The cervical spinal nerve 3 (C3) is a

spinal nerve A spinal nerve is a mixed nerve, which carries Motor neuron, motor, Sensory neuron, sensory, and Autonomic nervous system, autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each s ...

of the

cervical segment The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

.American Medical Association
Nervous System -- Groups of Nerves It originates from the spinal column from above the cervical vertebra 3 (C3).

References

Spinal nerves {{neuroanatomy-stub