Muscle Spasms

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Medical Author:

Benjamin Wedro, MD, FACEP, FAAEM

Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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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.

Muscles are complex structures that cause movement in the body. There are three types of muscle in the body:

• Heart muscle pumps blood (cardiac muscle).
• Skeletal muscle moves the external body parts, like the arms and legs, and the neck, back and trunk.
• Smooth muscle moves portions of hollow structures inside the body. Examples include the muscles that line the esophagus, stomach and intestine, muscles that line large arteries and the muscles of the uterus.

Skeletal muscles are anchored to bone, either directly or by a tendon. When the muscle contracts, the associated structure moves. This allows arms to lift, legs to run, and the face to smile. Most of these muscles are under willful or conscious control of the brain. This type of muscle is striated or striped with dark-colored muscles fibers containing large amounts of myoglobin, the protein that helps carry oxygen and light-colored fibers that have lesser amounts of the protein. The contraction of a skeletal muscle requires numerous steps within cells and fibers that need oxygen, electrolytes, and glucose, which are supplied by the bloodstream.

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 automatically for us. There is a balance between the sympathetic system (adrenergic nerves) that speed things up and the parasympathetic system (cholinergic nerves) that slow 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. Acetylcholine is the chemical that is the anti-adrenaline and is involved in the parasympathetic nervous system. Smooth muscle has the same basic contraction mechanism as skeletal muscle, though different proteins are involved.