dorsal ramus

(noun)

The posterior (or dorsal) branches (or divisions) of the spinal nerves are, as a rule, smaller than the anterior divisions. They are also referred to as the dorsal rami. They are directed backwards and—with the exceptions of those of the first cervical, the fourth and fifth sacral, and the coccygeal—divide into medial and lateral branches for the supply of the muscles and skin of the posterior part of the trunk.

Related Terms

Examples of dorsal ramus in the following topics:

  • Branches of Spinal Nerves

    • The spinal nerves branch into the dorsal ramus, ventral ramus, the meningeal branches, and the rami communicantes.
    • The dorsal ramus: Contains nerves that serve the dorsal portions of the trunk carrying visceral motor, somatic motor, and sensory information to and from the skin and muscles of the back.
    • The ventral ramus: Contains nerves that serve the remaining ventral parts of the trunk and the upper and lower limbs carrying visceral motor, somatic motor, and sensory information to and from the ventrolateral body surface, structures in the body wall, and the limbs.
    • The posterior division (dorsal ramus) is labeled at the top right.

  • Ischium

    • The superior ramus of the ischium extends inferiorly and posteriorly from the body.
    • Posteriorly the ramus forms a large swelling termed the tuberosity of the ischium, or ischial tuberosity, which supports weight while sitting and is the origin for the gemellus inferior and adductor magnus muscles.
    • Dorsally, the ramus contributes to the obturator foramen, a large opening in the pelvis through which key nervous and vascular vessels pass.
    • The inferior ramus of the ischium is thin and flattened and ascends from the superior ramus of the ischium to join the inferior ramus of the pubis.

  • Overview of the Spinal Nerves

    • The dorsal roots carry afferent sensory axons, while the ventral roots carry efferent motor axons.
    • The dorsal ramus contains nerves that serve the dorsal portions of the trunk; it carries visceral motor, somatic motor, and somatic sensory information to and from the skin and muscles of the back (epaxial muscles).
    • This branch is called the medial cutaneous ramus.
    • This sensitive branch is called the posterior cutaneous ramus.
    • Spinal nerves arise from a combination of nerve fibers from the dorsal and ventral roots of the spinal cord.

  • Pubis

    • The pubic bone is divisible into a body, a superior ramus, and an inferior ramus .
    • The superior pubic ramus is one third of the pubic bone.
    • The inferior pubic ramus is a thin and flat bone that makes up one third of the pubis.
    • It passes laterally and downward from the medial end of the superior ramus, and becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen.
    • (1) sacrum, (2) ilium, (3) ischium, (4) pubis: 4a-body; 4b-superior ramus; 4c-inferior ramus, (5) pubic symphisis, (6) acetabulum, (7) obturator foramen, (8) coccyx, (red dotted line) linea terminalis.

  • Spinal Cord Grey Matter and Spinal Roots

    • The cord has grooves in the dorsal and ventral sides.
    • Axons of these sensory neurons travel into the spinal cord via the dorsal roots.
    • The dorsal root ganglia lie along the vertebral column by the spine.
    • The dorsal root ganglia develops in the embryo from neural crest cells, not the neural tube.
    • The axons of dorsal root ganglion neurons are known as afferents.

  • Vertebrate Axis Formation

    • This suggested that the dorsal cells were genetically programmed to form the notochord and define the dorsal-ventral axis.
    • High Wnt signaling establishes the dorsal region while high Shh signaling indicates in the ventral region.
    • Wnt is also involved in the dorsal-ventral formation of the central nervous system through its involvement in axon guidance.
    • Wnt is also involved in the formation of the limb dorsal-ventral axis.
    • Specifically, Wnt7a helps produce the dorsal patterning of the developing limb.

  • Somatic Sensory Pathways to the Cerebellum

    • The ventral and dorsal spinocerebellar tracts convey proprioceptive information from the body to the cerebellum.
    • It is part of the somatosensory system and runs in parallel with the dorsal spinocerebellar tract.
    • The dorsal spinocerebellar tract does not decussate, or cross sides, at all through its path.
    • The axon runs via the fila radicularia (nerve rootlets) to the dorsal horn of the gray matter.
    • These central processes travel through the dorsal horn where they synapse with second order neurons of Clarke's nucleus.

  • Embryonic Development

    • At the dorsal end of the neural tube, BMPs are responsible for neuronal patterning.
    • A secondary signaling center is then established in the roof plate, the dorsal most structure of the neural tube.
    • BMP from the dorsal end of the neural tube seems to act in the same concentration-dependent manner as Shh in the ventral end.
    • Researchers observed changes in dorsal-ventral patterning; for example zebrafish deficient in certain BMPs showed a loss of dorsal sensory neurons and an expansion of interneurons.
    • Chick embryo of thirty-three hours' incubation, viewed from the dorsal aspect (30x magnification).

  • Characteristics of Chordata

    • Animals in the phylum Chordata share four key features: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
    • The dorsal hollow nerve cord derives from ectoderm that rolls into a hollow tube during development.
    • In chordates, it is located dorsally (at the top of the animal) to the notochord.
    • In chordates, four common features appear at some point during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

  • Establishing Body Axes during Development

    • Animal bodies have three axes for symmetry (lateral-medial, dorsal-ventral and anterior-posterior) which are established in development.
    • However, animal bodies have lateral-medial (left-right), dorsal-ventral (back-belly), and anterior-posterior (head-feet) axes .
    • This suggested that the dorsal cells were genetically programmed to form the notochord and define the axis.
    • The dorsal part of the neural tube contains the alar plate, which is primarily associated with sensation.
    • The dorsal (back) surface of the embryo is toward the top of this page, while the ventral (front) surface is toward the bottom.