Cardiac Muscle cells are striated, just as in skeletal muscle and are found only in the heart. They work on a rhythmn set by a group of pacemaker cells locted in the right atrium of the heart. This self-automated contraction property is called being 'myogenic'.
The Pacemaker releases an electrical impulse approximately 70 times per minute, which causes the heart to contract. The signals are sent via the involuntary nerves from the cardia control centre loacted in the medulla of the brain.
The rate of impulses can be increased by the cardiac accelerator nerve, or by the hormone adrenalin.
The rate of impulses can be decreased by the cardiac depressor nerve.
IB Biology Higher Level Revision Guide 2009 syllabus
Oxford IB Revision Guides
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