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 exits the
intervertebral foramen, it branches into the
dorsal ramus, the ventral ramus, and the
ramus communicans. Each of these three structures carries both
sensory and
motor information. Each
spinal nerve is a
mixed nerve that carries both sensory and motor information, via
efferent and
afferent nerve fibers—ultimately via the motor cortex in the frontal lobe and to somatosensory cortex in the parietal lobe—but also through the phenomenon of
reflex.
In the thoracic region they remain distinct from each other and each
innervates a narrow
strip of muscle and skin along the sides, chest, ribs, and abdominal wall. These rami are called the
intercostal nerves. In regions other than the thoracic, ventral rami converge with each other to form networks of nerves
called
nerve plexuses. Within each plexus, fibers from the various ventral rami branch and
become redistributed so that each nerve exiting the plexus has fibers from several different spinal nerves. One advantage to having plexes is that damage to a single spinal nerve will not completely paralyze a limb.
There are four main plexuses formed by the ventral rami:
the
cervical plexus contains ventral rami from spinal nerves C1–C4. Branches of the
cervical plexus, which include the phrenic nerve, innervate muscles of the neck, the diaphragm, and the skin of the neck and upper chest.
The
brachial plexus contains ventral rami from spinal nerves C5–T1. This plexus innervates
the pectoral girdle and upper limb.
The
lumbar plexus contains ventral rami from spinal nerves L1–L4. The
sacral plexus contains ventral
rami from spinal nerves L4–S4. The lumbar and sacral plexuses innervate the pelvic girdle and lower limbs.
Ventral rami, including the sinuvertebral nerve branches, also supply structures anterior to the facet joint, including the vertebral bodies, the discs and their ligaments, and joins other spinal nerves to form the
lumbosacral plexus.
References
External links
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* - "
Lumbosacral plexus"
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Spinal nerves
Thoracic nerves