muscle phys lab

frequencies will vary with the individual but incomplete tetanus should occur at a lower frequency than complete tetanus

at which frequencies does incompelte tetanus occur?

frequencies will vary with the individual but incomplete tetanus should occur at a lower frequency than complete tetanus

at which frequncy did complete tetanus first occur (how does this compare to the frequency of incomplete tetanus)?

latent period

following the AP, there is an interval of a few millisecond know as _____ ______ before the tension in the muscle fiber begins to increase. during this ______ ______, the processes associated with ______-______ coupling are occurring

contraction time is shorter than relaxation time because it takes time for the myofilaments to return to their resting positions

how does the contraction time of a typical finger twitch compare to the relaxation time?

second squeeze fatigue is quicker than first squeeze fatigue(muscles are still tired from the first attempt/have not recovered)

how does the time until fatigue in the first squeeze compared to the time to fatigue in the second squeeze?

summation

increase in muscle tension, or shortening of muscle, in response to rapid, repetitive stimuli

unfused tetanus (a)

increased frequency of stimulations on muscle will lead to what?

electromyogram (EMG)

looks at contraction intensity and muscle fatigue

twitch

mechanical response of a muscle fiber to a single action potential

fused tetanus

muscle contracts and stays contracted (no oscillations) until stimulus is removed; seen at higher frequencies due to more APs occurring closer together; in our experiments the muscle will recover quickly

central command fatigue

muscle fatigue due to failure of appropriate regions of cerebral cortex to excite motor neurons -can be likened to "will power" or lack thereof

not

muscle fibers do ___ relax completely between contractions due to increaed frequency of stimulation -not summation of graded potentials->this is the observation of the effects of additional cross bridges that create summation

# of motor units in a muscle that are activated

strength of contraction depends on what?

contraction time

the time interval from the beginning of tension development at the end of the latent period to the peak tension

Ca

the total duration of a contraction depends in part on the time that cytosolic _____ remains elevated so that cross-bridges can cont to cycle

one

there is ___ axon terminal per muscle cell; a single neuron may have many axon terminals and each terminal goes to a different muscle cell

complete tetanus (fused)

No relaxation; smooth sustained contraction

tension

______ increases with each stimulation of the muscle

1. Decrease in rate of Ca++ release, reuptake, & storage by the SR. 2. Decrease in sensitivity of the thin filament proteins to activation by Ca++. 3. Inhibition of binding & power-stroke motion of the myosin cross-bridges. also: 4. Central command fatigue.

acute muscle fatigue following contractions of skeletal muscles involvevs several metabolic changes. what are the the consequences of these changes? (in other words what are the mechanisms involved?)

1. decrease in rate of Ca release, reuptake, and storage by the SR 2. decrease in sensitivity of the thin filament proteins to activation by Ca 3. inhibition of binding and power-stroke motion of the myosin cross-bridges 4. central command fatigue

acute skeletal fatigue involves what 3 mechanisms?

motor unit

one motor neuron+all the muscle cells it innervates; increasing number of motor units recruited increases the force of the whole muscle contraction

incomplete tetanus (unfused)

partial muscle relaxation between stimuli

unfused tetanus

tension oscillates (move or swing back and forth at a regular speed) as muscle fiber partially relaxes between stimuli; seen at lower frequencies -may lead to fused tetanus

fatigue

the decline in the strength of the motor contraction as result of previous contractile activity -see graphically as 1/2 the amplitude of the original max tension

bp cuff will shorten time to fatigue (increases rate of fatigue) since muscles need blood flow (O2) to operate

what is the effect of blood occlusion on the rate of fatigue?

neuromuscular junction

where an axon terminal ommunicates with the motor end plate of a muscle cell (they do not touch)

fused tetanus: this is result of summation (additional cross bridges have been added as more APs are occurring)

which requires greater tension: a single twitch or fused tetanus and why?