Muscle Response

1
Muscle Response

• How do muscles respond to
• stimuli as an organ?

2
Muscle Tension vs. Load

• Muscle Tension Force exerted by a muscle on an
  object.

• Muscle Load Opposite of tension, force exerted
  on the muscle by the weight of the object being
  moved

3
Isometric vs. Isotonic Contractions

• Isometric Contraction
• Muscle tension Muscle load
• Load does not move
• Isotonic Contraction Load moves
• Two Types
• 1. Concentric
• Muscle tension gt Muscle load
• Muscle shortens
• 2. Eccentric
• Muscle tension lt Muscle load
• Muscles lengthens

4
Motor Unit

• A motor neuron and all of the muscle fibers it
  innervates

5
Motor Twitch

• Response of a motor unit to a single action
  potential
• All-or-nothing contractions, no partial

The time course of the action potential is
indicated in A Longer development of tension of
the twitch contraction is shown in B.
6
Wave Summation

• describes response to successive action
  potentials.
• Frequency of stimuli increases
• .so, muscle cant fully relax between
  contractions
• and contraction force increases (wave summation)
• Twitches link together and fuse to become a
  smooth contraction (tetanus)

7
Tetanus

• No relaxation between action potentials
• Allows for smooth, continuous contraction
• (important in maintaining posture,
  sitting/standing upright)
• Degree of contraction/tetanus depends on
• Speed of stimulation
• Number of muscle fibers activated. (recruitment)
• 100 to lift a pencil
• 1000s to lift a barbell
• Order of recruitment controlled by size of
  fibers small motor units first.

8
Treppe

• A staircase pattern in strength of contraction.
• Initial contractions weaker than response to
  stimuli of same strength later
• Warm-up period of muscles
• Heat increases enzyme activity
• Increases in Ca2 availability in Sarcoplasmic
  Reticulum

9
Muscle Tone

• Constant action potentials in different motor
  units causing muscle to maintain a slight
  contraction.
• Muscle firm, ready to respond.

10
Energy for Contractions

• ATP
• Little ATP stored in muscles.
• 4-6 seconds worth
• Must be regenerated quickly.

11
Methods of regenerating ATP

• Methods of regenerating ATP
• Creatine phosphate (for sudden, high demands of
  ATP)
• CP stored in muscle
• Directly makes ATP by phosphate transfer
• Glycolysis (splitting of sugar, prior to CR)
• Cellular Respiration (aerobic, mitochondrial)
• Anaerobic respiration w/o enough O2, pyruvic
  acid made in glycolysis is converted into lactic
  acid
• to regenerate NAD for glycolysis to continue
• some ATP can therefore be formed through
  glycolysis.
• Causes muscle soreness and fatigue

12
Sports Activities and Energy

• Sports involving burst of power tennis, soccer,
  sprints, diving, volleyball
• Rely on creatine phosphate and ATP stores.
• Anaerobic respiration fuels ATP production
• Sports involving endurance cross-country,
  basketball, swimming.
• Fueled by aerobic respiration
• If demands are too great, switch to anaerobic and
  muscle fatigue will set in.

13
Muscle Fatigue

• Physiological inability to contract
• Lactic Acid Build up
• Not enough ATP to keep muscle working.
• Cramps occur when no ATP available to detach
  myosin heads

14
Oxygen Debt

• Amount of O2 needed to restore body back to
  proper state after exercise.
• Lactic acid is converted back to pyruvic acid.
• New ATP and creatine phosphate made.
• Ion levels restored Na, K, Ca2