Blood nerve barrier is formed by:

Ref: Histology a Text and Atlas, 6th edition, Michael H. Ross, Page 376Explanation:"Together with endothelial cells of blood vessels within the fascicle, perineurial cells constitute part of the blood-nerve barrier, an important andselective diffusion barrier against entry of potentially infectious and toxic substances that may alter normal function of the nerve." Ref: Netter's Essential Histology by Ovalle WK, 2nd edition. Page 130"Tight junctions, providing the basis for the blood- ner\!e barrier, are present between the cells located within the same layer of the perineurium. " Ref: Histology by Ross MH, 5th edition. Page 342"The perineurium has the character of an epithelium, called perineurial epithelium, and functionally contributes to the formation of a blood- nerve barrier (blood-brain barrierRef: Functional Ultrastructure: Atlas of Tissue Biology and Pathology By Margit Pavelka, Page 324BLOOD NERVE BARRIERFormed by Perineurium of Peripheral Nerves and the endothelium of endoneurial Capillaries.The perineurium acts as a diffusion barrier.but ion permeability is higher than at the blood- brain barrier.ALSO NOTEBlood Brain Barrier (BBB)Formed by:o Tight junctions of endothelial cellso Foot process of the astrocytes around the capillaries.Filters only Lipid soluble substances.Areas outside BBB--Collectively known as Circumven-tricular organs: (Mnemonic-M. SOAP)o Median eminenceo Sub fornical organo Organum vasculosumo Area postrcmao Posterior pituitary.