In the neck. C stands for cervical.
Hello dear and welcome to the medhelp forum. C4-C5 is the cervical vertebrae in the neck, which encase the cervical part of the spinal cord. There is intervertebral disc in between the two vertebrae, which provide cushioning and act as shock absorbers. Nerve roots , C4 ,C5 traverse the spinal canal and exit at these neural foramina to follow the structures in the neck to reach their dermatome of supply. C4 C5 is the fourth and fifth of seven cervical vertebrae in the neck, located in the back of neck. Cheers and take care.