Posts Tagged ‘sympathetic’

Sympathetic Nerves, N.Phrenicus and Nn.Splanchnici

An article on sympathetic nerves, phrenic and splanchnic nerves.

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The sympathetic ganglia are swellings along the length of the pair of sympathetic trunks running longitudinally on either side of the vertebral column. The sympathetic trunks are located anterior to the cervical transverse processes, anterior to the heads of the ribs, on the antero- lateral aspects of the lumbar vertebral bodies, on the anterior aspect of the sacrum (medial to the ventral sacral foramina) and on the front of the coccyx. They are located at the site of synapses between the preganglionic and postganglionic neurons. There are a variable number of ganglia, approximately two (or three) cervical, eleven thoracic, four lumbar, four sacral and one coccygeal. The ventral rami of all spinal nerves are connected to the sympathetic trunk by gray rami communicantes. The ventral rami of T1 to L2 (L3) are also connected to the sympathetic trunk by white rami communicantes.

The Innervation of the Heart

An article on the innervation of the heart muscle.

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Initiation of the cardiac cycle is myogenic, originating in the sinuatrial node (SA). It is harmonizied in rate, force and output by autonomic nerves which operate on the nodal tissues and their prolongations, on coronary vessels and on the working atrial and ventricular musculature. All the cardiac branches of the N.vagus, X. cranial nerve, (parasympathetic) and all the sympathetic branches (except the cardiac branch of the superior cervical sympathetic ganglion) contain both afferent and efferent fibres; the cardiac branch of the superior cervical sympathetic ganglion is entirely efferent. Sympathetic fibres accelerate the heart and dilate the coronary arteries when stimulated, whereas parasympathetic (vagal) fibres slow the heart and cause constriction of coronary arteries.