Muscular System

Muscular System
  • Anatomy- This system includes muscles of the body. It includes only skeletal muscle, not smooth muscle or cardiac muscle.
  • Physiology- It allows for manipulation of the environment, provides locomotion, maintains posture and produces heat.
  • There are approximately 630 muscles in the human body.
Breaking down The Muscle and The Muscle Cell
  • Myocyte- A muscle cell.
  • Muscle cell- Known as muscle fibers in striated muscle.
  • Epimysium- A sheath of fibrous elastic tissue surrounding a muscle.
  • Perimysium- A sheath of connective tissue surrounding a bundle of muscle fibers.
  • Fascicle- A bundle of skeletal muscle fibers surrounded by perimysium.
  • Endomysium- A layer of areolar connective tissue surrounding each individual myocyte (muscle fiber, or muscle cell).
  • Sarcoplasm – The cytoplasm of a striated muscle cell (myocyte).
  • Sarcolemma- The cell membrane that encloses each muscle cell (myocyte).
  • Sarcomere- The basic unit of a muscle contraction.
  • Myosin- A contractile protein, which forms the thick filament.
  • Actin- Another contractile protein, which forms the thin filament.
  • Sliding Filament Theory- Describes a process used by muscles to contract.
3 Muscle Cell Types
Skeletal Muscle
  • Skeletal muscles are responsible for human movement.
  • Skeletal muscle cells are striated.
  • Skeletal muscles are are voluntarily controlled.
  • These muscle cells have many nuclei (multinucleated).
Smooth Muscle
  • Smooth muscle cells are responsible for sustained contractions in the blood vessels, gastrointestinal tract and other areas in the body.
  • Smooth muscle cells are not striated.
  • Smooth muscle cells are involuntarily controlled.
  • These cells are found in organs and blood vessels, excluding the heart.
  • Smooth muscle cells have only one nucleus.
Cardiac Muscle
  • Cardiac muscle is responsible for pumping blood
  • The heart is the only place where cardiac muscle cells are found.
  • This muscle cell type is striated and has one nucleus.
  • Cardiac muscle cells also contain intercalated discs, which act as a junction between the two muscle cells.
Type 1 and Type 2 Muscle Fibers
Type 1 Muscle Fibers
  • Slow Twitch
  • Red
  • Aerobic
  • Long
Type 2 Muscle Fibers
  • Fast Twitch
  • White
  • Anaerobic
Skeletal muscles are named by:
  1. Direction of Muscle Fibers
    • Rectus, Transverse, Oblique
  2. Location
    • Temporalis, Orbicularis
  3. Size
    • Maximus, Minimus
  4. Origin and Insertion
    • Sternocleidomastoid
  5. Number of Origins
    • Biceps, Triceps
  6. Shape
    • Deltoid, Trapezius
  7. Action
    • Flexors, Extensors
Muscle Tissue
  • Tendons- Tendons are connective tissue that connects muscles to bones.
  • Ligaments- Ligaments are tough, fibrous tissue that connect bones to other bones.
  • Aponeurosis- An aponeurosis is a sheet-like, tendinous expansion, mainly serving to connect a muscle with the parts it moves.
  • Bursae- These are small, connective tissue sacs. They are lined with synovial membrane and contain synovial fluid. They act as cushions for joints.
  • Cartilage- This is an elastic substance that cushions the bones and joints.
  • Muscle Belly- A muscle belly is the fleshy portion of a muscle.
  • Fascia- Fascia is a sheet or band of fibrous connective tissue. It is deep to the skin. It covers the entire body.
Muscle Stimulus
  • Twitch- A twitch is a single, quick muscular contraction from a single nerve impulse, followed by relaxation.
  • Threshold stimulus- This is the minimal stimulus needed to elicit a muscular contraction.
  • All or None Response- This is the rule that if one muscle fiber contracts at all, the entire muscle will contract.
    • The size of stimulus does not matter.
    • The greater stimulus ≠ greater contraction.
Muscle Tone
  • Tonic: Tone. A continual, partial contraction
  • Tetanic contraction or tetanus: A continuous, forceful muscular contraction (spasm or cramp)
  • Hypertonic: A state of abnormally high tension (in a muscle)
  • Hypotonic: Lacking normal tension or tone (in a muscle)
Muscle Injury
  • Strains- Strains are an injury to either a muscle or a tendon.
  • Sprains- Sprains are an injury to a ligament.
  • Adhesion- An adhesion occurs when two tissues join abnormally.
  • Body movement and origins and insertions are covered in the Kinesiology section.