Muscular System

Introduction

1. The muscular system comprises specialized tissues capable of contracting and generating force.
2. It enables movement, maintains posture, stabilizes joints, and generates heat.
3. Composed of three primary muscle types (skeletal, cardiac, and smooth), it works closely with the skeletal and nervous systems to perform vital functions.
4. This system allows voluntary actions, like walking and speaking, and regulates involuntary processes like heartbeat and digestion.

• • The muscular system contributes 40-50% of total body weight.
  • It plays a significant role in metabolic activities, including glucose utilization and thermogenesis.
  • Muscle cells (fibers) are highly specialized and organized, ensuring efficient force generation.

 

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Composition of the Muscular System

Muscles are composed of the following components:

Muscle Tissue

1. Skeletal Muscle Tissue:
   • Composed of elongated, cylindrical fibers.
   • Appears striated due to the arrangement of sarcomeres.
2. Cardiac Muscle Tissue:
   • Made up of branched fibers with a central nucleus.
   • Contains intercalated discs for synchronized contraction.
3. Smooth Muscle Tissue:
   • Composed of spindle-shaped cells with no visible striations.
   • Found in the walls of hollow organs.

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Connective Tissue

Muscles are enveloped and supported by layers of connective tissue:

• Epimysium: Surrounds the entire muscle.
• Perimysium: Covers bundles of muscle fibers called fascicles.
• Endomysium: Encloses individual muscle fibers.

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Blood Supply and Innervation

• A rich blood supply ensures the delivery of oxygen and nutrients.
• Nerves control muscle contraction by transmitting signals from the central nervous system.

Proteins in Muscle Fibers

1. Contractile Proteins:
   • Actin (thin filament): Involved in contraction.
   • Myosin (thick filament): Generates force by binding to actin.
2. Regulatory Proteins:
   • Troponin and Tropomyosin: Control the interaction between actin and myosin.
3. Structural Proteins:
   • Titin: Maintains sarcomere structure and elasticity.
   • Dystrophin: Links the sarcolemma to the cytoskeleton, providing stability.

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Structure of the Muscular System

Microscopic Structure

• Muscle Fiber:
  • Each muscle fiber is a multinucleated cell with a sarcolemma (plasma membrane) and sarcoplasm (cytoplasm).
  • Contains myofibrils, which are made up of repeating units called sarcomeres.
• Sarcomere:
  • The functional unit of contraction.
  • Comprised of actin and myosin arranged in overlapping patterns to create striations.
• Sarcoplasmic Reticulum (SR):
  • Stores calcium ions, essential for initiating muscle contraction.
• T-Tubules:
  • Allow rapid propagation of action potentials into the interior of the fiber.

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Macroscopic Structure

• Muscle Belly: The thick, central part of the muscle.
• Tendons: Attach muscles to bones, enabling movement.
• Fascicles: Bundles of muscle fibers visible under the microscope.

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Functions of the Muscular System

Primary Functions

1. Movement:
   • Skeletal muscles work with bones to produce voluntary movement.
2. Posture and Stability:
   • Maintains body alignment and stabilizes joints during activity.
3. Heat Production:
   • Muscle contractions generate heat, contributing to thermoregulation.

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Additional Functions

1. Circulation:
   • Cardiac muscles pump blood, while smooth muscles in vessels regulate blood flow.
2. Digestive Processes:
   • Smooth muscles perform peristalsis to move food through the gastrointestinal tract.
3. Respiration:
   • Skeletal muscles like the diaphragm and intercostal muscles facilitate breathing.
4. Control of Openings:
   • Sphincter muscles regulate the passage of substances through hollow organs.

 

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Types of Muscles

Muscles are categorized into three primary types based on structure and function:

Skeletal Muscle

• Appearance: Striated, multinucleated, cylindrical.
• Control: Voluntary.
• Function: Locomotion, posture, and heat production.
• Examples: Biceps brachii, quadriceps, hamstrings.

Cardiac Muscle

• Appearance: Striated, branched, single nucleus, intercalated discs.
• Control: Involuntary.
• Function: Pumps blood throughout the body.
• Location: Walls of the heart.

Smooth Muscle

• Appearance: Non-striated, spindle-shaped, single nucleus.
• Control: Involuntary.
• Function: Regulates internal movements like digestion and blood flow.
• Location: Walls of hollow organs (e.g., intestines, bladder, blood vessels).

 

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Clinical Aspects of the Muscular System

Common Disorders

1. Muscle Strain:
   • Overstretching or tearing of muscle fibers.
2. Muscular Dystrophy:
   • The genetic condition causes progressive muscle weakness and degeneration.
3. Myasthenia Gravis:
   • Autoimmune disease leads to impaired communication between nerves and muscles.
4. Fibromyalgia:
   • Chronic disorder characterized by widespread muscle pain and fatigue.
5. Rhabdomyolysis:
   • Breakdown of muscle fibers, releasing myoglobin into the bloodstream, potentially causing kidney damage.
6. Tendonitis:
   • Inflammation of tendons due to overuse.

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Diagnostic Tools

1. Electromyography (EMG):
   • Measures electrical activity in muscles.
2. MRI and Ultrasound:
   • Visualize muscle structures and detect injuries.
3. Blood Tests:
   • Assess levels of muscle enzymes like creatine kinase (CK) for damage.

Treatment and Management

1. Physical Therapy:
   • Improves muscle strength, flexibility, and recovery.
2. Medications:
   • Anti-inflammatory drugs for muscle pain.
   • Corticosteroids for autoimmune disorders.
3. Surgical Interventions:
   • Tendon repair or fasciotomy for compartment syndrome.
4. Lifestyle Modifications:
   • Regular exercise, balanced nutrition, and adequate hydration.