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Heart Structure - Anatomy & Physiology (view source)
Revision as of 14:13, 7 July 2008
, 14:13, 7 July 2008no edit summary
Although cardiac muscle fibres branch and interconnect with each other, they form two separate functional syncytia, one for the atria and another for the ventricles. The ends of each fibre in a network connect to its neighbours by irregular transverse thickenings of the sarcolemma called intercalated discs. The discs contain desmosomes, which hold the fibres together, and gap junctions, which allow ions to travel between cells and permit the rapid propagation of action potentials. Consequently, excitement of a single fibre of either network results in stimulation of all the other fibres in the network. As a result, each network contracts as a functional unit.
Although cardiac muscle fibres branch and interconnect with each other, they form two separate functional syncytia, one for the atria and another for the ventricles. The ends of each fibre in a network connect to its neighbours by irregular transverse thickenings of the sarcolemma called intercalated discs. The discs contain desmosomes, which hold the fibres together, and gap junctions, which allow ions to travel between cells and permit the rapid propagation of action potentials. Consequently, excitement of a single fibre of either network results in stimulation of all the other fibres in the network. As a result, each network contracts as a functional unit.
====Fibrous Skeleton====
In addition to cardiac muscle tissue, the heart wall also contains dense connective tissue that forms the fibrous skeleton of the heart. The fibrous skeleton is composed of dense connective tissue rings that surround the four heart orifices. The skeleton contains fibrocartilage in which nodules of bones (ossa cordis) may develop in some species. Although these bones occur most commonly in cattle, they are not restricted to this species. The skeleton performs several functions:
It serves as a point of attachment for the heart valves
The cardiac muscle bundles insert onto the fibrous skeleton.
It prevents the valves from overstretching as blood passes through them.
It acts as an electrical insulator thereby preventing the direct spread of action potentials from the atria to the ventricles.
===Chambers of the Heart===
===Chambers of the Heart===