Muscle Spasms

What is smooth muscle?

Smooth muscle is located in the walls of hollow internal structures in the body, like the arteries, intestines, bladder, and iris of the eye. They tend to circle the structure and when they contract, the hollow structure is squeezed. These muscles are involuntary and are controlled by the unconscious part of our brain function using the autonomic nervous system. The autonomic nervous system can run in the background, regulating body processes within the body. There is a balance between the sympathetic system (adrenergic nerves) that speeds things up and the parasympathetic system (cholinergic nerves) that slows things down. These names are based on the type of chemical that is used to transmit signals at the nerve endings. Adrenaline (epinephrine from the sympathetic nervous system) allows the body to respond to stress. Imagine seeing a bear in the woods; your heart beats faster, your palms get sweaty, your eyes dilate, your hair stands on end, and your bowels move all because the sympathetic nervous system is activated. Acetylcholine is the chemical that is the anti-adrenaline and is involved in the parasympathetic nervous system that acts to calm us down. Smooth muscle has the same basic contraction mechanism as skeletal muscle, though different proteins are involved.

What is a muscle spasm?

A muscle spasm, or muscle cramp, is an involuntary contraction of a muscle. Muscle spasms occur suddenly, usually resolve quickly, and are often painful.

A muscle spasm is different than a muscle twitch. A muscle twitch, or fasciculation, is an uncontrolled fine movement of a small segment of a larger muscle that can be seen under the skin.

Reviewed on 7/14/2014

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