Muscular Tissues Characteristics

Study Notes

Originate from the mesoderm
Muscle cells are differentiated into elongated cells called muscle fibers
- Cell membrane is called sarcolemma
- Cytoplasm is called sarcoplasm
- Sarcoplasm contains all cell organelles and cell inclusions and contains the main organelles responsible for contraction, the myofibrils

Origin: by fusion of many mono-nucleated embryonic mesodermal cells
Sites: all muscles attached to the skeleton
Function: voluntary, forcible short contraction
Characteristics:
- Elongated, cylindrical, multinucleated cells
- Muscles are formed mainly of masses of fibers arranged in a parallel manner and grouped in bundles invested with connective tissues
Connective tissue component:
- Epimysium: dense connective tissue, enclosing the whole muscle
- Perimysium: thin, less dense connective tissue, enclosing each bundle
- Endomysium: delicate, highly vascular connective tissue, enclosing each muscle fiber and uniting them together
Skeletal muscle fibers:
- Cylindrical, non-branched, very large
- Nuclei are multiple, oval, and peripheral situated immediately under the sarcolemma
- Sarcoplasm is acidophilic and full of myofibrils
- Numerous mitochondria around the nuclei and in rows between myofibrils
- Each myofibril shows alternative dark and light bands
- The contractile unit of a muscle is called a sarcomere

Limited to the wall of the heart
Function: rhythmic contraction from birth to death
Characteristics:
- Cylindrical, branching, and anastomosing fibers
- Divided into short segments (cardiac myocytes) by dark stained, serrated lines, transversely crossing the fibers, called the intercalated discs
- Nuclei are single, oval, and central in each myocyte
- Sarcoplasm is acidophilic, granular with less clear transverse striations

Found in the walls of hollow viscera, blood vessels, and dermis of the skin
Characteristics:
- Fusiform in shape (spindle-shaped)
- Non-branched and non-striated
- Small diameter
- Nuclei are single, oval, and central
- Sarcoplasm contains a lot of mitochondria and myofibrils
- Myofibrils are not regularly arranged, with 3 types of filaments:
  - Thick myosin filaments
  - Thin actin filaments
  - Intermediate filaments: desmin & vimentin
Functions:
- Regulate the size of the lumen of hollow organs
- Produce the peristaltic movements of the digestive tract