<prompt> Cellular junctions present in cardiac muscle are all exceptZonula occludensFascia adherensGap junctionsMacula adherens  <response>: Ans. a Zonula occludensRef: Ganongs Review of medical physiology 25th edp. 112Cardiac muscle cells are connected by,Fascia adherens - it is the structural analog of zonula adherensGap junctionsMacula adherensZonula occludens is the other name for tight junction. It is absent in cardiac muscleGap Junctions Gap junctions permits substances to pass between the cells without entering the extracellular fluid ECF Gap junctions are composed entirely of an integral membrane protein called connexons Each connexon is made up of six protein subunits called connexins Gap junctions are abundant in cardiac muscles which are called as intercalated discs. It is because of this,cardiac muscle functions as single unit called as functional syncytium Gap junctions are also seen in single unit smooth muscles seen in visceral organs Mutations in connexin leads to many human diseases namely,Connexin C x subtype mutationDiseaseCx32X-linked Charcot-Marie- Tooth diseaseCx26, Cx30, and Cx31Congenital sensorineural hearing lossCx30Clouston syndromeCx40Idiopathic atrial fbrillationCx46 and Cx50Cataract 