane
- Calcium channels open, allowing calcium to rapidly diffuse out of the SR and initiate muscle contraction
Calcium Regulation
- A calcium pump (SERCA 1a) removes calcium ions from the myofibrillar fluid after contraction occurs
- SERCA1a is a continually active calcium pump located in the walls of the SR that pumps Ca back into the SR
- Muscle contraction continues as long as Ca ion concentration remains high
Walk-Along Theory of Muscle Contraction
- Before muscle contraction begins, myosin heads bind with ATP (low energy configuration)
- ATPase activity of the myosin head cleaves the ATP into ADP and phosphate ion
- Cleavage products are kept bound to the head, which becomes energized in a “cocked position”
- Forces are generated by the interaction of the cross-bridges from myosin and actin filaments
- Calcium release from the SR exposes myosin-binding sites on the actin filament, allowing myosin heads to bind and form a cross-bridge
- The release of phosphate triggers the POWER STROKE – a conformational change in the myosin head, which moves from a high-energy to a low-energy state
This lecture covers the muscle contraction process, including excitation-contraction coupling, the role of T tubules, sarcoplasmic reticulum, and calcium, and the 'Walk Along Theory' of muscle contraction.
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