Here in the Dulin lab we have a plethora of experiments that focus on spinal cord injury and the affects after spinal cord injury. On project I have been honored to be a part of is developmentally restricted neural progenitor cell grafts in the spinal cord after a T12 contusion. However, it may be more palatable to say we transplanted a derivative of stems cells at different age points into the spinal cord after a injury that would represent paraplegia. In contrary to this being such a complex and in depth study we all had to begin somewhere before completely understanding the study. As a new undergraduate researcher, my first task was to learn the anatomy of the spinal cord.
What Is The Spinal Cord?
The spinal cord is the channel connecting the back/anterior CNS (brain, brainstem, &cerebellum) to the rest of the body. It is a highly complex structure comprised of long-range projecting axon tracts, thousands of specialized subtypes of neurons, and many different neuronal circuits that integrate and process diverse types of information. This can be looked at like electrical circuitry since there are electrical signals being sent to and from the brain into the spinal cord. You can also think of the spinal cord like the game of Telephone. For those that do not know, Telephone is where an originator has a code then has to communicate it through a line of people by each one whispering to another. When the message reaches the final person, they must say it out loud to see if it is the same message or not. With most of the time being that the message is miscommunicated and instead of saying, "My neighbor walked the dog," to "When I was a young warthog." In comparison to the spinal cord when healthy, the game of Telephone is successful each time. In humans, the spinal cord is about 40-50 cm long and between 1.0-1.5cm in diameter. It extends from the foramen magnum at the base of the skull, which is like a hollow passageway, where it is continuous with the medulla. The spinal cord terminates at the level of the first or second lumbar vertebrae. From this point forward it is referred to as cauda equina or in English translation, the horse's tail.
Dorsal Vs. Ventral
The spinal cord is organized into discrete, functionally specialized segments and each segment of the spinal cord is enclosed by vertebral segments on the dorsal (towards your back) and ventral aspects (towards your belly button). Two types of nerve roots emerge bilaterally from every individual spinal cord segment. Dorsal nerve roots and ventral nerve roots emerge from the dorsal or ventral aspects of the cord, and join distally to form 31 pairs of spinal nerves. In other words, at each part of the spinal cord there are two nerves that come from each side then connect at some point to make more outreaching nerves to make up the peripheral nervous system. The dorsal nerve roots are comprised of bundles of axons with cell bodies in the dorsal root ganglia of the peripheral nervous system. They transmit afferent (incoming)sensory information into the spinal cord. These nerve roots branch into filaments and enter the dorsal aspect of the spinal cord. The ventral nerve transmits efferent (Outgoing) sensory information into the spinal cord.
The ventral nerve transmits efferent (Outgoing) sensory information into the spinal cord. These are the axons of lower motor (movement) neurons of the spinal cord. Ventral roots join the spinal nerves and travel peripherally to interweave itself into the skeletal muscles. The branched dorsal and ventral nerve root filaments coalesce into dorsal and ventral nerve roots, respectively. These nerve roots join to form the spinal nerves (bundles of mixed motor and sensory axons) after exiting the vertebral foramen.
In summary, this was just a taste of the anatomy of the spinal cord. In more detail there are many different segments within the spinal cord that contain different features. You also have white and gray matter that make up the spinal cord. If you dive even deeper it is possible to study the different types of cells found within the spinal cord. With all of this being said, the spinal cord is very complex and many of its pathways are undiscovered. This is why we do spinal cord research, so we can contribute to the mapping of these pathways to hopefully help others.
As always, make sure to Follow The Science!
References:
England, M. A., & Wakeley, J. (2006). Color atlas of the brain and spinal cord: An introduction to normal neuroanatomy. Mosby Elsevier.
Netter, F. H., & Hansen, J. T. (2003). Human atlas of anatomy. Icon Learning Systems.