The nervous system, a complex communication network, relies on specialized cells. Neurons transmit electrical impulses, supported by various glial cells that maintain nerve health and efficiency. Among these, Schwann cells are important components of the peripheral nervous system (PNS). They are important for nerve function and recovery from damage.
What Are Schwann Cells?
Schwann cells are a type of glial cell found exclusively in the peripheral nervous system (PNS). Named after Theodor Schwann, who discovered them in the 19th century, these cells develop from the neural crest during embryonic development. They are essential for the maintenance and function of peripheral nerves.
There are two main categories of Schwann cells: myelinating and non-myelinating. Myelinating Schwann cells wrap around larger-diameter axons to form a protective, insulating myelin sheath. In contrast, non-myelinating Schwann cells surround multiple smaller, unmyelinated axons, providing support without forming a myelin sheath. Both types are covered by a basal lamina.
Roles in Nerve Function
Myelinating Schwann cells primarily form the myelin sheath, a fatty, insulating layer. This insulation enables rapid electrical signal transmission along nerve fibers. A single myelinating Schwann cell typically covers approximately 1 millimeter of an axon, with gaps between adjacent Schwann cells known as Nodes of Ranvier.
The myelin sheath enables saltatory conduction, where electrical impulses “jump” from one Node of Ranvier to the next. This significantly increases nerve impulse speed, allowing signals to travel up to 10 times faster than in unmyelinated nerves. This rapid transmission is important for muscle movement and sensory perception. Non-myelinating Schwann cells, while not producing myelin, still play an important role by providing support and protection to the smaller unmyelinated axons they ensheath. They also contribute to maintaining nerve health by providing trophic support, supplying nutrients and various growth factors to neurons, important for neuronal survival and function.
Their Role in Nerve Regeneration
Schwann cells play an important role in nerve repair and regeneration following injury. When a peripheral nerve is damaged, Schwann cells at the injury site transform into a repair-supportive state. They actively participate in clearing cellular debris, including damaged myelin and axon fragments, a process known as Wallerian degeneration.
Following this cleanup, these Schwann cells proliferate and align to form structures called Bands of Büngner. These band-like formations act as a guiding pathway or “tunnel” that directs regenerating axon sprouts toward their original targets. Schwann cells also secrete a variety of growth factors and extracellular matrix molecules, promoting axonal regrowth and guiding fibers to their destinations. This regenerative capacity in the peripheral nervous system contrasts with the limited ability of the central nervous system to repair itself after injury, largely due to the differing roles of their respective glial cells.