Muscle Physiology Quiz
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Questions and Answers

Which of the following accurately describes the role of ATP in muscle contraction?

  • ATP is solely responsible for maintaining the Na-K gradient in the muscle cell.
  • ATP is only used for the re-uptake of calcium into the sarcoplasmic reticulum.
  • ATP is only used to power the power stroke of the myosin head.
  • ATP is required for both the binding and detachment of the myosin head to actin. (correct)

What is the primary function of tropomyosin in muscle contraction?

  • Tropomyosin binds to calcium ions, triggering muscle contraction.
  • Tropomyosin directly pulls on the actin filament, causing it to slide past the myosin filaments.
  • Tropomyosin covers the active sites on actin, preventing myosin binding in the resting muscle. (correct)
  • Tropomyosin acts as an ATPase, hydrolyzing ATP to provide energy for contraction.

Which of the following events occurs directly AFTER the myosin head releases ADP and phosphate during the power stroke?

  • A new ATP molecule binds to the myosin head, causing detachment from actin. (correct)
  • Calcium ions bind to troponin, triggering the movement of tropomyosin.
  • The sarcoplasmic reticulum releases calcium ions into the cytosol.
  • The myosin head binds to the active site on actin, forming a cross-bridge.

What is the role of acetylcholinesterase (AChE) in muscle relaxation?

<p>AChE breaks down acetylcholine, removing it from the synaptic cleft. (C)</p> Signup and view all the answers

What is the direct consequence of calcium ions binding to troponin?

<p>Tropomyosin shifts, exposing the active sites on the actin filament. (D)</p> Signup and view all the answers

What is the primary source of energy for muscle contraction once the stored ATP is depleted?

<p>Creatine phosphate stores. (D)</p> Signup and view all the answers

What is the physiological significance of the Na-K gradient in muscle cells?

<p>It allows for the propagation of action potentials along the muscle fiber. (D)</p> Signup and view all the answers

Which of the following is NOT a direct consequence of acetylcholine (ACh) binding to its receptor on the muscle fiber?

<p>Inhibition of the enzymatic activity of acetylcholinesterase (AChE). (A)</p> Signup and view all the answers

Which of the following is NOT a primary function of muscles?

<p>Regulation of blood pH (C)</p> Signup and view all the answers

Which characteristic of muscle tissue allows it to respond to stimuli by producing action potentials?

<p>Excitability (B)</p> Signup and view all the answers

Which of the following muscle types is characterized by having a central nucleus and being under involuntary control?

<p>Smooth muscle (C)</p> Signup and view all the answers

What is the correct order of structural organization in skeletal muscle, from smallest to largest?

<p>Myofilament, myofibril, muscle fiber, muscle fascicle, skeletal muscle (C)</p> Signup and view all the answers

Which connective tissue layer directly surrounds individual muscle fibers?

<p>Endomysium (D)</p> Signup and view all the answers

What is the name of the structure that surrounds the muscle fiber?

<p>Sarcolemma (A)</p> Signup and view all the answers

What is the functional unit of muscle contraction?

<p>Sarcomere (C)</p> Signup and view all the answers

What are muscle tendons primarily composed of?

<p>Collagen fibers (C)</p> Signup and view all the answers

What type of filaments are actin and tropomyosin classified as?

<p>Thin myofilaments (B)</p> Signup and view all the answers

Which component connects myosin to the Z line in the sarcomere?

<p>Titin (D)</p> Signup and view all the answers

What is the function of the sarcoplasmic reticulum in muscle fibers?

<p>To store calcium ions (D)</p> Signup and view all the answers

What structure is formed by one T tubule and two terminal cisternae?

<p>Triad (B)</p> Signup and view all the answers

What is the primary role of dystrophin in muscle fibers?

<p>To provide intracellular stability (A)</p> Signup and view all the answers

Which protein is responsible for covering the active sites of actin?

<p>Tropomyosin (D)</p> Signup and view all the answers

What is the primary function of the neuromuscular junction?

<p>To transmit action potentials from motor neurons to muscle fibers (B)</p> Signup and view all the answers

In which zone of the sarcomere do only thick filaments reside?

<p>H zone (A)</p> Signup and view all the answers

What is the initial energy source used by muscle fibers for contraction?

<p>ATP stored in the muscle fiber (B)</p> Signup and view all the answers

During aerobic glycolysis, what substance is generated from glucose?

<p>Pyruvate (D)</p> Signup and view all the answers

What is the role of motor neurons in muscle contraction?

<p>To stimulate muscle fibers for contraction (B)</p> Signup and view all the answers

Which term describes the stimulus that increases contraction power by activating more motor units?

<p>Recruition (D)</p> Signup and view all the answers

What primarily influences the strength of a muscle contraction?

<p>Intensity of the nervous system stimulus and number of activated motor units (A)</p> Signup and view all the answers

Which muscle fiber characteristics are associated with small motor units?

