muscular Chapter_009

Muscular System Overview

  • Chapter 9

  • Focuses on the structure and function of the muscular system.

Learning Objectives

  • Identify and compare the three types of muscle tissue: skeletal, cardiac, and smooth.

  • Discuss the structure and function of skeletal muscle.

  • Explain how various body systems contribute to movement.

Introduction to Muscular Tissue

  • Function: Enables body movement through the contraction of muscle cells (fibers).

  • Mechanism: Muscle cells shorten by converting chemical energy from food into mechanical energy.

  • Types of muscle tissue present in the body:

    • Skeletal muscle

    • Cardiac muscle

    • Smooth muscle

Types of Muscle Tissue

Skeletal Muscle Tissue

  • Also known as striated or voluntary muscle.

  • Accounts for 40%-50% of body weight, attached to bones.

  • Identified under a microscope by crosswise strips (striations).

  • Under voluntary control.

Cardiac Muscle Tissue

  • Forms the bulk of the heart.

  • Features branched cells with intercalated disks.

  • Functions as a synchronized unit due to cell interconnection.

Smooth Muscle Tissue

  • Known as nonstriated, involuntary, or visceral muscle.

  • Appears smooth under microscopic examination.

  • Found in walls of structures like digestive tract and blood vessels.

  • Contractions are involuntary.

Structure of Skeletal Muscle

Major Structures

  • Composed of muscle cells (fibers) and connective tissues.

  • Extends across a joint connecting two bones.

Parts of a Skeletal Muscle

  • Origin: Attachment to the stationary bone during movement.

  • Insertion: Attachment to the movable bone when muscle contracts.

  • Body: The main part of the muscle.

Tendons and Bursae

  • Muscles attach to bones via tendons, which are fibrous connective tissues.

  • Tendon sheaths lubricated by synovial fluid.

  • Bursae: Small fluid-filled sacs that ease movement between tendons and bones.

Microscopic Structure

  • Muscle fibers grouped in bundles with intricate arrangements.

  • Myofilaments: Thick (myosin) and thin (actin) filaments within fibers.

  • Sarcomeres (functional units) contain Z lines and are responsible for muscle contraction.

Mechanism of Muscle Contraction

  1. Nerve impulse triggers electrical impulse in the fiber.

  2. Release of calcium ions from the endoplasmic reticulum into the cytoplasm.

  3. Calcium binds to thin filaments, enabling interactions between actin and myosin, causing contractions.

Function of Skeletal Muscle

Movement

  • Muscles pull on bones; movement occurs at joints.

Groups of Muscles

  • Prime mover: Primary muscle responsible for movement.

  • Synergist: Assists the prime mover.

  • Antagonist: Opposes the action of the prime mover.

Posture

  • Tonic contractions maintain body position without movement.

  • Skeletal muscle tone counters gravity’s pull for good posture.

Heat Production

  • Muscle contractions generate heat, essential for maintaining body temperature.

  • Body temperature can indicate health (fever vs. hypothermia).

Fatigue

  • Occurs from repeated muscle stimulation without rest.

  • Results from depleted ATP stores and insufficient oxygen/nutrients.

  • Excess lactic acid accumulation causes muscle burning.

  • Oxygen debt requires increased metabolism to restore energy and oxygen levels post-exercise.

Integration with Other Body Systems

  • Muscle function relies on several systems: respiratory, circulatory, nervous, muscular, and skeletal.

  • Conditions like multiple sclerosis or brain injuries can impact muscle movement.

Learning Objectives for Muscle Stimulation and Contraction

  • Comprehend motor unit functions in muscle contraction.

  • Differentiate skeletal muscle contractions and effects of exercise.

  • Understand types of movement produced by skeletal muscles.

  • Identify major muscular disorders.

Motor Unit

  • Motor neurons transmit impulses to muscles, facilitating contraction.

  • Neuromuscular Junction (NMJ): Connection point between nerve and muscle fiber.

  • Comprises a motor neuron and its associated muscle fibers.

Muscle Stimulus

  • A threshold stimulus is required for muscle contractions.

  • Muscle fibers respond completely to a threshold stimulus (all or none response).

  • Varied motor units allow graded force contractions across the muscle.

Types of Muscle Contractions

Twitch and Tetanic Contractions

  • Twitch: Quick, jerky responses to stimulus.

  • Tetanic: Sustained contractions from rapid successive stimuli.

Isotonic Contractions

  • Produce joint movement; muscle changes length (e.g., walking).

  • Types:

    • Concentric: Muscle shortens.

    • Eccentric: Muscle lengthens.

Isometric Contractions

  • No movement occurs; muscle tension increases but does not shorten.

Effects of Exercise on Skeletal Muscles

  • Regular exercise improves muscle tone, posture, and overall endurance.

  • Disuse Atrophy: Results from prolonged inactivity.

  • Hypertrophy: Muscle size increases with consistent activity.

Muscle Groups and Movements

Types of Movements

  • Flexion: Decreasing angle between bones.

  • Extension: Increasing angle between bones.

  • Abduction: Moving a part away from the midline of the body.

  • Adduction: Moving a part toward the midline.

  • Rotation/Circumduction: Movement around an axis.

  • Special Movements: Supination, pronation, dorsiflexion, and plantar flexion.

Skeletal Muscle Groups Overview

Muscles of the Head and Neck

  • Facial Muscles: Orbicularis oculi, orbicularis oris, zygomaticus.

  • Muscles of mastication: Masseter, temporalis.

Muscles of the Upper and Lower Extremities

  • Upper: Pectoralis major, latissimus dorsi, biceps, and triceps.

  • Lower: Iliopsoas, gluteus maximus, quadriceps, hamstrings.

Muscle Injuries and Disorders

  • Includes muscle strains, cramps, crush injuries, and infections.

  • Muscular Dystrophy: Genetic disorders causing muscle atrophy, notably Duchenne (DMD).

  • Myasthenia Gravis: Autoimmune condition leading to muscle weakness.

Conclusion

  • Understanding muscles is critical for movement and body function.

  • A foundation for recognizing muscular disorders and their implications on overall health.