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The majority of this type of muscle tissue is found in the digestive and urinary systems where it acts by propelling forward food, chyme, and feces in the former and urine in the latter. Other places smooth muscle can be found are within the uterus, where it helps facilitate birth, and the eye, where the pupillary sphincter controls pupil size. [3]
The quadriceps femoris muscle (/ ˈ k w ɒ d r ɪ s ɛ p s ˈ f ɛ m ər ɪ s /, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large fleshy mass which covers the front and sides of the femur.
[14] [15] There are between 600 and 840 muscles within the typical human body, depending on how they are counted. [ 16 ] [ 17 ] [ 18 ] In the present table, using statistical counts of the instances of each muscle, and ignoring gender-specific muscles, there are 753 skeletal muscles.
In mammals, triads are typically located at the A-I junction; [1] that is, the junction between the A and I bands of the sarcomere, which is the smallest unit of a muscle fiber. Triads form the anatomical basis of excitation-contraction coupling , whereby a stimulus excites the muscle and causes it to contract.
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 septa are formed from the fascia which is made up of a strong type of connective tissue. The fascia also separates the skeletal muscles from the subcutaneous tissue. [2] Due to the great pressure placed on the leg, from the column of blood from the heart to the feet, the fascia is very thick in order to support the leg muscles. [3]
In the upper esophagus, part of the externa is skeletal muscle, rather than smooth muscle. In the vas deferens of the spermatic cord, there are three layers: inner longitudinal, middle circular, and outer longitudinal. In the ureter, the smooth muscle orientation is opposite that of the GI tract. There is an inner longitudinal and an outer ...
A tendon connects muscle to bone, while a ligament connects bone to bone. [1] Injuries are common to this tendon, with tears, either partial or complete, being the most common. If the quadriceps tendon is completely torn, surgery will be required to regain function of the knee. [2] Without the quadriceps tendon, the knee cannot extend.