Antagonist (muscle)
Encyclopedia
Most muscles work in pairs, and when a muscle works it needs to have an agonist
and an antagonist, unless the muscle's natural state is opposite to that which is produced by the muscle, example Sphincter ani externus muscle
.
An "antagonist" is a classification used to describe a muscle
that acts in opposition to the specific movement generated by the agonist
and is responsible for returning a limb to its initial position.
These consist of an extensor muscle, which "opens" the joint (i.e. increasing the angle between the two bones),
flexor muscle, which does the opposite to an extensor muscle.
Antagonistic pairs are needed in the body because muscles can only exert a pulling force, and can't push themselves back into their original positions.
An example of this kind of muscle pairing is the biceps brachii and triceps brachii.
When the biceps are contracting, the triceps are relaxed, and stretches back to its original position. The opposite happens when the triceps contract.
Agonist (muscle)
Agonist is a classification used to describe a muscle that causes specific movement or possibly several movements to occur through the process of its own contraction. This is typically a term designated for skeletal muscles...
and an antagonist, unless the muscle's natural state is opposite to that which is produced by the muscle, example Sphincter ani externus muscle
Sphincter ani externus muscle
The Sphincter ani externus is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus.-Anatomy:...
.
An "antagonist" is a classification used to describe a muscle
Muscle
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...
that acts in opposition to the specific movement generated by the agonist
Agonist (muscle)
Agonist is a classification used to describe a muscle that causes specific movement or possibly several movements to occur through the process of its own contraction. This is typically a term designated for skeletal muscles...
and is responsible for returning a limb to its initial position.
Antagonistic Pairs
Antagonistic muscles are found in pairs called antagonistic pairs.These consist of an extensor muscle, which "opens" the joint (i.e. increasing the angle between the two bones),
flexor muscle, which does the opposite to an extensor muscle.
Antagonistic pairs are needed in the body because muscles can only exert a pulling force, and can't push themselves back into their original positions.
An example of this kind of muscle pairing is the biceps brachii and triceps brachii.
When the biceps are contracting, the triceps are relaxed, and stretches back to its original position. The opposite happens when the triceps contract.