Muscular System

Front

Skeletal Muscle Noun

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[skel-i-tl muhs-uhl]

Back

Skeletal Muscle

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A voluntary, striated muscle tissue attached to the skeleton by tendons, which facilitates conscious control of body movement.

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Example: This image shows that skeletal muscles are attached to bones and are made of long cells (fibers) that have visible stripes (striations).

Front

Smooth Muscle Noun

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[smooth muhs-uhl]

Back

Smooth Muscle

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An involuntary, non-striated muscle tissue found within the walls of internal organs that functions automatically to move substances.

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Example: This diagram shows smooth muscle is found in internal organs like the stomach and intestines, and is made of spindle-shaped, involuntary, uninucleated cells.

Front

Cardiac Muscle Noun

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[kahr-dee-ak muhs-uhl]

Back

Cardiac Muscle

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An involuntary, striated muscle tissue found exclusively in the heart wall, responsible for the rhythmic contractions known as heartbeats.

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Example: This diagram shows that cardiac muscle is found in the wall of the heart and is made of unique, branched muscle cells.

Front

Tendon Noun

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[ten-duhn]

Back

Tendon

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A tough, flexible band of fibrous connective tissue that connects skeletal muscle to bone, enabling movement across a joint.

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Example: This diagram shows how a tendon, a tough connective tissue, attaches a muscle to a bone, allowing the muscle's contraction to move the skeleton.

Front

Voluntary Muscle Noun

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[vol-uhn-ter-ee muhs-uhl]

Back

Voluntary Muscle

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A muscle whose contraction is under conscious, willful control from the brain, such as the skeletal muscles used for movement.

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Example: This diagram shows how voluntary muscles, like the biceps and triceps, work in pairs to consciously bend and straighten the arm.

Front

Involuntary Muscle Noun

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[in-vol-uhn-ter-ee muhs-uhl]

Back

Involuntary Muscle

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A muscle that contracts automatically without conscious control, regulating internal organ functions like digestion and heart rate.

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Example: This diagram shows the structure of heart muscle cells, which are involuntary muscles because they contract automatically to make the heart beat.

Front

Striated Adjective

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[strahy-ey-tid]

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Striated

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Describing muscle tissue that appears striped due to the regular, repeating arrangement of sarcomeres within its muscle fibers.

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Example: This diagram shows that cardiac muscle cells have a striped pattern, which is what 'striated' means. The label points directly to these stripes, called striations.

Front

Myofibril Noun

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[mahy-oh-fahy-bril]

Back

Myofibril

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A basic rod-like, threadlike structure within a muscle cell, composed of repeating contractile units called sarcomeres.

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Example: This diagram shows a myofibril, a rod-like structure in muscle cells, is made of repeating units called sarcomeres containing thick and thin filaments.

Front

Sarcomere Noun

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[sahr-kuh-meer]

Back

Sarcomere

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The basic functional and contractile unit of a striated muscle fiber, containing actin and myosin protein filaments.

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Example: This diagram shows a sarcomere, the basic contracting unit of a muscle, defined as the area between two Z lines containing thick and thin filaments.

Front

Actin Noun

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[ak-tin]

Back

Actin

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A thin protein filament within a sarcomere that slides along myosin filaments, causing the muscle fiber to shorten during contraction.

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Example: This diagram shows an actin filament, a key protein in muscles. It is made of many small units linked together, forming a chain with a 'plus' end and a 'minus' end.