Introduction to Muscle Contraction Flashcards
A complex consisting of a T tubule and usually two small cisternae of sarcoplasmic reticulum is known as a _______________
Triad
At the __________, depolarization of the sarcolemma-derived T tubules is transmitted to the sarcoplasmic reticulum membrane
Triad
Muscle contraction depends on the availability of _____________ and its relaxation is related to the absence of ____________
Calcium ions
Calcium ions
The sarcoplasmic reticulum specifically regulates ___________ flow, which is necessary for rapid contraction and relaxation cycles
Calcium
What neutransmitter stiumlates a nerve impluse?
Acetylcholine
There are three overall steps to muscle contraction:
- Neurally mediated depolarization of the __________________
- ______________ are passively released into the vicinity of overlapping thick and thin filaments
- ______________ binds to ________________, allowing actin and myosin to bridge together
Sarcoplasmic reticulum
Calcium
Calcium
Troponin
Initiation of the nerve impulse:
A nerve impulse triggers release of ___________________ from the synaptic knob inAto the synaptic cleft. This neurotransmitter then binds to its receptors in the ____________________ of the neuromuscular junction, initiating a muscle impulse in the __________________ of the muscle fiber
As the muscle impulse spreads quickly from the ___________________ along ___________________, _____________________ ions are released from terminal cisternae into the sarcoplasm
Acetylcholine
Motor end plate
Sarcolemma
Sarcolemma
T-tubules
Calcium
Muscle contraction:
________________ ions bind to ___________________, which changes shape and moves ____________________ onto actin. This exposes active sites on actin molecules so that __________________ heads of thick filaments can attach to the exposed active sites, forming ______________________
As __________________ heads pivot, the thin filaments move toward the __________________ center. _________ binds myosin heads and is broken down into ______________ at which point the myosin heads detach from the filaments and return to their pre-pivot position
Calcium
Troponin
Tropomyosin
Myosin
Crossbridges
Myosin
Sarcomere
ATP
ADP and P
The power stroke: __________ is released from the sarcoplasmic reticulum where it binds to ________________, which changes conformation and pulls _____________ away so as to expose _____________-binding sites on the actin filament. __________ ____________ bind to actin, which releases its _______. In the __________________, the myosin head changes conformation and the thick and thin filaments slide past each other. _______ binds to myosin, casuing myosin to release actin.
If calcium is returned to the sarcoplasmic reticiulum, the muscle relaxes; if calcium remains available, the cycle repeats
Calcium
Troponin
Tropomyosin
Myosin-binding sites
Myosin heads
ADP
Power stroke
ATP
___________________ sarcomeres consist of partially overlapping thick and thin filaments
Resting
_______________ sarcomeres consist of increased overlap between thick and thin filaments
Contracting
During muscle contraction, do thick or thin filaments change their lengths?
No; contraction is the result of an increase in the amount of overlap between the filaments caused by the sliding of thin and thick filaments past one another
Contraction is induced by an _________________ produced at a ___________________, the neuromuscular junction, between the muscle fiber and terminus of a motor axon
Action potential
Synpase
What visible changes result when a muscle becomes contracted?
The I band decreases in size
the H zone becomes significantly contracted and can be used to identify quickly whether a sarcomere is relaxed or contracted
During contraction the ____________ decreases in size as thin filaments penetrate the _____________
I band
A band
During contraction, the ___________, part of the _________ with only thick filaments, diminishes in width as the thin filament completely overlap the thick filaments
H band
A band
The net result of contraction is that each sarcomere and subsequent muscle cell (fiber) is greatly ___________________
Shortened
Where does the neural signal for contraction come from?
Neuromuscular junction or the motor end-plate
At the synaptic cleft, the sacrolemma has numerous deep folds to increase the _______________ available to receive chemical transmitting signals
Surface area
Muscle Tissue Innervation Steps #1 - 4:
- The action potential reaches the _______________
- ______________ is released from the axon terminal
- This neurotransmitter diffuses across the synaptic celft and binds its receptors in the folded _____________
- Binding of the neurotransmitter opens _______ changes in the sacrolema and produces membrane depolarization
Motor end plate
Acetylcholine
Sarcolemma
Na+
Muscle Tissue Innervation Steps #5 - 7
- Depolarization initated at the motor end-plate is _____________ along the surface
- The signal is passed to the ___________________ a, which releases ______________ that initate the contraction cycle
- When depolarization ceases, the _____________ is actively transported back into the sarcoplasmic reticulum cisternae and the muscle relaxes
Propagated
Sarcoplasmic reticulum
Calcium ions
Calcium ions
A single nerve fiber or ____________ can innervate one muscle fiber or branch and innervate hundred of fibers
Axon
A single nerve fiber and all of the muscle fibers it innervates is called a _____________________
Motor unit
Do individual striated muscle fivers should graded contraction?
No, they contract either all the way or not at all
What do we mean by varied force?
Fibers within a muscle bundle do not all contract at the same time; since muscles are composed of many motor units, the firing of a single motor axon will generate tension proportional to the number of muscle fibers innervated by that axon
