The sympathetic nervous system (part of the autonomic nervous system) is concerned mainly with activating the “fight or flight” response. The nerves of the SNS communicate with organs within the body in response to certain stimuli. As a response, either epinephrine, or norepinephrine will be released (from adrenal medulla). The body’s response to stress for example is to release ephinephrine which reduces blood flow to the digestive organs, and increases heart rate and blood pressure. The origin or this response is a set of neurons (two neuron chains) in the thoracic and lumbar area of the spinal cord, which result in a connection to visceral organs and blood vessels. The connection between a preganglionic and postganglionic sympathetic neuron (via the synapse, dendrites and axons) results in a change in the body’s function.
The parasympathetic nervous system (also part of the autonomic nervous system) acts in a complimentary way to the sympathetic system, by slowing the body down, increasing intestinal and glandular activity, and relaxing sphincter muscles. It be summarized as “rest and digest”. The areas of the spinal cord associated with the parasympathetic system are the sacral and cranial divisions.