Voluntary vs. involuntary muscles: definition, 16 differences, examples (2023)

Definition of voluntary muscles

Voluntary muscles are those muscles that can be moved by the person's free will and are almost always associated with the skeletal system.

• These muscles are connected to the bones by tendons and are responsible for all types of movement in vertebrates.
• Voluntary muscles account for about 40% of total body weight and are usually long and present close to the bones.
• Voluntary muscles are striated muscles because muscles are made up of long, thin, multinucleated muscle fibers that intersect with a regular pattern of red and white lines, resulting in a striated appearance.
• Every muscle cell is nucleated, where theKernremains at the cell periphery.
• Muscle fibers are also covered by a specialized cell membrane called the myolemm or sarcolemma.
• The sarcolemma is thick in voluntary muscles and connects muscle fibers to each other and to connective tissues.
• In addition, muscle fibers have contractile units called sarcomeres that shorten, causing the muscle to contract and relax. Sarcomeres contain actin and myosin proteins that work together to cause muscle contraction by sliding against each other.
• Each muscle fiber is connected to each other by connective tissue and interacts with each other through nerves and blood vessels.
• The voluntary control of these muscles is regulated by a part of the peripheral nervous system called the somatic nervous system.
• The somatic nervous system consists of afferent and efferent nerves, with the afferent nerves carrying information to the central nervous system and the efferent nerves carrying information from the CNS to the voluntary muscles for contraction.
• These muscles are not myogenic and require external nerve input to contract.
• Voluntary muscles require a large amount of energy to contract and relax. Therefore, they have multiple mitochondria to meet their energy needs.
• Voluntary muscles show rapid contraction and relaxation compared to involuntary muscles. However, they also tire quickly and need regular rest breaks.
• These muscles are essential as they are involved in the movement of body parts and locomotion of the body.
• Some examples of voluntary muscles are biceps, triceps, quadriceps, diaphragm, pecs, abs, hamstrings, etc.

Definition of involuntary muscles

Involuntary muscles are muscles that cannot be controlled by will or consciousness and are often associated with organs that exhibit slow, regular contraction and relaxation.

• Involuntary muscles are also called smooth muscles or non-striated muscles because they do not have striations when viewed under a microscope.
• These muscles are mainly found on the walls of internal organs such as the stomach, intestines, urinary bladder and blood capillaries.
• Individual muscle cells in smooth muscle are long, thin, and spindle-shaped with a centrally located nucleus.
• The myolema or sarcolemma is present as the cell membrane of the muscle fibers that serves to connect the muscle fibers together. The present sarcolemma is comparatively thinner and less concentrated.
• One of the examples of involuntary muscles is the heart muscle, which differs in structure and function from other involuntary muscles.
• The heart muscle consists of individual heart muscle cells, the so-called cardiomyocytes, which are connected by intercalated intervertebral discs. These muscle cells are surrounded by collagen fibers and other substances that make up the extracellular matrix.
• Cardiac muscle contraction differs from that of skeletal and smooth muscle. Heaction potentialIt is generated in the form of electrical stimulation in the muscles.
• This potential causes the release of calcium ions from the cells into the sarcoplasmic reticulum. The increase in calcium ions causes the myofilaments to slide over each other, causing an excitation contraction.
• The cardiac muscle is myogenic, with nerve stimulus generated within the muscles.
• Most muscle cells within the muscle fibers of involuntary muscles function as a unit where contraction and relaxation occur together.
• The involuntary muscles are controlled by the autonomic nervous system of the peripheral nervous system.
• The motor nerves of the autonomic nervous system are made up of a type of bulge filled with neurotransmitters called varicose veins.
• Because gap junctions connect cells in involuntary muscles, neuronal signals can travel from one cell to another via neurotransmitters.
• The contraction and relaxation of the involuntary muscles are slow and occur at regular intervals.
• As a result, these muscles do not tire as quickly and can work continuously.
• They also have lower energy requirements compared to voluntary muscles and therefore fewer mitochondria.
• The involuntary muscles are involved in the movements of the internal organs and also help in the passage of liquids and food into thedigestive system.
• Some examples of involuntary muscles are the heart muscle and the smooth muscle that lines the intestinal tract, blood vessels, genitourinary tract, respiratory tract, etc.

Key Differences (voluntary muscles vs. involuntary muscles)

Examples of voluntary muscles

Membrane

• The diaphragm is a primary respiratory muscle that aids in the breathing process by increasing and decreasing the volume of the chest wall.
• It is a dome-shaped skeletal muscle that is present below the lungs and heart. Separate the abdominal area from the chest.
• The diaphragm is a voluntary muscle controlled by the phrenic nerve, which runs from the throat to the diaphragm.
• There are large openings in the diaphragm for the passage of certain structures, such as the esophageal opening for the vagus nerve, the aortic opening for the aorta, and the caval opening for the inferior vena cava.
• In addition to respiratory functions, the diaphragm is also involved in other non-respiratory functions. The diaphragm increases abdominal pressure to allow vomit, urine, and feces to pass. It also puts pressure on the esophagus to prevent acid reflux.
• The spasmodic inhalation movement of the diaphragm creates the characteristic sound known as cupping.

biceps

• The biceps muscles are the muscles with two heads or two points of origin, which in humans are the biceps brachii and biceps femoris.
• The biceps brachii is the muscle present at the front of the upper arm. Its tendons connect this muscle to the inner bulge near the radial head, one of the two bones of the forearm.
• The biceps brachii flexes the forearm towards the upper arm and is therefore used in lifting and pulling movements.
• The size of the biceps brachii is considered a symbol of physical strength.
• The biceps femoris is one of the muscles present on the back of the thighs.
• It arises from the posterior part of the isthmus and the posterior part of the femur and is attached to the head of the fibula and tibia.
• It is involved in the movement of the thighs and the bending of the leg at the knee.

Examples of involuntary muscles

Herzmuskel

• The heart muscle is an involuntary striated muscle that is present in the wall of the heart and experiences contractions and relaxations at regular intervals.
• The heart muscle consists of individual heart muscle cells, the so-called cardiomyocytes, which are connected by intercalated intervertebral discs. These muscle cells are covered by collagen fibers and other substances that make up the extracellular matrix.
• Cardiac muscle contraction differs from that of skeletal and smooth muscle.
• The cardiac muscle is myogenic, with nerve stimulus generated within the muscles.
• The action potential is generated within the muscles in the form of electrical stimulation.
• This potential causes the release of calcium ions from the cells into the sarcoplasmic reticulum. The increase in calcium ions causes the myofilaments to slide over each other, causing an excitation contraction.
• Heart muscles are innervated by vagus and sympathetic nerves, which control muscle fiber contractions.

smooth muscle cells

• Smooth muscle is an involuntary nonstriated muscle composed of unitary or unitary muscles and multiunit muscles.
• Smooth muscle lines the walls of various internal organs such as the intestinal tract, urinary tract and blood vessels.
• The ciliary muscle of the eye is also a smooth muscle that dilates and controls the iris, changing the shape of the lens.
• Smooth muscles with a single unit are the muscles where the contraction and relaxation of the whole muscle as a whole takes place. Multi-unit muscles can contract and relax separately as different units.
• Muscle fibers are surrounded by nerve fibers, which are made up of vesicles called varicose veins or buttons that carry neurotransmitters.

references and sources

• Hall JE and Guyton AC. (2011) Textbook of Medical Physiology. Twelfth edition. Elsevier Saunders.
• Waugh A and Grant A (2004) Anatomy and Physiology. Ninth edition. Churchill Livingston.
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