Sympathetic nervous system 1
Of course, you already know that the source of all preganglionic sympathetic fibers is the lateral horn of the spinal cord between T1 and L2. These fibers leave the spinal cord via the ventral rootlet, spinal nerve, ventral primary ramus, and white ramus communicans at each level between T1 and L2 only.
Because tissues in the head require sympathetic innervation, some of the higher thoracic preganglionic fibers ascend into the neck without synapsing - forming the cervical sympathetic trunk. These fibers will synapse in one of three cervical sympathetic chain ganglia - superior, middle, or inferior. (The inferior cervical ganglion often fuses with the first thoracic ganglion to form a stellate or cervicothoracic ganglion.)
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