Anatomy of the Spine: Nerves

spinal-cord

The spinal cord extends from the brain stem, down through the spine. It sits safely inside the vertebral bones so that it is protected. It is made up of nerve fibres all bundled up together, which then branch off out all over the body to carry the signals sent from the brain to the body, and back again.

The spinal cord is composed of both grey and white matter. The grey matter is on the inside and the white matter faces towards the outsideIn the white matter are the spinal tracts

Firstly, these spinal tracts can be split into two groups. The ascending tracts (also known as afferent) that travel upwards towards the brain are sensory tracts, and they deliver information to the brain. Descending (or efferent) tracts are motor tracts, and they deliver information downward from the brain to the body.

In total there are 13 spinal tracts that are split between sensory and motorIf the tract name begins with “spino” it is a sensory tract that is delivering information upwards, such as the pressure and touch nerve ventral spinothalamic or the pain and temperature nerve lateral spinothalamic. If the tract name ends with “spinal” it is a motor tract that is delivering information downwards. Examples of these are the reticulospinal nerve, which tells the flexor muscles within your body to contract to bend a limb, whilst resting the extensor muscle that wants to straighten the limb. The rubrospinal nerve does the opposite, telling the extensor muscle to contract and the flexor muscle to rest, moving the limb back to the original position.

Injury 

If the spinal cord is damaged, it can cause a permanent or temporary change to what the person can feel. Often, there’s a loss of muscle function, sensation and/or a loss of the use of some limbs or body parts.

A spinal cord injury is classified according to where the break has occurred in correspondence to the spinal nerves, and to where the lowest level of sensation and function is still possible. There are also two further variations - a complete or an incomplete break. A complete break means that the cord has been completely severed, so there is no function below it. An incomplete break is when the cord is compressed or injured so the brain is still able to send and receive signals below where it is damaged, to varying degrees. 

A break between C1-C7 (the cervical section) tends to affect a larger portion of the body due to it being so close to the brain, causing tetra- or quadriplegia, with limited or absent feeling below the neck or shoulders. 

Damage to the T1 - T12 (thoracic section) normally results in paraplegia. T1 - T5 breaks normally affect the upper chest, mid-back and abdominal muscles, as well as the trunk and legs. T6 - T12 affects the abdominal and back muscles. 

Breaks in the Lumbar section (L1 - L5) bypasses damage to most of the upper body's functionality, but can still affect the hips and legs. 

The lowest part of the spine is the sacral section, S1 - S5. A break here will most likely leave the individual able to walk, but there may be little to no control of bladder or bowel organs. 

Spinal nerves related AnatomyStuff resources:

Spinal Nerves Anatomy Chart
Budget Half Size Skeleton Model with Spinal Nerves
Spinal Cord Model (5 times life size)
Classic Unisex Torso Model with Open Neck and Back (18 part)
Spinal Injection Simulator Model

Further reading / sources

Conduction of nerve impulses
https://byjus.com/biology/conduction-of-nerve-impulse/
Spinal cord anatomy
http://vanat.cvm.umn.edu/neurLab2/pages/AscDescTracksConcept.html 
Ascending and descending tracts of the spinal cord
https://www.kenhub.com/en/library/anatomy/ascending-and-descending-tracts-of-the-spinal-cord
Spinal cord presentation
http://www.napavalley.edu/people/briddell/documents/bio%20218/15_lecture_presentation.pdf

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