Nerve damage is a relatively common injury with many possible causes, but very debilitating consequences. A severed nerve could potentially result from breaking a bone, stabbing or even during surgery.

Depending on the nerve that is damaged, the consequences can be very different. Some common examples are listed below.

Damage to the ulnar nerve can cause a claw hand…

This is commonly caused by a fracture of the forearm resulting in damage to the ulnar nerve.

Damage to the long thoracic nerve can cause a winged scapula (shoulder blade)…

This damage is usually caused by axillary lymph node clearance which damages the long thoracic nerve.

Damage to the common fibular nerve can cause foot drop…

Foot drop is commonly caused through hip replacement surgery damaging the common fibular element of the tibial nerve.

The most common type of peripheral nerve injury is defined as ‘neuropraxia’, where there is no injury to the axon but there is a temporary disruption in nerve conduction, possibly due to damage to the myelin sheath. ‘Axonotmesis’ and ‘neurotmesis’ are increasingly severe forms of nerve trauma in which there is damage to the axons and, in some cases, damage to the connective tissue in the nerve. A labelled nerve cell is shown below.

When nerves are damaged, they undergo a process called Wallerian degeneration. In this process, the nerve axon degrades along with the myelin sheath. Following this white blood cells, known as macrophages, ingest the debris of the damaged nerve cell.

Can nerves repair themselves?

Yes, to an extent. If the cell body of the nerve cells is damaged (known as the soma) then there is no scope for repair and the nerve cell will die. However, if the axon is damaged, and undergoes Wallerian degeneration, then there is potential for the connection to be reformed and for some nervous function to be regained. Unfortunately, only nerve cells in the peripheral nervous system are able to regenerate, those within the brain and spinal cord do not possess this repair ability.

Regeneration is, from a cellular and molecular perspective, a very busy period; new genes are expressed and new proteins are synthesised, many similar to those detected during neural development. Axons can regenerate by following guidance cues to be able to reconnect to each other, but, may form incorrect connections. Some axons grow inappropriately, perhaps into connective tissue, and a single proximal axon stump may give rise to multiple new axon ‘sprouts’. This means that overall functional recovery is incomplete, slower and less precise.

Therefore, those people afflicted with claw hands, winged scapula or foot drop, do have the hope of recovering some function and ability. But, a nerve will never be able to fully recover.

Similar reading:
What happens after you break a bone?

References:
Image 1
Image 2: ulnar claw
Image 3: winged scapula
Image 4: foot drop
Image 5: nerve cell
https://www.asianscientist.com/2015/01/in-the-lab/putting-severed-nerves/
http://orthoinfo.aaos.org/topic.cfm?topic=A00016