University of Mount Saint Vincent 9

Introduction to the Muscle System

• Importance of self-care: eating right, avoiding illness.

• Overview of muscle types learned previously in Chapter 3.

Types of Muscles

• Three types of muscles:

  • Skeletal Muscle:

    • Voluntary control.

    • Striated appearance.

    • Found in limbs, attached to skeleton.

  • Smooth Muscle:

    • Involuntary control.

    • Found in hollow organs (e.g., digestive tract).

    • Lacks striations; spindle-shaped fibers.

  • Cardiac Muscle:

    • Involuntary control.

    • Striated appearance.

    • Found in the heart; contains intercalated discs.

Muscle Fiber Characteristics

• Voluntary vs Involuntary:

  • Skeletal: Voluntary, controlled consciously.

  • Smooth & Cardiac: Involuntary, automatic function.

• Nuclear Structure:

  • Skeletal: Multinucleated.

  • Smooth & Cardiac: Uninucleated (one nucleus).

Muscle Anatomy and Structure

• Prefixes in Muscle Nomenclature:

  • Myo- or Mys: Indicating muscle.

  • Example Diseases: Myasthenia gravis, fibromyalgia, muscular dystrophies.

• Key Structures:

  • Sarcolemma: Plasma membrane of a muscle cell.

  • Sarcoplasmic reticulum: Specialized endoplasmic reticulum; stores/releases calcium for muscle contraction.

Muscle Layers

• Three Layers of Muscle Tissue:

  • Epimysium: Outer layer surrounding whole muscle.

  • Perimysium: Middle layer surrounding fascicles (bundles of muscle fibers).

  • Endomysium: Inner layer surrounding individual muscle fibers.

Muscle Attachments

• Tendons: Connect muscles to bones.

• Ligaments: Connect bones to other bones.

• Aponeurosis: Sheet-like structures connecting muscles or holding organs.

Muscle Functioning

• Contraction Mechanism:

  • Involves sliding of thick (myosin) and thin (actin) filaments.

  • Z disc: Anchor point for thin filaments.

  • M line: Anchor point for thick filaments.

  • I Band: Contains only thin filaments (actin).

  • A Band: Contains both thin and thick filaments (darker area).

  • H Zone: Only contains thick filaments; reduces during contraction.

Properties of Muscles

• Excitability: Ability to receive electrical signals.

• Contractility: Ability to shorten/contract.

• Extensibility: Ability to stretch.

• Elasticity: Ability to recoil to original length after stretching.

Muscle Nervous System Interaction

• Nerve Supply: Motor neurons send signals to muscles.

  • Efferent Nerves: Carry signals from the spinal cord to muscles (ventral side).

• Neuromuscular Junction: Point where nerve and muscle meet; where neurotransmitters like acetylcholine are released.

Muscle Contraction Process**

• Action potential generated by nervous system reaches muscle fiber.

• Acetylcholine binding triggers muscle fiber activation.

• Calcium ions released from sarcoplasmic reticulum enable actin-myosin interaction.

• Formation of cross-bridges between actin and myosin, resulting in muscle shortening.

Conclusion & Next Steps

• Study embedded videos on muscle physiology and definitions.

• Review microanatomy (actin, myosin, sarcolemma, acetylcholine).

• Prepare for practical applications of knowledge about muscle movement and interactions.