muscles

Extended Modular Program on Muscles by Dr. Shahira Youssef

Prof. of Anatomy & Embryology

Voluntary and Involuntary Muscles

  • Definition:

    • Voluntary muscles: Muscles that are under conscious control.

    • Involuntary muscles: Muscles that function without conscious control.

Types of Muscles

  1. Skeletal Muscles:

    • Characteristics:

      • Striated with alternating light and dark bands.

      • Voluntary in nature.

    • Location:

      • Constitute the main bulk of the body, primarily found in limbs.

    • Function:

      • Capable of rapid contractions.

  2. Smooth Muscles:

    • Characteristics:

      • Non-striated and involuntary.

    • Location:

      • Found in the gastrointestinal tract, urinary tract, genital system, and blood vessels.

    • Control:

      • Regulated by the autonomic nervous system or hormonal signals.

  3. Cardiac Muscles:

    • Characteristics:

      • Striated, involuntary, and capable of spontaneous rhythmic contractions.

    • Control:

      • Also controlled by the autonomic nervous system.

Muscle Classification

According to Shape and Line of Pull

  • A. Parallel Muscles:

    • Wide range of movement but less force.

    • Examples:

      • Quadrilateral: Quadratus lumborum

      • Fusiform: Biceps

      • Strap Muscles: Sartorius

      • Strap with tendinous intersections: Rectus abdominus

  • B. Oblique Muscles:

    • Range of movement is less while force is greater.

    • Variants:

    1. Pennate Muscles:

      • Unipennate: Fibers align along one side of tendon (e.g., Flexor pollicis longus).

      • Bipennate: Fibers on both sides of a tendon (e.g., Dorsal interossei, Rectus femoris).

      • Multipennate: Series of bipennate (e.g., Deltoid).

      • Circumpennate: Fibers converge from all directions towards a central tendon (e.g., Tibialis anterior).

    2. Triangular Muscles:

      • Fibers converge from a wide attachment to a narrow tendon (e.g., Temporalis).

    3. Cruciate Muscles:

      • Fibers composed of two planes running in different directions (e.g., Sternomastoid).

    4. Circular Muscles:

      • Form a complete circle (e.g., Orbicularis oculi).

    5. Spiralized Muscles:

      • Upon contraction, they approximate their attachments and may twist (e.g., Trapezius).

Attachments of Muscles

  • Types of Muscle Attachments:

    • Fleshy Fibers: Example: Popliteus

    • Tendon: Fibrous cord, Example: Tendocalcaneus

    • Aponeurosis: Flat fibrous sheet, Example: Aponeurosis of external oblique

    • Raphe: Fibrous band that separates two fleshy muscles (e.g., palatopharyngeal sphincter).

Sites of Attachment

  • Common sites for muscle attachment include:

    • Bones

    • Cartilage

    • Other muscles

  • Definitions:

    • Origin: Attachment point with the least movement.

    • Insertion: Attachment point that moves the most.

Action of Muscles

  • Prime Mover: Initiates movement (agonist).

  • Antagonist: Opposing muscle that performs the opposite action of the agonist.

  • Synergist: Assists the prime mover and prevents unwanted movements when the prime mover can move two joints.

  • Fixator: Stabilizes the origin of the prime mover, allowing for efficient action.

  • Examples of Actions:

    • Flexion of the Elbow:

    • Prime Mover: Biceps brachii

    • Synergist: Brachioradialis

    • Antagonist: Triceps

    • Extension of the Elbow:

    • Prime Mover: Triceps

    • Antagonist: Biceps

Nerve Supply of Skeletal Muscle

  • Nerves enter the muscle through the deep surface.

  • The point of nerve entrance is termed the motor point.

Summary

  • Muscles can be classified into skeletal, smooth, and cardiac.

  • Skeletal muscles can be further classified into parallel or oblique.

  • Muscles attach via tendons, ligaments, raphe, or aponeurosis.

  • Muscles can serve different roles such as prime mover, antagonist, synergist, or fixator.