Lab 6 Muscle Physiology
During what phase in the graph below do the sarcomeres begin to shorten?
B
T/F A motor neuron and all the muscle cells that it stimulates are referred to as a motor end plate.
False
T/F Once a motor neuron has fired, all the muscle fibers in a muscle contract.
False
T/F Once a muscle is completely *fatigued* there is no recovery for that muscle--new muscle fibers must be generated.
False
T/F When a whole muscle is stimulated the force of the contraction is an all or nothing response with no variation in the amount of tension exerted.
False
Treppe is the phenomenon that results in _______.
a progressive increase in the force generated with repetitive stimulation
What is the process called of all the events from the acetylcholine to end-plate potential?
excitation-contraction coupling (EC coupling)
Define fatigue.
failure of a muscle fiber to produce tension because of previous contractile activity; a decline in the muscle's ability to maintain a constant force of contraction after prolonged, repetitive stimulation
What phenomenon best describes part "D" of the graph below?
fatigue
___________ is a decline in the muscle's ability to maintain a constant force of contraction after prolonged repetitive stimulation.
fatigue
What does a weak muscle contraction imply?
fewer motor units are activated, but each motor unit still develops its maximal tension
What the effect of treppe?
for the first few twitches, each successive twitch produces slightly more force than the previous twitch as long as the muscle is allowed to fully relax between stimuli and the stimuli are delivered relatively close together
What is changing to cause the variation in tension (force of contraction) seen in part B of the graph?
frequency of stimulation
Where is the interneuron located?
in the spinal cord
What phenomenon best describes part "B" of the graph below?
incomplete tetanus
With rapid, multiple stimulations, the contraction-relaxation cycles are shorter but there still is some degree of relaxation. This stage in the multiple stimuli graph is called:
incomplete tetanus
To transition from incomplete tetanus to complete tetanus, ______.
increase the stimulus frequency
As the stimulus voltage increased, the resulting muscle tension _______.
increased to a point until it reached a plateau
How does the duration of rest periods between multiple stimulation affect the duration the maximal force can be maintained by the muscle?
increasing the duration of the rest period increased the duration the maximal force can be maintained
What is motor unit recruitment?
increasing the number of active motor units, producing a steady increase in muscle force
The strongest muscle contractions are normally achieved by ________.
increasing the stimulation voltage up to the maximal stimulus
What would result in complete or incomplete tetanus?
increasing the stimulus frequency
What is occurring on a molecular level during rest periods?
intracellular ADP and inorganic phosphate are decreasing
Where does acetylcholine go after being released from its terminal?
it diffuses onto the sarcolemma and binds to receptors in the motor end plate
How does the duration of the rest period affect muscle tension (force of contraction)?
it has no affect
What is the result of acetylcholine binding to receptors on the motor end plate?
it initiates an ion permeability that results in a graded depolarization of the muscle plasma membrane (end-plate potential)
The muscles of the thigh exhibit gross movements for walking. What size are the motor units in the thigh?
large
What phase of a single muscle twitch is indicated by A?
latency
Immediately following the arrival of the stimulus at a skeletal muscle cell there is a short period called the ________ period during which the events of excitation-contraction coupling occur.
latent
The shortest phase of a muscle twitch, usually lasting less than 5 milliseconds, is called the:
latent period
What are the phases of a single muscle twitch?
latent, contraction, relaxation
Which muscle will give the highest tension (force of contraction) when stimulated--all else being equal among the muscles?
moderately stretched
A motor neuron and all the muscle cells it innervated is called a:
motor unit
Increasing the applied voltage corresponds to what in vivo event?
motor unit recruitment
What phenomenon best describes the graph?
multiple motor unit summation
Why does muscle force decrease over time?
muscle fatigue develops
Why does wave summation occur?
muscle fibers are partially contracted when the next stimulus arrives
What is tension?
muscle force, when nervous or electrical stimulation is applied
A muscle contraction in response to a single stimulus of adequate strength is called a ________.
muscle twitch
The muscles of the eye need to make need to make small precise motor movements. What size are the motor units in the eye?
small
What is unfused (incomplete) tetanus?
some relaxation occurs between contractions,
What is a threshold stimulus?
stimulus strength (voltage) at which the first observable muscle contraction occurs
What is maximal voltage?
the stimulus required to induce maximal tension
Random, asynchronous motor unit contractions provide a low-level tension and resistance to stretch called muscle _________.
tone
Where is the motor neuron located?
traveling to the muscle
During the initial phase of muscle contraction, each successive stimulus produces a slightly stronger contraction because of increased muscle warming and efficiency of enzymes. This stage is called:
treppe
What phenomenon best describes the graph?
treppe
T/F Muscle tone is the small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units.
true
The development of tension in a muscle, in response to a single stimulus above a threshold, is called a muscle __________.
twitch
When the frequency of the stimulation of a muscle is great enough, ______.
wave summation results and muscle twitches overlap
What does wave summation look like on a graph?
#2
What does incomplete (unfused) tetanus look like on a graph?
#3
What does complete (fused) tetanus look like graphically?
#4
What is a subthreshold stimulus for the muscle tested in the graph below?
2V
In a lab, a researcher finds that the threshold stimulus to induce an action potential in a muscle fiber's sarcolemma was 3.0 volts. What voltages would result in muscle tension in this muscle?
3.0 volts until max
What is the threshold stimulus for the muscle tested in the graph?
3V
What is the maximum contraction for the muscle tested in the graph below?
