Dominic Stone
Muscle tone is the continuous and passive partial contraction of a muscle, which helps maintain posture and balance, and control the proper function of other organ systems. It is the maintenance of muscle tone that allows the body to respond to an outside force, such as a stretch or change in direction, and is controlled by the sensory muscle spindle, which measures muscle stretch. Muscle tone is influenced by receptors found in the muscle and tendons, and is maintained through autonomous feedback from the muscle fibres, neurons, and associated tissues.
| Characteristics | Values |
|---|---|
| Definition | Muscle tone is the maintenance of partial contraction of a muscle. |
| Function | Generating reflexes, maintaining posture and balance, controlling the proper function of other organ systems. |
| Controlled by | The sensory muscle spindle, which measures muscle stretch. |
| Influenced by | Neuronal impulses and receptors found in the muscle and tendons. |
| Muscle tone in smooth and cardiac muscles | Maintained through autonomous feedback from the muscle fibres, neurons, and associated tissues. |
| Muscle tone in skeletal muscles | Controlled by the muscle spindle and influenced by the golgi tendon organ, which prevents damage to the muscle. |
| Low muscle tone | Perceived as "lax, flabby, floppy, mushy, dead weight". |
| High muscle tone | Perceived as "tight, light, strong". |
| Abnormal muscle tone | Hypotonia (low muscle tone) and hypertonia (high muscle tone) can be caused by physical disorders or neurological diagnoses. |
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What You'll Learn
Muscle tone is the maintenance of partial contraction of a muscle
Muscle tone is controlled by the sensory muscle spindle, which measures muscle stretch. Both cells of the muscle spindle contain sensory neurons. When stretched, muscle spindles become activated, triggering impulses to the spinal cord that can generate an immediate reflex. Spindles can also trigger impulses to the cerebral cortex, providing information about the degree of stretch within the muscle. To maintain tone, spindles also operate a feedback loop by directly triggering motor neurons linked to their associated muscles. If the tone decreases and the muscle stretches the spindle, an impulse results in a muscle contraction.
Smooth and cardiac muscles do not have specialised muscle spindles. Tone is maintained through autonomous feedback from the muscle fibres, neurons, and associated tissues. Muscle tone is controlled by neuronal impulses and influenced by receptors found in the muscle and tendons. Interneurons are an integral part of the stretch reflex arc and play a major role in maintaining muscle tone. They are inhibited or excited by multiple descending fibre systems.
Muscle tone is an adaptive function of the neuromotor apparatus that responds adequately to commands from upper levels of movement construction by fine-tuning the excitability of the sensory and motor cells for the tasks of active postural or movement control. Muscle tone adapts dynamically to meet biomechanical requirements, varying across different postures to counteract changing static loads. While one maintains a posture, tonic activity increases to resist deformation due to external loading. The tone system is extremely sensitive to changes in position and force, allowing it to readily compensate for disturbances.
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Muscle tone is controlled by the sensory muscle spindle
Muscle tone is the maintenance of partial contraction of a muscle, which is important for generating reflexes, maintaining posture and balance, and controlling the proper function of other organ systems. It is the muscle's response to an outside force, such as a stretch or change in direction. For example, if someone straightens your elbow, your bicep muscle will contract in response to protect you from injury.
To maintain tone, spindles also operate a feedback loop by directly triggering motor neurons linked to their associated muscles. If the tone decreases and the muscle stretches the spindle, an impulse results in a muscle contraction. With this contraction, the spindle is no longer stretched. A similar system is found in the tendons attaching muscle to bone. Distinct stretch receptors called Golgi tendon organs assess the level of stretch within the tendon. The sensitivity of the Golgi tendon organ is significantly less than that of the spindle, so it is thought they exist to prevent damage rather than control muscle tone.
Smooth and cardiac muscles do not have specialized muscle spindles. Tone is maintained through autonomous feedback from the muscle fibres, neurons, and associated tissues. Muscle tone is an active contributor to movement and postural tasks. It adapts dynamically to meet biomechanical requirements, varying across different postures to counteract changing static loads. It is extremely sensitive to changes in position and force, allowing it to readily compensate for disturbances.
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Disorders of muscle tone can arise from dysfunction in neural circuits
Muscle tone is the continuous and passive partial contraction of muscles, which helps to maintain posture and balance. It is regulated by the activity of motor neurons and influenced by receptors in the muscles and tendons. Smooth and cardiac muscles, for example, do not have specialised muscle spindles and instead rely on autonomous feedback from muscle fibres, neurons, and associated tissues to maintain tone.
Dystonia and paratonia are additional abnormalities of muscle tone that arise from network dysfunction between the basal ganglia and thalamo-cerebello-cortical connections. Dystonia is defined as sustained or intermittent muscle contractions resulting in abnormal, often repetitive, movements, postures, or both. These movements are typically patterned and may be aggravated by voluntary action. Paratonia is associated with dementia.
