Navel centre. Manipura - governs the larger vital. 
NATURE (CHANGE OF)
Regulating moral habits.  The Niyamas are a discipline of the mind by regular practices of which the highest is meditation on the divine Being, and their object is to create a sattwic calm, purity and preparation for concentration upon which the secure pursuance of the rest of the Yoga can be founded. 
The Navel centre (Nābhipadma) commanding the larger life-forces and passions and larger desire-movements is the main seat of the centralised vital consciousness (dynamic centre) which ranges from the heart level (emotional) to the centre below the navel (lower vital, sensational desire centre). 
The navel is the vital centre in the physical body but the natural seat of the vital is in the vital sheath of the subtle body, which sheath it pervades; but for action through the gross body it is centred at the navel and below it. 
Faith . Concentrated will in devotion.
The name of the Divine is usually called in for protection, for adoration, for increase of bhakti, for the opening up of the inner consciousness, for the realisation of the Divine in that aspect. As far as it is necessary to work in the subconscious for that, the Name must be effective there. Repetition of the name. 
Repressive contraction of the nature; 
Nigraha (coercion and suppression) is a violence done to the nature by the will, which in the end depresses the natural powers of the being. 
Nigraha means holding down the movement, but a movement merely held down is only suspended—it is better to reject and dismiss, detaching yourself from it. 
The difference between suppression (nigraha) and self-control (saṁyama) is that one says, “I cannot help desiring but I will not satisfy my desire”, while the other says, “I refuse the desire as well as the satisfaction of the desire”. 
The difference between nigraha and saṁyama is that in the first process there is a violent struggle to put down, coerce and, if possible, crush the tendency, the reality of which is not questioned, but in the second process it is envisaged as a dead or dying force, its occasional return marked with disgust, then with impatience, finally with indifference as a mere ghost, vestige or faint echo of that which was once real but is now void of significance. 
The physical nerves are part of the material body, but they are extended into subtle nerves in the subtle body and there is a connection between the two. 
The nerves are distributed all over the body—but the vital physical action is concentrated in its origin between the Muladhara and the centre just above it.