What is a Nerve?

In the simplest form, a nerve is a bundle of nerve fibers (Figure1, 2) that transmits electrical messages between the brain and other areas of the body. These messages convey sensory or motor function information.

Nerves are comprised of nerve cells called neurons.

nerve
Figure 1

They receive and transmit electrical messages to and from the brain. One end of the neuron receives the message, while the other end transmits the message.

nerve2
Figure 2

When traveling from one neuron to the next, electrical messages cross a gap called a synapse. Neurons communicate with one another through axons and dendrites – projection of a neuron – that extend from their cell bodies.

 

Axons and dendrites of multiple neurons serving a similar function come together with a piece of connective tissue to form nerves.

Neurons are very similar to other cells in the body (Figure3) as they are surrounded by a cell membrane, have a nucleus that contains genes, and contain cytoplasm. However, they differ from other cells in the body because they have axons and dendrites that bring

nerve-cell
Figure 3

information to and from the cell body. In addition, they communicate with each other through electromechanical processes.

 

Nerves are part of the peripheral nervous system, which connects the central nervous system to the limbs and organs. While it is similar to the central nervous system, it differs because it is not as well protected, leaving it susceptible to toxins and mechanical injuries. There are two types of nerves: afferent nerves and efferent nerves.

1- Afferent nerves, also known as sensory nerves, convey sensory signals to the central nervous system. They receive sensory stimuli. For instance, if you stub your toe, you sense pain. These are your sensory nerves at work.

2-Efferent nerves, also known as motor nerves, send stimulatory signals from the central system to muscles and glands. Motor nerves lead to muscles and stimulate movement. For instance, when you move your arm to wave hello, your motor nerves are at work.

Damage to nerves can arise several different ways, including swelling, physical injury, infection, autoimmune disease, or failure of the blood vessels surrounding the nerve. Nerve damage may present symptoms such as pain, numbness, weakness or paralysis. An interesting aspect of pain related to nerve damage is that patients may feel symptoms in areas far from the actual site of damage. This type of pain, known as referred pain, occurs because signaling is defective from the damaged nerve area. Nerve damage is diagnosed several different ways. First, doctors rely on thorough physical examination that test reflexes, directed movements, muscle weakness, and sense of touch. Additional testing may be ordered in the form of a nerve conduction study and an electromyography.

regeneration-stages
Figure 4
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