The Spinal cord is a long cylindrical bundle of nerves, nervous tissue & support cells running from the base of the brain or medulla oblongata through the vertebral column to the lumbar region of the backbone. The spinal cord and the brain form the central nervous system. The spinal cord is around eighteen inches or forty five centimeters long in men and around seventeen inches or forty three centimeters long in women. It has varying thickness as it extends from the occipital bone to the foramen magnum and downtown through the spinal canal, where it meets the cervical vertebrae and finally ends at the lumbar vertebrae. The spinal cord is around half an inch thick in both cervical and lumbar vertebrae. It is around quarter of an inch thick in thoracic vertebrae.
The human spinal cord has different segments, each of which has a pair of roots. These roots are nerve fibers. One pair is towards the back and is known as dorsal roots while the other is away from the back and is known as ventral roots. The diameter of the spinal cord is around two centimeters for adults. It is responsible for the transmission of signals from nerves in the motor cortex to different parts of the body. It also transmits signals from afferent fibers in the sensory neurons to the sensory cortex. The spinal cord controls reflexes, various kinds of electrical communication up and down the tube, establishes direct contact between the brain and different parts of the body and coordinates contraction & expansion of muscles to help facilitate motion.
The spinal cord is encased in the vertebral column, its protective skeletal structure.
All the way from the base of our skull to the filum terminale, which is the fibrous extension that marks the end of the spinal cord, the bundle of nerves runs through spaces inside the vertebral column. These nerves are called spinal nerves and they are named as per the region where they originate. These regions are neck or cervical, chest or thoracic, abdominal or lumbar, pelvic or sacral and tailbone or coccygeal. There are eight cervical
nerves, named as C1, C2 & C3 and so on till C8. All these are in the neck. There are twelve thoracic nerves, na
med as T1 and so on till T12. These are in the chest. The five lumbar nerves are named L1 to L5 and are in the abdominal region. There are five sacral nerves named as S1 to S5 and one coccygeal nerve named as Co in the pelvic region and tailbone respectively.
The vertebral or spinal column is longer than the spinal cord. Most adults have their spinal cord end at the first lumbar vertebrae or just before the second lumbar vertebrae. If you cut open a part of the spinal cord and look at a cross-section then you will find grey matter and white matter. The grey matter is at the center, shaped like a butterfly, surrounded by white matter. The grey matter is the core and it has two dorsal and two ventral roots. The grey matter comprises of neurons and inter-neurons as well as glial cells. The white matter has axons or nerve fibers. There are ascending and descending bundles of axons called tracts. These facilitate the communication to and from the brain, also between different segments of the spinal cord.