Sympathetic nerves may leave the spinal cord at which vertebra?
a. first coccyx
b. first thoracic
c. third lumbar
d. second cervical

b. first thoracic

Explanation:

Sympathetic nervous system is one of the divisions of the autonomic nervous system. The other divisions are parasympathetic nervous system and enteric nervous system.

Autonomic nervous system is composed of preganglionic neurons and postganglionic neurons.

Similarly, the sympathetic nervous system is composed of postganglionic and preganglionic neurons.

The cell bodies of preganglionic neurons of sympathetic nervous system is found in intermediolateral cell columns of spinal cord segments T-T12 and L1-2 or 3. Therefore, sympathetic nervous system is also called thoracolumbar division.

The cell bodies of parasympathetic nervous system are found in the brainstem  nuclei which exit via cranial nerves 3, 7, 9, 10 and also in the sacral spinal cord segements S2-4, therefore parasympathetic nervous system is also known as craniosacral division.

QUESTION:

b. first thoracic

This is the correct answer choice as sympathetic nervous system cell bodies are found in intermediolateral cell column of T1-12 and L1-2 or 3 spinal cord segments. Hence, a sympathetic nerve is most likely to leave via first thoracic vertebra.

Third lumbar is less likely as sympathetic nervous system does not extend to this level in every individual.