The ventral root plays a vital role in the spinal cord. The ventral root, also known as the anterior, and dorsal root, known as the posterior, are all subdivisions of the spinal cord's white matter. Each includes axon tracts linked to particular functions.
The efferent motor root of a spinal nerve is known in neuroanatomy as the ventral root of the spinal nerve, motor root, or anterior root. The axons of the motor neurons are housed in a ventral root made up of ventral rootlets. Ventral roots differ from dorsal roots as there is no nodal formation.
The ventral root is essential as it enables communication to be sent to the body's muscles so that action can take place. However, even it isn't immune to damage. Here is all to know about the structure of the ventral root, its function, how damage can occur, and whether or not it can be healed or regenerated.
What Is The Structure Of The Ventral Root?
One of the two roots that extend from the spinal cord is the ventral root of the spinal nerve, also known as the anterior root of the spinal nerve or the motor root. A spinal nerve's ventral root is created when the rootlets come together. A string of rootlets that protrude from the ventrolateral sulcus of the spinal cord connects each ventral root to the spinal cord.
The ventral root has many alternative names, such as the anterior root, radix ventralis, radix anterior, or radix motoria. They start as nerve roots from a specific spinal cord area. There are two anterior on each side of the spinal column. About eight nerve rootlets make up each of these roots separately.
The visceral motor neurons in the lateral horns, which are mainly found in the thoracic area, transmit to the sympathetic ganglia. Two ventral roots in each spinal cord segment connect to the spinal sympathetic ganglion through a white ramus. These ganglia form two sympathetic chains on either side of the vertebral column, communicating with each other up and down the spinal cord.
The white rami only provide input to specific sets of spinal sympathetic ganglia. Fibers that come from the thoracic segments, that ascend the sympathetic chain, provide information to other spinal sympathetic ganglia pairs. Preganglionic fibers from the lower thoracic and lumbar ganglia descend the chain and provide input to the ganglia below a certain point of the spinal cord.
The motor neuron cell bodies that transmit axons via the ventral roots of spinal nerves are found in the ventral horns. The spinal nerve's ventral root is home to efferent fibers. Efferent simply means to bear away from. Therefore, these efferent fibers send outgoing signals to control motor and glandular functions.
The ventral horns of the central grey matter of the spinal cord house the cell bodies of such motor neurons. Through the ventral root, these multipolar neurons exit the spinal cord. A spinal nerve is created when the ventral and dorsal roots converge outside the vertebral column.[1]
What Is The Function Of A Ventral Root?
The peripheral nervous system includes spinal nerves as a vital component. They are the parts that the central nervous system uses to receive sensory input from the periphery and to control the movement of the entire body. Additionally, the spinal nerves deliver motor instructions from the central nervous system to the muscles in the periphery.
Skeletal muscle is controlled by motor neurons. The spinal cord's core grey matter is home to the cell bodies of the ventral root neurons. Efferent nerve-fibers are found in the ventral root. They convey sensations away from the central nervous system and toward their target structures.
The ventral column of the spinal cord's core grey matter is where somatic efferent fibers start. They pass through the spinal nerve's ventral root. Therefore, the skeletal muscles' motor innervation is carried out by them. The efferent motor signals that travel from the anterior spinal cord toward the periphery are mostly carried via the ventral roots.
The revelation that the ventral area of the spinal cord is associated with motor function and the dorsal part of the spinal cord contains sensory information was one of the earliest significant discoveries regarding the nervous system.[2]
What Makes The Ventral Root Different To The Dorsal Root?
Incoming or afferent, which as the name states means to bear toward, fibers transporting sensory data from the periphery are found in the spinal nerve's dorsal root. As mentioned above, the ventral root consists of efferent fibers. However, the one big difference that makes the ventral root different from the dorsal root is that the dorsal root has a ganglion in comparison.
The dorsal root proceeds to the dorsal root ganglion after emerging from the back of the spinal cord. The dorsal root ganglion contains the sensory nerve cell bodies that send any sense of touch, more commonly known as somatosensory information, to the brain. These ganglia at each spinal cord level, often referred to as knotlike masses, create swellings along the dorsal root.
Even though the dorsal root ganglia includes many somatosensory cell bodies, other sensory systems are also represented. The axon of these unipolar somatosensory neurons divides into two branches, one of which travels to the sensory receptor. At the same time, the other goes to the brain for processing.
Wondering why the ventral root does not have a ventral root ganglion? As mentioned, the spinal cord's dorsal column is sensory while the motor is in the ventral. The motor is simple: the brain, nerve, muscle, and action. However, the sense is what protects the body from dangers and keeps it alive. The motor is not as life-critical as the sensory. The brain can easily send the motor neurons straight to the muscles.
They are made up of nerve fibers originating from neurosomas in the spinal cord's anterior and lateral horns. The locations of neurosomas outside the spinal cord are called ganglia. Sensory input from the skin, tendons, and joints is far more complicated. It must be processed before being transmitted to the following relay station.
