Exam 3- skeletal muscle phys Flashcards
skeletal muscles are composed of hundreds to thousands of individual cells called [a] [b] which produce muscle tension
muscle fibers
an action potential in a motor neuron triggers the release of ________ from its terminal
aceytlcholine
a motor unit consists of a [a][b] and all of the muscle fibers it innervates
motor neuron
the motor neuron and muscle fiber intersect at what is called the [a] [b]
neuromuscular junction
The graded depolarization in the skeletal muscle fiber that is elicited in response to one action potential from the motor neuron is called
EPP (end-plate potential)
the end-plate potential is a
graded potential
one contractile response to a single action potential is a [a][b]
muscle witch
the length of time that elapses the peak of tension muscle tension to the end of muscle contraction is the [a][b]
relaxation phase
A sufficiently strong electrical stimulus applied to an isolated, mounted skeletal muscle induces the development of muscle force, or muscle tension. Which of the following statements concerning this observation is true
the electrical stimulus mimics acetylcholine release at a Neuromuscular junction
by definition the ________ voltage is the amount of stimulus required to successfully recruit ALL the muscle fibers into developing active force
maximal
In Pex 2-1 you changed the stimulus voltage
did this alter the duration of the latent perio
no changing the stimulus voltage did not change the latent period
the [a] [b] is the smallest stimulus required to induce an action potential in a muscle fiber’s plasma membrane or sarcolemma
threshold voltage
the threshold voltage for this experiment in PEX 2 act 2 was______volts
0.8
What occurs during the latent period of isometric contractions?
All the steps of excitation-contraction coupling occur
the lowest voltage that produced the peak force (the maximal voltage) in exercise 2 PEX 2 was_______volts
8.5
in exercise 2 PEX 2 as the stimulus voltage increased from 1.0 volt to 10 volts
the active force increased as the simulus voltage increased but then plateaud at a maximal value
the maximal active force in exercise 2 PEX 2 was_______g
1.82
contraction phase
myofilaments utilize the cross-bridge cycle
latent phase
calcium is released into the sarcoplasmic reticulum
relaxation phase
crossbridges between actin and myosin are released
the reason a maximal voltage was observed is that
at the maximal voltage, all the muscle fibers contained in this muscle are depolarized and they all develop active force
a weak muscle contraction
implies that few motor units are activated
In activity PEX 2 exercise 2 the simulations rely on indirect stimulation of the skeletal muscle by an electrode. This differs from In VITRO
because in vivo each muscle fiber receives direct stimulation via Ach from a nerve ending
motor unit recruitment refers to
an increase in the # if active muscle fibers to increase the force developed in a muscle
a decline in a skeletal muscle’s ability to maintain a constant level of force or tension after prolonged, repetitive stimulation is ______
fatigue
when a skeletal muscle is stimulated repeatedly, such that the stimuli arrive one after another within a short period of tie, muscle twitches can overlap with each other and result in a stronger muscle contracton than a stand-alone twitch. This phenomenon is [a][b]
wave summation
the progressive increase in force generated when a muscle is stimulated in succession, such that muscle twitches follow one another closely with each successive twitch peaking slightly higher than one before is ________
treppe
Wave summation is achieved by increasing the stimulus______
frequency
When a muscle receives a stimulus frequency that causes NON-overlapping twitches to follow each other closely in time such that the peak tension of each twitch rises in a stepwise fashion up to a plateau value, the result is known as
treppe
Which of the following is NOT one of the ways that the body can increase the force produced by a skeletal muscle
application of higher voltages to the whole muscle
In Activity 3 you repeated a stimulus as the relaxation phase started what happened to the muscle force generated with each successive stimulus?
as the stimulus frequency increased the muscle force generated by each successive stimulus increased there is a limit to the increase
isolated skeletal muscle was repetitively stimulated such that individual twitches overlapped with each other and resulted in a stronger muscle contraction than a stand alone twitch. This phenomenon is
wave summation
in activity 3 you elicited a second stimulus as soon as the muscle force returned to baseline from the first stimulus
select the true statement
the 2nd twitch generated more muscle force
Wave summation is achieved by
increasing the rate of stimulus delivery (frequency) to the muscle
To achieve an active force of 5.2 g did you have to increase the stimulus voltage above 8.5 volts? If not how did you achieve an active force of 5.3 g? How well did the results compare with your prediction?
I did not increase the stimulus above 8.5 volts. I achieved the active force of 5.3g by repeatedly stimulating the muscle continuously through the contraction phase. My results proved to be consistent with the prediction I made that voltage would not have to be increased
What is the difference between stimulus intensity and stimulus frequency
Stimulus intensity is related to the amount of voltage being applied to the muscle where stimulus frequency is related the the number of times the muscle is stimulated by the voltage in a time frame.
compare and contrast frequency-dependent wave summation with motor unit recruitment (previously observed by increasing the stimulus voltage) How are they similar: How was each achieved in the experiment: Explain how each is achieved in vivo?
Frequency- dependent wave summation is dependent upon stimulation by the nervous system. The motor recruitment depends on the number of motor fibers available. They both work to increase force production by the muscle. Wave summation depends on the frequency of the stimulation whereas motor unit recruitment depends on the intensity of the stimulus- more motor units recruited for stronger stimulus.
n the introduction to exercise 2 activity the major factor causing fatigue, in the case of high-intensity exercise,were listed as
accumulations of lactic acid
accumulations of ADPi
accumulations of Pi
during fatigue
the # of active cross bridges begins to decline although the rate of stimulus delivery remains constant
if a rest period is imposed on active skeletal muscle
the development of fatigue will be delayed
tetanus refers to
sustained muscle tension due to repetitive stimuli
during cross bridge cycling in skeletal muscle force is created by the
power stroke of the myosin heads
maximal active tension will be produced in a skeletal muscle fiber when
the fiber is at its resting length
what key variable was studied in activity 6 in an isometric contraction of skeletal muscle
starting muscle length
xplain why active force varies with the muscle’s starting length relative to its resting length
active force depends on the number of crossbridge cycles. At the resting length the maximum number of myosin heads can attach to actin
over what length in activity 6 did you start to see passive force
over 80 mm
explain what effect a heavier load had on the latent period and why it had this effect
heavier loads increased the latent period
more force is required to move a heavier load so more fibers had to be recruited. This takes more time
during an isotonic contraction there is a [a][b] during which there is a rise in muscle tension but no observable movement of the weight
latent period
as the load on the muscle increased what happened to the latent period, the shortening velocity, the distance the weight moved and the contraction duration
the latent period increased
the shortening velocity decreased
the distance moved decreased
the contract duration decreased
which takes more time: 10 repititions of 10kg or 10 repititions of 5kg?
the 10kg repititon would have a longer latent period-start more slowly, and lower velocity thus longer duration
