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==Introduction==

==Introduction==

Nerves of the peripheral nervous system (PNS) are composed of numerous bundles of nerve fibers that are surrounded by connective tissue. This connective tissue also contains a specific layer that is specialised to neurons; the ''peri-neurium''. The outer layer of this connective tissue is called the ''epineurium''; which surrounds both the perineurium and the nerve itself. Individual neurons found within each bundle are surrounded by the ''endoneurium''.

Nerves of the peripheral nervous system (PNS) are composed of numerous bundles of nerve fibers that are surrounded by connective tissue. This connective tissue also contains a specific layer that is specialised to neurons; the [[PNS_Structure_-_Anatomy_%26_Physiology#Structure|''peri-neurium'']]. The outer layer of this connective tissue is called the [[PNS_Structure_-_Anatomy_%26_Physiology#Structure|''epineurium'']]; which surrounds both the perineurium and the nerve itself. Individual neurons found within each bundle are surrounded by the [[PNS_Structure_-_Anatomy_%26_Physiology#Structure|''endoneurium'']].

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Each nerve fibre that is visible on histologic section represents an axon which is surrounded by the ''neurilemma'' or as it is also known, the sheath of a ''Schwann cell''. However, depending on whether the cell is myelinated or unmyelinated, this layer may not be visible. Where present, the Schwann cell will be visible as as a dense layer immediately adjacent to the nerve fibre. This layer is then also immediately surrounded by the cytoplasm of the Schwann cell. The sheath and cytoplasm of the Schwann cell collectively form the neurilemma. Unmyelinated axons can often be seen running within small grooves of Schwann cells.

Each nerve fibre that is visible on histologic section represents an axon which is surrounded by the ''neurilemma'' or as it is also known, the sheath of a [[PNS_Structure_-_Anatomy_%26_Physiology#The_Schwann_Cell|''Schwann cell'']]. However, depending on whether the cell is myelinated or unmyelinated, this layer may not be visible. Where present, the Schwann cell will be visible as as a dense layer immediately adjacent to the nerve fibre. This layer is then also immediately surrounded by the cytoplasm of the Schwann cell. The sheath and cytoplasm of the Schwann cell collectively form the neurilemma. Unmyelinated axons can often be seen running within small grooves of Schwann cells. Therefore even unmyelinated nerves retain some degree of myelin covering.

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