Maximus Gage
The strength of a muscle contraction produced by either a voluntary or electrical stimulation source is modulated by processes of recruitment and firing rate modulation. When the same axon is excited by both sources at different locations, the resulting action potentials will interact. The relationship between muscle firing period and the firing periods of the two action potential sources is illustrated in Fig. 2. The voluntary firing rate had an average period of 0.05 s with a 0.1 coefficient of variation.
| Characteristics | Values |
|---|---|
| Muscle contraction strength | Modulated by processes of recruitment and firing rate modulation |
| Muscle contraction source | Voluntary or electrical stimulation |
| Muscle firing period | Decreases when the stimulus period is less than the voluntary period |
| Muscle tension | Increases when the muscle is stretched beyond its resting length to a point |
| Muscle tension at resting length | Not maximal due to actin and myosin filament overlap |
| Muscle contraction | Skeletal muscle contracts primarily in response to a voluntary stimulus |
| Muscle firing period | Simultaneous excitation decreases the average firing period |
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What You'll Learn
Muscle contraction produced by voluntary or electrical stimulation
The strength of a muscle contraction produced by either a voluntary or electrical stimulation source is modulated by processes of recruitment and firing rate modulation. The firing period of the muscle decreases when there is simultaneous excitation, regardless of whether the stimulus period is higher or lower than the voluntary period. This means that the average frequency increases.
In a simulation study, the voluntary period was fixed at 0.05 s (20 Hz), and the stimulus period was varied over a range of periods both longer and shorter than the voluntary firing period. Each point in the study's graph represents the muscle’s average firing period calculated over a 3 s period of constant activity.
The conduction time between the two sources is tc, (distance divided by velocity), and the conduction time from the stimulating electrode to the muscle is designated as tp. The voluntarily elicited orthodromic action potential will collide with the electrically elicited antidromic action potential if the time between the generation of the two action potentials is less than the conduction time between the neuron and the electrical stimulation source. The mutual annihilation at the point of collision of the two action potentials will prevent the voluntary action potential from reaching the muscle and the electrically generated antidromic action potential from reaching the motor neuron.
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The relationship between muscle firing period and the firing periods of the two action potential sources
The strength of a muscle contraction produced by either a voluntary or electrical stimulation source is modulated by processes of recruitment and firing rate modulation. When the same axon is excited by both sources at different locations, the resulting action potentials will interact. Action potentials from the motor neuron are conducted orthodromically to the muscle fibres. The electrical stimulus excites the axon at some point between the motor neuron and the muscle, and produces pairs of action potentials that travel in both the orthodromic and antidromic directions.
Simultaneous excitation decreases the average firing period, i.e. increases the average frequency, regardless of whether the stimulus period is higher or lower than the voluntary period. The red symbol marks the point where the two firing periods would be equal.
Assume that a voluntary action potential is elicited at time tv, and an electrical stimulus elicits a pair of action potentials after an amount of ts. since the most recent stimulus pulse. The conduction time between the two sources is tc, (distance divided by velocity), and the conduction time from the stimulating electrode to the muscle is designated as tp. The voluntarily elicited orthodromic action potential will collide with the electrically elicited antidromic action potential if the time between the generation of the two action potentials is less than the conduction time between the neuron and the electrical stimulation source, i.e. if either ts < tv + tc or tv < ts + tc. The mutual annihilation at the point of collision of the two action potentials will prevent the voluntary action potential from reaching the muscle and the electrically generated antidromic action potential from reaching the motor neuron.
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The conduction time between the two sources
Simultaneous excitation decreases the average firing period, i.e. increases the average frequency, regardless of whether the stimulus period is higher or lower than the voluntary period. The strength of a muscle contraction produced by either a voluntary or electrical stimulation source is modulated by processes of recruitment and firing rate modulation. In the case of simultaneous excitation, the same axon is excited by both sources at different locations, and the resulting action potentials will interact. Action potentials from the motor neuron are conducted orthodromically to the muscle fibres. The electrical stimulus excites the axon at some point between the motor neuron and the muscle, and produces pairs of action potentials that travel in both the orthodromic and antidromic directions.
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The average firing period
When a muscle is stimulated, either voluntarily or through electrical stimulation, action potentials are produced. These action potentials travel in both the orthodromic and antidromic directions. The orthodromic action potential conducts the signal from the motor neuron to the muscle fibres, while the antidromic action potential travels in the opposite direction.
In summary, the average firing period of a muscle is the time it takes for the muscle to contract and relax, and it is influenced by the interaction and timing of action potentials, as well as the presence of simultaneous excitation.
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The strength of muscle contraction
The strength of a muscle contraction is determined by the processes of recruitment and firing rate modulation. The firing rate of a muscle is the average frequency with which it contracts. When a muscle is excited by two sources at different locations, the resulting action potentials will interact. The action potentials from the motor neuron are conducted orthodromically to the muscle fibres. The electrical stimulus excites the axon at some point between the motor neuron and the muscle, producing pairs of action potentials that travel in both the orthodromic and antidromic directions.
The relationship between the muscle firing period and the firing periods of the two action potential sources can be observed in a simulation study. In this example, the voluntary period was fixed at 0.05 s (20 Hz), and the stimulus period was varied over a range of periods both longer and shorter than the voluntary firing period. Each point in the study represents the muscle’s average firing period calculated over a 3 s period of constant activity.
The conduction time between the two sources is tc, or the distance divided by velocity. The conduction time from the stimulating electrode to the muscle is designated as tp. If the time between the generation of the two action potentials is less than the conduction time between the neuron and the electrical stimulation source, the voluntarily elicited orthodromic action potential will collide with the electrically elicited antidromic action potential. This mutual annihilation will prevent the voluntary action potential from reaching the muscle and the electrically generated antidromic action potential from reaching the motor neuron.
Simultaneous excitation decreases the average firing period, increasing the average frequency regardless of whether the stimulus period is higher or lower than the voluntary period.
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Frequently asked questions
Skeletal muscle contracts primarily in response to a voluntary stimulus, whereas smooth and cardiac muscle do not.
A muscle is composed of cells collectively referred to as muscle fibres. Each muscle fibre is multinucleated with its nuclei located along the periphery of the fibre.
Muscles will generate more force when stretched beyond their resting length to a point. Muscles stretched beyond this point will produce less tension.
A voluntary stimulus is elicited by a person, whereas an electrical stimulus is elicited by a machine.
Either decreasing or increasing the stimulus period results in an average decrease in muscle firing period.
