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Muscles with short fibers will have higher PCSA per unit muscle mass, thus greater force production, while muscle with long fibers will have lower PCSA per unit muscle mass, thus lower force production. However, muscles with longer fibers will shorten at greater absolute speeds than a similar muscle with shorter fibers. [2]
where ε x = longitudinal strain (or muscle-shortening velocity) and ε f is fiber strain (or fiber-shortening velocity) In fusiform muscle, the fibers are longitudinal, so longitudinal strain is equal to fiber strain, and AGR is always 1. As the pennate muscle is activated, the fibers rotate as they shorten and pull at an angle.
Both ends of these fibers contract, but the central region only stretches and does not contract. Intrafusal muscle fibers are walled off from the rest of the muscle by an outer connective tissue sheath consisting of flattened fibroblasts and collagen. [5] This sheath has a spindle or "fusiform" shape, hence the name "intrafusal". [2]
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]
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 ...
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.
smooth muscle: cardiac muscle: skeletal muscle: Anatomy Neuromuscular junction: none present Fibers fusiform, short (<0.4 mm) branching cylindrical, long (<15 cm) Mitochondria: numerous many to few (by type) Nuclei: 1 1 >1 Sarcomeres: none present, max. length 2.6 μm present, max. length 3.7 μm Syncytium: none (independent cells)
Bipennate muscle is stronger than both unipennate muscle and fusiform muscle, due to a larger physiological cross-sectional area. Bipennate muscle shortens less than unipennate muscle but develops greater tension when it does, translated into greater power but less range of motion. Pennate muscles generally also tire easily.