Sympathetic nervous system

The division of the autonomic nervous system that mobilizes the body for activity, including by increasing heart rate, widening airways, and redirecting blood flow.

Thoracolumbar outflow: The sympathetic preganglionic nerve supply arising from spinal cord segments T1 through L2 or L3. Its spinal origin distinguishes sympathetic pathways from the craniosacral parasympathetic outflow.
Fight-or-flight response: A coordinated physiological response that prepares an organism to confront or escape an acute threat. It is the familiar whole-body pattern produced by strong sympathetic activation.
Autonomic nervous system: The nervous system that regulates involuntary functions such as heart activity, digestion, and gland secretion. The sympathetic division is one of its major branches.
Somatic nervous system: The nervous system division that controls skeletal muscles and carries sensory information to the central nervous system. Unlike sympathetic output, somatic motor pathways directly control skeletal muscle.
Sympathetic chain: A paired series of ganglia running alongside the vertebral column, where sympathetic neurons can relay signals. These ganglia distribute spinal signals to targets at multiple levels of the body.
Pupil dilation: An increase in pupil diameter caused by contraction of the iris dilator muscle. Sympathetic activation widens the pupil, increasing light entry during alert states.
Parasympathetic nervous system: The autonomic division that supports functions such as digestion and energy conservation, often opposing sympathetic effects. Its contrasting patterns clarify how the two divisions jointly regulate organs.
Enteric nervous system: The network of neurons in the gastrointestinal tract that coordinates local digestive functions. It can organize gut activity locally, though sympathetic input modulates it.
Adrenal medulla: The inner region of the adrenal gland, which releases catecholamines into the bloodstream in response to sympathetic input. It extends sympathetic signaling through circulating hormones rather than nerve terminals alone.
Bronchodilation: An increase in airway diameter caused by relaxation of bronchial smooth muscle. This response helps increase airflow during exertion and acute stress.

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