Antagonist (muscle)
The antagonist is a muscle that is the antagonist of another muscle, the agonist. The interplay of muscular limbs of the body, which is characterized by alternating contraction of the flexor and extensor muscles, is also known as an opponent principle. To the opponent is called an antagonist.
The classic anatomy thereby assumes that this principle can be the example of the flexor and extensor muscles described the arm basically as follows: If the flexors ( biceps ) when Anbeugen of the arm is actively shortened is the opposite at the same time the extensor ( triceps ) passively stretched. Conversely, when stretching the arm of the extensors is actively shortened, while the flexors is passively stretched.
In fact, almost all antagonists with in the movement and even at rest innervated ( tonus ). In many cases (eg shoulder joint ) would be a movement without a dislocation of the joint impossible when the antagonist would not contract in a certain ratio to the agonist. This is about an eccentric contraction.
There are also numerous muscles, which formally apply as antagonists, but act as synergists. This is particularly important when two joints pulling muscles of the case. A familiar example is the muscles of the so-called hamstrings muscles, to stretching movements of the knee ( rising from a chair, shows, sprinting, etc. ) are involved, although they diffracting function is attributed in relation to the knee joint ( Lombard'sches paradox ).
The antagonistic action principle is also observed in the pupillary reaction in which the enlargement and reduction by dilator muscle of pupil sphincter muscle of the pupil and done.
For external eye muscles
To each eye every six external eye muscles, which are responsible for its coordinated movements exist. Two of them have a similar muscle level and turn the eye to an almost identical rotational axis, but this each in an opposite direction of rotation. These muscles are called antagonists. In contrast, refers to muscles that move the eye around a similar axis of rotation in the same direction as synergists. This terminology is also used when only match partial functions of the respective muscles or counteract each other. It is only for productions, ie movements of an eye, completely applicable. Extending the observation also to the counter eye for the description of contralateral synergists and antagonists during the execution of binocular eye movements, so must this definition for vergences, reverse eye movements are restricted.
The movements of the eyes are finally completed by a reciprocal change in the innervation. So the law states Sherrington that the innervation of an antagonist decreases to the extent in which the increase of the agonist. That this also applies equally to the contralateral synergists and antagonists of the other eye, says the Hering's law of equal innervation page.
- Ipsilateral ( equilateral ) synergists and antagonists in relation to the respective muscle function
Superior rectus, inferior rectus
Rectus lateralis, M. obl superior, M. obl inferior
M. obl superior, M. obl inferior
Medial rectus, superior rectus, inferior rectus
Innenrollung
Adduction
M. obl superior
Medial rectus, inferior rectus
Rectus inferior, M. obl inferior
Rectus lateralis, M. obl superior, M. obl inferior
Außenrollung
Adduction
M. obl inferior
Medial rectus, superior rectus
M. obl superior, superior rectus
Rectus lateralis, M. obl superior, M. obl inferior
Innenrollung
Abduction
Rectus superior
Rectus lateralis, M. obl inferior
Rectus inferior, M. obl inferior
Medial rectus, superior rectus, inferior rectus
Außenrollung
Abduction
Rectus inferior
Rectus lateralis, M. obl superior
M. obl superior, superior rectus
Medial rectus, superior rectus, inferior rectus
- Graphical representation of the involvement of individual muscles ( synergists ) at the respective rotational movements using the example of the right eye