<p>Precise movements with fewer muscle cells (A)</p> Signup and view all the answers

What defines muscle fatigue in skeletal muscle fibers?

<p>Decreased tension despite ongoing stimulation (B)</p> Signup and view all the answers

How does the number of cells per motor unit relate to motor unit size?

<p>Fewer cells indicate a smaller motor unit (A)</p> Signup and view all the answers

Flashcards

Excitability

The ability of a muscle cell to respond to a stimulus, such as a nerve impulse, by generating an electrical signal known as an action potential.

Contractility

The ability of a muscle cell to shorten and thicken, generating force that can move bones or other structures.

Extensibility

The ability of a muscle cell to be stretched or extended without being damaged.

Elasticity

The ability of a muscle cell to return to its original shape after being stretched.

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Tendon

A bundle of connective tissue that connects a skeletal muscle to a bone.

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Sarcomere

The functional unit of a muscle fiber, consisting of a repeating pattern of sarcomeres.

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Sarcoplasm

The cytoplasm of a muscle cell, containing various organelles and structures.

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Sarcoplasmic Reticulum (SR)

The endoplasmic reticulum of a muscle cell, specialized for storing and releasing calcium ions, which are essential for muscle contraction.

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Sliding Filament Theory

The theory explaining how muscle fibers shorten during contraction. It involves the sliding of myosin filaments along actin filaments, shortening the sarcomere.

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Tropomyosin

A protein that covers the active sites on actin filaments in a relaxed muscle, preventing myosin from binding.

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Troponin

A protein that binds to calcium ions and initiates the movement of tropomyosin, exposing the active sites on actin for myosin binding.

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SERCA (Sarcoplasmic Reticulum Calcium-ATPase)

A protein complex in the sarcoplasmic reticulum (SR) that actively pumps calcium ions back into the SR after muscle contraction, leading to relaxation.

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Acetylcholine Breakdown

The breakdown of acetylcholine by the enzyme acetylcholinesterase (AChE) in the synaptic cleft. This terminates the signal at the neuromuscular junction, leading to muscle relaxation.

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Calcium Reuptake

The process in which calcium levels in the sarcoplasm decrease as calcium ions are pumped back into the sarcoplasmic reticulum.

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Relaxed Muscle State

The state of a muscle when it is not actively contracting, with tropomyosin covering the active sites on actin and myosin not bound.

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Skeletal Muscle Energy Metabolism

The energy source used for muscle contraction, including ATP stored in the muscle, creatine phosphate stores, and aerobic and anaerobic metabolism.

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What is a sarcomere?

The basic unit of a muscle fiber, consisting of a repeating pattern of sarcomeres. It contains both thick (myosin) and thin (actin) filaments, arranged in a specific order. The sarcomere is responsible for muscle contraction.

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What is the H zone?

The region within the sarcomere that contains only thick (myosin) filaments. It is located in the middle of the sarcomere and is characterized by the absence of thin (actin) filaments.

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What is the A band?

The region within the sarcomere that contains both thick (myosin) and thin (actin) filaments. It is the darkest region of the sarcomere, as it contains both types of filaments.

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What is the M line?

A protein that connects thick (myosin) filaments together in the middle of the H zone. It is not involved in muscle contraction but plays a structural role.

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What is the Z line?

A thin, dark line that marks the boundary between two sarcomeres. It is made up of α-actinin, a protein that connects actin filaments together.

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What does α-actinin do?

A protein found in the sarcomere that plays a crucial role in connecting actin filaments to the Z line. It helps to maintain the structural integrity of the sarcomere.

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What is titin?

A large protein that acts as a spring-like molecule, connecting myosin filaments to the Z line. It helps to prevent overstretching of the sarcomere and maintains its structural integrity.

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What is nebulin?

A protein that plays a role in assembling actin filaments. It helps to regulate the length of the thin filament.

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ATP (Adenosine Triphosphate)

The immediate energy source for muscle contraction, stored in small amounts within muscle fibers.

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Creatine Phosphate

A high-energy phosphate compound that quickly replenishes ATP during the initial phase of muscle contraction.

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Anaerobic Glycolysis

The breakdown of glucose or glycogen to produce energy, primarily used during intense exercise lasting 30 seconds to 2 minutes.

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Aerobic Glycolysis

A metabolic process that uses oxygen to produce ATP from glucose and other fuels, providing energy for sustained exercise.

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Motor Unit

A single motor neuron and all the muscle fibers it innervates.

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Recruitment

The process of recruiting additional motor units to increase the strength of muscle contraction.

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Muscle Fatigue

A decrease in muscle tension as a result of previous contractile activity, leading to reduced force production and fatigue.

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Motor Unit Size

The number of muscle fibers innervated by a single motor neuron.

