muscular system

• Muscular System


  The system responsible for all types of body movement - muscles contract or shorten and are the machine of the body

  
• Three basic muscle types


  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle

  
• Functions of muscles


  • Support the body
  • Allow for movement by making bones and other body parts move
  • Maintain constant body temperature
  • Assist in movement of cardiovascular veins and lymph
  • Protect internal organs and stabilize joints

  
• Skeletal muscles


  • They are organs containing muscle fibers, nerves, and blood vessels
  • Connective tissue membranes separate each muscle structure

  
• Coverings of a skeletal muscle from largest to smallest


  • Epimysium
  • Perimysium
  • Endomysium

  
• Tendon


  Cord-like structure that connects skeletal muscle to bone

  
• Sites of muscle attachment

  • Bones
  • Cartilages
  • Connective tissue coverings

  
• Muscle fiber (muscle cell)


  • Cells are multinucleate
  • Nuclei are just beneath the membrane
  • Sarcolemma - specialized plasma membrane
  • Sarcoplasmic reticulum - specialized smooth endoplasmic reticulum involved in muscle contraction
  • Myofibril - bundles of myofilaments

  
• Sarcomere


  Contractile unit of a muscle fiber

  
• Sarcomere


  • Thick filaments = myosin protein
  • Thin filaments = actin protein
  • Myosin filaments have heads (extensions) that can 'grab' onto actin forming a crossbridge
• Skeletal muscles must be stimulated by a nerve (motor neuron) to contract

  
• Transmission of nerve impulse to muscle

  1. Nerve releases neurotransmitter (acetylcholine)

  2. Neurotransmitter causes muscle cell membrane gates to open

  3. Ions (Na⁺ & K⁺) exchange places causing sarcoplasmic reticulum to release Ca²⁺

  4. Release of Ca²⁺ starts muscle contraction as actin filaments slide past myosin filaments
• Sliding Filament Theory of Muscle Contraction

  A muscle contracts when the thin filament in the muscle fiber slides over the thick filament, activated by ATP and calcium (Ca²⁺) ions

  
• Sliding Filament Theory of Muscle Contraction

  1. Ca²⁺ influx causes thick myosin filaments to form crossbridges with thin actin filament

  2. Crossbridges change shape, pulling on filaments which slides towards center of sarcomere in power stroke

  3. Crossbridges detach from actin filament when ATP bonds to myosin head

  4. Myosin head gets ready to bond to actin again using ATP energy

  
• Muscle contraction


  • Muscle fiber contraction is "all or none"
  • Within a skeletal muscle, not all fibers may be stimulated during the same interval
  • Different combinations of muscle fiber contractions may give differing responses
  • Muscle force depends upon the number of fibers stimulated

  
• Muscles can continue to contract unless they run out of ATP or Ca²⁺
• One molecule of ATP supplies enough energy for one actin and myosin cross-bridge
• Three ways for muscle to make energy (ATP)


  • Creatine Phosphate
  • Cellular Respiration
  • Fermentation (Anaerobic Respiration)

  
• Creatine Phosphate


  A high-energy compound that is the fastest way to make ATP available for muscles, used for activities lasting < 15 seconds, anaerobic (no oxygen needed)
• Cellular Respiration


  Mitochondria use glucose molecules to make ATP in the presence of oxygen, provides most of a muscle's ATP, aerobic (needs oxygen), used for activities lasting hours
• Anaerobic Respiration/Fermentation


  Reaction that breaks down glucose without oxygen, used for activities lasting 30 – 60 seconds, anaerobic (no oxygen)
• Heavy breathing after exercise is a sign of oxygen deficiency
• It takes up to two days to replace all of the glucose in the muscles and glycogen in the liver
• Insertion


  Attachment of a muscle to a moveable bone
• Origin


  Attachment of a muscle to an immovable bone
• Types of ordinary body movements


  • Flexion
  • Extension
  • Rotation
  • Abduction
  • Adduction
  • Circumduction
• Types of muscles


  • Prime mover
  • Synergist
  • Antagonist
• Factors used in naming skeletal muscles

  • Direction of muscle fibers
  • Relative size of the muscle
  • Location of the muscle
  • Number of origins
  • Location of the muscles origin and insertion
  • Shape of the muscle
  • Action of the muscle

  
• Muscles that are not used are replaced by connective tissue then by fat
• With age comes degeneration of mitochondria due to exposure to oxygen and free radicals
• Changes in the nervous system and endocrine system also effect structure and function of muscles
• Muscles become weaker as we age but exercise can stimulate muscle build-up
• Muscular Dystrophy


  Inherited, muscle enlarge due to increased fat and connective tissue, but fibers degenerate and atrophy

  
• Duchenne MD


  Lacking a protein to maintain the sarcolemma
• Myasthemia Gravis


  Progressive weakness due to a shortage of acetylcholine receptors
• Sprain


  Twisting of a joint leading to swelling and injury to ligaments, tendons, blood vessels and nerves
• Strain


  Overstretching of a muscle near a joint
• Myalgia


  Inflammation of muscle tissue
• Tendinitis


  Inflammation of the tendon due to strain of repeated activity