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Réponse :
introduction
Muscles are active organs always acting in groups of two antagonistic or opposite muscles. They cause a passive displacement of the bones on which they are firmly fixed by tendons. Let's show how does muscles act on bone to cause movement
Development
When a muscle produces a movement there is a message that is made so that the muscle reacts. This message will be sent to the nerve centers, brain, spinal cord. The muscles which, by contracting, cause the movements, are they effector organs. They contract in a coordinated way following the reception of a motor nervous message, emitted by the nervous centers.
The muscles cause a passive displacement of the bones on which they are firmly fixed by tendons. The muscles are also contracted and elastic: they shorten or lengthen. When they contract, it's always to respond to nervous messages.
Let's take an example
• A muscle of the arm, such as the biceps, has an elongated spindle shape with a swollen part: the belly. Its red hue indicates the presence of a red pigment specific to the muscle. Every muscle is irrigated by the blood, which is necessary for its functioning, and well innervated.
• During the flexion of the forearm, we find, by palpation, that the biceps (anterior muscle of the arm) is shortened, hardens: it is in contraction. The change of state of this muscle, compared to rest, obviously causes the approach of the forearm to the arm: the biceps is a flexor muscle. In the same flexion, the triceps (posterior muscle of the arm) remains elongated and soft: it is relaxed or relaxed. Thus, the only flexion of the arm involves two opposing or antagonistic muscles: the contracted biceps and the relaxed triceps. These two muscles act in a coordinated way to allow this movement.
• When extending the forearm, palpation shows us that the biceps lengthens and becomes softer (relaxes), while the triceps shortens and hardens (contracts): the triceps is a extensor muscle.
Conclusion
The muscles are also contractile and elastic organs: they shorten or elongate. When they contract, it's always to respond to nervous messages.
Explications :