The maintenance of muscle tone is a complex process involving various neural circuits in the brain, spinal cord, and muscle spindle. Muscle tone is influenced by interneurons, which are regulated by multiple descending fibre systems. These interneuronal pathways play a significant role in spasticity and are essential for maintaining muscle tone.
In summary, disorders of muscle tone, such as hypertonia and hypotonia, can result from dysfunction in neural circuits regulating muscle tone. This can lead to conditions like spasticity, rigidity, dystonia, and paratonia, which affect posture, movement, and flexibility.
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Muscle tone is an adaptive function of the neuromotor apparatus
Muscle tone is the continuous and passive partial contraction of a muscle, which is important for generating reflexes, maintaining posture and balance, and controlling the proper function of other organ systems. It is controlled by the sensory muscle spindle, which measures muscle stretch. Muscle tone is not limited to skeletal muscles but is also a property of cardiac and smooth muscles.
The simple definition of tone as the resistance to passive stretch is physiologically a complex interlaced network encompassing neural circuits in the brain, spinal cord, and muscle spindle. Disorders of muscle tone can arise from dysfunction in these pathways and manifest as hypertonia or hypotonia.
Bernstein, in his hierarchical model of movement construction, postulated that muscle tone is an adaptive function of the neuromotor apparatus that responds adequately to commands from upper levels of movement construction. This definition makes muscle tone an active contributor to movement and postural tasks. It is the muscle's response to an outside force, such as a stretch or change in direction. Appropriate muscle tone enables our bodies to quickly respond to a stretch. For example, if someone straightens your elbow, your biceps muscle will automatically contract in response to protect you from injury.
Muscle tone adapts dynamically to meet biomechanical requirements, varying across different postures to counteract changing static loads. While maintaining a posture, tonic activity increases to resist deformation due to external loading. The tone system is extremely sensitive to changes in position and force, allowing it to readily compensate for disturbances. Muscle tone also adapts in the opposite way, yielding to a load to allow a change in posture. This creates postural plasticity through "lengthening and shortening" reactions, which decrease tone during muscle lengthening and increase it during shortening.
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Muscle tone is distinct from muscle strength
Muscle tone is the continuous and passive partial contraction of muscles, or the muscle's resistance to passive stretch during a resting state. It is controlled by the sensory muscle spindle, which measures muscle stretch. Muscle tone is important for generating reflexes, maintaining posture and balance, and controlling the proper function of other organ systems. It is regulated by the activity of motor neurons and can be affected by factors such as age, disease, and nerve damage.
Muscle strength, on the other hand, is the muscle's ability to contract and create force in response to resistance. It is what muscles do when they are not at rest. When a muscle is purposefully moved, the brain sends signals to the muscle fibres to contract. The power of the contraction depends on muscle mass, which can be altered by weight training and exercise.
While muscle tone is about the muscle's response to an outside force, muscle strength is about the muscle's ability to generate force. For example, if someone straightens your elbow, your bicep muscle will automatically contract in response to protect you from injury. This is an example of muscle tone. However, the strength of that contraction, or your ability to resist that force, would be determined by your muscle strength.
Muscle tone and muscle strength are related but distinct concepts. High muscle tone does not necessarily indicate high muscle strength. For instance, athletes who require explosive movements, like sprinters, usually have high muscle tone, but they may not have the same level of muscle strength as weightlifters, who require a high degree of muscle strength but may have lower muscle tone.
Additionally, individuals with physical disorders may exhibit abnormal muscle tone, which can be either low (hypotonia) or high (hypertonia). Hypotonia is often characterised by floppy limbs and decreased stretch reflex responses, while hypertonia can result in spasticity or rigidity. These conditions can impact an individual's muscle strength, but they are distinct from it.
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Frequently asked questions
Muscle tone is the maintenance of partial contraction of a muscle, which is important for generating reflexes, maintaining posture and balance, and controlling the proper function of other organ systems. It is the muscle's response to an outside force, such as a stretch or change in direction.
Low muscle tone, or hypotonia, is often seen in children who are slower to react to a stretch and are unable to sustain a prolonged muscle contraction. There may be a neurological diagnosis that is the cause of low tone, but some children exhibit low tone with an unknown cause. High muscle tone, or hypertonia, is commonly seen in people with cerebral palsy or other pathological disorders such as a stroke. It is caused by damage to the cerebral cortex and can result in rigidity and resistance to movement.
Muscle tone is controlled by the sensory muscle spindle, which measures muscle stretch. The muscle spindle contains sensory neurons that, when activated, trigger impulses to the spinal cord that can generate an immediate reflex. To maintain tone, the spindles operate a feedback loop by directly triggering motor neurons linked to their associated muscles. Interneurons are also an integral part of the stretch reflex arc and play a major role in maintaining muscle tone.
