Cardiac Muscle Fibres :

Occurrence : They are present in myocardium of heart.

Structure : Each cardiac muscle fibre is bounded by plasmalemma. They are separated from each other by intercalated discs. These intercalated discs act as boosters. The adjacent muscle fibres are connected by oblique cross walls. The cardiac muscle fibre has deep in centre a slightly oval nucleus. The myofibrils are present and have light and dark bands. The cardiac muscle fibres have abundant blood supply that is why they are of dark red colour. These fibres contract quickly and take double the time to relax and that is why they never feel fatigued.

Control : They are controlled by central and autonomic nervous system.