posterior ramus of spinal nerve
Definition: the smaller, posteriorly directed major terminal branch (with the anterior ramus) of all 31 pairs of mixed spinal nerves, formed at the intervertebral foramen and then turning abruptly posteriorly to divide into lateral and medial branches, both of which will supply the deep (true) muscles of the back. The medial branch (rami medialis [TA]) of the dorsal primary ramus also supplies articular branches to the zygapophysial joints and the periosteum of the vertebral arch. In the neck and upper back, the medial branch continues through the deep and superficial back muscles to supply overlying skin; in the lower back, the lateral branch does this. Terminologia Anatomica lists posterior rami (rami dorsales) for each group of spinal nerves: 1) cervical (nervorum cervicalium [TA]), 2) thoracic (nervorum thoracicorum [TA]), 3) lumbar (nervorum lumbalium [TA]), 4) sacral (nervorum sacralium [TA]), and 5) coccygeal (nervi coccygei [TA]).
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