Muscle Physiology Quiz

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Questions and Answers

What initiates the contraction of muscle fibers?

The arrival of Na+ in the sarcoplasm

The release of ATP in the cytoplasm

The arrival of Ca++ in the sarcoplasm (correct)

The stimulation of the skeletal muscle by insulin

Which sequence is involved in the contraction of skeletal muscle?

Stimuli from the endocrine system

Activating smooth muscle via autonomic signals

Signaling from the somatic motor division of the nervous system (correct)

Direct activation by neurotransmitters in the bloodstream

What is the sliding filament theory primarily focused on?

The mechanism by which actin and myosin filaments slide past each other (correct)

The role of calcium in muscle relaxation

The process of energy production in muscle cells

The electrical potential changes in sarcomeres

What role do Z discs play in muscle contraction?

They are the points where actin filaments are anchored Signup and view all the answers

During muscle contraction, what happens to the sarcomere?

It shortens as Z discs are pulled closer together Signup and view all the answers

What is released by the motor neuron to stimulate muscle fibers?

Acetylcholine Signup and view all the answers

What cycle occurs during muscle contraction according to the sliding filament theory?

Thick myosin filaments bind and pull on thin actin filaments Signup and view all the answers

What component is critical for conduction of electrical impulses in muscle contraction?

T-tubules Signup and view all the answers

What initiates a skeletal muscle contraction?

Conscious effort from the brain Signup and view all the answers

What role does acetylcholine play in muscle contraction?

It diffuses across the synaptic cleft and binds to muscle fiber receptors Signup and view all the answers

How does the action potential travel to initiate muscle contraction?

It travels down the axon to the neuromuscular junction Signup and view all the answers

What is the primary function of acetylcholinesterase (AChE) in the synaptic cleft?

To degrade acetylcholine and prevent muscle overstimulation. Signup and view all the answers

What occurs immediately after depolarization of the membrane?

The membrane re-establishes its negative potential. Signup and view all the answers

What occurs at the neuromuscular junction during muscle contraction?

Neurotransmitters are released from motor neuron axon terminals Signup and view all the answers

What happens when acetylcholine binds to its receptors on muscle fibers?

It initiates the depolarization of the sarcolemma Signup and view all the answers

What is the arrangement of a T-tubule with the membranes of the sarcoplasmic reticulum (SR) on either side called?

Triad Signup and view all the answers

What happens to calcium after the action potential reaches the sarcoplasmic reticulum?

Calcium binds to troponin to initiate muscle contraction Signup and view all the answers

How does the action potential travel into the muscle cell?

Via the transverse tubules (T-tubules). Signup and view all the answers

How does the interaction of thick and thin filaments lead to muscle contraction?

It leads to shortening of the sarcomere Signup and view all the answers

What triggers the opening of calcium channels in the sarcoplasmic reticulum?

The propagation of an action potential along the sarcolemma. Signup and view all the answers

What is the role of Ca++ that diffuses out of the sarcoplasmic reticulum?

To facilitate muscle contraction. Signup and view all the answers

What is the source of the depolarization of the sarcolemma?

Entrance of sodium ions through sodium channels Signup and view all the answers

Which component of muscle fibers is primarily involved in the contraction process?

Myofibrils Signup and view all the answers

What happens if acetylcholine cannot rebind to its receptor after synaptic transmission?

Muscle relaxation is ensured. Signup and view all the answers

What is the primary function of the sarcoplasmic reticulum (SR) in muscle fibers?

To regulate intracellular levels of calcium Signup and view all the answers

What are the components of a muscle fiber triad?

One T-tubule and two terminal cisternae Signup and view all the answers

Which proteins interact with calcium ions to enable muscle contraction?

Troponin and tropomyosin Signup and view all the answers

What must occur for a skeletal muscle fiber to begin contracting?

The muscle fiber must be excited and generate an action potential Signup and view all the answers

During muscle contraction, how do actin filaments move?

They are pulled toward the center of the sarcomere Signup and view all the answers

What is the outcome of crossbridge cycling during muscle contraction?

Actin filaments slide over each other Signup and view all the answers

What role do myosin heads play in muscle contraction?

They bind to actin filaments and facilitate their movement Signup and view all the answers

What happens to the H zone during muscle contraction?

It reduces in size Signup and view all the answers

What initiates the power stroke during the cross-bridge cycle?

Release of ADP and Pi from the myosin head Signup and view all the answers

Which molecules remain bound to the myosin head before the power stroke occurs?

ADP and phosphate (Pi) Signup and view all the answers

What is the role of ATP in the cross-bridge cycling process?

It causes the myosin head to detach from actin Signup and view all the answers

What happens immediately after the power stroke in the cross-bridge cycle?

ADP and Pi are released from the myosin head Signup and view all the answers

How is the myosin head repositioned after the power stroke?

With the energy released from splitting ATP Signup and view all the answers

What binds to the actin filament when the tropomyosin-troponin complex is disassembled?

Myosin heads Signup and view all the answers

What triggers the cross-bridge binding sites on actin to become available for myosin attachment?

Binding of calcium ions to troponin Signup and view all the answers

What is formed when the myosin head binds to an actin filament?

A cross-bridge Signup and view all the answers

Study Notes

Muscle Contraction Initiation

Calcium ions (Ca++) entering the sarcoplasm trigger muscle fiber contraction through sarcomeres.
Skeletal muscle excitation is signaled by the somatic motor division of the nervous system.

Sliding Filament Theory

Muscle contraction involves the sliding of actin and myosin filaments past each other.
Myosin heads bind to actin filaments, pulling them to shorten the sarcomere during contraction.
Actin filaments are anchored to Z discs, which define the boundaries of each sarcomere.

Action Potential Propagation

Action potentials are conducted quickly; they depolarize the membrane before repolarizing.
Acetylcholine (ACh) from the motor neuron degrades in the synaptic cleft via acetylcholinesterase, preventing prolonged muscle excitation.
Action potentials travel along the sarcolemma and into T-tubules, stimulating the sarcoplasmic reticulum (SR) to release Ca++.

Neuromuscular Junction

The brain sends signals through the somatic nervous system to motor neurons that activate muscle fibers.
Each motor neuron can innervate multiple muscle fibers at a neuromuscular junction.
The transmission of signals at this junction initiates muscle contraction via ACh binding to receptors on muscle fibers.

Excitation-Contraction Coupling

Muscle contractions require excitation of the sarcolemma to trigger an action potential.
Released Ca++ interacts with troponin and tropomyosin, exposing myosin-binding sites on actin for contraction.

Crossbridge Cycling

Crossbridge cycling describes the molecular events of muscle contraction.
Myosin heads bind to actin filaments, initiating a power stroke that pulls actin filaments inward.
ADP and inorganic phosphate (Pi) are released after the power stroke, but the myosin head remains attached to actin until ATP binds.

Muscle Fiber Relaxation

Binding of ATP to myosin causes detachment from actin, allowing the cycle to continue.
The process of ATP hydrolysis helps reposition the myosin head for subsequent binding with actin for contraction.

Structural Components

T-tubules, which are invaginations of the sarcolemma, couple with the SR to facilitate Ca++ release.
A triad consists of two terminal cisternae and one T-tubule, surrounding myofibrils that contain actin and myosin.

Functional Importance

The interaction and sliding of actin and myosin continue as long as Ca++ is available and ATP is present, allowing for sustained muscle contraction and relaxation.

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Description

Test your understanding of muscle contraction and the mechanisms behind it, including the sliding filament theory and action potential propagation. This quiz covers key concepts related to the neuromuscular junction and the role of calcium ions in muscle fiber contraction.