The ventral ramus (pl. ''rami'') (Latin for ''branch'') is the anterior 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 th ...
. The ventral rami supply the antero-lateral parts of the
trunk and the limbs. They are mainly larger than the
dorsal rami
The dorsal ramus of spinal nerve (or posterior ramus of spinal nerve, or posterior primary division) is the posterior division of a spinal nerve. The dorsal ramus (Latin for branch, plural ''rami'' ) is the dorsal branch of a spinal nerve that form ...
.
Shortly after a spinal nerve exits the
intervertebral foramen
The intervertebral foramen (also called neural foramen, and often abbreviated as IV foramen or IVF) is a foramen between two spinal vertebrae. Cervical, thoracic, and lumbar vertebrae all have intervertebral foramina.
The foramina, or openi ...
, it branches into the
dorsal ramus
The dorsal ramus of spinal nerve (or posterior ramus of spinal nerve, or posterior primary division) is the posterior division of a spinal nerve. The dorsal ramus (Latin for branch, plural ''rami'' ) is the dorsal branch of a spinal nerve that form ...
, the ventral ramus, and the
ramus communicans
Ramus communicans (plural rami communicantes) is the Latin term used for a nerve which connects two other nerves, and can be translated as "communicating branch".
Structure
When used without further definition, it almost always refers to a commu ...
. Each of these three structures carries 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. Each
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 th ...
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 biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
. Spinal nerves are referred to as "mixed nerves".
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 plexus
A nerve plexus is a plexus (branching network) of intersecting nerves. A nerve plexus is composed of afferent and efferent fibers that arise from the merging of the anterior rami of spinal nerves and blood vessels. There are five spinal nerve ple ...
es. 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
The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...
contains ventral rami from spinal nerves C5-T1. This plexus innervates
the pectoral girdle and upper limb.
The
lumbar plexus
The lumbar plexus is a web of nerves (a nervous plexus) in the lumbar region of the body which forms part of the larger lumbosacral plexus. It is formed by the Ventral ramus of spinal nerve, divisions of the first four lumbar nerves (L1-L4) and ...
contains ventral rami from spinal nerves L1-L4. The
sacral plexus
In human anatomy, the sacral plexus is a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg and foot, and part of the pelvis. It is part of the lumbosacral plexus and emerges from the lumbar verte ...
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
The anterior divisions of the lumbar nerves, sacral 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 ...
.
References
External links
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Lumbosacral plexus
The anterior divisions of the lumbar nerves, sacral 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 ...
"
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Spinal nerves