Muscular system

• Myology


  The scientific study of muscles
• Types of muscular tissue

  • Skeletal
  • Cardiac
  • Smooth
• Skeletal muscle tissue


  • Most skeletal muscles move the bones of the skeleton
  • Striated: Alternating light and dark protein bands (striations) are seen when the tissue is examined with a microscope
  • Works mainly in a voluntary manner
  • Activity can be consciously controlled by neurons (nerve cells) that are part of the somatic (voluntary) division of the nervous system
  • Also controlled subconsciously to some extent
• Cardiac muscle tissue


  • Only the heart contains cardiac muscle tissue
  • Striated
  • Action is involuntary
  • Has a natural pacemaker that initiates each contraction (autorhythmicity)
  • Heart rate can be adjusted by hormones and neurotransmitters
• Smooth muscle tissue


  • Located in the walls of hollow internal structures
  • Lacks the striations of skeletal and cardiac muscle tissue
  • Action is usually involuntary
  • Some has autorhythmicity
  • Regulated by neurons that are part of the autonomic (involuntary) division of the nervous system and by hormones
• Functions of muscular tissue

  • Producing body movements
  • Stabilizing body positions
  • Storing and moving substances within the body
  • Generating heat
• Producing body movements


  • Movements of the whole body and localized movements rely on the integrated functioning of skeletal muscles, bones, and joints
• Stabilizing body positions


  • Skeletal muscle contractions stabilize joints and help maintain body positions
  • Postural muscles contract continuously when awake
• Storing and moving substances within the body

  • Storage is accomplished by sustained contractions of ringlike bands of smooth muscle called sphincters
  • Cardiac muscle contractions in the wall of the heart pump blood
  • Contraction and relaxation of smooth muscle in the walls of blood vessels help adjust blood vessel diameter and regulate blood flow
  • Smooth muscle contractions move food, substances, and gametes through various systems
  • Skeletal muscle contractions promote the flow of lymph plasma and aid the return of blood in veins to the heart
• Generating heat


  • As muscular tissue contracts, it produces heat (thermogenesis)
  • Involuntary contractions of skeletal muscles (shivering) can increase the rate of heat production
• Properties of muscular tissue

  • Electrical excitability
  • Contractility
  • Extensibility
  • Elasticity
• Electrical excitability


  Ability to respond to certain stimuli by producing electrical signals called action potentials
• Contractility


  Ability of muscular tissue to contract forcefully when stimulated by a nerve impulse
• Extensibility


  Ability of muscular tissue to stretch, within limits, without being damaged
• Elasticity


  Ability of muscular tissue to return to its original length and shape after contraction or extension
• Connective tissue components


  • Subcutaneous tissue (hypodermis)
  • Fascia
  • Epimysium
  • Perimysium
  • Endomysium
• Subcutaneous tissue (hypodermis)


  • Composed of areolar connective tissue and adipose tissue
  • Provides a pathway for nerves, blood vessels, and lymphatic vessels
  • Adipose tissue stores triglycerides, insulates, and protects muscles
• Fascia


  • Dense sheet or broad band of irregular connective tissue
  • Lines the body wall and limbs
  • Supports and surrounds muscles and other organs
  • Allows free movement of muscles
  • Carries nerves, blood vessels, and lymphatic vessels
  • Fills spaces between muscles
• Epimysium


  • Outer layer, encircling the entire muscle
  • Consists of dense irregular connective tissue
• Perimysium


  • Layer of dense irregular connective tissue
  • Surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called muscle fascicles
• Endomysium


  • Penetrates the interior of each muscle fascicle and separates individual muscle fibers from one another
  • Mostly reticular fibers
• The epimysium, perimysium, and endomysium are all continuous with the connective tissue that attaches skeletal muscle to other structures, such as bone or another muscle
• Tendon


  Ropelike connective tissue that attaches a muscle to the periosteum of a bone
• Aponeurosis


  Broad, flat sheet of connective tissue