How does a contraction work?
Muscles are simply a tool that enables a contraction to take place. It's actually the brain that gives the command and decides to contract a muscle.
When we decide to execute this action, we order the brain to send a signal to the muscle. The motor cortex is the area of the brain that receives the order. It receives information from various regions of the brain that give the direction or speed of a movement, etc. The cortex analyses the information and translates it into a nerve impulse that it sends to a neuron. The electrical signal generated by the nerve impulse travels along the nerve channel.
The nerve impulse has to go through a number of stages to get to the muscle. So, in the upper part of the spinal cord, a second neuron, known as a motor neuron, takes over and reaches the muscle so that the nerve impulse stimulates it. The motor neuron is divided into many nerve endings at the tip and each of these endings enters into contact with the muscle fibre. The association of a motor neuron and fibres is called a motor unit.
Furthermore, the meeting point between the motor neuron and the fibres is called the neuromuscular junction. This is where the electrical signal triggers the liberation of chemical molecules, the famous neurotransmitters.
This is when a sequence of electrical phenomena take place that enables the liberated molecules to travel to the filaments so that they contract. This takes place simultaneously in numerous muscle fibres dispersed throughout the muscle.
After all of this, here we are with a muscle that works!