topic 3

• 2 types of isotonic contractions

  concentric and eccentric
• concentric contractions


  muscle shortens; muscle tension exceeds the load
• eccentric contractions


  tension increases; muscle lengthens because the force of the load is greater than the muscle tensions
• isometric contractions


  no shortening; muscle tension is constant and does not exceed the load
• motor unit


  a motor neuron and all muscle fibers it supplies
• muscle twitch


  response of a muscle to a single, brief threshold stimulus
• 3 phases of a twitch

  latent period

  period of contraction

  period of relaxation
• latent period


  events of excitation contraction coupling
• period of contraction


  cross bridge formation; tension increases
• period of relaxation


  ca2+ re-entry into the sr; tension declines to zero
• graded muscle responses


  variations in the degree of muscle contraction

  required for proper control of skeletal movement
• muscle responses are graded by

  changing the frequency of stimulus and changing the strength of the stimulus
• muscle tone


  refers to the constant, slightly contracted state of all muscles

  due to spinal reflexes that activate groups of motor unit alternately in response to input from stretch receptors in muscles
• ways to get energy for contraction

  1. direct phosphorylation

  2. anaerobic pathway

  3. aerobic pathway
• direct phosphorylation


  Coupled reaction of creatine phosphate (CP) and ADP
• anaerobic pathway


  glycolysis and lactic acid formation, energy source: glucose
• aerobic pathway


  aerobic cellular respiration

  energy source: glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism

  oxygen use: required
• oxygen deficit


  negative effect of not meeting the bodys o2 needs during activity
• oxygen debt


  extra o2 needed after exercise for replenishment of oxygen reserves, glycogen stores, atp and cp reserves, reconversion of lactic acid to pyruvic acid, conversion of lactic acid in the blood to glucose or glycogen by the liver
• muscle fatigue


  physiological inability to contract
• muscle fatigue occurs when

  Ionic imbalances (K+, Ca2+, Pi) interfere with E-C coupling

  Prolonged exercise damages the SR and interferes with Ca2+ regulation and release
• signs of rigor mortis

  no obvious muscle stiffness

  molecular death

  cold body temperature

  no muscle response to electrical stimuli

  acidic muscle ph

  provides information about time of death

  onset 2-4 hours

  peak 12-13 hours

  fade 50-60 hours
• signs of cadaveric spasm

  extreme muscle stiffness

  no molecular death before rigor mortis

  warm body temperature

  muscle response to electrical stimuli

  alkaline muscle ph

  provides mode of death

  onset immediate

  peak immediate

  fades never
• factors affecting the force of muscle contraction

  1. Number of Muscle Fibers Recruited: the more motor units recruited, the greater the force

  2. Size of Muscle Fibers: Bigger=more tension developed. regular resistance exercise increases muscle force by causing muscle cells to hypertrophy (increase in size)

  3. Frequency in Stimulation: the higher the freq the greater the force the muscle exerts. when a muscle is stimulated more frequently, contractions are summed, becoming more vigorous and producing tetanus.

  4. Degree of Muscle Stretch: Ideal Length-Tension relationship occurs when the muscle is stretched and the thin and thick filaments overlap optimally which permits sliding along the entire length of the thin filaments.
• recruitment


  results in a faster contraction and a longer duration of contraction
• muscle system disorders can be caused by

  injury or overuse

  genetics

  infection and inflammation

  cancer

  reactions to drugs and medications
• many muscle system disorders are also linked to the nervous system

  Parkinson's disease

  muscular disease

  myasthenia gravis

  amyotrophic lateral sclerosis

  fibromyalgia
• why the latent period occurs

  1. the action potential has to be fully spread along the sarcolemma to the t-tubules of the muscle fiber

  2. only then can the ca+ channels open to release ca+ into the sarcolemma

  3. it takes time for the ca+ to bind to the troponin-tropaseyosin complex