Our breath is directly responsible for the state of our nervous system.
In short nervous system divides into parasympathetic and sympathetic.
The sympathetic system is activated when danger arising and the result is in so called fight and flight response. Breathing through mouth activates sympathetic nervous system.
When the sympathetic system is on adrenaline level raises rapidly, we feel blood rushes to our extremities and they start to become active. Our hands and legs receive big boost of energy making the body efficient enough to whether escape or win a fight. While extremities receiving such an enormous boost of energy, digestive, immune and reproductive systems are deprived from the essential energy supply. These systems become irrelevant in danger situations, so brain decides to divert the energy in this case where it needed to be – in extremities – to save the life.
When we breathe through nose parasympathetic system becomes activated. It is on when the there is peace and tranquillity in the environment, brain switches the organism into parasympathetic mode. This is when immune, digestive and reproductive systems receive vital energy to function and whole organism becomes rejuvenated and healing occurring.
In the modern world we often in the sympathetic mode activation since our brain recognizes danger where there is none. Our ego often doesn’t let go of the past situations playing it again and again in our mind. While we are still clinging to the situation, our stress level remains in the system, stimulating sympathetic system to be activated. Hence we are suffering from lack of immunity, depression, pure digestion and so on.
The purpose of yoga class is to bring you to complete parasympathetic state. Breathing through nose is essential for that as well as breath leading and movement follows the breath. Observation becomes possible only in this state.