**4.5 Special junctional tissues of the healthy heart**

A healthy heart muscle is primarily made up of some specialized structures that play critical roles in commencing and transmitting impulses at a rate that is significantly faster than that of the remaining muscles. These structures are inclusively termed as the "Junctional Tissues of the Heart". They consist of the following structures—(i) S.A. (sino-atrial) node, (ii) A.V. (atrioventricular) node, (iii) Bundle of His, (iv) Bundle branch, (v) Purkinje fibers. A brief description is given below:


ventricles by these bundle branches. These branches can generate cardiac impulses at a rate of 36 beats/min in the event of failure of the S.A. and A.V. nodes.
