There are many physiological pathways and mechanisms that regulate the cardiovascular system. One of the most important of these is the autonomic nervous system. The sympathetic outflow originates from preganglionic neurons located in the lateral horns of the spinal cord (T1-L2). These neurons connect through synapses to postganglionic neurons. These synapses are located in the two sympathetic chains that lie on either side of the vertebral column. The postganglionic neurons form the sympathetic nerves supply the effector organs.
The vagus nerve supplies the only important parasympathetic nerve fibres to the cardiovascular system. Parasympathetic ganglia are embedded in the heart, mainly on the SA and AV nodes. Postganglionic parasympathetic fibres are very short.
ß2 receptors are present on other organs, stimulation causes relaxation e.g. of bronchial and uterine smooth muscle.
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