The muscles are in fact simply a tool that implements the contraction. Indeed, it is the brain that gives the order and chooses to contract the muscle.
When we decide to perform this action, we order the brain to send a signal to the muscle. The motor cortex is the area of the brain that receives this order. The latter receives the information from several regions of the brain which give the direction of the movement, its speed, etc.
The cortex analyses this information and translates it into nerve impulses that are sent to an initial neuron. The electrical signal generated by the nerve impulse flows through the length of this neuron.
In order to reach the muscle, the nerve impulse must go through several stages. Then in the upper part of the spinal cord, the relay is passed to a second neuron called the motor neuron that reaches the muscle so that the nerve impulse can stimulate it.
The end of this motor neuron is divided into several nerve endings and each of these endings comes into contact with the muscle fibre.
The connection of the motor neuron with the fibres is called the motor unit.
Moreover, the meeting point between the motor neuron and the fibres is called the neuromuscular junction. This is where the electrical signal triggers the release of chemical molecules, i.e. the so-called neurotransmitters.
A sequence of electrical phenomena then occurs which allows the released molecules to move to the filaments so that they contract. This occurs at the same time in the large number of muscle fibres distributed throughout the muscle.
After all that, the muscle works!
This is a painful and lasting contracture of a muscle caused by its excessive use. There are different kinds of contractures:
• Primitive muscle contracture: when the muscle is used intensively and for a prolonged period without recovery
• Muscle contracture with lesion: the muscle is physically injured in the case of a tear, elongation or strain
• Defensive muscle contracture: defence mechanism of an injured joint.
Muscle contractures affect especially the calves, the thighs, the buttocks, the muscles of the neck and the back. They are caused by the muscle fibres contracting.