How are the Cytons and Axons of neurons arranged in the following?
Spinal cord
Topic: Grey and white matter — spinal cord
Answer
In the SPINAL CORD the arrangement is REVERSED — the cytons lie INSIDE, forming the inner GREY matter, and the axons lie OUTSIDE, forming the outer WHITE matter.
This is the exact opposite of the brain, and that reversal is the whole question.
HOW TO REMEMBER IT: in the spinal cord the grey matter is in the middle and is shaped like a BUTTERFLY or the letter H, surrounded by white matter. In the brain, grey is on the outside.
WHY: the spinal cord’s main job is to CONDUCT impulses up and down between the body and the brain, and the long myelinated axons that do the conducting are placed on the outside where they run lengthwise. The cell bodies handling reflexes sit protected in the centre.
Examiners nearly always ask about both together, precisely because the arrangement is inverted.