Myology, the study of muscles
Three different types of muscle
• Skeletal
– Move skeleton – Striated – Voluntary
• Cardiac
– Striated – Involuntary – Autorhythmicity
• Smooth
– Not striated – Usually involuntary – Some autorhythmicity
Major functions of muscle
• • • • • Regulating movement Stabilizing body positions Movement of materials around body Regulating body temperature Properties:
– – – – Excitability Contractility Extensibility Elasticity
Organization of skeletal muscle
• Superficial fascia separate muscle from skin • Deep fascia separate groups of muscles from each other
– Epimysium-entire muscle – Perimysium-fascicle – Endomysium- individual muscle fibers
Organization of a muscle fiber
“Sarco” refers to muscle
• Sarcolemma-excitable membrane (T tubules) • Sarcoplasm- glycogen, myoglobin, myofibrils • Sarcoplasmic reticulum
– Stores calcium – Triad- regulates calcium movement
Organization of the sarcomere
Muscle proteins
• Contractile proteins
– Actin, myosin
• Regulatory proteins
– Tropomyosin, troponin
• Structural proteins
– Titin, myomesin, dystrophin
Sliding filament model
The sliding filament mechanism
Roles of actin and myosin
The neuromuscular junction
Many drugs affect muscle function through effects on NMJ
• Botulism toxin
– Prevents release of acetylcholine
• Curare
– Blocks ACh receptors
• Tetanus toxin
– Blocks inhibitory neurons
Importance of Ach function
Myasthenia gravis
Botox treatment
Muscle tone
• Subset of muscle fibers produces continuous contraction
– Stabilizes but does not contribute to movement in skeletal muscles
• Too much: rigidity, too little- spasticity • Electrolyte imbalance
• Important in smooth muscle function
Types of muscle fibers
• Red and white • Slow oxidative fibers
– Lots of mitochondria, myoglobin – Good blood supply (oxygen) – Postural muscles
• Endurance
More muscle fibers
• Fast glycolytic fibers
– Largest; most powerful contractions – Poor blood supply (“white” fibers”) – Lots in arm muscles – Fatigue easily
• Fast oxidative-glycolytic fibers
– Intermediate – Use ATP faster than slow fibers – Lots in leg muscles
Cardiac muscle is specialized in the heart
Smooth muscle
• Single-unit
– Most common – Autorhythmic – Stimulation of one fiber spreads to another
• Multiple-unit
– Larger arteries, lungs, etc. – Only stimulated fiber is affected
Unique features of smooth muscle compared to skeletal muscle:
• Smooth muscle has longer, slower contraction • Calcium regulation method is different • Can stretch and still be able to contract • Best at regeneration