By: Robert L. Shepherd, MS, Certified Medical Illustrator, President & CEO, MediVisuals Inc.
One of the key issues to be understood and explained in “mild” Traumatic Brain Injuries (TBIs) is just how delicate and fragile axons truly are. The fact that tens of thousands of axons can travel though an area of the brain the size of the head of a pin (which is the smallest size of brain defect that typical MRIs can detect) is very helpful in appreciating the diameters of axons. However, in order to further understand how injuries to axons during a traumatic event can occur, even without physical evidence of a blow to the head, it is also critical to appreciate just how long these structures are.
In cellular terms, axons are by far the longest cells in the body. The most extreme examples are the axons that stretch from the tip of the spinal cord (from the level of the first lumbar vertebrae) to the tip of the big toe. Within the brain, axons still span incredible cellular distances – from the front of the brain to the back or from one side of the brain to the other.
Analogies and comparisons are often very valuable in explaining unfamiliar or difficult to appreciate concepts because they allow us to compare the unfamiliar with the familiar. An excellent way to appreciate the extremely thin and delicate shape of an axon that stretches from one side of the brain to the other is to compare it to a spaghetti noodle. In this comparison, we will enlarge the axon proportionately, so the diameter of the axon is increased to be the same diameter as that of a spaghetti noodle, and the length is also increased by the same factor.