Muscular System Notes

Muscular System Study Notes

Overview of Muscular System

  • The muscular system is crucial for movement, posture, and bodily functions.

  • Contains three types of muscle tissues:

    • Skeletal Muscle: Striated muscle attached to bones, responsible for voluntary movement.

    • Smooth Muscle: Non-striated muscle found in walls of internal organs, responsible for involuntary movements.

    • Cardiac Muscle: Striated muscle found only in the heart, also involuntary.

Unit Topics

1. Muscular System Anatomy

  • Macroscopic and Microscopic Anatomy

    • Vocabulary List to be reviewed.

2. Muscular Movement

  • Neuromuscular Junction: Connection point between motor neuron and muscle fiber.

  • Contraction - Sliding Filament Theory: Mechanism of muscle contraction where actin and myosin filaments slide over one another.

3. Major Muscles of the Human Body

  • Identify and label major muscles based on anatomy and physiology nomenclature.

4. Muscular Disorders

  • Projects and presentations relating to various muscular disorders.

Muscle Structure

1. Types of Muscle

  • Skeletal Muscle: Voluntary, striated, multinucleate.

  • Smooth Muscle: Involuntary, non-striated, single nucleus.

  • Cardiac Muscle: Involuntary, striated, branched, single nucleus.

2. Structures of Muscle

  • Muscle Fiber: Basic unit of muscle.

  • Myofibril: Bundles of myofilaments within muscle fibers.

  • Sarcomere: The functional unit of muscle contraction.

  • Actin: Thin filaments of muscle.

  • Myosin: Thick filaments of muscle.

3. Muscle Contraction

  • Sliding Filament Theory: Muscle contractions occur as thin filaments slide past thick filaments:

    • Requires the presence of ATP, Calcium, Myosin, and Actin.

4. Muscle Hierarchy

  • Epimysium: Outermost layer surrounding the entire muscle.

  • Perimysium: Surrounds bundles of muscle fibers (fasciculus).

  • Endomysium: Surrounds individual muscle fibers.

  • Muscle Belly: Central part of a muscle.

5. Muscle Fiber Components

  • Sarcolemma: Muscle fiber membrane.

  • Sarcoplasm: Cytoplasm of muscle fibers.

  • Sarcoplasmic Reticulum: Stores calcium ions.

  • T-Tubules: Extensions that allow electrical impulses to penetrate muscle fibers.

Neuromuscular Junction

  • Action Potential: Electrical impulse that stimulates muscle contraction.

    • Sequence of events at the neuromuscular junction:

    1. Action potential arrives at the axon terminal.

    2. Voltage-gated Ca²⁺ channels open, Ca²⁺ enters.

    3. ACh is released from synaptic vesicles.

    4. ACh binds to receptors on sarcolemma, ion channels open.

    5. Na⁺ inflow depolarizes the membrane, generating an action potential.

    6. ACh effects terminated by acetylcholinesterase.

Muscle Stimulation and Contraction

  • All-or-Nothing Principle: A muscle fiber is either fully stimulated or not at all.

  • Muscle Tetanus: Continuous contraction of muscle fibers.

    • Incomplete Tetanus: Muscle exhibits partial relaxation.

    • Complete Tetanus: No relaxation occurs between contractions.

1. Contraction Phases

  • Resting Phase: State of muscle at rest.

  • Latent Period: Time between action potential and contraction.

  • Contraction Phase: Tension increases in the muscle.

  • Relaxation Phase: Time required to return to original length.

2. Sliding Filament Mechanism Steps

  1. Action potential stimulates muscle.

  2. Calcium ions are released from the sarcoplasmic reticulum.

  3. Calcium binds to troponin, exposing myosin binding sites on actin.

  4. Myosin heads, powered by ATP hydrolysis, attach to actin and perform power stroke.

  5. ADP and P are released; myosin returns to resting position if ATP is available.

Muscle Fiber Types and Properties

  • Fast Twitch: Quick to contract, fatigue faster.

  • Slow Twitch: Slower contraction, fatigue resistant, used for longer activities.

Muscle Disorders and Diseases

  1. Duchenne Muscular Dystrophy (DMD): Genetic disorder, progressive muscle degeneration.

  2. Tetanus: Continuous muscular contractions due to a bacterial toxin.

  3. Myotonia: Delayed relaxation of muscle after contraction.

  4. Amyotrophic Lateral Sclerosis (ALS): Progressive neurodegenerative disease affecting motor neurons.

  5. Fibromyalgia: Widespread musculoskeletal pain with fatigue and mood issues.

  6. Tendinitis: Inflammation of tendons due to overuse.

  7. Myasthenia Gravis: Autoimmune disorder affecting neuromuscular transmission.

  8. Pompe Disease: Genetic disorder causing glycogen buildup in muscles.

Muscular Growth and Hypertrophy

  • Hypertrophy: Increase in muscle size through exercise.

  • Mechanisms include muscle tension, muscle damage/repair, and metabolic stress.

Muscle Nomenclature

  • Muscles are named based on:

    • Location

    • Shape

    • Size

    • Orientation

    • Depth

    • Function

Anatomical Muscle Attachments

  1. Origin: Fixed attachment point.

  2. Insertion: Moveable attachment point during contraction.

Muscle Actions

  • Prime Mover (Agonist): Primary muscle responsible for an action.

  • Antagonist: Opposes the action of the prime mover.

  • Synergist: Assists the prime mover.

Summary of Important Muscles

Major Muscles of the Body

  • Deltoid, Pectoralis Major, Biceps Brachii, Triceps Brachii: Key muscles in arm movement and stability.

  • Latissimus Dorsi, Gluteus Maximus: Major muscles for back and hip movement.

  • Rectus Abdominis, External Oblique: Core muscles providing support and movement.

  • Quadriceps, Hamstrings: Important for leg movement.