Nerves, Muscles, and Synapse

Your peripheral nervous system consists of several distinct, highly complex components that work together to effect movement and sense your environment. A malfunction of any of these components may cause neuromuscular disease.

Nerves

Your nerve cells are highly specialized structures that convey information throughout your body with speed and accuracy. They are classified by their anatomic position and function.

Some nerve cells produce action (motor nerve cells) by conveying signals directing movement from your brain to your muscles. Other nerve cells convey sensory information about the environment or your body to your spinal cord and brain. Autonomic nerve cells are intimately concerned with “housekeeping” functions, such as regulating your blood pressure, blood supply, and temperature.

Your nerve cells consist of the following parts:

  • Cell body. The cell body houses the nucleus of the cell where DNA is stored. DNA is necessary for the production of proteins. Your cells need these proteins to function properly — for instance, for proper growth and repair.
  • Axon. This markedly elongated portion of the nerve cell carries electrical signals and proteins over long distances to their targets. A protective coating called myelin supplies the axon with physical protection and insulation to allow accurate transmission of the electrical signals. Myelin enables the nerve signals to travel at speeds 30 times faster than those without it.
  • Terminal branches. The final stage of transmitting signals from your nerves to your muscles involves the terminal branches. The terminal branches transmit signals to the next cell in line. In the case of your motor nerves, that cell is a muscle cell. As for the sensory nerves, the end of the nerve is connected directly to a specific sense organ designed to detect a select type of stimulus, such as touch, taste, smell, or pain.

Muscles

Your muscle cells are made of repeating groups of long chemical filaments. These filaments are bound to stationary structures within the muscle fiber as well as to one another. The major chemical filaments are known as actin and myocin. When the muscle cell receives a signal from the motor nerve via the neuromuscular junction, an electrical signal is generated. This in turn leads to the release of calcium within the muscle cells. The release of calcium allows the reorganization of the chemical bonds between the muscle filaments, leading to a shortening of these repeating units. This causes movement.

Neuromuscular junction/synapse

Your motor nerve cells connect with your muscle cells at small but highly specialized gaps known as the neuromuscular junctions (synapses). When electrical signals arrive at the synapse, they trigger the release of a chemical, acetylcholine, which travels to your muscle fibers and activates them, causing movement.


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David M. Simpson, MD
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Mark A. Sivak, MD
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