Total tension formula
Passive force(preload) + active force
Isometric twitch
Muscle developes force but does not shorten.
- myosin pulls on actin but there is no movement (no contraction)
- TENSION is the key word…tension is created from actin and myosin pulling
- length stays the same but force does not
What happens to your total force as your preload force goes up ?
It increases
-spring will cause more force when contraction occurs
What is active force ?
Represents sacromere contraction
When does the muscle shorten ?
When the tension is greater than the load
Afterload
The force the muscle must generate on top of the passive force(preload) for the muscle to contract
What is constant during isometric and isotonic phases ?
Length is constant during the isometric phase and force is constant during the isotonic phase
What is the force velocity relationship
The less force the higher the velocity…also the greater the length
Why are isotonic contractions important
They are used to determine force velocity relationships
Why is the isometric contraction important ?
Force-length curve
Sliding filament theory
During contraction both thick and thin filaments keep the same length but the amount of overlap increases
-thin filaments slide towards center of sacromere and the distances between the Z line shortens
What is part of the triad for skeletal muscle contraction
Sarcoplasmic reticulum, receptors(dihyrdopyridine voltage center and ryanodine), t tubules
Why can you say skeletal muscle requires neuronal action potential for stimulation ?
Because skeletal muscle contraction can occur in the absence of extracellular calcium
Myasthenia gravis
Weakness worse as the day goes on . Autoimmune that attacks nicotinic reports at NMJ.
- ptosis with repeated blinking, jaw gets tired and diplolpia
- antibody therpay can be used but is more extreme then just giving cholinesterase
Curare
Bind to ACh receptors and block ACh from binding to open cation channels thus PREVENTING DEPOLARIZATION.
- die from respiratory muscles stop working even though heart is fine
- patient can survive with artificial respiratory until poison goes away
- now used as a muscle relaxant during surgery
Succinylcholine and decamethonium
Causes cation channels to stay open causing persistent depolarization thus relaxant of muscle if depolarizer for too long
What does contraction mean ?
Interaction of myosin with actin to generate force of tension
- can have contraction without muscle shortening
- during isometric contraction there is muscle contraction
What prevents force as such short length of the sacromere ?
Actin filament overlap on each other is hiding the active sites for myosin to bind onto
What does maximum velocity represent and what determines Vmax ?
The maximum velocity represents the velocity at which there is no load. This value is determined by the muscles ATPase activity
What does increasing Afterload do to velocity until the load cannot be moved ?
Increasing Afterload decreases velocity
Tetanus
Successive stimulation with no relaxtio between contraction.
Tetanus toxin blocks inhibitory NTs in the CNS. You get unrestrained alpha neuron stimulation and sustained skeletal contractions
EXAMPLE OF TEMPORAL SUMMATION
Spatial summation is the same as what ?
It is the same as recruitment. Force increases by increasing the number of motor units activated at one time
What is a motor unit
It is made up by all of the muscle fibers ONE motor neuron innervates