5g
What is the maximal stimulus for the muscle tested in the graph below?
7V
During what phase in the graph below do the Sarcolemma and T tubles depolarize?
A
During what phase in the graph below are calcium ions actively transported back into the terminal cisternae?
C
What occurs during the latent period of muscle contraction?
Calcium is released from the sarcoplasmic reticulum
A smooth, sustained contraction is called ________.
Complete tetanus
Build up of acidic compounds which affect protein functioning is happening in what part of the graph?
D
Will changes to the stimulus voltage alter the duration of the latent period?
No
What is changing to cause the variation in tension (force of contraction) seen in the graph?
Number of motor units recruited
What is maximal stimulus?
Strongest stimulus that produces an increase in contractile force; all motor units recruited
T/F By increasing the stimulation voltage in the graph below we are simulating the bodies control over the number of motor neurons that are stimulated by the central nervous system.
True
T/F For treppe to be demonstrated by a muscle stimulated multiple times, the sequential stimulations must not happen until the muscle has completed the relaxation phase of the previous twitch.
True
What does the motor unit consist of?
a motor neuron and all of the muscle fibers it innervates
What are thought to be some causes of fatigue?
accumulations of lactic acid, ADP, and Pi
What triggers the release of acetylcholine from its terminal?
action potential
What does the tracing on the oscilloscope indicate?
active muscle force
What occurs during the latent period of these isometric contractions?
all the steps of excitation-contraction coupling occur
What is stimulus voltage?
amount of voltage applied
What kind of muscle is more likely to be overstretched?
cardiac muscle
What are ways muscle contractions can be graded?
changing the strength of the stimulus changing the length (stretch) of the muscle changing the frequency of stimulation
What is NOT a way muscle contractions can be graded?
changing the type of muscle fibers involved in the contraction
What phenomenon best describes part "C" of the graph below?
complete tetanus
With rapid, multiple stimulations, the contractions fuse into a smooth, continuous contraction. This stage in the multiple stimuli graph is called:
complete tetanus
The speed of the _______ period of a sigle muscle twitch depends on whether slow or fast twitch fibers are involved.
contraction
What phase of a single muscle twitch is indicated by B?
contraction
What does the end-plate potential trigger?
contraction of a muscle cell
What occurs during the contraction phase of the muscle twitches?
cross-bridge cycling is taking place
What do the events that occur at the neuromuscular junction lead to?
end-plate potential
What is being "added" to achieve wave summation?
muscle twitches
The synapse between a motor neuron and the muscle it innervated is called a:
neuromuscular junction
If you increase the voltage after maximal contraction occurs, will the force of contraction also increase?
no
Is force generated during the latent period?
no
Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped, ________.
no muscle tension could be generated
What is complete (fused) tetanus?
no relaxation, maximum tension
What device shows the active force of a muscle over time?
oscilloscope
Stimulation of additional motor units will increase the strength of contraction. This process is called:
recruitment
An increase in the strength of the stimulus will cause an increase in tension development caused by:
recruitment of more motor units
What phase of a single muscle twitch is indicated by C?
relaxation
Sarcomeres lengthen during which phase/period of muscle twitch?
relaxation phase
What can trigger a muscle twitch?
release of acetylcholine and electrical stimulation
What phenomenon best describes part "A" of the graph?
temporal (wave) summation
When a second stimulus is applied before complete relaxation, there is a greater development of tension. What is this called?
temporal summation
What happens as the stimulus voltage is increased beyond the threshold voltage?
the amount of force produced by the whole muscle also increases, more muscle fibers are activated
When is the contraction period from?
the end of the latent period to when muscle tension peaks
What reflects the number of active motor units at a given moment?
the force generated by the whole muscle
What happens to the latency period of the muscle twitch when you raise the stimulation voltage?
the latency period of the muscle twitch stays the same
What is the period of time that elapses between the generation of an action potential and the start of muscle tension development in a muscle fiber?
the latent period
What is a muscle twitch?
the mechanical response to a single action potential
What is the sarcolemma?
the muscle fiber's plasma membrane
As the stimulus voltage was increased in this activity, what occurred?
the muscle force generated increased
When wave summation occurs, ______.
the muscle force generated increases
What are the two conditions in the muscle that must be met in order to achieve treppe?
the muscle must have completed the relaxation phase before being stimulated again, and the consecutive stimuli must be delivered to the muscle relatively close together
When the the relaxation phase?
the period of time between peak tension until the end of the muscle contraction
What is the latent period?
the period of time that elapses between the generation of an action potential in a muscle cell and the start of muscle contraction
What chemical changes occur during the latent period?
the release of calcium from the sarcoplasmic reticulum
Describe the relaxation phase.
the sarcomeres are increasing in length, and the force generated decreases
What is threshold voltage?
the smallest stimulus required to induce an action potential in the sarcolemma
What is the motor end plate?
the specialized region of the muscle fiber's plasma membrane when the axon terminal meets the muscle fiber in the neuromuscular junction
When does maximal tension occur?
when all the muscle fibers have been activated by a sufficiently string stimulus (maximal voltage)
Describe the relationship between stimulus frequency and muscle tension.
when stimulus frequency increases, muscle tension increases to a maximum value
When is maximal titanic tension reached?
when the stimulus frequency reaches a value beyond which no further increases in force are generated by the muscle
What is the neuromuscular junction?
where the motor neuron and a muscle fiber intersect; specifically, where the axon terminal of the neuron meets a specialized region of the muscle fiber's plasma membrane