Nerves leaving the ventral ramus of the spinals nerve cord pass through the chain of sympathetic ganglia so that from thoracic roots T2 to T4 the head and neck are innervated and from T2 to T8 the upper limbs are supplied.
There is some evidence of some innervation of the face and upper extremities from T1, even though autonomic function is presumed to arise only below the first thoracic root. For example, destruction of stellate ganglia (C8-T1 or T2) produces anhidrosis of the upper body and it's extremities. Despite these generalizations, the supply of nerves to small areas such as a finger may originate from as many as seven spinal segments. It may also be very important to recognize that the anatomy of the sympathetic chain is highly varied and that many nerves may bypass the ganglia entirely, thus accounting for numerous discrepancies in the literature concerning pathways and control.
List and Peet concluded from lesions at various levels that that section of the spinal cord and specific lesions within the cord result in loss of sweating in response to heat, but not to exogenous drugs. On the other hand, destruction of peripheral nerves by interruption of the nerve trunk results in loss of sweating in response to heat and drugs within two week.
Antiperspirants and Deodorants by Karl Laden
Edition: 2, illustrated, revised
Published by CRC Press, 1999, p.31