Skeletal Muscle Contraction and Types
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Questions and Answers

What is the first energy source used during explosive power generation in muscles?

  • ATP stored in muscle fibers (correct)
  • Glycogen
  • Creatine phosphate
  • Glucose

Which process is responsible for converting pyruvate into energy in the mitochondria?

  • KREBS cycle (correct)
  • Creatine phosphate breakdown
  • Direct phosphorylation
  • Anaerobic glycolysis

What is the primary function of skeletal muscles?

  • Protection of organs
  • Heat production
  • Movement (correct)
  • Maintain blood pressure

Which connective tissue layer surrounds an entire skeletal muscle?

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

What term describes the recruitment of additional motor units to increase muscle contraction power?

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

What is muscle fatigue defined as?

<p>A decrease in muscle tension during continuous stimulation (D)</p> Signup and view all the answers

What characteristic of muscle cells allows them to return to their original shape after being stretched?

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

Which factor does NOT contribute to the strength of muscle contraction?

<p>Length of muscle fibers (B)</p> Signup and view all the answers

Which structure is known as the functional unit of muscle contraction?

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

What best describes a small motor unit?

<p>Allows for precise movements with fewer muscle fibers (A)</p> Signup and view all the answers

Which type of muscle tissue is under voluntary control?

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

Which of the following structures surrounds a muscle fiber?

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

Which muscle fiber property affects the rate of shortening during contraction?

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

During which activity would you primarily utilize aerobic glycolysis?

<p>Walking or swimming (B)</p> Signup and view all the answers

What are the smallest contractile elements of a muscle unit called?

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

What allows muscle cells to respond to stimuli by producing action potentials?

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

What are the components of thick myofilaments?

<p>Myosin tail and light chains (C), Myosin tails with heavy chains (D)</p> Signup and view all the answers

Which protein connects the Z line to the muscle cell membrane?

<p>Dystrophin (B), Desmin (C)</p> Signup and view all the answers

What is the function of tropomyosin in muscle contraction?

<p>Covers the active points of actin (B)</p> Signup and view all the answers

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

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

Which of the following provides structural support within the sarcomere?

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

What is the role of dystrophin in muscle cells?

<p>Connects actin to the extracellular matrix (C)</p> Signup and view all the answers

What happens when an action potential reaches the T tubules?

<p>Calcium channels in the SR open (A)</p> Signup and view all the answers

What function do the motor end plates serve at the neuromuscular junction?

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

What initiates the power stroke during muscle contraction?

<p>Separation of phosphate from myosin head (B)</p> Signup and view all the answers

Which step does NOT occur during the relaxation of skeletal muscle?

<p>Myosin heads form new cross bridges with actin (B)</p> Signup and view all the answers

What role does ATP play in muscle contraction?

<p>It is used to pump calcium back into the SR (D)</p> Signup and view all the answers

In the Sliding Filaments Theory, which molecule covers actin's active sites when the muscle is at rest?

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

What happens to calcium ions in the muscle cell when the action potential ends?

<p>Calcium ions are reabsorbed by the sarcoplasmic reticulum (B)</p> Signup and view all the answers

Which is NOT a function of ATP during the muscle contraction cycle?

<p>To facilitate the conformational change in tropomyosin (B)</p> Signup and view all the answers

What is formed when ATP is hydrolyzed in the myosin head?

<p>ADP + Phosphate (A)</p> Signup and view all the answers

What maintains the resting potential and readiness for a new action potential in muscle cells?

<p>Re-establishment of the Na-K gradient (D)</p> Signup and view all the answers

Flashcards

Excitability

The ability of a muscle to respond to stimulation by producing electrical impulses.

Contractility

The capacity of a muscle to shorten and thicken, generating force.

Extensibility

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

Elasticity

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

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Sarcomere

The functional unit of a muscle, responsible for contraction.

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Sarcolemma

The plasma membrane of a muscle fiber, responsible for transmitting electrical signals

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Sarcoplasm

The cytoplasm of a muscle cell, containing organelles like mitochondria, providing energy for contraction.

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Sarcoplasmic Reticulum (SR)

The endoplasmic reticulum of a muscle cell, responsible for storing and releasing calcium ions, crucial for muscle contraction.

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Muscle contraction

The process of muscle contraction, starting with the movement of calcium ions (Ca2+) into the sarcoplasm.

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Troponin

A protein that binds to actin and regulates muscle contraction. It is found on tropomyosin.

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Tropomyosin

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

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Myosin

The protein responsible for muscle contraction. It has a head that binds to actin and a tail.

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α-Actinin

A protein that connects actin filaments to the Z line, helping to maintain the integrity of the sarcomere.

