Muscle tone
Encyclopedia
In physiology
, medicine
, and anatomy
, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle’s resistance to passive stretch during resting state. It helps maintain posture
, and it declines during REM sleep.
s in a partially contracted state. If a sudden pull or stretch occurs, the body responds by automatically increasing the muscle's tension, a reflex which helps guard against danger as well as helping to maintain balance
.
The presence of near-continuous innervation makes it clear that tonus describes a "default" or "steady state" condition. There is, for the most part, no actual "rest state" insofar as activation is concerned.
In terms of skeletal muscle, both the extensor
and flexor
muscles, under normal innervation
, maintain a constant tone while "at rest" that maintains a normal posture.
Cardiac muscle
and smooth muscle
, although not directly connected to the skeleton, also have tonus in the sense that although their contractions are not matched with those of antagonist muscles, the non-contractive state is characterized by (sometimes random) enervation.
) or high (hypertonia
) muscle tone. Another form of hypertonia is paratonia
, which is associated with dementia
. Hypotonia is seen in lower motor neuron disease like poliomyelitis. Hypotonia can present clinically as muscle flaccidity
, where the limbs appear floppy, stretch reflex responses are decreased, and the limb’s resistance to passive movement is also decreased. Hypertonia is seen in upper motor neuron diseases like lesions in pyramidal tract and extrapyramidal tract. Hypertonia can present clinically as either spasticity
or rigidity. While spasticity
is velocity-dependent resistance to passive stretch (i.e. passively moving an elbow quickly will elicit increased muscle tone, but passively moving elbow slowly may not elicit increased muscle tone), rigidity is velocity-independent resistance to passive stretch (i.e. there is uniform increased tone whether the elbow is passively moved quickly or slowly).
Spasticity
can be in the form of the clasp-knife response
, in which there is increased resistance only at the beginning or at the end of the movement. Rigidity can be of the leadpipe type, in which there is resistance throughout to passive movement, or it may be of cogwheel type, in which the resistance to passive movement is in a jerky manner.
, tonus may be a central consideration in eye surgery
, as in the manipulation of extraocular muscles to repair strabismus
. Tonicity aberrations are associated with many diseases of the eye (e.g. Adie syndrome
).
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
, medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, and anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle’s resistance to passive stretch during resting state. It helps maintain posture
Neutral spine
A neutral spine or good posture refers to the "three natural curves [that] are present in a healthy spine."- Posture :The word "posture" comes from the Latin verb "ponere" which is defined as "to put or place." The general concept of human posture refers to "the carriage of the body as a whole, the...
, and it declines during REM sleep.
Purpose
Unconscious nerve impulses maintain the muscleMuscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s in a partially contracted state. If a sudden pull or stretch occurs, the body responds by automatically increasing the muscle's tension, a reflex which helps guard against danger as well as helping to maintain balance
Balance disorder
A balance disorder is a disturbance that causes an individual to feel unsteady, for example when standing or walking. It may be accompanied by feelings of giddiness or wooziness, or having a sensation of movement, spinning, or floating...
.
The presence of near-continuous innervation makes it clear that tonus describes a "default" or "steady state" condition. There is, for the most part, no actual "rest state" insofar as activation is concerned.
In terms of skeletal muscle, both the extensor
Extension (kinesiology)
In kinesiology, extension is a movement of a joint that results in increased angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extending the flexed elbow. Straightening of...
and flexor
Flexion
In anatomy, flexion is a position that is made possible by the joint angle decreasing. The skeletal and muscular systems work together to move the joint into a "flexed" position. For example the elbow is flexed when the hand is brought closer to the shoulder...
muscles, under normal innervation
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
, maintain a constant tone while "at rest" that maintains a normal posture.
Cardiac muscle
Cardiac muscle
Cardiac muscle is a type of involuntary striated muscle found in the walls and histologic foundation of the heart, specifically the myocardium. Cardiac muscle is one of three major types of muscle, the others being skeletal and smooth muscle...
and smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
, although not directly connected to the skeleton, also have tonus in the sense that although their contractions are not matched with those of antagonist muscles, the non-contractive state is characterized by (sometimes random) enervation.
Pathological tonus
Physical disorders can result in abnormally low (hypotoniaHypotonia
Hypotonia is a state of low muscle tone , often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength...
