It refers to a tubular structure or endoneurial channel. It separates axons from each other inside a peripheral nerve.
It is also known by other names like “Connective tissue sheath of Key and Retzius” and “Henle’s sheath.”
It can be found within the peripheral nerves.
This structure is composed of connective tissue cells that surround the axons (that send information from one end of a neuron to the other) of a peripheral nerve. They are made of collagen.
Peripheral nerves comprise of more than one axon and can send information to various muscles. It is the Endoneurium that keeps the signals isolated so that they can be transported to the correct destination. They are also responsible for protecting the axons, which are delicate in shape, from any possible damage. Along with the epineurium and the perineurium, they also insulate the neurons from injuries.
These images will help you know how this structure looks like.
Picture 1 – Endoneurium
Picture 2 – Endoneurium Image