1. Muscle Contraction I
Department of Biology, WCU

2. Motor unit
spinal cord, motor nerve, axons, axonal terminals, muscle fiber
motor neuron and muscle fibers

3. Motor unit Number of fibers per motor unit Small motor units
fine control (fingers, eyes)
Large motor units
course control (arms, legs)

4. Muscle contraction
1. Muscle twitch
single threshold stimulus
myograph

5. Muscle twitch
Periods
i. Latent period

6. Muscle twitch
ii. Period of contraction
iii. Period of relaxation

7. Frequency of stimulation
Short bursts
Increase in frequency
Further increase in frequency

8. Muscle contraction 2. Isotonic contraction Muscle contracts (shorten)
muscle tension vs load
Muscle contracts (shorten)
Tension mostly constant (biceps curl)

9. Muscle contraction 3. Isometric contraction 4. Combination
tension without contraction
e.g. posture, immovable object
4. Combination
movement requires both isotonic and isometric contraction

10. Energetics Muscles store limited energy ATP generation
1. Creatine phosphate
quick energy

11. Energetics 2. Aerobic respiration O2 from Hb, myoglobin Mitochondria
slow, high energy

12. Energetics 3. Anaerobic respiration Glucose from glycogen, blood
Pyruvic acid
quick, low energy

13. Fatigue Psychological Physiological ATP production less than usage
depletion of neurotransmitter (later lecture)

14. Types of skeletal muscle
1. Red
Slow contractions
Color - myoglobin (more O2)
Aerobic pathway
Slow oxidative fibers
e.g. abdominal and back muscles (posture), marathon runners

15. Types of skeletal muscle
2. White
Fast contractions
Color - few mitochondria (only glycolysis)
Anaerobic pathway
Fast glycolytic fibers
e.g. movement muscles (arms, legs), sprinters