) or high (hypertonia
Hypertonia
Hypertonia a condition marked by an abnormal increase in muscle tension and a reduced ability of a muscle to stretch. It is caused by lesions to upper motor neurons in the central nervous system, which carry information from the central nervous system to the muscles and control posture, muscle...
) muscle tone. Another form of hypertonia is paratonia
Paratonia
Paratonia or gegenhalten is classified as a form of hypertonia with an involuntary variable resistance during passive movement . Paratonia develops during a period of dementia and the degree of effect is dependent upon the disease's progress...
, which is associated with dementia
Dementia
Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
. Hypotonia is seen in lower motor neuron disease like poliomyelitis. Hypotonia can present clinically as muscle flaccidity
Flaccid paralysis
Flaccid paralysis is a clinical manifestation characterized by weakness or paralysis and reduced muscle tone without other obvious cause .-Polio:...
, where the limbs appear floppy, stretch reflex responses are decreased, and the limb’s resistance to passive movement is also decreased. Hypertonia is seen in upper motor neuron diseases like lesions in pyramidal tract and extrapyramidal tract. Hypertonia can present clinically as either spasticity
Spasticity
Spasticity is a feature of altered skeletal muscle performance in muscle tone involving hypertonia, which is also referred to as an unusual "tightness" of muscles...
or rigidity. While spasticity
Spasticity
Spasticity is a feature of altered skeletal muscle performance in muscle tone involving hypertonia, which is also referred to as an unusual "tightness" of muscles...
is velocity-dependent resistance to passive stretch (i.e. passively moving an elbow quickly will elicit increased muscle tone, but passively moving elbow slowly may not elicit increased muscle tone), rigidity is velocity-independent resistance to passive stretch (i.e. there is uniform increased tone whether the elbow is passively moved quickly or slowly).
Spasticity
Spasticity
Spasticity is a feature of altered skeletal muscle performance in muscle tone involving hypertonia, which is also referred to as an unusual "tightness" of muscles...
can be in the form of the clasp-knife response
Clasp-knife response
Clasp-knife response refers to a stretch reflex with a rapid decrease in resistance when attempting to flex a joint, usually during a neurological examination. It is one of the characteristic responses of a upper motor neuron lesion...
, in which there is increased resistance only at the beginning or at the end of the movement. Rigidity can be of the leadpipe type, in which there is resistance throughout to passive movement, or it may be of cogwheel type, in which the resistance to passive movement is in a jerky manner.
Tonus in surgery
In ophthalmologyOphthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
, tonus may be a central consideration in eye surgery
Eye surgery
Eye surgery, also known as orogolomistician surgery or ocular surgery, is surgery performed on the eye or its adnexa, typically by an ophthalmologist.-Preparation and precautions:...
, as in the manipulation of extraocular muscles to repair strabismus
Strabismus
Strabismus is a condition in which the eyes are not properly aligned with each other. It typically involves a lack of coordination between the extraocular muscles, which prevents bringing the gaze of each eye to the same point in space and preventing proper binocular vision, which may adversely...
. Tonicity aberrations are associated with many diseases of the eye (e.g. Adie syndrome
Adie syndrome
Adie syndrome, sometimes known as Holmes-Adie's syndrome or Adie's Tonic Pupil, is a neurological disorder characterized by a tonically dilated pupil. It is named after the British neurologist William John Adie...
).
See also
- GHK current equationGHK current equationThe Goldman–Hodgkin–Katz flux equation describes the ionic flux carried by an ionic species across a cell membrane as a function of the transmembrane potential and the concentrations of the ion inside and outside of the cell...
- Nernst-Planck equationNernst-Planck equationThe Nernst–Planck equation is a conservation of mass equation used to describe the motion of chemical species in a fluid medium. It describes the flux of ions under the influence of both an ionic concentration gradient \nabla c and an electric field E=-\nabla \phi...
- Hodgkin-Huxley modelHodgkin-Huxley modelThe Hodgkin–Huxley model is a mathematical model that describes how action potentials in neurons are initiated and propagated....
- Hindmarsh-Rose modelHindmarsh-Rose modelThe Hindmarsh–Rose model of neuronal activity is aimed to study the spiking-bursting behavior of the membrane potential observed in experiments made with a single neuron. The relevant variable is the membrane potential, x, which is written in dimensionless units...
- Muscle weaknessMuscle weaknessMuscle weakness or myasthenia is a lack of muscle strength. The causes are many and can be divided into conditions that have true or perceived muscle weakness...