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Lecture 12

PNB 2264 Lecture Notes - Lecture 12: Muscle Fatigue, Myosin Light Chain, Contracture

Physiology and Neurobiology
Course Code
PNB 2264

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Macro properties
- Power
o Defined as the ebility to move a load (weight) quickly
o Whats the most powerful muscle in the human body
- Speed
o The speed at which a muscle can shorten and move a load
o Whats the fastest human muscle
- Endurance
o How long can a muscle maintain tension?
o Which muscles have te greatest endurance?
What to consider
- Tension length curve
o Maximal cross-bridge formation
o Optimal length
o Too far no CBs, no tension
o Too close no CBs, no tention
- Tension velocity curve
o Dependent on load
o Load = 0, maximum velocity
o Load = infinity, velocity = 0
Power (strength) generation
- Contraction velocity times tention (T x V = P)
- Isometric, P = 0 (T x 0 = 0
Factors affecting strength
- Muscle length
- NMJ No.
o Equals Muscle activation equals tension
- Training
- Biomechanics
o Equals Levers, force angle, moment arm, length, joints, soft tissues equals
- Cross-sectional area
o Equals Cross-bridge density equals tension
Strongest muscle
- Muscles always work in groups
o Hip flexor pull up the knee
Psoas major and minor, iliacus, rectur femoris, Sartorius, tensor fasciae
latae, pectineus, adductor longus and brevis and gracilis
- Muscles that move the eye
o Can move the eye very fast, therefore they are very powerful
- Endurance, nothing beats the heart
o Continuously puts out 1 to 5 watts
o Puts out enough energy to lights a 100 watt light bulb for 1 year
o Over a lifetime, puts out 3 gigajoules of power
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Muscle efficiency
- Power/metabolic cost
- No power, efficiency = 0
- Isometric no power, no load moved, efficiency = 0
- Highest efficiencies highest power/least cost
- Isolated muscle prep 65%
- In humans exercising
- 14% to 27% (rowing and cycling)
- increased by training
Muscle fatigue
- inability to do work
- asthenia psychological very common; diet, emotional state, training
o protective to prevent muscle damage from overuse
- muscular
o less common; ATP depletion, O2 availability K+, Mg, Cl- build up within muscle
- Synaptic
o Least common, NMJ problems
Chronic disease like ALS
- Amyotophic lateral sclerosis
o Motor neuron degeneration
Contracture and rigor mortis
- Insufficiency of ATP, cannot relax, strenuous activity
Energy sources
- ATP seconds worth
o Constantly made and lost
- Creatine phosphate like ATP 10 to 12 seconds
o Temporary storage pool
- Anerobic metabolism no O2 3 minutes
o Rapid burst of power for short periods
- Aerobic metabolism with O2 long time, slow develop
Fiber types
- Carcomeres are the same
- Different performance
- 4 basic types
- types 1
- extensice vascularization
- slow ATPase activity
- high aerobic/low anaerobic
- numerous mitochondria
- CNS slow response
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