[LEC] Muscular System

• What are the three types of muscle tissue?

  Cardiac, skeletal, and smooth muscle
• What is the primary function of skeletal muscle?


  To facilitate movement and stability of the body
• What is the term for a muscle having its origin and insertion in the same body region?

  Intrinsic muscle
• What is the role of tendons in the muscular system?


  Tendons attach muscles to bones
• What are the functions of muscles?


  • Movement
  • Stability
  • Control of body openings and passages
  • Communication
  • Heat production
• What is the definition of flexion in muscle actions?


  Flexion is the action that bends a part of the body anteriorly
• What is the exception to the flexion of the knee?


  Flexion of the knee moves the lower leg posteriorly
• What is the sarcolemma?


  The sarcolemma is the plasma membrane of a muscle cell
• What is the role of the sarcoplasmic reticulum in muscle cells?


  It stores calcium ions necessary for initiating muscle contraction
• What are myofibrils composed of?


  Myofibrils are composed of thick and thin myofilaments
• What is a sarcomere?


  A sarcomere is the functional/contractile unit of a muscle fiber
• What do thick myofilaments consist of?


  Thick myofilaments consist of myosin subunits
• What is the function of tropomyosin in muscle contraction?


  Tropomyosin holds the actin chains together and covers binding sites
• What is the role of acetylcholine in muscle contraction?


  Acetylcholine stimulates muscle contraction by binding to receptors
• What happens when the threshold stimulus is reached in muscle contraction?


  The muscle cell will contract in an all-or-nothing manner
• What are the physiological characteristics of muscle tissue?


  1. Excitability: Ability to respond to stimuli
  2. Conductivity: Transmission of action potential
  3. Contractility: Ability to shorten with force
  4. Extensibility: Ability to stretch
  5. Elasticity: Ability to return to original shape
• What is excitation-contraction coupling?


  It links the electrical signal to muscle contraction
• What is the role of T tubules in muscle contraction?


  T tubules allow action potentials to enter the muscle cell
• What is the function of the enzyme acetylcholinesterase?


  It breaks down acetylcholine in the synaptic cleft
• What is the effect of depolarization in muscle cells?


  Depolarization generates an action potential along the muscle membrane
• What are the types of muscle actions?

  • Flexion
  • Extension
  • Abduction
  • Adduction
  • Protraction
  • Retraction
  • Dorsiflexion
  • Plantar flexion
  • Inversion
  • Eversion
  • Rotation
  • Circumduction
  • Supination
  • Pronation
  • Opposition
  • Reposition
  • Elevation
  • Depression
• What is the smallest unit of muscle organization?

  Myofilaments
• What is plantar flexion?


  Position of standing on tiptoes with the heels off the floor
• What is inversion in terms of foot position?


  Position in which the soles of the feet are together, facing each other
• What is eversion in terms of foot position?


  Position in which the soles of the feet point away from each other
• What does rotation refer to?


  The act of spinning on an axis
• What is circumduction?


  The act of making a circle with part of the body
• What is supination?


  Rotation that turns the palms up
• What is pronation?


  Rotation that turns the palms down
• What is opposition in terms of thumb movement?


  The act of bringing the thumb to the palm
• What is reposition in terms of thumb movement?


  The act of taking the thumb away from the palm
• What does elevation refer to in muscle movement?


  The act of closing the jaw or raising the shoulders
• What does depression refer to in muscle movement?


  The act of opening the jaw or lowering the shoulders
• What are the levels of organization of a muscle?

  • Myofilaments form myofibrils
  • Myofibrils form muscle fibers
  • Muscle fibers form fascicles
  • Fascicles form muscles
• What is the fibrous covering of an entire muscle called?

  Epimysium
• What surrounds each fascicle in a muscle?

  Perimysium
• What surrounds each muscle fiber?

  Endomysium
• What forms a tendon in muscle tissue?


  The connective tissues of the muscle come together at the end of the muscle fiber
• What are the structural components of a thigh muscle?

  • Myofilaments: smallest contractile units
  • Mitochondria: required for ATP production
  • Sarcoplasm: cytoplasm of the muscle cell
  • Sarcolemma: muscle cell membrane
  • Calcium depot: organelle that stores calcium ions
  • Triad: T tubule and two terminal cisternae
• What is the excitation-contraction coupling mechanism?


  1. Action potential propagates along the sarcolemma
  2. Depolarization opens gated Ca2+ channels in the SR
  3. Calcium ions bind to troponin, exposing active sites on actin
  4. Myosin heads bind to actin, forming cross-bridges