Ganglion stellatum, one on hay. and one on the left. side, is a fusion of the sympathetic border cord's lower cervical ganglion (C7,8) and uppermost thoracic ganglion (T1). The star-shaped fusion is located in front of the first rib's attachment to the vertebral column and is relatively easily accessible.
Note that all preganglionic threads that are to contact the postganglionic neuron of the cervical ganglia enter the boundary cord at a level below the lower cervical ganglia. After all, no preganglionic threads emerge from the cervical spinal cord segments (segments C1 through C8).
If you anesthetize the ganglion stellatum, "put a stellatum blockade", then the sympathetic nerve signals in the border cord cannot travel further upwards, which means that the sympathetic functions in the neck and head on the corresponding side cease. The "paralysis" that then arises is called "Horner's syndrome" and is characterized by
1/ drooping eyelids (ptosis), this is due to smooth muscle that keeps the eyelid raised paralyzed.
2/ severely constricted pupil (miosis), this is due to smooth muscles that dilate the pupil paralysis and
3/ "sunken eye" (enophthalmus), this is due to smooth muscle that pulls the eye globe forward into the eye socket paralyzed.
4/ Blood flow through the head increases.