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There are two rhomboid muscles on each side of the upper back: [1] [2] [3] Rhomboid major muscle; Rhomboid minor muscle; The large rhombus-shaped muscle, located under the trapezius muscle, in the upper part of the thoracic region of the back, and the small muscle, in the same way, participate in the movement of the scapula. [4]
In geometry, a rhombohedron (also called a rhombic hexahedron [1] [2] or, inaccurately, a rhomboid [a]) is a special case of a parallelepiped in which all six faces are congruent rhombi. [3] It can be used to define the rhombohedral lattice system , a honeycomb with rhombohedral cells.
A direction (meaning a line without an arrow) is called polar if its two-directional senses are geometrically or physically different. A symmetry direction of a crystal that is polar is called a polar axis. [2] Groups containing a polar axis are called polar. A polar crystal possesses a unique polar axis (more precisely, all polar axes are ...
Agonist muscles and antagonist muscles are muscles that cause or inhibit a movement. [5] Agonist muscles are also called prime movers since they produce most of the force, and control of an action. [6] Agonists cause a movement to occur through their own activation. [7]
The parallel muscle architecture is found in muscles where the fibers are parallel to the force-generating axis. [1] These muscles are often used for fast or extensive movements and can be measured by the anatomical cross-sectional area (ACSA). [3] Parallel muscles can be further defined into three main categories: strap, fusiform, or fan-shaped.
The muscle fibers belonging to one motor unit can be spread throughout part, or most of the entire muscle, depending on the number of fibers and size of the muscle. [2] [3] When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contract. The activation of one motor neuron will result in a ...
The muscle cross-sectional area (blue line in figure 1, also known as anatomical cross-section area, or ACSA) does not accurately represent the number of muscle fibers in the muscle. A better estimate is provided by the total area of the cross-sections perpendicular to the muscle fibers (green lines in figure 1).
The rhomboid major is a skeletal muscle of the back that connects the scapula with the vertebrae of the spinal column. [1] It originates from the spinous processes of the thoracic vertebrae T2–T5 and supraspinous ligament; it inserts onto the lower portion of the medial border of the scapula. [2]