Muscle Contraction I Department of Biology, WCU

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

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

Muscle contraction 1. Muscle twitch single threshold stimulus myograph

Muscle twitch Periods i. Latent period

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

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

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

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

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

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

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

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

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

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