As I know the apnea's root cause is not only from the airway obstruction, but from my brain which does not send orders to breathe. Is that true?

Yes. Apnea comes in three varieties: central sleep apnea (csa) - the brain tells the body to stop breathing. This is not common in a normal, healthy patient. It can be seen in normal patients with transitions from one stage of sleep to the next. Csa is common in patients with heart disease and/or stroke. Obstructive apnea (osa) is where the airway collapses. Mixed apnea is a combination of osa/csa.
Apnea. Its true that some people have an element of what is called central apnea. They may have both central and obstructive sleep apnea. In most cases, obstructive causes predominate.