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Titin

A large protein that spans the entire length of the sarcomere, connecting myosin to the Z line and preventing excessive stretching.

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Sliding Filament Theory

The process where thin (actin) and thick (myosin) filaments slide past each other, causing muscle shortening and contraction.

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Acto-myosin Cross Bridge

The connection formed between the myosin head and the active site on actin during muscle contraction.

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ATP (Adenosine Triphosphate)

The energy required to power the sliding of the filaments and muscle contraction, used in various stages of the process.

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Acetylcholinesterase (AChE)

An enzyme that breaks down acetylcholine (Ach) in the synaptic cleft, terminating the muscle contraction.

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SERCA (Sarcoplasmic Reticulum Calcium-ATPase)

A calcium pump located in the sarcoplasmic reticulum (SR) that actively transports calcium ions back into the SR, causing muscle relaxation.

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Skeletal muscle energy metabolism

The storage and use of ATP by muscle cells for contraction.

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ATP Use in Muscle Contraction

The use of ATP stored in the muscle fiber for immediate energy, lasting only 1-2 seconds.

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Creatine Phosphate System

The breakdown of creatine phosphate into creatine and phosphate, providing energy for muscle contraction lasting 8-10 seconds.

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Aerobic Glycolysis

The process of breaking down glucose or glycogen to produce energy through the Krebs cycle and oxidative phosphorylation, providing long-lasting energy.

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Motor Neuron

A single nerve cell that transmits signals from the brain or spinal cord to a muscle.

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Motor Unit

The combination of a motor neuron and the muscle fibers it innervates, responsible for a specific muscular movement.

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Recruitment

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

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Muscle Fatigue

The decrease in muscle tension due to repeated stimulation, caused by the depletion of energy reserves and accumulation of metabolic byproducts.

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Skeletal Muscle Fiber Types

Different types of muscle fibers with varying mechanical and contractile properties, such as slow-twitch and fast-twitch fibers.

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Study Notes

Skeletal Muscle Contraction

  • Skeletal muscles are responsible for movement, posture maintenance, and heat production. They also protect bones and internal organs.
  • Muscle cells exhibit excitability, responding to stimuli by generating action potentials.
  • Contractility allows muscles to shorten and thicken, producing force.
  • Extensibility enables muscles to extend without damage.
  • Elasticity allows muscles to return to their original shape after contraction.

Muscle Types

  • Skeletal muscle: Characterized by striated fibers, voluntary control, and multiple nuclei. Typically attached to bones.
  • Smooth muscle: Non-striated, spindle-shaped, involuntary control, and a single nucleus. Found in internal organs.
  • Cardiac muscle: Striated, branched, and involuntary control. Only found in the heart.

Skeletal Muscle Structure

  • Organized into fascicles, fibers, myofibrils, and myofilaments (actin and myosin).
  • Myofilaments are the smallest contractile units and are organized into repeating units called sarcomeres.
  • Skeletal muscles are attached to bones via tendons. Connective tissues surround the muscle at different levels: endomysium (around a cell), perimysium (around a fascicle), and epimysium (around the entire muscle).

Sarcomere Structure

  • I band: Contains thin filaments (actin).
  • H zone: Contains thick filaments (myosin) only.
  • A band: Contains both thick and thin filaments.
  • Z line: Separates sarcomeres.
  • M line: In the middle of the H zone.
  • Myosin heads bind to actin forming cross bridges.
  • Filaments slide past each other during contraction, shortening the sarcomere.
  • Muscles use ATP to power these contractions.

Muscle Proteins

  • Dystrophin, titin, nebulin, and others are essential structural proteins that maintain muscle integrity.
  • Dystrophin-glycoprotein complex links the intracellular proteins to the extracellular matrix.

Neuromuscular Junction

  • Junction between motor neuron and muscle fiber.
  • Acetylcholine (ACh) is the neurotransmitter.
  • Release of ACh at the synapse triggers the muscle action potential.
  • Enzymes degrade ACh after contraction.

Muscle Fatigue

  • Repeated stimulation of a muscle fiber decreases tension.
  • Reduced rate of shortening and relaxation occurs.
  • Factors like ATP depletion, ion imbalance and accumulation of metabolic byproducts contribute to fatigue.

Skeletal Muscle Fiber Types

  • Slow-twitch fibers (Type I): Used for endurance activities, slow contraction speed, and high resistance to fatigue.
  • Fast-twitch fibers (Type IIa and IIx): Used for rapid, powerful movements, high contraction speed, but fatigue quicker.

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Description

Explore the essential functions and structures of skeletal muscles, along with their types and characteristics. This quiz covers muscle contraction, muscle fiber types, and the anatomy of muscle tissue critical for movement and support in the human body.

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