Muscular System

• Fascia

  Connective tissue that covers individual muscles.
• aponeuroses

  Connects muscle to muscle. Sheet-like connective tissue.
• Two sources of energy for muscle contraction:

  • Creatine phosphate: naturally made in the liver and kidneys, some people take it as a supplement
  • Cellular respiration
• Creatine phosphate stores energy that quickly converts ADP to ATP
• Supplement version of creatine phosphate can be taxing on the kidneys
• Cellular respiration occurs in two phases:

  • Anaerobic phase (no oxygen): Glycolysis occurs in the cytoplasm, producing little ATP
  • Aerobic phase (oxygen): Citric acid cycle and Electron transport system occur in the mitochondria, producing most ATP
• Myoglobin stores extra oxygen in muscles
• Oxygen debt: amount of oxygen needed by liver cells to use accumulated lactic acid to produce glucose
• Muscle fatigue can be caused by decreased blood flow and ion imbalances across the sarcolemma
• Doctors recommend taking magnesium supplements to help relax muscles and prevent constant contractions
• Calcium needs magnesium to help with absorption
• Potassium is important for muscle function and high blood pressure
• Accumulation of lactic acid can lead to a burning sensation, cramps, and tetany

  Lactic Acid is a byproduct of the Anaerobic Phase and it helps produce energy without using oxygen
• Heat production in muscles is a byproduct of cellular respiration
• Myogram is used to measure the contractility of a muscle fiber
• Threshold stimulus is the minimal strength required to cause muscle contraction
• Summation occurs when individual twitches combine to create a sustained contraction
• Recruitment of motor units increases the number of activated motor units for muscle movement
• Muscle tone is a continuous state of partial contraction
• Types of muscle contractions:

  • Isotonic: muscle contracts and changes length (concentric and eccentric)
  • Isometric: muscle contracts but does not change length
  • Concentric muscle shortens the muscle.
  • Eccentric muscle lengthens the muscle
• Fast twitch fibers and slow twitch fibers have different characteristics and functions
• Slow twitch fibers (Type 1) are always oxidative, resistant to fatigue, and have good blood supply
• Fast twitch fatigue fibers (Type 2B) are intermediate fibers, resistant to fatigue, and have an intermediate amount of myoglobin
• Fast twitch glycolytic fibers (Type II A) are white fibers, have poorer blood supply, and are susceptible to fatigue
• Masseter:

  • Located on the lateral surface of the mandible (lower jaw)
  • Considered the strongest muscle in the body
  • Helps with chewing and always pulls up the mandible
• Epicranius:

  • Originates from the occipital bone
  • Responsible for raising the eyebrows
• Sternocleidomastoid:

  • Strong muscle on the sides of the neck
  • Helps with turning the neck and elevating the sternum
• Platysma:

  • Starts at the chin and drapes down the neck
  • Used when sad and pouting to pull the lower jaw down
• Orbicularis oculi:

  • Activated whenever you blink
• Orbicularis oris:

  • Muscle around the mouth used when puckering lips
• Buccinator:

  • Located towards the cheek
  • Utilized when compressing the cheeks, like when whistling or blowing air out
• Trapezius:

  • Located on the back, giving a v-back look
  • Extends from the shoulders to the thoracic area of the back
  • Responsible for rotating and moving the scapula
• Deltoid:

  • Rounded area of the shoulder and upper arm
  • Helps in keeping the shoulders back
• Latissimus dorsi:

  • Large back muscle that extends, adducts, and rotates the arm medially
  • Assists in rotating the shoulder back and helps in maintaining an upright posture
• Pectoralis major:

  • Muscle that flexes and adducts the arms
  • Rotates the arm medially
• Pectoralis minor:

  • Raises the ribs during deep breathing
  • Assists in pulling the scapula forward
  • Located in the pectoral girdle and underneath the pectoralis major
• Rectus abdominis:

  • Creates the "6 pack" appearance
  • Flexes the vertebral column and contracts in the abdominal area
  • Tenses the abdominal wall and contents of the stomach
• Gluteus maximus:

  • Largest muscle in the body
  • Extends the hip, useful for kicking a soccer ball
• Gluteus medius:

  • Located underneath the gluteus maximus
  • Also extends the hip
• Hamstrings:

  • Comprised of the biceps femoris, semimembranosus, etc
  • Flex the knee and rotate the leg