Why Can’t Bono Play His Guitar?

U2 frontman Bono is still unable to play his guitar.

Last November, Bono sustained some pretty severe injuries to his left arm during a high impact bicycle accident. Bono continues to have some nerve damage in his left arm/hand as a result the open fracture of his elbow.

Bono told the NY Times that although he is able to use his left hand to hold a microphone, he is still recovering. His fourth and fifth fingers remain curled, and his forearm and elbow have areas of numbness.

“It feels like I have somebody else’s hand. “I can’t bend these  [pointing to the curled fingers].  But they say that nerves heal about a millimeter a week, so in about 13 months I should know if it’s coming back.”

This has put his guitar playing on hold, but jokes that the other band members “ don’t seem to mind.”

Neurons and Axons and Dendrites – A Crash Course on the Nervous System

The nervous system consists of two main parts: the central nervous system and the peripheral nervous system:

  • The central nervous system is made up of the brain and spinal cord.
  • The peripheral nervous system is made up of the nerve fibers that branch off from the spinal cord and extend to all parts of the body, including the neck and arms, torso, legs, skeletal muscles and internal organs.

The brain sends messages through the spinal cord and nerves of the peripheral nervous system to control the movement of the muscles and the function of internal organs.

axon and synapseThe basic working unit of the nervous system is a cell called a neuron. The human brain contains about 100 billion neurons. A neuron consists of a cell body containing the nucleus, and special extensions called axons and dendrites. Axons are wrapped in a fatty substance called myelin which protects the nerve fibers, and acts like insulation to allow rapid transmission of nerve signals along the axon. This layer is referred to as the myelin sheath.

Neurons communicate with each other using axons and dendrites. When a neuron receives a message from another neuron, it sends an electrical signal down the length of its axon. At the end of the axon, the electrical signal is converted into a chemical signal, and the axon releases chemical messengers called neurotransmitters.

The neurotransmitters are released into the space between the end of an axon and the tip of a dendrite from another neuron. This space is called a synapse. The neurotransmitters travel the short distance through the synapse to the dendrite. The dendrite receives the neurotransmitters and converts them back into an electrical signal. The signal then travels through the neuron, to be converted back into a chemical signal when it gets to neighboring neurons.

Motor neurons transmit messages from the brain to control voluntary movement. Sensory neurons detect incoming light, sound, odor, taste, pressure, and heat and send messages to the brain. Other parts of the nervous system regulate involuntary processes, such as the release of hormones like adrenaline, dilation of the eye in response to light, or regulation of the digestive system, which are involved in the function of the body’s organs and glands.

What happens when a nerve is injured? Can a nerve regenerate?

Nerves can be damaged either by trauma or disease. Nerve trauma may be caused by motor vehicle accidents, falls or lacerations. Trauma may occur acutely, either by cutting or crushing a nerve, or can happen over time by compressing a nerve, such as in carpal tunnel syndrome.

Nerve injuries first should be classified as complete or incomplete.

  • Complete injuries disrupt all the neurons in the affected nerve. This causes total loss of motor or sensory function beyond the injury.
  • Incomplete lesions- some neurons are affected but others are OK, leaving some distal motor or sensory function. This is important in terms of prognosis and treatment, because it implies that at least part of the nerve remains continuous.

Injury of a nerve can lead to demyelination and axonal loss.

Demyelination means that the myelin sheath has been disrupted. This may be a mild distortion, up to complete stripping of the myelin sheath. Demyelination prevents nerves from being able to properly conduct messages to and from the brain.

If the axon inside is still intact, this is referred to as neurapraxia. This typically occurs in cases of blunt trauma.  Nerve transmission may be slowed, leading to muscle weakness. Re-myelination begins within a few days and lasts 6-8 weeks.

Wallerian_DegenerationIf the axon is damaged, the  injured axon undergoes a very specific process known as wallerian degeneration. Shortly after the injury, the axon beyond the injury begins to breakdown. This triggers the body to release inflammatory cells called macrophages (which “chew up the debris”) along with Schwann cells- nervous system cells which produce myelin as well as nerve growth factors. The Schwann cells begin to line up along where the axon previously was. At the same time, the neuron’s cell body slowly starts re-extending the cut end of the axon. This is a very slow process which adds about 1mm of length a day.

If axons, and their myelin sheath are damaged, but the supporting connective tissue sheath around the nerve is spared, this is known as axonotmesis. Axonotmesis is usually the result of a more severe crush or contusion.  Wallerian degeneration occurs, but the intact connective tissue acts like a tunnel through which the axon can regenerate from the cell body to the target muscle.

Injuries that disrupt the whole nerve, affecting both the axon and supporting connective tissue, are known as If axons, and their myelin sheath are damaged, but the supporting connective tissue sheath around the nerve is spared, this is known as axonotmesis. Axonotmesis is usually the result of a more severe crush or contusion.  The intact connective tissue acts like a tunnel through which the axon can regenerate from the cell body to the target muscle.

Injuries that disrupt the whole nerve, affecting both the axon and supporting connective tissue, are known as neurotmetic. These are the most severe nerve injuries. While partial recovery may occur, complete recovery is impossible. These injuries are less likely to recover by axonal regeneration; they more often require surgical repair.

Surgical options may include an end-to-end repair of cut nerve edges, nerve grafting, and nerve transfer from somewhere else in the body. Promising areas of research for nerve cells regeneration include the use of stem cells, growth factors, guidance channels, and gene therapy.

 

 

 

Michele R. Berman, M.D. was Clinical Director of The Pediatric Center, a private practice on Capitol Hill in Washington, D.C. from 1988-2000, and was named Outstanding Washington Physician by Washingtonian Magazine in 1999. She was a medical internet pioneer having established one of the first medical practice websites in 1997. Dr. Berman also authored a monthly column for Washington Parent Magazine.

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