Muscular Physiology Chapter 2
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Questions and Answers

What are the three main types of muscles in the human body?

  • Skeletal, Smooth, Voluntary
  • Skeletal, Smooth, Cardiac (correct)
  • Skeletal, Cardiac, Involuntary
  • Striated, Smooth, Cardiac

Skeletal muscles are responsible for involuntary movements.

False (B)

Smooth muscles are found in the walls of organs and blood vessels.

True (A)

What is the primary function of cardiac muscle?

<p>To pump blood throughout the body.</p> Signup and view all the answers

What is the structural and contractile unit of myofibrils?

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

What is the role of ATP in muscle contraction?

<p>ATP provides the energy necessary for the movement of the myosin heads along the actin filaments, resulting in muscle contraction.</p> Signup and view all the answers

The release of calcium ions (Ca2+) into the cytoplasm is essential for muscle contraction.

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

Which of the following is NOT a property of skeletal muscle?

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

The motor unit is composed of a motor neuron and the muscle fibers it innervates.

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

The neuromuscular junction is the junction between the motor neuron and the muscle fiber.

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

What is the role of acetylcholinesterase?

<p>Acetylcholinesterase breaks down acetylcholine in the synaptic cleft, stopping the signal for muscle contraction.</p> Signup and view all the answers

Rigor mortis occurs because the myosin cross-bridges cannot detach from actin due to the lack of ATP.

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

Smooth muscle is found in the walls of hollow organs and blood vessels, but not in the heart.

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

What is the difference between thick and thin filaments in smooth muscle compared to skeletal muscle?

<p>In smooth muscle, thick filaments have myosin heads along their entire length, whereas in skeletal muscle, myosin heads are only found on the ends of the thick filaments.</p> Signup and view all the answers

Smooth muscles require ATP for contraction, but not for relaxation.

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

What is the role of calmodulin in smooth muscle contraction?

<p>Calmodulin binds to calcium ions and activates myosin light chain kinase (MLCK), which phosphorylates myosin, allowing it to interact with actin and initiate contraction.</p> Signup and view all the answers

Muscle fatigue is a complex phenomenon that can result from metabolic, endocrine, or central factors.

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

The duration and intensity of muscle exercise are the main factors influencing the metabolic component of fatigue.

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

The endocrine system is not involved in muscle fatigue.

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

Flashcards

Contractility

The ability of a muscle fiber to shorten forcefully when stimulated.

Extensibility

The ability of a muscle fiber to be stretched beyond its resting length.

Elasticity

The ability of a muscle fiber to return to its resting length after being stretched.

Muscle fibers (muscle cells)

Specialized cells responsible for contraction.

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Sarcomere

The structural and contractile unit of myofibrils, responsible for muscle contraction.

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Thin filaments (actin)

Long, thin filaments composed of the protein actin, found in myofibrils.

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Thick filaments (myosin)

Thick filaments composed of the protein myosin, found in myofibrils.

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Sliding filament theory

The sliding of thin actin filaments past thick myosin filaments, which shortens the sarcomere and causes muscle contraction.

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Motor unit

The functional unit of skeletal muscle, consisting of a motor neuron and all the muscle fibers it innervates.

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Neurotransmitter

A chemical messenger released by a nerve cell that triggers muscle contraction.

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Neuromuscular junction

The junction of a motor neuron with a muscle fiber, where neurotransmitters are released.

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Motor endplate

A specialized region of the muscle fiber's plasma membrane, where the neuromuscular junction is located.

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Nicotinic acetylcholine receptor

A type of receptor protein on the motor endplate that binds acetylcholine, causing muscle fiber depolarization.

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Excitation-contraction coupling

The process by which an action potential in a motor neuron triggers muscle contraction.

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Sarcoplasmic reticulum

A specialized organelle in muscle fibers that stores calcium ions, which are essential for muscle contraction.

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ATP hydrolysis

The hydrolysis of ATP to ADP and Pi, providing the energy for myosin head movement and muscle contraction.

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Calcium reuptake

The process by which calcium ions are pumped back into the sarcoplasmic reticulum, leading to muscle relaxation.

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Muscle fatigue

The depletion of ATP and other energy stores, leading to a decrease in muscle performance.

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Rigor mortis

The stiffening of muscles after death, due to the depletion of ATP and the inability of myosin heads to detach from actin.

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Smooth muscle

A type of muscle tissue found in the walls of hollow organs, such as the digestive system and blood vessels.

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Calmodulin

A protein that binds calcium ions in smooth muscle, activating myosin light chain kinase.

