Muscle Types and Properties

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Questions and Answers

Which muscle type is characterized by a striated appearance and is under voluntary control?

Smooth Muscle

Skeletal Muscle (correct)

Cardiac Muscle

Multinucleated Muscle

What unique feature is associated with cardiac muscle that aids in contraction synchronization?

Nuclei

Striations

Intercalated discs (correct)

Z-discs

Which connective tissue surrounds individual fascicles in skeletal muscle?

Endomysium

Sarcolemma

Perimysium (correct)

Epimysium

What property of muscle tissue allows it to stretch without damage?

Extensibility Signup and view all the answers

What is the primary function of smooth muscle?

Regulate internal organ function Signup and view all the answers

Which component is NOT a part of the skeletal muscle structure?

Chondrocytes Signup and view all the answers

What is the primary role of the Z-discs in a sarcomere?

Serve as attachment points for actin filaments Signup and view all the answers

Which type of muscle tissue contains spindle-shaped fibers and is typically involved in involuntary functions?

Smooth Muscle Signup and view all the answers

What is the role of the Z-discs in muscle contraction?

They anchor actin filaments and pull closer during contraction. Signup and view all the answers

Which proteins form the troponin complex in thin filaments?

Troponin T, Troponin I, Troponin C Signup and view all the answers

What characterizes the A-band in a sarcomere?

Contains both thick and overlapping thin filaments Signup and view all the answers

What is the primary function of myosin heads during contraction?

To hydrolyze ATP and form cross-bridges with actin Signup and view all the answers

What happens to the I-band during muscle contraction?

It shortens as actin filaments slide toward the M-line. Signup and view all the answers

What is the structural role of the M-line in the sarcomere?

Anchors thick filaments and stabilizes myosin position. Signup and view all the answers

Which of the following statements is true regarding the H-zone?

It contains only thick filaments without overlapping thin filaments. Signup and view all the answers

What is the function of tropomyosin in muscle contraction?

To block myosin-binding sites on actin when muscles are relaxed. Signup and view all the answers

What happens to the H-zone during muscle contraction?

It becomes narrower. Signup and view all the answers

What role do T-tubules play in muscle contraction?

They ensure action potential reaches deep into the muscle fiber. Signup and view all the answers

During the cross-bridge cycle, what occurs during the power stroke phase?

Myosin pulls actin towards the M-line. Signup and view all the answers

What initiates depolarization of the muscle fiber at the neuromuscular junction?

Binding of ACh to receptors on the sarcolemma. Signup and view all the answers

Which mechanism leads to muscle relaxation?

Breakdown of ACh by acetylcholinesterase. Signup and view all the answers

What is required for continuous muscle contraction?

Availability of calcium and ATP. Signup and view all the answers

What condition can lead to muscle fatigue?

Depletion of ATP. Signup and view all the answers

What structure is formed by a T-tubule and two adjacent terminal cisternae of the SR?

Triad structure. Signup and view all the answers

Study Notes

Muscle Types

Skeletal Muscle: Voluntary control, striated appearance, multinucleated fibers, attached to bones via tendons
Cardiac Muscle: Involuntary control, striated, branched fibers, one to two nuclei per cell, located in heart walls, contains intercalated discs for synchronized contractions
Smooth Muscle: Involuntary control, non-striated, spindle-shaped fibers, one nucleus, found in walls of hollow organs

Common Muscle Properties

Contractility: Ability to shorten forcefully
Extensibility: Capacity to stretch without damage
Elasticity: Ability to return to resting length after stretching

Skeletal Muscle as an Organ

Composed of muscle fibers, blood vessels, nerve fibers, and connective tissues
Connective tissue layers provide support and structure:
- Epimysium: Surrounds entire muscle
- Perimysium: Surrounds individual fascicles
- Endomysium: Encloses individual muscle fibers

Muscle Fibers (Cells)

Long and cylindrical, up to 100 μm in diameter and 30 cm in length
Sarcolemma: Plasma membrane
Sarcoplasm: Cytoplasm
Sarcoplasmic Reticulum (SR): Specialized ER that stores and regulates calcium ions

The Sarcomere: Functional Unit

Composed of actin and myosin filaments
Approximately 2 μm long
Z-Discs: Attachment points for thin (actin) filaments
Thin Filaments: Primarily made of actin (G-actin) molecules forming filamentous actin (F-actin)
- Regulatory Proteins:
  - Troponin: Binds Ca++ to expose myosin-binding sites on actin
  - Tropomyosin: Wraps around actin, blocking myosin-binding sites when relaxed
Thick Filaments: Made up of myosin proteins with a long tail and globular head
- Myosin Heads: Have ATPase activity for energy during contraction

Sarcomere Components

M-Line: Central line where thick filaments are anchored
A-Band: Contains thick filaments and overlapping thin filaments, appears dark under a microscope
I-Band: Contains only thin filaments, appears light under a microscope
H-Zone: Central region of the A-band with only thick filaments, appears lighter than the rest of the A-band

Neuromuscular Junction and Excitation-Contraction Coupling

Neuromuscular Junction: Connection between a motor neuron and a muscle fiber
Action Potential: Neurotransmitter acetylcholine (ACh) binds to receptors, initiating depolarization and action potential generation
T-Tubules: Invaginations of the sarcolemma carrying action potential into the muscle fiber
Triad Structure: T-tubule and two terminal cisternae of the SR, allowing rapid calcium release

Sliding Filament Model of Contraction

Cross-Bridge Formation: Myosin heads attach to exposed binding sites on actin
Cross-Bridge Cycle:
- Binding: Myosin heads attach to actin
- Power Stroke: Myosin pulls actin towards the M-line, shortening the sarcomere
- Release: ATP binds to myosin, causing detachment from actin
- Re-cocking: ATP is hydrolyzed, re-energizing the myosin head
Continuous contraction occurs as long as Ca++ and ATP are available

Muscle Relaxation

ACh Breakdown: Acetylcholinesterase breaks down ACh, stopping action potential generation
Ca++ Re-uptake: Calcium is pumped back into SR, restoring tropomyosin covering on actin-binding sites

Muscle Fatigue

Depletion of ATP or accumulation of metabolic byproducts (e.g., lactic acid)
Neural factors, such as reduced motor neuron firing can also contribute

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Description

This quiz covers the three main types of muscle tissue: skeletal, cardiac, and smooth muscle. You'll explore their characteristics, properties, and functions, including the composition of skeletal muscle as an organ. Test your knowledge on muscle fibers and their unique properties!