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Study Notes

Skeletal Muscle Contraction

  • Skeletal muscles are responsible for movement, posture maintenance, and heat production.
  • They protect bones and internal organs.
  • Muscle cells are excitable, meaning they respond to stimuli by producing action potentials.
  • Muscles shorten and thicken to generate force.
  • Muscles are extensible, meaning they can extend without damage.
  • Muscles are elastic, meaning they return to their original shape.

Muscle Types

  • Skeletal muscle:
    • Peripheral nuclei
    • Voluntary
    • Striated, tubular, multi-nucleated fibers
    • Attached to the skeleton
  • Smooth muscle:
    • Central nuclei
    • Involuntary
    • Non-striated, spindle-shaped, single nuclei
    • Lines internal organs
  • Cardiac muscle:
    • Central nuclei
    • Involuntary
    • Striated, branched, single nuclei
    • Found only in the heart

Skeletal Muscle Structure

  • Organized into:
    • Myofilaments (actin and myosin)
    • Myofibrils
    • Muscle fibers
    • Fascicles
    • Muscle
  • Surrounded by connective tissue layers: endomysium, perimysium, epimysium
  • Muscle fibers are electrically isolated by endomysium.
  • Fascicles are surrounded by perimysium.
  • Epimysium surrounds the skeletal muscle.

Sarcomere Structure

  • I band: thin filament (actin) region.
  • H zone: thick filament (myosin) region.
  • A band: thick and thin filaments.
  • M line: middle of H band, connects myosins.
  • Z line: region between two I bands.

Muscle Proteins

  • Dystrophin, titin, actinin, desmin, nebulin are sarcomere intracellular proteins.
  • Titin connects myosin to the Z line.
  • Nebulin produces F-actin from G-actins.
  • α-actinin connects actin to the Z-line.
  • Desmin connects the Z line to the cell membrane.
  • Dystrophin-glycoprotein complex maintains muscle fiber and myofibril integrity.
  • Duchenne and Becker muscular dystrophies are associated with dystrophin mutations.

Sarcotubular System

  • Sarcolemma: surrounds the muscle fiber.
  • Sarcoplasm: muscle cell cytoplasm.
  • Sarcoplasmic reticulum (SR): stores calcium.
  • T-tubules: extensions of sarcolemma into the cell, transmit action potentials.
  • Terminal cisternae: enlargements of SR, release calcium to initiate contraction.
  • Triad: T-tubule and two terminal cisternae.

Neuromuscular Junction

  • Junction of axon terminal and motor end plate.
  • Action potential travels down axon, releasing acetylcholine.
  • Acetylcholine binds to receptors, initiating muscle fiber action potential.

Muscle Contraction

  • Requires ATP energy.
  • Sliding filament theory: actin and myosin filaments slide past each other.
  • Ca2+ release initiates contraction.
  • Myosin heads bind to actin, forming cross-bridges.
  • Power stroke: myosin pulls actin filaments.
  • ATP binds to myosin to detach it from actin.
  • ATP hydrolysis cocks myosin head for next cycle.
  • Cycle repeats until Ca2+ levels fall and muscle relaxes.

End of Skeletal Muscle Contraction

  • Acetylcholine is degraded by acetylcholinesterase.
  • Sarcoplasmic reticulum (SR) reuptakes Ca2+.
  • Myosin heads detach from actin, relaxing muscle fibers.

Muscle Metabolism

  • Stored ATP is used first.
  • Creatine phosphate stores are used next.
  • Anaerobic (lactic acid) system for short-duration, high-intensity exercise.
  • Oxidative phosphorylation (aerobic) for longer durations.

Motor Neuron

  • Motor neuron extends from CNS to muscle, stimulating contraction.
  • Motor unit is a motor neuron and its innervated muscle fibers.
  • Motor unit size dictates precision or strength of contraction.
  • Recruitment: increasing the number of active motor units increases contraction force.

Muscle Fatigue

  • Repeated stimulation of a muscle fiber leads to decreased tension and eventually muscle fatigue.
  • Characteristics of muscle fatigue include slower relaxation, reduced shortening velocity.
  • Factors contributing to fatigue can include reduced ATP production and ionic imbalances within muscle cells.

Skeletal Muscle Fiber Types

  • Slow-twitch (Type I): adapted for endurance activities.
  • Fast-twitch (Type IIa): intermediate properties
  • Fast-twitch (Type IIb or IIx): suited for rapid, powerful movements..
  • Different fiber types (Slow or Fast twitch) are categorized further into subdivisions, using the oxygen-using capacity and glycolysis efficiency criteria.

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Skeletal Muscle Physiology PDF 2024-2025

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Test your knowledge on the physiology of muscle contraction, including the roles of ATP, tropomyosin, and calcium ions. This quiz covers essential concepts related to muscle function, energy sources, and cellular responses. Perfect for students specializing in biology or sports science!

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