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Soleus muscles have more slow muscle fibers than many other muscles. In some animals, such as the guinea pig and cat, soleus consists of 100% slow muscle fibers. [6] [7] Human soleus fiber composition is variable, containing between 60% and 100% slow fibers. [8] The soleus is the most effective muscle for plantar flexion in a bent knee position.
Muscle spindles are fusiform (spindle-shaped), and the specialized fibers that make up the muscle spindle are called intrafusal muscle fibers. The regular muscle fibers outside of the spindle are called extrafusal muscle fibers. Muscle spindles have a capsule of connective tissue, and run parallel to the extrafusal muscle fibers unlike Golgi ...
Broadly there are two types of muscle fiber performing in muscle contraction, either as slow twitch or fast twitch . A single muscle such as the biceps brachii in a young adult human male contains around 253,000 muscle fibers. [11] Skeletal muscle fibers are the only muscle cells that are multinucleated with the nuclei usually referred to as ...
Skeletal muscle, is a type of striated muscle, composed of muscle cells, called muscle fibers, which are in turn composed of myofibrils. Myofibrils are composed of sarcomeres, the basic building blocks of striated muscle tissue. Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere.
Many nuclei are needed by the skeletal muscle cell for the large amounts of proteins and enzymes needed to be produced for the cell's normal functioning. A single muscle fiber can contain from hundreds to thousands of nuclei. [25] A muscle fiber for example in the human biceps with a length of 10 cm can have as many as 3,000 nuclei. [25]
The number of muscle fibers within each unit can vary within a particular muscle and even more from muscle to muscle: the muscles that act on the largest body masses have motor units that contain more muscle fibers, whereas smaller muscles contain fewer muscle fibers in each motor unit. [1]
Each muscle fiber contains sarcolemma, sarcoplasm, and sarcoplasmic reticulum. The functional unit of a muscle fiber is called a sarcomere. [2] Each muscle cell contains myofibrils composed of actin and myosin myofilaments repeated as a sarcomere. [3] Many nuclei are present in each muscle cell placed at regular intervals beneath the sarcolemma.
Unipennate muscles are those where the muscle fibers are oriented at one fiber angle to the force-generating axis and are all on the same side of a tendon. [1] The pennation angle in unipennate muscles has been measured at a variety of resting length and typically varies from 0° to 30°. [ 1 ]