Skeletal muscles attached to the arms, legs, neck, back, and trunk bones are voluntary and consciously controlled. Weakness or inability to control these muscles can signal a health issue like a neuromuscular disorder or electrolyte imbalance. Can recognizing the symptoms can help healthcare providers develop effective treatment programs?
Table of Contents
Voluntary muscles are the skeletal muscles that attach to bones and control movement of the limbs, head, neck, and body under an individual’s conscious control. Skeletal muscles are controlled by neuromuscular signals from the brain that communicate with individual muscle fibers and cause them to contract.
Voluntary muscles are skeletal muscles that comprise 40% of the body’s weight and 50% to 75% of the body’s proteins. These muscles can convert chemical and mechanical energy to cause voluntary muscle contraction and movement. (Trovato F.M. et al., 2016) Skeletal muscle comprises fascicles or bundled units of multiple muscle fibers or muscle cells. Each muscle fiber consists of a cross-banded structure further divided into myofibrils containing thick myosin and thin actin myofilaments, which give the muscle its stripe appearance, and the structure gives the characteristic striated structure. (Trovato F.M. et al., 2016) Muscle contraction occurs when these myofilaments move closer together, stimulated by the release of the neurotransmitter acetylcholine from nerve cells that communicate with the muscle fiber.
The autonomic nervous system controls involuntary muscles, regulating their contraction and relaxation. This system also controls the activity of organs and blood vessels for essential daily functions, including breathing, circulation, digestion, heartbeat regulation, and urination. Most involuntary muscles are composed of smooth muscles. Smooth muscles do not have the striated structure of skeletal muscles and consist of sheets or layers of smooth muscle cells. When the autonomic nervous system stimulates these muscle cells to contract by releasing hormones or other chemical signals, smooth muscle cells shorten through the movement of actin and myosin myofilaments. Involuntary smooth muscles include the blood vessel walls, diaphragm, intestines, and bladder. (Webb R. C. 2003) One exception of an involuntary muscle is the myocardium, or heart muscle. The myocardium comprises a specialized cardiac muscle cell found only in the heart. Cardiac muscle is striated like skeletal muscle but is controlled by the autonomic nervous system and pacemaker cells, causing it to contract automatically and rhythmically.
Skeletal muscle diseases, neuromuscular disorders, and other causes can weaken muscles. Neuromuscular or skeletal muscle disorders affect the nerves that send electrical signals to voluntary skeletal muscles to control movement. When the nerves are damaged, communication between the nerves and muscles becomes disrupted. This can result in significant muscle weakness, atrophy, and loss of function. Most neuromuscular disorders are genetic or caused by issues with the immune system. Nerves communicate with muscles through the release of neurotransmitters at the neuromuscular junction, which is the space between a nerve cell and muscle fiber. Neuromuscular disorders can damage the nerve or the neuromuscular junction. Neuromuscular disorder symptoms can include: (Cleveland Clinic, 2023)
Always seek immediate medical attention for any sudden, unexplained muscle weakness. Individuals who experience skeletal muscle weakness should discuss the type and duration of symptoms with their doctor, specialist, physical therapist, or chiropractor, as this might be a sign of a medical condition such as a neuromuscular disorder. Working with a chiropractic team can help expedite healing. Injury Medical Chiropractic and Functional Medicine Clinic works with primary healthcare providers and specialists to develop a personalized treatment program through an integrated approach to treat injuries and chronic pain syndromes, improving flexibility, mobility, and agility, relieving pain, and helping individuals return to normal activities. If other treatments are needed, Dr. Jimenez has teamed up with top surgeons, clinical specialists, medical researchers, and rehabilitation providers to provide the most effective treatments.
Trovato FM, I. M., Conway N, Castrogiovanni P. (2016). Morphological and functional aspects of human skeletal muscle. J Funct Morphol Kinesiol., 1(3), 289-302. doi.org/https://doi.org/10.3390/jfmk1030289
Webb R. C. (2003). Smooth muscle contraction and relaxation. Advances in physiology education, 27(1-4), 201–206. doi.org/10.1152/advan.00025.2003
Cleveland Clinic. (2023). Mitochondrial diseases. my.clevelandclinic.org/health/diseases/15612-mitochondrial-diseases
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The information herein on "Voluntary Muscles: A Key Component of Human Physiology" is not intended to replace a one-on-one relationship with a qualified health care professional or licensed physician and is not medical advice. We encourage you to make healthcare decisions based on your research and partnership with a qualified healthcare professional.
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