The muscle fiber of Hirudo medicinalis represents a special type of muscle. The sarcoplasm, containing the nucleus and a great number of mitochondria, is located in the axial region of the fiber. The contractile part of the fiber, a system of flat, ribbonlike myofibrils can be found around the axial sarcoplasm. The planes of the myofibrils are arranged radially, i.e., perpendicularly to the sarcolemma. Each myofibril consists of 10-60 myofilaments having a mean diameter of 280 Å. The interfibrillar sarcoplasm contains the tubules of the sarcoplasmic reticulum and peculiar structures, the cross filaments. Both run alternately in the middle of the interfibrillar sarcoplasm layer in a radial direction. The cross filaments have a mean diameter of 450 Å; their outer end is fixed to the sarcolemma, the inner one reaches into the axial sarcoplasm and is lost. Their possible role is discussed in the text.
ASJC Scopus subject areas
- Molecular Biology