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what is the neuromuscular junction?
region where a motor neuron communicates with a skeletal musle fiber
how does the acetylcholine (ACh) cross to the sarcolemma?
- axon terminal of the neuron vesicles filled with ACh can cross the synaptic cleft to bind to receptors on the sarcolemma
- ACh binds to receptor on the motor end plate.
- Neurons stimulate sarcolemma by generating an action potential
- AChE breaks down ACh thus inactivating the signal
what is calsequestrin?
special protein filaments that sequester Ca2+ in bunches inside SR
how is calcium stored and released?
- calcium ion pumps in the SR pulls Ca+2 in
- calsequestrin sequester Ca+2 in bunches
- when stimulated, Ca+2 channels open, releasing flood of Ca+2
- Ca+2 channels relcose instantly and Ca+2 is pumped back into SR
what happens when sarcomeres contract?
- so does th entire muscle fiber
- as fibers contract, tension is created by tendons pulling on bones
how does movement occur?
when tension is greater than the resistance
how does variation in tension occur?
- amount of overlap of the myofilaments
- frequency of stimulation
what is the maximal strength that a muscle can develop directly related to?
initianl length of its fibers
define a muscle twitch
a single stimulus-contraction-relaxation cycle in a muscle fiber or whole muscle
what happens in the latent period of muscle twitch?
includes the action potential, release of Ca2+, activitation of troponin/tropomyosin
describe the contraction phase
development of tension b.c of the cross-bridge cycle of mysosin and actin
what happens in the relaxation period?
tension decreases due to the restorage of Ca2+ and covering of actin active sites
repeated, frequent stimuli that tirgger a response before full relaxtion has occured
near peak tension with little relaxation, while complete tetanus occurs when stimuli are so frequent that relaxtion does not occur
gradual increase in muscular contraction following rapidly repeated stimulation
why is the initial contraction weaker than subsequent?
- increase in ca+2 within sarcoplasm, so more active sites exposed, more cross-bridgin gof actin-myosin
- neural component: more moto units firing
what is a motor unit?
a single motor neuron and all the muscle fibers it innervates
what are two types of motor unit?
- fine control movement: use motor units with very few fibers per neuron
- gross movements: use motor units have a high fiber-to-neuron ration
how are motor units recruited?
activiation of more and more units to produce adequate tension beginning with the small neurons first (smooth gradation of increasing strength)
what is isotonic muscle contraction?
when the length of the muscle changes, but the tension remains the same until relaxation
what is isometric contraction?
when the whole muscle length stays the same, the tension produced does not exceed the load
elongation of muscle after contraction passively uses a combination of what?
gravity, elastic forces, oposing muscle movement
what happens to glucose and fatty acids as being catabolized
ATP produced to used to power contractions
what are the products for lactic acid fermentation?
- pyruvate reduced to lactate and NADH oxidzed to NAD+
- lactate is carrie by the blood to theliver, whiere it is converted to another time
energy sources of skeletal muscle during work?
- creatine phosphate
- aerobic glycolysis