The dorsal ramus of spinal nerve, posterior ramus of spinal nerve, or posterior primary division is the posterior division of 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 ...

. The dorsal rami provide motor innervation to the deep (a.k.a. intrinsic or true) muscles of the back, and sensory innervation to the skin of the posterior portion of the head, neck and back. A spinal nerve splits within the

intervertebral foramen The intervertebral foramen (also neural foramen) (often abbreviated as IV foramen or IVF) is an opening between (the intervertebral notches of) two pedicles (one above and one below) of adjacent vertebra in the articulated spine. Each interve ...

to form a dorsal ramus and a ventral ramus. The dorsal ramus then turns to course posterior-ward before splitting into a medial branch and a lateral branch. Both these branches provide motor innervation to deep back muscles. In the neck and upper back, the medial branch is also responsible for providing sensory innervation of the skin; in the lower back, the lateral branch does so. All medial branches additionally also provide sensory innervation to the zygapophyseal joints and

periosteum The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. (At the joints of long bones the bone's outer surface is lined with "articular cartila ...

of the

vertebral column The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmente ...

Structure

Ventral root axons join with dorsal root ganglia to form mixed spinal nerves (below). These then merge to form peripheral nerves. Shortly after this

forms, it then branches into the dorsal ramus and

ventral ramus The ventral ramus (: rami) (Latin for 'branch') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami. Shortly after a spinal nerve e ...

. Spinal nerves are

mixed nerve A mixed nerve is any nerve that contains both sensory ( afferent) and motor ( efferent) nerve fibers. All 31 pairs of spinal nerves are mixed nerves. Four of the twelve cranial nerves – V, VII, IX and X are mixed nerves. Examples Spinal n ...

s that carry both sensory and

motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gene ...

information. It also branches to form the grey and the white rami communicantes which make connections with the

sympathetic ganglia The sympathetic ganglia, or paravertebral ganglia, are autonomic ganglia of the sympathetic nervous system. Ganglia are 20,000 to 30,000 afferent and efferent nerve cell bodies that run along on either side of the spinal cord. Afferent nerve cel ...

. After it is formed, the dorsal ramus of each spinal nerve travels backward, except for the first cervical, the fourth and fifth sacral, and the coccygeal. Dorsal rami divide into medial, intermediate, and lateral branches. The lateral branch supplies innervation to the

iliocostalis Iliocostalis muscle is the muscle immediately lateral to the longissimus that is the nearest to the furrow that separates the epaxial muscles from the hypaxial. It lies very deep to the fleshy portion of the serratus posterior muscle. It late ...

muscle, as well as the skin lateral to the muscle on the back. The Intermediate branch supplies innervation to the spinalis muscle and the longissimus muscle. The medial branch supplies innervation to the rest of the epaxial derived muscles on the back (including the transversospinales, intertransversarii muscles, interspinalis muscles, suboccipital muscles, and splenius), and the zygapophyseal joints.

Function

Because each

carries both sensory and motor information, spinal nerves are referred to as

s. Posterior rami carry visceral motor, somatic motor, and sensory information to and from the skin and deep muscles of the back. The posterior rami remain distinct from each other, and each innervates a narrow strip of skin and muscle along the back, more or less at the level from which the ramus leaves the spinal nerve.

References

Additional images

Image:Spinal nerve.svg, The formation of the spinal nerve from the dorsal and ventral roots.

External links

* () {{DEFAULTSORT:Dorsal Ramus Of Spinal Nerve Spinal nerves Thoracic nerves