MUSCULAR SYSTEM

  • Instructor: Dr. Dalia M. Biram, Assistant Professor of Anatomy & Embryology
  • Affiliations: Faculty of Medicine, Alexandria University; Faculty of Pharmacy, AAST

OVERVIEW OF MUSCLES

  • Composition: Muscles constitute approximately 40% of body weight.
  • Key Property: Contractility
    • Definition: The ability of muscles to shorten in response to a stimulus.

TYPES OF MUSCLES

1. Skeletal Muscles

  • Location: Attached to the skeleton.
  • Characteristics:
    • Voluntary: Under conscious control.
    • Striated: Exhibits a striped appearance.
    • Multi-nucleated Fibers: Contains multiple nuclei per fiber.
    • Eccentric Nuclei: Nuclei are located on the periphery of the muscle fibers.
  • Functions:
    • Movement: Enables voluntary movements.
    • Heat Generation: Produces heat through muscle contractions.
    • Posture Maintenance: Provides stability to the body posture.

2. Smooth Muscles

  • Location: Found in the walls of various organs, including:
    • Digestive tract
    • Urinary bladder
    • Blood vessels
  • Characteristics:
    • Involuntary: Operates without conscious control.
    • Non-striated: Lacks the striped appearance of skeletal muscles.
    • Spindle-Shaped: Characteristic shape of muscle fibers.
    • One Central Nucleus: Typically features a single nucleus per fiber.
  • Functions:
    • Peristalsis: Facilitates movement of substances through hollow organs.
    • Blood Pressure Regulation: Controls the contraction and relaxation of blood vessels.
    • Pupil Size Control: Adjusts the size of the pupil in the eye.
    • Hair Erection: Triggers contraction of arrector pili muscles.

3. Cardiac Muscle

  • Location: Found exclusively in the heart.
  • Characteristics:
    • Involuntary: Functions autonomously without conscious control.
    • Striated: Has a striped appearance similar to skeletal muscle.
    • One Central Nucleus: Typically has a single nucleus per fiber.
  • Function:
    • Continuously Pumps Blood: Essential for maintaining circulation throughout the body.

TYPES OF SKELETAL MUSCLES

  • Categories Based on Fiber Arrangement:
    • Parallel: Fibers are arranged parallel to the length of the muscle (e.g., Sartorius).
    • Unipennate: Fibers attach obliquely to one side of a tendon (e.g., Palmer interossei).
    • Bipennate: Fibers attach obliquely on both sides of a central tendon (e.g., Dorsal interossei).
    • Multipennate: A fusion of several bipennate muscles (e.g., middle fibers of the Deltoid).

PARTS OF A SKELETAL MUSCLE

  • Belly:
    • Definition: The middle, fleshy part of the muscle; typically reddish in appearance.
  • Tendon:
    • Definition: The rounded, whitish, fibrous ends of a muscle; can be flat and termed aponeurosis.
  • Origin:
    • Definition: The fixed proximal part of the muscle; remains stationary during contraction.
  • Insertion:
    • Definition: The mobile distal part of the muscle; moves when the muscle contracts.

CLASSIFICATION OF SKELETAL MUSCLES ACCORDING TO FUNCTION

  • Prime Mover:
    • Definition: The main muscle responsible for a specific movement.
  • Antagonist:
    • Definition: Muscle that opposes the action of the prime mover; helps in muscle control and regulation.
  • Synergist:
    • Definition: A muscle that assists the prime mover in performing its action; can provide stability.
  • Fixator:
    • Definition: Muscle that stabilizes intermediate joints to prevent unwanted movement during contraction.

CLOSING

  • Acknowledgment: Thank you for participating in this overview of the muscular system.