sympathetic

Meaning: The sympathetic division of the autonomic (involuntary) nervous system prepares the body for fight or flight. Its preganglionic neurons leave the thoracic and lumbar spinal cord, are short, and synapse in ganglia near the cord (including the sympathetic chain) onto long postganglionic neurons. Preganglionic neurons release acetylcholine; most postganglionic neurons release norepinephrine, with sweat glands as a notable exception (acetylcholine). The adrenal medulla works like a modified ganglion: preganglionic fibers stimulate it to release epinephrine and norepinephrine into the blood. Typical effects are faster heart rate, bronchodilation, pupil dilation, glucose release, and slower digestion.

On the MCAT: Expect questions that ask you to predict the effect of sympathetic stimulation on heart rate, pupil size, or gut motility, or to identify the division from anatomy: short preganglionic and long postganglionic fibers point to sympathetic. Passages may also describe an adrenergic agonist or blocker, and you reason from the receptor's normal response.

Common confusion: Students mix up the sympathetic and parasympathetic divisions. The parasympathetic division (rest and digest) has long preganglionic and short postganglionic neurons, arises from cranial and sacral regions, and uses acetylcholine at both synapses. Sympathetic does not speed up every organ; digestion slows.