Myelin sheath is the covering or wrap around the nerves that provide insulation to nerves which is made up of protein and fatty acids like plasma membrane and therefore known as modified plasma membrane.
It helps to transmit electrical impulses along the nerve cells quickly. Schwann cells are major glial cells of the pns which wrap around neurons to form a covering of the the myelin sheath.
Behavior Modification is the alteration of behavioral patterns through the use of such learning techniques as biofeedback and positive or negative reinforcement.