Muscle Contraction Flashcards
What kind of receptor does skeletal muscle have?
Nicotinic
Motor nerves release ____
acetylcholine
The acetylcholine-nicotinic receptor interaction results
in the nicotinic receptor opening as a sodium channel
Skeletal muscle depolarization causes activation of __________
L calcium channels (dihydropyridine receptors)
Calcium entry into muscle releases calcium from intracellular storage sites (sarcoplasmic reticulum) via ___________
calcium-induced calcium release (ryanodine receptors - physically coupled, don’t actually need Ca to go into cell)
Elevated intracellular calcium concentrations result in _______
calcium binding to troponin C
calcium binding to troponin C
—-> ____________
releases inhibition of actin-myosin interactions
______ heads then contact ________ to create muscle shortening and force generation, provided ________ is present
Myosin - actin
Requires ATP
acetylcholinesterase
breaks down acetylcholine into choline and acetate to stop signal
______ indicate borders of sarcomere
Z lines indicate borders of sarcomere
Muscle __ band remains same size but ____ bands decrease in width
A band
I band
Power stroke occurs as a result of _______
Release of Phosphate after cleaving ATP –> ADP + Pi which cocked the myosin head
When is ADP released during muscle contraction?
During/because of power stroke
_______ allows myosin head to be released from actin
Binding of ATP
Amyotrophic lateral sclerosis
degeneration of motor neurons
Lambert-Eaton syndrome
antibodies against Ca channels in motor neurons resulting in inability to release Ach
Botulism toxin
prevents Ach release by cleaving synaptic associated proteins (SNAPs)
Myasthenia gravis
autoantibodies against nicotinic receptors in skeletal muscle
Malignant hyperthermia
caused by mutation of ryanodine receptor allowing excessive release of Ca - usually triggered by anesthetics
Duchenne’s muscular dystrophy
mutation in dystrophin, skeletal muscle support protein
Pesticides and nerve gases
Pesticides and nerve gases are anticholinergics (acetylcholinesterase inhibitors) → overstimulation of nicotinic receptors
Amount of force generated by muscle directly proportional ______
to number of actin-myosin crossbridges per cross-sectional area
Work best when considerable overlap between actin and myosin
Stretched muscle → actin/myosin no longer interacting → no strength
As shorten muscle → actin and myosin interacting, force increases linearly
Maximal point - maximal # cross bridges (no more in center)
If go past that - disordered by no more cross bridges
Force-velocity relationship
Muscles contract most rapidly when there is no load on the muscle
Isotonic contraction
Load on muscle is constant
Isometric contration
Load is larger than muscle’s ability to move it (shorten tendon, but can’t move bony attachment)
Type I muscle Fiber
Slow twitch
Slower myosin ATPase enzyme
High proportions in distance runners or in postural muscles (soleus)
Contain lots of myoglobin → “Red Fibers”
Need myoglobin because they require a lot of oxygen to maintain contractions
Type II muscle fiber
High proportions in extraocular muscles of eye
Faster myosin ATPase
White fibers (less myoglobin)
Anaerobic metabolism
Concentric contractions
Muscle contracts resulting in shortening
Typical biceps curl in weightlifting
Eccentric contractions
Muscle lengthens while attempting to shorten Much more damage to muscle with this type of contraction Running downhill (trying to contract while stretching)
Muscle conduction to contraction
AP depolarization opens presynaptic VG Ca channels inducing NT release –> Postsynaptic ligand binding leads to muscle cell depolarization in motor end plate –> depolarization travels along muscle cell and down Ttubule –> Depolarization at Voltage-sensitive DHP receptor, mechanically coupled to ryanodine receptor on SR, induced conformational change causing Ca release from SR –> release Ca binds to troponin C causing conformational change that moves tropomyosin out of myosin-binding groove on actin filaments –> myosin releases bound ADP and Pi - displacement of myosin on actin filament (power stroke) –> binding of new ATP molecule causes detachment of myosin head from actin filament, hydrolysis of ATP to ADP + Pi cocks head
Contraction of muscles results in what of bands
H and I bands shorten between Z lines (HIZ shrinkage)
A band is Always same length
Darker regions contain ______
Lighter regions contain ______
dark - myosin
lighter - actin
Motor neurons release _____
acetylcholin
Cardiac muscle has ___ channels, more reliant on
L channels, ca-induced-ca-release (not physically coupled)
Smooth muscle contraction controlled by
Ca interacting w/ calcium dependent myosin light chain kinase
