The dorsal ramus of spinal nerve (or 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, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...

. The dorsal ramus (

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

for branch, plural ''rami'' ) is the dorsal branch of a

that forms from the

dorsal root The dorsal root of spinal nerve (or posterior root of spinal nerve or sensory root) is one of two "roots" which emerge from the spinal cord. It emerges directly from the spinal cord, and travels to the dorsal root ganglion. Nerve fibres with the ve ...

of the nerve after it emerges from the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...

. The spinal nerve is formed from the dorsal and

ventral rami The ventral ramus (pl. ''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 ...

. The dorsal ramus carries information that supplies

muscles Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of musc ...

and skin sensation to the

human back The human back, also called the dorsum, is the large posterior area of the human body, rising from the top of the buttocks to the back of the neck. It is the surface of the body opposite from the chest and the abdomen. The vertebral column r ...

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 (pl. ''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 n ...

. Spinal nerves are

mixed nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...

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 g ...

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 nerve fiber, afferent and Efferent nerve fiber, efferent nerve cell bodies that run along on either s ...

. 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 The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and other ...

. 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 latera ...

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 The transversospinales are a group of muscles of the human back. Their combined action is rotation and extension of the vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral c ...

, 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