skeletal muscles- contraction prof. k. sivapalan
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Skeletal Muscles- Contraction
Prof. K. Sivapalan
Skeletal Muscle Contraction 2
Actin Filament
• It is made up of actin, tropomyosin and troponin.
• Troponin I is bound to actin and tropomyosin and covers the myosin binding site
• Ca++ binds to Troponin C
• This causes exposure of Myosin binding site.June 2013
Skeletal Muscle Contraction 3June 2013
Skeletal Muscle Contraction 4
Myosin Filament
• Myosin has a head and a tail
• Each filament may have 200 or more myosin molicules
• The tails are bundled as the body while the heads hang outwards on a small arm – cross bridge
• The head has ATPase activity
• The cross bridge is flexible at hingesJune 2013
Skeletal Muscle Contraction 5
Contraction
June 2013
Skeletal Muscle Contraction 6
Sliding of Actin on Myosin
• At rest ATP binds to the head of the myosin, converted to ADP, the energy stored in the head.
• At this state, the head is perpendicular to the filament.
• When binding site of the actin is exposed, actin – myosin binding occurs.
• This binding changes the conformation of the cross bridge and causes ‘power stroke’ with energy stored as a ‘cocked spring’
• the stroke results in detachment of the cross bridge, release of ADP and attachment of another ATP
June 2013
Skeletal Muscle Contraction 7
Muscle Twitch- Experimental Design
June 2013
Skeletal Muscle Contraction 8
Muscle Twitch
• When one single stimulus is given, the muscle contracts and relaxes after a latency
• The latency is the time taken for excitation- contraction coupling
June 2013
Skeletal Muscle Contraction 9
Staircase Phenomenon
June 2013
Skeletal Muscle Contraction 10
Summation
June 2013
Skeletal Muscle Contraction 11
Tetanization
June 2013
Skeletal Muscle Contraction 12
Length – Strength
• The force developed by the muscle depends on the length of the muscle.
• It increases to maximum and then decreases.
June 2013
Skeletal Muscle Contraction 13
Actin-Myosin Overlap and Tension Developed
• When muscle shortened, action myosin linkages are less.
• When the length increases, more and more linkages become possible
• When over stretched, again linkages are less
June 2013
Skeletal Muscle Contraction 14
Motor Units and Strength
• Muscle fibers innervated by one axon constitute one motor unit.
• The size of the motor unit is the number of muscle fibers in it.
• The tension developed will depend on the number of myofibriles in each fiber and the size of the motor unit.
June 2013
Skeletal Muscle Contraction 15
Fast and Slow Fibers
• Muscle fibers vary in myosin ATPase activity, contractile speed and other properties
• The muscles can contain a mixture of three fiber types: – type I (or SO for slow-oxidative);
– type IIA (FOG for fast-oxidative-glycolytic)
– type IIB (FG for fast glycolytic).
June 2013
Skeletal Muscle Contraction 16
Muscle Type and Response
June 2013
Skeletal Muscle Contraction 17
Fiber Types
SO FOG FGColour [Myoglobin] Red Red White Myosin ATPase Slow Fast FastCa++ pumping out Moderate High High Diameter Small Large LargeGlycolytic capacity Moderate High High Oxidative capacity High Moderate Low
June 2013
Skeletal Muscle Contraction 18
Metabolism in Muscle
• Glucose and free fatty acids
• Oxygen debt mechanism
• Importance of glycogen and myoglobin
• Depends on the muscle type
• Genetic suitability to type of sports
• Alcohol and muscle performance
June 2013
Skeletal Muscle Contraction 19
Electromyography- EMG
June 2013
Skeletal Muscle Contraction 20June 2013
Skeletal Muscle Contraction 21
Effects of Denervation
• Atrophy – less myofibrils
• Fibrillations- receptor hypersensitivity
• Fasciculation – motor unit function
June 2013
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