 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 these 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. Iska mukabhle mein jus skeletal muscle cells hai go multinucleate hote hain. The cardiac muscle fibers are innervated only diffusely by the excitatory, sympathetic neurons and inhibitory parasympathetic neurons. Iska mukabhle mein jus skeletal muscle fibers hai go individually innervated hote hain by only excitatory motor neurons axons. Dear students, the cardiac neural innervations are only modulatory in their role. Contractions in cardiac muscles are produced because of the electrical activity of pacemaker not because of the nerve impulses. Ye jo cardiac neural innervations hai ye post-synaptic potentials bhi produce nahin karthi cardiac cells mein. Toh inka bhi role jo hai ho sirf ye hai ke ye cardiac cells ki contractions ki strength ko increase or decrease karthi. Dear students, the cardiac muscle cells are connected with each other through interclated disks. Ye jo interclated disks hain ye elektrikali connect kati hain cells ko. Isliye pacemaker region mein jo action potential generate hote hain wo rapidly hartke ek cell se du se cell tak in fast conducting pathways ke through transfer ho jata hai. Dear students, now we shall discuss the contraction mechanism of cardiac muscles. The contraction mechanism of cardiac muscles fundamentally resembles to that of skeletal twitch muscles, yani ke 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. Iske mukabh le mein action potentials in cardiac muscles have a palliative ways of hundreds of milliseconds long. Dear students, ye jo action potential ki long duration hain aur uske baad longer refractory period hain that prevents the tattinic contractions of cardiac muscle fibres. It also permits the muscles to relax. As a result ventricles ke feeling ke liye jo time required hain wo isi gap ke dhoran hain jis me ke do action potentials ke dar mein anka jo gap hain wo 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 betor pump ke jab heart ne kama karna hain toh phir ye wali regular pacing and prolonged apes are required jo ke heart ke muscles ke paas hain. Dear students, heart ke muscles e contraction ka jo mechanism hain, excitation contraction coupling jo hain that involves raising of the calcium ion concentration in cytoplasm. Calcium ions ka influx do trikon se jaisi ke skeletal muscle fibres me hota hain usi taray se hota hain that is across the plasma membrane and from the cells internal resources involving sarcoplasmic reticulum. Choke sarcoplasmic reticulum me calcium ions ka store hain is liye cardiac muscle fibres ke under b jo network hain sarcoplasmic reticulum ka aur T-tubules ka wo bohot elaborate hota hain.