T

Actin

Myosin

Myosin bridges (crossings)

Stretched muscle

Fig. 14.2 Structure and contractile mechanism in a normal skeletal muscle. The muscle is composed of muscle fiber bundles that consist of striated muscle cells or fibers. An individual fiber generally contains ca. 1000 myofibrils. Every myofibril is surrounded by a tangle with a sack-like structure, the sarcoplasmic reticulum Enlargements: Adenosine triphosphate (ATP) and free calcium (Ca'"*) activate the myosin crossings, as a result of which these pull on the actin filaments. This pull brings the Z-lines closer together and shortens the sarcomeres, the contractile unit by which the muscle is shortened. The segments of actin filaments that do not contain myosin filaments on both sides of a Z-disk form the l-band. The A-band corresponds in length to the myosin filaments. If only an A-. but no l-band exists, a maximal shortening is present

Fig. 14.3 Isometric muscle tone in relation to sarcomere length.

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Fig. 14.4 Comparison between sarcomeres of equal length in a normal muscle and the sarcomeres in a muscle with trigger points, which are affected in their length. Shortened sarcomeres in the trigger point region increase tension in the area of the hypertonic muscle spindle and reduce the stretchability of this muscle.

■ Muscular Weakness and Fast Tiring

Patients with trigger points most likely manifest these symptoms due to reduced circulation and resulting hypoxia in the affected muscle.

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