To organize sensory input, the ganglia have a topographical layout and a ton of cell bodies. Your skin is extensively innervated by free nerve endings, including a few specialized receptors. Anywhere someone lightly touches you with a hand, or an object will be felt accurately and instantly. In the dorsal root ganglia, the first sensory screening is carried out. Signals are processed once they arrive.
Some reactions are reflexive, and the signal stops there. Others are trickier. Simply put, there is no ventral root ganglion because the peripheral synapse does not exist. The motor neuron axons that leave the spinal cord and go through the ventral root to the mixed nerve are found in the ventral root. Since the neuronal cell bodies are located in the spinal cord, there is no growth or nodule formation.[1]
What Happens If The Ventral Root Gets Damaged?
As with any body anatomy, damage to these fragile parts can lead to severe consequences. Any minor or significant damage to the spinal roots of the spinal cord typically causes deficiencies that affect the areas of distribution of the motor nerves that are transmitted through the spinal root.
You may be pondering what happens if the ventral root somehow gets cut. When this kind of injury takes place, the motor neurons die. Once they die, it leads to the axons in those damaged ventral roots dying, and finally, any muscles they innervate will die.
The flow of motor input from the spinal cord going to the muscles would be severed should the spinal nerve's ventral root get badly injured or severed. The spinal roots, compared to the spinal cord, technically belong to the peripheral nervous system.
It is thought that peripheral nerves have a capacity for regeneration. The spinal roots, meanwhile, are distinct from peripheral nerves in two ways. First, the dorsal root ganglia, situated immediately outside the spinal column, are home to the neurons from which sensory axons emerge.
Secondly, the spinal cord's ventral roots, via which the spinal cord motor axons travel to innervate muscles, are located in the cauda equina. The motor neuron itself may be damaged if the ventral root is harmed near the motor neurons which send axons. Compared to peripheral nerve damage, the chances of neurological recovery are much lower due to the characteristics of cauda equina injuries. [3]
What Other Ways Can The Ventral Root Get Damaged?
Losing neuronal and motor function is the primary outcome of axonal injuries at the boundary between the central and peripheral nervous systems. Ventral root avulsion elicits critical degenerative processes. For example, an arm entirely paralyzed and anesthetized due to the avulsion of both the dorsal and ventral roots at the brachial plexus area of the spine will experience neuropathic pain.
Although frequently referred to as longitudinal spinal cord injury, it is actually a central nervous system injury. There is an additional atrophic issue that can occur. Since the ventral roots also transmit trophic components, in addition to motor impulses, various structures will experience atrophic alteration to varying degrees.
Although the precise degree of demineralization is unknown, the affected limbs' bones will demineralize quickly. Pressure sore recovery will be compromised since the skin will deteriorate and become fragile. A ventral root's ability to function correctly may be harmed or constricted because it leaves the spinal column.
Foraminal stenosis is a condition in which the foramen, the empty area in between vertebras made for spinal nerves to travel to other areas of the body, begins to narrow. Following this constriction, nerves traveling through them are subjected to undue stress, resulting in numbness, tingling, pain, or, in severe cases, the absence of muscle movement.
Things like herniated discs are potential causes of foraminal stenosis.[3]
Can Healing Be Done On A Damaged Ventral Root?
The motor function may be slightly improved by placing the avulsed ventral roots back into the spinal cord. Peripheral nerve transplantation and ventral root implantation are the two most popular recovery procedures to re-establish the link between motoneurons and their target muscles following brachial plexus injury.
The fundamentals are still insufficient despite the information gained over the last ten years. Re-implantation of ventral roots, whether immediately after root avulsion or when there was a slight delay, dramatically boosts the survival and restoration of motoneurons in the spinal cord section that had its roots severed. This was according to a study done on rats.
Spinal root avulsion, which separates spinal nerves from their connection to the spinal cord, provides a practical model that can be repeated when needed to examine axotomy-induced degenerative alterations in motoneurons and associated underlying mechanisms. In experimental animals, avulsion of the ventral roots causes massive spinal motoneuron atrophy and fatality.
This was observed in the cases where as much as 80% died within 2 weeks of the damage. Several animal models showed that surgically replanting avulsed ventral roots saved motoneurons, causing motor axons to regenerate into the re-implanted ventral roots. They even enable functioning reinnervation of peripheral targets.
The majority of these implantation trials implanted the ventral rootlets that were avulsed into the spinal cord's parenchyma to promote regeneration. However, scientists have created a unique microsurgical procedure to repair the connection instead of the ventral rootlets being inserted into the spinal cord's parenchyma.
This involves placing the avulsed ventral root on the spinal cord's ventrolateral pial surface. The new technique implies that directly implanting the ventral root into the spinal cord parenchyma is unnecessary. This is because the ventrolateral pial surface uses the dorsal route, is considered less technically tricky, and can be more easily handled.
Consequently, doctors may suggest physical therapy, anti-inflammatory drugs, or chiropractic care as a conservative form of treatment if you have been diagnosed with a disorder that has to do with the constricted ventral root.[3]
Conclusion
The ventral root is an integral part of the body. How it functions is important as motor neurons are essential in how the body moves and specific actions occur. Ventral roots can also get damaged, but luckily, they can be regenerated so the axons can get to work again.
