Lecture 8: The Physiology of Muscle

• What exists across the membranes of virtually all cells in the body?

  Electrical potentials
• What type of cells can generate rapidly changing electrochemical impulses?

  Nerves and muscle cells
• How are muscles classified according to structure?

  • Striated Muscle
  • Smooth Muscle
• How are muscles classified according to nerve innervation?

  • Voluntary Muscle
  • Involuntary Muscle
• How are muscles classified according to function?

  • Skeletal Muscle
  • Cardiac Muscle
  • Smooth Muscle
• What type of muscle makes up the great mass of somatic musculature?

  Skeletal muscle
• What appearance does skeletal muscle have due to its microstructures?

  Striated appearance
• What does the term "voluntary" refer to in skeletal muscle?

  It can be controlled consciously
• What is the characteristic of skeletal muscle fibers regarding nuclei?

  They are multinucleated
• How many nerve endings usually innervate each skeletal muscle fiber?

  Usually one nerve ending
• What are the functions of skeletal muscle?

  • Production of force for locomotion and breathing
  • Production of force for posture
  • Heat production during cold stress
• What binds muscle fibers together?

  Connective tissue
• What covers individual skeletal muscle fibers?

  Endomysium
• What are bundles of muscle fibers called?

  Fascicles
• What encases the fascicles in skeletal muscle?

  Epimysium
• What is the plasma membrane of a muscle fiber called?

  Sarcolemma
• What cylindrical structures do muscle fibers contain?

  Myofibrils
• What pushes the nuclei to the outer edge of muscle fibers?

  Myofibrils
• What are the light and dark bands in myofibrils called?

  I bands and A bands
• What is the Z line or Z disc associated with?

  The I band
• What is the H zone in myofibrils?

  Light zone in the middle of the A band
• What is the basic contractile unit of the muscle fiber called?

  Sarcomere
• What does an individual sarcomere extend from?

  One Z line to another
• What are the two major types of myofilaments?

  Thick myosin and thin actin myofilaments
• What are thick myofilaments made up of?

  Proteins called myosin
• How are myosin molecules shaped?

  Like golf clubs with long shafts
• Where do the myosin tails point in the sarcomere?

  Toward the center of the sarcomere
• What do the heads of myosin filaments form with actin?

  Cross bridges
• What do the heads of thick myofilaments use to power muscle contraction?

  Energy in the ATP molecule
• What are thin myofilaments composed of?

  Protein actin
• What do thin myofilaments have that allows myosin heads to attach?

  Binding sites
• What is attached to each actin molecule?

  One molecule of ADP
• What is the backbone of the actin filament made up of?

  Double-stranded F-actin molecules
• What are believed to be the active sites on actin filaments?

  ADP molecules
• What do tropomyosin molecules do during the resting state?

  Lie on top of the active sites of actin
• What is troponin made up of?

  Three loosely bound protein subunits
• What does troponin I have a strong affinity for?

  Actin
• What does troponin T have a strong affinity for?

  Tropomyosin
• What does troponin C have a strong affinity for?

  Calcium ions
• What serves as the storage site for calcium within the sarcoplasm?

  Sarcoplasmic reticulum