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Muscular System Overview

• Chapter 9 Summary

  • Focus on the structure, function, and types of muscular tissue in the human body.

Learning Objectives (Lesson 9.1)

• Understand and compare the three major types of muscle tissue:

  • Skeletal Muscle

  • Cardiac Muscle

  • Smooth Muscle

• Discuss the structure and function of skeletal muscle.

• Describe the involvement of other body systems in movement.

Types of Muscle Tissue

1. Skeletal Muscle

• Characteristics:

  • Striated appearance due to organized fibers.

  • Voluntary control of movements.

  • Makes up approximately 40-50% of body weight.

• Function:

  • Responsible for body movements and posture.

2. Cardiac Muscle

• Characteristics:

  • Found in the heart, branched structure.

  • Unique intercalated disks allow for synchronized contractions.

• Function:

  • Pumps blood through the heart and circulatory system.

3. Smooth Muscle

• Characteristics:

  • Non-striated, involuntary muscle.

  • Forms the walls of hollow organs (e.g., blood vessels, digestive tract).

• Function:

  • Controls the movement of substances within hollow organs.

Muscular Function and Energy Mechanics

• Muscle contraction occurs when fibers shorten, converting chemical energy into mechanical energy.

• Average person has 50 pounds of skeletal muscle enabling a range of motions from blinking to athletic activities.

Skeletal Muscle Structure

• Components of Skeletal Muscle:

  • Origin: The fixed attachment point.

  • Insertion: The point that moves during contraction.

  • Body: The main part of the muscle.

• Muscle Attachments:

  • Tendons connect muscles to bones and are robust structures.

  • Bursae facilitate tendon movement over bones, reducing friction.

Microscopic Structure of Skeletal Muscle

• Skeletal muscle composed of:

  • Muscle Fibers: Long cylindrical cells forming bundles.

  • Myofilaments:

    • Thick (Myosin) and thin (Actin) filaments organized into sarcomeres, the contractile unit.

Muscle Contraction Mechanics

• Action of the Sarcomere:

  • Myofilaments slide past each other (Sliding Filament Model) during contraction, powered by calcium and ATP.

• Each contraction is triggered by a nerve impulse that stimulates calcium release.

Functions of Skeletal Muscle

• Produces Movement:

  • Muscle contractions pull bones at joints, creating movement.

• Maintains Posture:

  • Tonic contractions maintain body position against gravity.

• Produces Heat:

  • Muscle fibers generate heat during contractions, helping to regulate body temperature.

Types of Muscle Contractions

• Tonic: Maintain muscle tone.

• Twitch: Quick, minimal role in normal function.

• Tetanic: Sustained contractions from rapid successive stimulation.

• Isotonic: Involves shortening and lengthening of muscle, causing movement.

• Isometric: Muscle tension increases without shortening.

Effects of Exercise

• Regular exercise improves muscle tone, posture, lung and heart function, and overall well-being.

• Hypertrophy: Increase in muscle size from consistent exercise.

• Disuse Atrophy: Reduction in muscle size from inactivity.

Motor Unit and Muscle Stimulation

• A motor unit consists of a motor neuron and the muscle fibers it innervates.

• Motor units allow for graded muscle responses based on stimulus strength (threshold stimulus).

Integration with Body Systems

• Normal movement requires collaboration of muscular, skeletal, respiratory, and circulatory systems.

• Pathological conditions in these systems can severely affect movement.

Muscular Disorders

Common Conditions

• Myopathies: Muscle disorders ranging from mild to serious.

• Strains: Overexertion or trauma.

• Cramps: Involuntary twitching often due to imbalance.

• Infections: Caused by bacteria, viruses, or parasites, can lead to serious conditions

• Muscular Dystrophy: Genetic disorders causing muscle wasting, particularly Duchenne Muscular Dystrophy.

• Myasthenia Gravis: Autoimmune disorder affecting acetylcholine receptors, leading to muscle weakness.