sympathetic nervous system

n. (SNS) The division of the autonomic nervous system, which tends to be associated with catabolism, the expenditure of energy, in contrast with the parasympathetic system, which is associated with anabolism, the storage of energy. When the SNS is stimulated, blood flow to skeletal muscles is increased and epinephrine levels are raised, leading to an increase in heart rate and blood sugar levels, as well as piloerection (goose bumps).

Preganglionic neurons are cholinergic: they release acetylcholine, which binds to nicotinic receptor sites, leading to a rapid, brief response. Some of these neurons also release acetylcholine to muscarinic metabotropic receptor sites, leading to a slow response or even inhibition of response, depending on the type of stimulation. When the SNS motor neurons emerge from thoracic and lumbar levels of the spinal cord, they are then organized into a chain of sympathetic ganglia which lies along the spinal cord to coordinate appropriate responses.

A portion of the SNS not organized into the sympathetic ganglia is the medulla of 
the adrenal gland, which secretes adrenaline (epinephrine) in response to sympathetic preganglionic stimulation.

Postganglionic SNS neurons are adrenergic, sending axons directly to enervate their 
target organs. – VS