Thoracic Sympathetic Nervous System

Anatomy and Function

• The cardiac sympathetic outflow originates from a broader range of thoracic segments than the upper four or five thoracic spinal cord segments, with preganglionic neurons supplying cardiac function distributed across multiple thoracic levels, typically T1-T5 or T6 1
• The primary cardiac sympathetic effects include increased heart rate, enhanced contractility, and improved conduction velocity, with the coronary arteries possessing both alpha-adrenergic receptors and beta-2 adrenergic receptors, resulting in vasodilation to meet increased myocardial oxygen demand during sympathetic activation 1, 2

Sympathetic Nerve Pathways

• The splanchnic nerves (greater, lesser, and least) are composed of preganglionic sympathetic fibers that originate from the intermediolateral cell column of the thoracolumbar spinal cord, passing through the sympathetic chain without synapsing and traveling to prevertebral ganglia where they synapse with postganglionic neurons 1