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Myosin light chain kinase (MLCK)

An enzyme that phosphorylates myosin light chains, allowing myosin to interact with actin and initiate smooth muscle contraction.

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Excitation

The process by which a chemical signal triggers a muscle fiber to contract.

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Excitability

The ability of a muscle fiber to respond to a stimulus.

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Neurotransmitter release

The release of a neurotransmitter from a nerve cell.

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Muscle action potential

The production of an electrical signal along the sarcolemma, which triggers muscle contraction.

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Heat production

The production of heat as a byproduct of muscle contraction.

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Muscle metabolism

The metabolic pathways responsible for ATP production during muscle contraction.

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Creatine phosphate (CP)

A high-energy phosphate compound that provides ATP for initial muscle contraction.

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Anaerobic glycolysis

The breakdown of glucose to pyruvate, producing ATP without oxygen.

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Anaerobic lactic pathway

The breakdown of glucose to pyruvate, with the production of lactate, producing ATP without oxygen.

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Aerobic pathway

The breakdown of glucose to carbon dioxide and water, producing ATP with the use of oxygen.

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Study Notes

Chapter 2: Muscular Physiology - Skeletal Striated Muscle

  • Types of Muscles: Skeletal, smooth, and cardiac muscles.
  • Muscle Functions: Movement production, posture maintenance, joint stabilization, heat release.
  • Skeletal Striated Muscle (SSM): Experimental study of contraction.

Mechanical Phenomena

  • Neuromuscular Junction: Acetylcholine (ACh) release from nerve terminal diffuses across synaptic cleft, and binds to receptors. This triggers a potential action that propagates the along the sarcolemma and T-tubules.

  • Calcium Release: The potential action leads to calcium ion release from the terminal cisternae of the sarcoplasmic reticulum.

  • Increased Calcium: Results in higher calcium concentration inside sarcoplasm.

  • Filament Sliding (Contraction): Increased intracellular Calcium causes myosin heads to bind to actin filaments, creating cross-bridges. The sliding of thin (actin) filaments over thick (myosin) filaments shortens the sarcomere, leading to contraction.

  • Contraction Termination: After the action potential ends, increased Calcium is recaptured into the sarcoplasmic reticulum.

  • Relaxation (Termination): Calcium levels decrease, myosin releases from actin, and the sarcomere returns to its resting length.

Anatomical Support of Contraction

  • Muscle Fiber: Specialized cells adapted for contraction. Elongated shape allows for shortening.
  • Mitochondria: Cellular structures required for ATP production (energy for contraction).
  • Myofibrils: Contractile units of the muscle fiber, made up of actin and myosin filaments.
  • Sarcomere: Structural and contractile unit of myofibrils (fundamental unit of muscle contraction forming the striations).

Muscle Fiber Structure

  • Myofibrils: Contain thin actin and thick myosin filaments organized into repeating units (sarcomeres).
  • Sliding Filament Theory: The mechanism by which myosin filaments pull on actin filaments to cause contraction.

Contractile Proteins

  • Myosin: Thick filaments with myosin heads that bind to actin.
  • Actin: Thin filaments that interact with myosin heads to produce movement during contraction.

Excitation-Contraction Coupling

  • Molecular Mechanism: Depolarization of sarcolemma propagates through the T-tubules, triggering calcium release from the sarcoplasmic reticulum.

  • Energy Source: ATP hydrolysis provides the energy for myosin head movement during muscle contraction. Myosin binds to actin and changes shape pulling the actin filaments towards the center of the sarcomere.

  • ATP binding to myosin allows detachment from actin preventing rigor mortis.

Muscle Fatigue

  • Metabolic and Peripheral Component: Factors like metabolic changes (glycogen depletion, ion imbalances) and ionic changes affect muscle contractile ability and performance for short high intensity workouts.

  • Central Component: Nervous system fatigue reduces peripheral stimulation leading to decreased contraction capabilities. Central nervous system fatigue reduces cortical motor control.

Smooth Muscle

  • Structure: Spindle-shaped, single nucleus, fibers found in organs like airways, blood vessels, etc.

  • No striations (smooth appearance).

  • Contains actin and myosin but not organized in sarcomeres.

  • Excitation-Contraction Coupling Mechanism: Similar sliding filament mechanism but differs in regulation. Calcium entry is necessary for contraction, but it’s regulated by different proteins.

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Description

Explore the intricacies of muscular physiology in this quiz focused on skeletal striated muscle. Test your understanding of muscle types, functions, and the mechanical phenomena involved in contraction at the neuromuscular junction. Ideal for students studying human anatomy and physiology.

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