Question

define pacemaker, and Sn node brief description

Answer 1

Once your pacemaker is implanted, the battery should last five to 15 years, which is the average battery life. When a pacemaker's battery wears out, thepacemaker's pulse generator is replaced. ... By preventing a slow heart rate, pacemakers can treat symptoms, such as fatigue, lightheadedness and fainting.

Answer 2

A pacemaker is a small electrical device, fitted in the chest or abdomen. It's used to treat some abnormal heart rhythms  that can cause your heart to either beat too slowly or miss beats. Some pacemakers can also help the chambers of your heart beat in time.

The sinoatrial node (SA node), also known as sinus node, is a group of cells located in the wall of the right atrium of the heart.[1] These cells have the ability to spontaneously produce an electrical impulse , that travels through the heart via the electrical conduction system  causing it to contract. In a healthy heart, the SA node continuously produces action potential, setting the rhythm of the heart and so is known as the heart's natural pacemaker. The rate of action potential production (and therefore the heart rate) is influenced by nerves that supply it.