read your comment saw the pics. understood.its T tubule invagination along with the 2 cisternae (3 structures) form the triad
in skeletal muscle, where as in cardiac muscle only 1 cisternae along with t tubule form the diad
hope u got it
hello seetal,hi kabutar111,
it is invaginated because with the NTs ACh, the muscarinic receptors at the NMJ are triggered n this causes release of Ca2+ to cause muscle contractions. without a stimulation n also with depletion of ATP, muscle contractions do not occur. which is y in myasthenia gravis, where the ACh receptors are blocked by autoantibodies, the muscles become paralyzed.