Muscules

Muscle is a tissue characterized by irritability
and contractility. It is composed of elongated cells
called myocytes that contain contractile proteins
organized as cytoplasmic filaments. Muscle cells are
attached to bones and soft tissues, and thereby
accomplish mechanical movements as a consequence
of their contraction (shortening). Traditionally,
three types of muscle tissue are recognized:
skeletal, cardiac, and smooth. Skeletal and
cardiac muscle are classified as striated muscles
based on the appearance of striations that run
perpendicular to the long axis of the cells. The
striations are due to a highly ordered, repetitive
organization of two filamentous contractile proteins
- actin and myosin, which are arranged into thin and
thick filaments, respectively. Smooth muscle lacks
striations due to a less structured, looser
arrangement of its contractile filaments. In muscle
terminology, the sarcolemma refers to the muscle
cell membrane, the sarcoplasm refers to the
cytoplasm, and the sarcoplasmic reticulum
refers to the smooth endoplasmic reticulum.
Muscle is a tissue characterized by irritability
and contractility. It is composed of elongated cells
called myocytes that contain contractile proteins
organized as cytoplasmic filaments. Muscle cells are
attached to bones and soft tissues, and thereby
accomplish mechanical movements as a consequence
of their contraction (shortening). Traditionally,
three types of muscle tissue are recognized:
skeletal, cardiac, and smooth. Skeletal and
cardiac muscle are classified as striated muscles
based on the appearance of striations that run
perpendicular to the long axis of the cells. The
striations are due to a highly ordered, repetitive
organization of two filamentous contractile proteins
- actin and myosin, which are arranged into thin and
thick filaments, respectively. Smooth muscle lacks
striations due to a less structured, looser
arrangement of its contractile filaments. In muscle
terminology, the sarcolemma refers to the muscle
cell membrane, the sarcoplasm refers to the
cytoplasm, and the sarcoplasmic reticulum
refers to the smooth endoplasmic reticulum.