<P> The sympathetic nervous system (SNS) is one of the two main divisions of the autonomic nervous system, the other being the parasympathetic nervous system . (The enteric nervous system (ENS) is now usually referred to as separate from the autonomic nervous system since it has its own independent reflex activity .) </P> <P> The autonomic nervous system functions to regulate the body's unconscious actions . The sympathetic nervous system's primary process is to stimulate the body's fight - or - flight response . It is, however, constantly active at a basic level to maintain homeostasis homeodynamics . The sympathetic nervous system is described as being complementary to the parasympathetic nervous system which stimulates the body to "feed and breed" and to (then) "rest - and - digest". </P> <P> There are two kinds of neurons involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic . The shorter preganglionic neurons originate from the thoracolumbar region of the spinal cord specifically at T1 to L2 ~ L3, and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron . From there, the long postganglionic neurons extend across most of the body . </P> <P> At the synapses within the ganglia, preganglionic neurons release acetylcholine, a neurotransmitter that activates nicotinic acetylcholine receptors on postganglionic neurons . In response to this stimulus, the postganglionic neurons release norepinephrine, which activates adrenergic receptors that are present on the peripheral target tissues . The activation of target tissue receptors causes the effects associated with the sympathetic system . However, there are three important exceptions: </P>

Where do the cell bodies of preganglionic neurons of the sympathetic nervous system originate