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The segmental organization of the spinal cord
Oral presentation by Peter Bogdány
The spinal cord is a part of the central nervous system.
It collects data from the peripherical nervous system – sensory information - , and innervate
skeletal and smooth muscles – motoric function - that mediate voluntary and involuntary
reflexes. As an example, the knee jerk reflex can happen without the role of the brain and as
a result, it is much faster.
The spinal cord is divided into four different regions: the cervical, thoracic, lumbar and sacral
regions. The cord is segmentally organized. There are 31 segments, defined by 31 pairs of
nerves exiting the cord. These nerves are divided into 8 cervical, 12 thoracic, 5 lumbar, 5
sacral, and 1 coccygeal nerve. These nerves collect and spread, transfer information from/to
differents parts of the body.
The cord is sheathed in the same three meninges as is the brain: the pia, arachnoid and dura.
The dura is the tough outer sheath, the arachnoid lies beneath it, and the pia closely adheres
to the surface of the cord.
Each nerve emerges in two short branches (roots): The motor or anterior root exits at the
front of the cord, while the sensoy or posterior root enters at the back. The motor roots
carry commands from the brain and spinal cord to other parts of the body, particularly to
skeletal muscles. The sensory roots carry information to the brain from other parts of the
body. The butterfly-shape part of the cord is the grey matter, which contains cell bodies of
neurons. The outer part is the white matter, which contains myelinated axons.
The amount of the white and grey matter is different in sections of the cord. Lower levels
contain less ascending and descending nerve fibers, so the gray matter is more than the
white one.
The central canal, also known as ependymal canal, is the cerebrospinal fluid-filled space that
runs longitudinally through the length of the entire spinal cord. The central canal helps to
transport nutrients to the spinal cord as well as protect it by cushioning the impact of a force
when the spine is affected.
Sources:
http://neuroscience.uth.tmc.edu/s2/chapter03.html
http://www.merckmanuals.com/home/brain,-spinal-cord,-and-nerve-disorders/biology-ofthe-nervous-system/spinal-cord
https://en.wikipedia.org/wiki/Central_canal