Histology of peripheral nerve - Shotgun Histology

📌 𝐅𝐨𝐥𝐥𝐨𝐰 𝐨𝐧 𝐈𝐧𝐬𝐭𝐚𝐠𝐫𝐚𝐦:- 📌𝗝𝗼𝗶𝗻 𝗢𝘂𝗿 𝗧𝗲𝗹𝗲𝗴𝗿𝗮𝗺 𝗖𝗵𝗮𝗻𝗻𝗲𝗹 𝗛𝗲𝗿𝗲:- 📌𝗦𝘂𝗯𝘀𝗰𝗿𝗶𝗯𝗲 𝗧𝗼 𝗠𝘆 𝗠𝗮𝗶𝗹𝗶𝗻𝗴 𝗟𝗶𝘀𝘁:- Histology of peripheral nerve - Shotgun Histology Peripheral nerves contain fascicles of nerve fibers consisting of axons. In peripheral nerve fibers, axons are ensheathed by Schwann cells, which may or may not form myelin around the axons, depending on their diameter. Nerve fibers are grouped into fascicles of variable numbers. PERIPHERAL NERVE HISTOLOGY NERVE VS NERVE FIBERS (AXONS) • A peripheral nerve encompasses bundles of nerve fibers (axons) and has various connective tissue coverings (superficial epineurium, perineurium, and endometrium). NERVE COVERINGS ------------------------------- Outside to Inside: Superficial epineurium • Superficial epineurium is the outer covering of the nerve. • It is a supporting coat: a cylindrical, dense connective tissue sheath. Perineurium • Perineurium encases separate nerve fascicles. • It is a mechanically strong sheath that is dense and forms a protective barrier around the nerve fascicle: a blood-nerve barrier. • Perineurium comprises a flattened form of epithelial cells that are joined by special junctions, which helps it withstand tremendous pressure. Endoneurium • Endoneurium is a loose connective tissue; it comprises collagenous fibers. Additional, less often addressed terminology: Deep epineurium 1 / 8 • Deep epineurium accounts for the connective tissue sandwiched between the nerve fascicles. • We find vasculature in this region. Perineurial septa • Perineurial septa pass through the nerve fascicles and carry vasculature to the nerve fibers. NERVE FIBERS (AXONS) --------------------------------------- • The nerve fiber is the nerve cell axon. • Myelin sheath surrounds myelinated axons. • Schwann cells: each myelinates at most one axon internode. MYELIN ------------- Unmyelinated cell In an unmyelinated cell, we see: • The Schwann cell nucleus intermixed with axons within Schwann cell cytoplasm. • The mesaxon is the zone of apposition for the Schwann cell membrane and the axon. • Multiple axons can pass through a Schwann cell, when the nerve fiber is unmyelinated. Myelinated cell In a myelinated cell, we see: • The Schwann cell nucleus lies off to the side of the axon, which is enveloped in concentric circles of myelin: a myelinated sheath. Schwann cells vs oligodendrocytes • Unlike oligodendrocytes, which can myelinate up to 50 individual axons, a Schwann cell only myelinates one axon, as shown here (specifically only one peripheral nervous system internode). DORSAL ROOT GANGLION ------------------------------------------- We highlight the following: • Ganglion cell • Cell nucleus 2 / 8 • Surrounding satellite cells (which support the ganglionic neurons). - Satellite cells are derived from neural crest cells in the same way that Schwann cells are. #histologyofpns #histologyofperipheralnerve #peripheralnervehistology #peripheralnerve #histology #shotgunhistology #histologyvideos #histologyshotgun