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Questions and Answers
What role does calcium play in muscle contraction?
What role does calcium play in muscle contraction?
- It prevents the movement of tropomyosin on the actin filament.
- It acts as a neurotransmitter to trigger muscle activation.
- It binds to Troponin C, causing a conformational change. (correct)
- It directly interacts with actin to initiate contraction.
What happens after the formation of the Actin-Myosin complex?
What happens after the formation of the Actin-Myosin complex?
- ADP and Pi are released, causing a power stroke. (correct)
- Tropomyosin rebinds to the active site on actin.
- Myosin detachment from actin occurs immediately.
- The myosin head remains unchanged in orientation.
What is the effect of tropomyosin movement during muscle contraction?
What is the effect of tropomyosin movement during muscle contraction?
- It promotes the formation of the ADP-Pi complex.
- It exposes the active binding sites on actin. (correct)
- It stabilizes the actin filament against muscle tension.
- It blocks the active sites on myosin.
During the power stroke, what is the result of the myosin head flexing?
During the power stroke, what is the result of the myosin head flexing?
Which of the following correctly describes the process of cross-bridge cycling?
Which of the following correctly describes the process of cross-bridge cycling?
What happens to the A band during muscle contraction?
What happens to the A band during muscle contraction?
Which statement correctly describes the changes in the I band during muscle contraction?
Which statement correctly describes the changes in the I band during muscle contraction?
What is the role of ATP hydrolysis in muscle contraction?
What is the role of ATP hydrolysis in muscle contraction?
During the Fenn effect, what is proportional to the amount of work performed by the muscle?
During the Fenn effect, what is proportional to the amount of work performed by the muscle?
Which of the following statements is true regarding muscle relaxation?
Which of the following statements is true regarding muscle relaxation?
What happens to the H zone during muscle contraction?
What happens to the H zone during muscle contraction?
What occurs to the Z line during muscle contraction?
What occurs to the Z line during muscle contraction?
What initiates the new cycle of muscle contraction after myosin disconnects?
What initiates the new cycle of muscle contraction after myosin disconnects?
What is the primary role of acetylcholine in nerve signal transmission?
What is the primary role of acetylcholine in nerve signal transmission?
What is the main characteristic of the channel opened by acetylcholine?
What is the main characteristic of the channel opened by acetylcholine?
What role does myelin play in the conduction of action potentials?
What role does myelin play in the conduction of action potentials?
How is the diffusion potential generated across a membrane?
How is the diffusion potential generated across a membrane?
What is the significance of the Nodes of Ranvier in neuronal communication?
What is the significance of the Nodes of Ranvier in neuronal communication?
What does the equilibrium potential represent?
What does the equilibrium potential represent?
What occurs during the depolarization phase of an action potential?
What occurs during the depolarization phase of an action potential?
What initiates the movement of ions across the membrane aside from concentration differences?
What initiates the movement of ions across the membrane aside from concentration differences?
Which of the following best defines resting membrane potential?
Which of the following best defines resting membrane potential?
How is the threshold potential of a neuron defined?
How is the threshold potential of a neuron defined?
What does the 'all-or-nothing' principle of action potentials imply?
What does the 'all-or-nothing' principle of action potentials imply?
Which ions are predominantly affected by the electrical potential applied across the membrane?
Which ions are predominantly affected by the electrical potential applied across the membrane?
What is a common result when a channel opened by acetylcholine allows ions to pass?
What is a common result when a channel opened by acetylcholine allows ions to pass?
What happens during hyperpolarization of a neuron?
What happens during hyperpolarization of a neuron?
Which of the following best describes the role of sodium ions during action potential generation?
Which of the following best describes the role of sodium ions during action potential generation?
What characterizes excitatory synapses in neuronal communication?
What characterizes excitatory synapses in neuronal communication?
What role does calcium play in cross bridge cycling?
What role does calcium play in cross bridge cycling?
According to the sliding filament theory, what occurs in the contracted state?
According to the sliding filament theory, what occurs in the contracted state?
What prevents the binding of myosin to actin at rest?
What prevents the binding of myosin to actin at rest?
Which of the following theories relates to muscular contraction as proposed by Huxley and Huxley?
Which of the following theories relates to muscular contraction as proposed by Huxley and Huxley?
In the context of cross bridge cycling, what happens during the power stroke?
In the context of cross bridge cycling, what happens during the power stroke?
What is the function of troponin T in muscle contraction?
What is the function of troponin T in muscle contraction?
What outcome occurs when the myosin head reactivates during the cross bridge cycle?
What outcome occurs when the myosin head reactivates during the cross bridge cycle?
What is the primary mechanism by which calcium causes contraction in muscle fibers?
What is the primary mechanism by which calcium causes contraction in muscle fibers?
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Study Notes
Ryanodine Receptors and Calcium Dynamics
- Calcium increases in the intracellular fluid (ICF) by 2000 times due to diffusion into the cytoplasm.
Muscle Contraction Mechanics
- Power stroke occurs during muscle contraction, followed by detachment and reactivation of the myosin head.
- Cross bridge cycling consists of various steps, starting from the initiation at rest, where Troponin I is loosely bound to actin.
- Troponin T is attached to tropomyosin, forming the troponin-tropomyosin complex that blocks myosin binding sites on actin.
Sliding Filament Model
- Proposed by A. Huxley and H.E. Huxley, the sliding filament theory explains:
- In a relaxed state, actin filaments barely overlap.
- In a contracted state, actin filaments are pulled inward, maximizing overlap with myosin and bringing Z discs closer together.
Calcium’s Role in Contraction
- Calcium released into the cytosol binds to Troponin C, causing a conformational change that shifts tropomyosin.
- Active binding sites on actin become available, leading to the formation of an Actin-Myosin-ADP-Pi complex.
- Release of Pi and ADP from the complex triggers the power stroke, resulting in mechanical force generation.
Sarcomere Changes During Contraction
- During muscle contraction, the width of the A band remains constant.
- The H zone disappears, I band width decreases, and the Z lines move closer together, resulting in sarcomere shortening.
ATP’s Role in Contraction and Relaxation
- ATP hydrolysis provides energy for cross bridge cycling and muscle contraction.
- ATP binding causes detachment of myosin from actin, restarting the cycle.
- The Ca ATPase uses ATP hydrolysis to transport calcium back, facilitating muscle relaxation.
- The Fenn effect describes the increased ATP cleavage proportional to the work performed by the muscle.
Steps of Muscle Relaxation
- Calcium pumps move calcium from sarcoplasm, restoring levels in the sarcoplasmic reticulum.
- Acetylcholine interacts with channels, facilitating the movement of ions.
Membrane Potentials and Action Potentials
- The resting membrane potential is influenced by diffusion potentials due to ion concentration gradients.
- Equilibrium potential balances diffusion caused by concentration differences, also referred to as Nernst potential.
- Myelin insulation prevents current leakage in axons; voltage-gated ion channels activate at Nodes of Ranvier for rapid action potential transmission.
- Excitatory synapses cause depolarization of the neuron through the influx of positive ions, lowering voltage difference, while action potentials are initiated when the threshold potential is reached.
- Action potentials follow an all-or-nothing principle, with complete depolarization to around +40 mV before returning to resting potential after hyperpolarization.
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