Logan Steele
Tetanus is a sustained muscle contraction that occurs when a muscle's motor unit is stimulated by multiple impulses at a high frequency. During this state, a motor unit has been maximally stimulated by its motor neuron and remains that way for some time. This is also called a tetanized state, tetanus, or physiologic tetanus. The latter term is used to differentiate it from the disease called tetanus.
| Characteristics | Values |
|---|---|
| Definition | A sustained muscle contraction |
| Cause | High-frequency stimulus (50-100 Hz) |
| Muscle activity | Contractile elements are maintained |
| Muscle tension | Maximum tension is reached |
| Muscle force | Strongly dependent on the length of the muscle |
| Muscle relaxation | No relaxation occurs between stimuli |
| Muscle fatigue | Sustained tetany will fatigue the muscle |
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What You'll Learn
Twitch and tetanus responses
A tetanus, or tetanic contraction, on the other hand, is a sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate. This occurs when a muscle's motor unit is stimulated by multiple impulses at a sufficiently high frequency (50-100 Hz). Each stimulus causes a twitch, but because the stimuli are delivered at a high frequency, there is no relaxation between successive twitches. During a tetanus, the activity of the contractile elements is maintained, and they can eventually shorten enough to extend fully the series of elastic elements. When this has been accomplished, the maximum tension is apparent at the ends of the muscle.
The rate of stimulation that produces a fused tetanus is called the fusion frequency. This is the frequency between the extremes of twitch and tetanus at which the tension developed by the muscle remains constant. Sustained tetany will fatigue the muscle, and over 10-20 seconds the tension will begin to decrease. Post-tetanic potentiation is the augmentation of the force of any contraction that occurs after tetany, and is thought to be due to the increase in the availability of calcium in the presynaptic nerve terminal.
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Tetanic contraction
During tetanic contraction, the activity of the contractile elements is maintained, and they can eventually shorten enough to extend fully the series of elastic elements. When this has been accomplished, the maximum tension is apparent at the ends of the muscle. The force developed by a muscle, whether it is contracting or resting, is strongly dependent on the length of the muscle.
The rate of stimulation that produces tetanic contraction is called the fusion frequency. Post-tetanic potentiation is the augmentation of the force of any contraction that occurs after tetany, and is thought to be due to the increase in the availability of calcium in the presynaptic nerve terminal.
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Fused tetanus
A muscle contraction produced by a single action potential is called a twitch. During a twitch, the activity of the muscle is so brief that the contractile elements cannot extend the elastic elements completely before relaxation begins. As a result, the tension at the ends of the muscle does not reach the maximum possible level.
A tetanic contraction, also known as tetanus, is a sustained muscle contraction that occurs when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate. During this state, a motor unit has been maximally stimulated by its motor neuron and remains that way for some time. Each stimulus causes a twitch, and if the stimuli are delivered slowly enough, the tension in the muscle will relax between successive twitches.
Tetany, or tetanisation, is produced with a high-frequency stimulus (50-100 Hz), where there is no relaxation between stimuli. The maximum tension developed is usually about four times the tension generated by a single twitch. Sustained tetany will fatigue the muscle, and over 10-20 seconds the tension will begin to decrease.
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Tetany
During tetany, the activity of the contractile elements is maintained, and they can eventually shorten enough to extend fully the series of elastic elements. When this has been accomplished, the maximum tension is apparent at the ends of the muscle. The force developed by a muscle, whether it is contracting or resting, is strongly dependent on the length of the muscle. Sustained tetany will fatigue the muscle, and over 10-20 seconds the tension will begin to decrease.
Post-tetanic potentiation is the augmentation of the force of any contraction that occurs after tetany, and is thought to be due to the increase in the availability of calcium in the presynaptic nerve terminal.
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Post-tetanic potentiation
Tetanus is a sustained muscle contraction that occurs when a muscle's motor unit is stimulated by multiple impulses at a high frequency. This is also known as a tetanized state or physiologic tetanus. During this state, a motor unit has been maximally stimulated by its motor neuron and remains that way for some time. Each stimulus causes a twitch, and if the stimuli are delivered slowly enough, the tension in the muscle will relax between successive twitches.
The frequency at which tetanus is achieved is usually 50-100 Hz, and the specific critical frequency depends on the duration of the action potential of the cell. This type of contraction is called a fused tetanus, and the rate of stimulation that produces it is called the fusion frequency.
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Frequently asked questions
Tetanus is a sustained muscle contraction that occurs when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate.
A muscle contraction produced by a single action potential is a twitch, whereas tetanus is produced by the summation of the tension of multiple frequent action potentials.
Fused tetanus occurs when there is no relaxation of the muscle fibres between stimuli, whereas unfused tetanus occurs when the muscle is relaxing as the second pulse is given, causing the tension to appear in waves in phase with the stimulation.
The maximum tension developed by tetanus is usually about four times the tension generated by a single twitch.
