Describe the mechanism by which the human heart beat is initiated and controlled.

Explanation

The heart in human is myogenic (cardiomyocytes can produce spontaneous rhythmic depolarisation that initiates contractions). The sequence of electrical conduction of heart is shown below.

1. The cardiac cells with fastest rhythm are called the Pacemaker cells, which are located in the right sinuatrial (SA) node/ Pacemaker.
2. On the left side of the right atrium is a node called auriculo ventricular node (AV node).
3. Two special cardiac muscle fibres originate from the auriculo ventricular node and are called the bundle or llis which runs down into the interventricular septum and the fibres spread into the ventricles. These fibres are called the Purkinjle Abres.
4. Pacemaker cells produce excitatoion through depolaeisation of their call membrane, Early depolarisation is slow and takes place by sodium influx and reduction in potassium efflux.
5. Minimum potential is required to activate voltage paied calcium (Ca) channels that causes rapid depolarisation which results in action potential. The pace maker cells repolarise slowly via K. efflux.