 Dear students, in this topic we shall discuss the features of cardiac muscles. The cardiac muscles are found only in the heart. These muscles are striated muscles like the skeletal muscles. So, they share many characteristics with skeletal muscles, however they differ from skeletal muscles in several important features. The cardiac muscle cells are called myocytes and these cells are mononucleate, that is, they have only single nucleus in each cell. The skeletal muscle cells are mononucleated. The cardiac muscle fibers are innervated only diffusely by the excitatory, sympathetic neurons and inhibitory parasympathetic neurons. The skeletal muscle fibers are individually innervated by the excitatory motor neurons axons. Dear students, the cardiac neural innervations are only modulatory in their role. Hence, these cardiac muscles are produced because of the electrical activity of pacemaker, not because of the nerve impulses. These cardiac neural innervations do not produce post-synaptic potentials in the cells. So, their role is only to increase and decrease the strength of the contractions of the cardiac cells. Dear students, the cardiac muscle cells are connected with each other through interclated disks. These interclated disks are electrically connected to the cells, so the action potential generated in the pacemaker region is rapidly transferred from one cell to another through these fast conducting pathways. Dear students, now we shall discuss the contraction mechanism of cardiac muscles. The contraction mechanism of cardiac muscles fundamentally resembles two that of skeletal twitch muscles, meaning it is activated by an increase in cytosolic calcium ion concentration. However, difference kaha pe hai that is the action potentials length differ in both cardiac and skeletal muscles. Skeletal muscles' action potentials are of very short duration. Is ke mukab le mein, action potentials in cardiac muscles have a plaito phase of hundreds of milliseconds long. Dear students, ye jo action potential ki long duration hai aur uske baad longer refractory period hai that prevents the tattinic contractions of cardiac muscle fibres. It also permits the muscles to relax. As a result ventricles ki feeling ke liye jo time required hai wo issi gap ke dhoran hai jisme ke do action potentials ke dar mein anka jo gap hai, us dhoran mein ventricles are filled with blood. Dear students, the regular pace and prolonged duration of action potentials causes the heart to beat, iterate which is suitable for its functioning as a pump. To batohar pump ke jab heart ne kama karna hai toh phir ye wali regular pacing and prolonged apis are required jo ke heart ke muscles ke paas hai. Dear students, heart ke muscles ki contraction ka jo mechanism hai, excitation contraction coupling jo hai that involves raising of the calcium ion concentration in cytoplasm. Calcium ions ka influx 2-3 kon se jaisi ke skeletal muscle fibres me hota hai usi tarah se hota hai that is across the plasma membrane and from the cells internal resources involving sarcoplasmic reticulum. Choke sarcoplasmic reticulum mein calcium ions ka store hai isliye cardiac muscle fibres ke andar bhi jo network hai sarcoplasmic reticulum ka aur T-tubules ka wo bohot elaborate hota hai.