Clinical meaning
Neurogenic shock is a distributive form of shock that results from the sudden loss of sympathetic nervous system tone following injury to the spinal cord, typically at the cervical or upper thoracic level (above T6). Under normal physiological conditions, the sympathetic nervous system maintains vascular tone by releasing norepinephrine from postganglionic sympathetic nerve fibers, which acts on alpha-1 adrenergic receptors on vascular smooth muscle to cause vasoconstriction. This tonic vasoconstriction is essential for maintaining systemic vascular resistance (SVR) and blood pressure. The sympathetic nervous system also innervates the heart through cardiac accelerator fibers originating from T1 through T4, which increase heart rate and contractility through beta-1 adrenergic receptor stimulation. When a spinal cord injury disrupts these sympathetic pathways, unopposed parasympathetic (vagal) activity dominates. The parasympathetic nervous system, carried by the vagus nerve (cranial nerve X), slows the heart rate and has no direct effect on peripheral vascular tone. The result is a triad of findings that distinguishes neurogenic shock from other forms of shock: hypotension (from massive vasodilation and loss of SVR), bradycardia (from unopposed vagal tone on the heart,...