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?