Ryanodine Receptors in Muscle Physiology

Questions and Answers

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?

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?

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?

Mechanical force is generated to shorten the muscle. Signup and view all the answers

Which of the following correctly describes the process of cross-bridge cycling?

Calcium must bind to Troponin C for actin sites to be exposed. Signup and view all the answers

What happens to the A band during muscle contraction?

It remains constant. Signup and view all the answers

Which statement correctly describes the changes in the I band during muscle contraction?

It decreases in width. Signup and view all the answers

What is the role of ATP hydrolysis in muscle contraction?

It provides energy for cross bridges. Signup and view all the answers

During the Fenn effect, what is proportional to the amount of work performed by the muscle?

Amount of ATP cleaved. Signup and view all the answers

Which of the following statements is true regarding muscle relaxation?

It depends on the hydrolysis of ATP for calcium pumps. Signup and view all the answers

What happens to the H zone during muscle contraction?

It disappears. Signup and view all the answers

What occurs to the Z line during muscle contraction?

It moves closer together. Signup and view all the answers

What initiates the new cycle of muscle contraction after myosin disconnects?

ATP binding to myosin. Signup and view all the answers

What is the primary role of acetylcholine in nerve signal transmission?

To open the gate of a channel for positive ions and uncharged molecules Signup and view all the answers

What is the main characteristic of the channel opened by acetylcholine?

It provides a negatively charged pore around 0.65 nanometer in diameter Signup and view all the answers

What role does myelin play in the conduction of action potentials?

It insulates the axon to prevent current leakage. Signup and view all the answers

How is the diffusion potential generated across a membrane?

Due to a concentration difference of an ion Signup and view all the answers

What is the significance of the Nodes of Ranvier in neuronal communication?

They contain ion channels that facilitate rapid conduction. Signup and view all the answers

What does the equilibrium potential represent?

The potential that exactly balances the diffusion potential Signup and view all the answers

What occurs during the depolarization phase of an action potential?

Sodium channels open, allowing sodium ions to enter. Signup and view all the answers

What initiates the movement of ions across the membrane aside from concentration differences?

Application of electrical potential across the membrane Signup and view all the answers

Which of the following best defines resting membrane potential?

The potential difference maintained by diffusion potentials from ions Signup and view all the answers

How is the threshold potential of a neuron defined?

The voltage level at which an action potential is initiated. Signup and view all the answers

What does the 'all-or-nothing' principle of action potentials imply?

An action potential will not occur unless the threshold is reached. Signup and view all the answers

Which ions are predominantly affected by the electrical potential applied across the membrane?

Both positively and negatively charged ions Signup and view all the answers

What is a common result when a channel opened by acetylcholine allows ions to pass?

Generation of a new diffusion potential Signup and view all the answers

What happens during hyperpolarization of a neuron?

Potassium ions exit the neuron, making the inside more negative. Signup and view all the answers

Which of the following best describes the role of sodium ions during action potential generation?

They contribute to the depolarization phase when their channels open. Signup and view all the answers

What characterizes excitatory synapses in neuronal communication?

They decrease the voltage difference across the neuron's membrane. Signup and view all the answers

What role does calcium play in cross bridge cycling?

It promotes the attachment of myosin to actin. Signup and view all the answers

According to the sliding filament theory, what occurs in the contracted state?

The actin filaments overlap maximally with myosin filaments. Signup and view all the answers

What prevents the binding of myosin to actin at rest?

The coverage of myosin binding sites by tropomyosin. Signup and view all the answers

Which of the following theories relates to muscular contraction as proposed by Huxley and Huxley?

Sliding filament theory Signup and view all the answers

In the context of cross bridge cycling, what happens during the power stroke?

The Z discs are pulled toward each other. Signup and view all the answers

What is the function of troponin T in muscle contraction?

It connects tropomyosin to actin. Signup and view all the answers

What outcome occurs when the myosin head reactivates during the cross bridge cycle?

It hydrolyzes ATP to reset the cycle. Signup and view all the answers

What is the primary mechanism by which calcium causes contraction in muscle fibers?

By displacing tropomyosin away from actin binding sites. Signup and view all the answers

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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Description

Explore the role of Ryanodine Receptors in skeletal and smooth muscle function. Understand how calcium diffusion leads to significant intracellular calcium concentration increases. This quiz will test your knowledge on key muscle physiology concepts and processes.