The central and peripheral nervous systems

Damage to nerves can be severe.  Because of their structure and function, nerves do not heal as quickly as some body parts do, but sometimes nerve damage can heal on its own.
Damage to nerves can be severe. Because of their structure and function, nerves do not heal as quickly as some body parts do, but sometimes nerve damage can heal on its own.

Nerves are the communication system of the body. They carry messages between the brain and spinal cord and all parts of the body. Damage to nerves can be severe. Because of their structure and function, nerves do not heal as quickly as some body parts do. But sometimes nerve damage can heal on its own. 

The nervous system consists of two parts, the central nervous system, and the peripheral nervous system. The central nervous system is made up of the brain and spinal cord, both protected by bony structures. The central nervous system contains complex cells that don't reproduce themselves. For this reason, damage to the central nervous system does not heal on its own. 

The peripheral nervous system connects the central nervous system with the rest of the body. These nerves are not protected by bone and are easily damaged. They can repair themselves if the injury is not too severe. 

Types of nerve damage

Three types of damage can occur to the peripheral nerves. Damage can be caused by:

A covering called the myelin sheath protects most nerves in the body.  Usually, stretching or bruising injuries damage the nerve fibers without damaging the myelin sheath. The nerve fibers can grow back slowly. If the myelin sheath is damaged, as may occur with cutting injuries, the nerves can't heal themselves.  

How nerves regenerate

A neuron or nerve cell has three main parts. It has a cell body and short branches called dendrites that receive messages. The third part is a long fiber called an axon that transmits messages. Nerve impulses travel down the axon to the end, where they jump to the dendrites of the next neuron. The point where the nerve impulse is transmitted to the next nerve cell is called a synapse. 

When a peripheral nerve is damaged, the body cleans up the damaged tissue. Then damaged axons may regrow, beginning at the end nearest the brain. In time they may grow enough to re-establish a connection and allow the nerve to work again. 

Symptoms of nerve damage

There are two main types of nerves, motor and sensory. Motor nerves tell parts of the body to move. Damage to a motor nerve can cause weakness and loss of function. Sensory nerves carry heat, cold, pressure, pain, and other sensations. If you damage a sensory nerve, you won't get accurate information about what is going on with your body.

Other symptoms of nerve damage can include:

  • Burning sensations
  • Pain
  • Numbness
  • Tingling

Diagnosis of nerve damage

An electrical conduction test can diagnose nerve damage. Sometimes a CT scan, MRI, or MRI neurography can also be helpful. These tests can show whether a nerve is likely to heal on its own or whether it may need surgery. 

Doctors may use the Sunderland classification system to describe nerve damage. The classifications are. 

  • First degree: You should quickly recover from this type of injury, often within hours, although it may take a few weeks.
  • Second degree: This level of injury involves broken axons but should heal without surgery. 
  • Third degree: Damage is not confined to the axons. Sometimes the damaged area may need to be cleaned up surgically or repaired. 
  • Fourth degree: Damage is severe enough that the nerve will not repair itself. Testing shows that no electrical energy can pass down the nerve pathways. This level of injury may require surgery with nerve grafting. 
  • Fifth degree: These injuries involve laceration or severe stretching. The nerve has been split in two and requires surgery. 

Acupuncture, massage, physical therapy, and other non-invasive strategies can be a part of the treatment for nerve damage. These therapies won't fix nerve damage but may promote healing.

Surgery for damaged nerves

If your nerve is unlikely to heal on its own, your doctor may offer surgery as an option. Usually, the surgeon begins by repairing the myelin sheath around the nerve. The nerve fibers should start to regrow within three to four weeks. Nerves typically grow about one inch a month. As the nerve regrows, you may have tingling in the area.

Sometimes surgeons take a nerve from another part of the body to fix the damaged nerve. You may lose feeling in the area where the surgeon takes the graft. 

Recovery from nerve surgery

Many factors influence the rate at which your nerves heal. These include:

  • Your age
  • Your general state of health
  • The quality of your sleep
  • Whether you use alcohol, tobacco, or other substances
  • How well you follow your doctor's instructions

After surgery, it can take a year for a nerve to regrow completely. Then it can take another year or more for the nerve to mature and for the nerve and muscle to form a good connection. 

The brain may require training to recognize the new connection when healing is complete. Physical therapy can re-educate the brain. 

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Medically Reviewed on 1/10/2022
References
SOURCES:

Christopher and Dana Reeve Foundation: "How the spinal cord works."

Hospital for Special Surgery: "Managing Expectations for Recovery after Nerve Reconstruction."

Johns Hopkins: "Peripheral Nerve Injury."

Merck Manual Consumer Version: "Quick Facts: The Nerves," "Nerves."

OrthoInfo: "Nerve Injuries."

Society for Neuroscience: "No Pain, No Gain? Evidence for a Relationship Between Peripheral Nerve Regeneration and Pain."