Answer:
Inhibitory influences from neuroglia, and the absence of growth-stimulating cues.
Explanation:
Neurogenesis in adults is limited by Inhibitory influences from neuroglia, mainly from oligodendrocytes, and the absence of growth-stimulating cues that are present during fetal development. It is so hard to repair a damaged nerve because nerve cell like other cells can't divide and increase in number, they can't renew themselves. Due to no division, the nerve cells does not increase in number and therefore can't repair themselves.
