Nerves are complicated structures, made of many axons (the actual connections or wires) some surrounded by a layer of myelin shealth (insulation), all bundled together with connective tissue into a giant cable.
Nerve injuries come in different varieties, depending on the mechanism and severity of the trauma:
The mildest injury is neurapraxia, which is a short area of segmental demyelination. Because the underlying axon is left intact, recovery can occur within days to week by simple remyelination.
The more severe injuries axonotomesis and neurotmesis involve axonal injury. Once the axon is injured, the whole segment distal to the injury undergoes a pre-programmed process of degeneration called Wallerian degeneration:
Even if the nerve injury is repaired, or gets better on it’s own, the axon has to grow back all the way from the injury site to the end of the nerve at the muscle before functional recovery can occur.
Even if a severed nerve is repaired (in this case by direct suturing), the axons have to regrow down the entire distal nerve segment before functional recovery can occur
Axonal regrowth is slow, occurring at a rate of no more than 1mm/d.
If we have a patient with a proximal nerve injury, for example a brachial plexus injury:
Axonal regrowth will have to occur over 600-800mm to restore function to the hand, and that will take more than 2 years, by which time the muscle may have deteriorated so much it can no longer receive a new nerve supply and recover.
However, new research in animals has led to a technique that reconnects the severed ends of a nerve, allowing it to begin carrying messages again very quickly, restoring conductivity before Wallerian degeneration has a chance to begin. This allows for almost immediate function recovery after nerve repair surgery.
In the experiments, the severed nerve are exposed and treated with chemical compounds to keep the axonal ends open, then the two nerve ends are sutured together, and are finally treated with more chemicals that cause the nerve ends to fuse. Rats treated with his technique got better as soon as they began to recover from the surgery.
Researchers hopes to try the approach on people within a year.
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