Muscles DLA Flashcards
What are myofibrils?
Specialized organelles composed of cytoskeletal elements
- Banded structures which extend the length of the cell
- Composed of bundles of myofilaments
What are myofilaments?
The contractile elements of myofibrils
-The two types: thick and thin filaments with accessory proteins
-Arrangements of filaments creates dark and light bands which accounts for the cross striations characteristic of ALL striated muscle
What is an epimysium?
Dense connective tissue encasing multiple fascicles
- Contains major blood vessels and nerves - Continues with tendon to attach muscle at the myotendinous junction
What is a perimysium?
Groups of skeletal myocytes /fibers form a fascicles (F)
- Each fascicle is surrounded by a layer of connective tissue or perimysium
- Contains larger blood vessels & nerves
What is the endomysium ?
Delicate layer of reticular fibers that surrounds individual muscle fiber (myocyte)
-Contains small blood vessels and very fine neuronal branches
What is seen in a cross section of skeletal muscle?
-In cross section skeletal muscle fibers are regular shaped and encased by endomysium (End) all cells appear to be the same size and the nuclei (N) are peripheral deep to the plasma Membrane (sacrolemma)
Describe the skeletal muscle development
- Mesenchymal cells form myoblasts which dude to form a single skeletal myocyte
- Skeletal myocyte is an elongated multinucleated cell (synctium)
- This accounts for its variable length
- Skeletal myocyte = muscle fiber
- Other myogenic stem cells form satellite cells which can regenerate myocytes
Give the development of skeletal muscle in eatable
At 4 weeks- Mesenchymal cells form myoblasts which begin to form aggregates and line up into tubes
At 5 weeks-Myotubes lengthen by incorporating additional myoblasts via cell fusion
At 9 weeks- myofilaments have appeared that nuclei are still centralized
At 20 weeks- Developing muscle fibers now have cross striated appearance and nuclei more peripherally
At birth- muscle fibers have formed and nuclei have shifted to periphery
In adult- muscle fibers are now thick and mature and consist of alternate thick and thin myofilaments grouped into longitudinal bundles as myofibrils with nuclei located at periphery
Where are cardiac muscles found?
Forms the bulk of the myocardium and extends slightly into the walls of some great vessels
Describe cardiac muscle
- Striated and has the same type & arrangement of contractile filaments as skeletal muscle
- Unlike skeletal muscle, cardiac myocytes are branched
- They May have one or two centrally placed nuclei
- Perinuclear region is free of myofibrils and houses the organelles
- Granules containing diuretic hormones: atrial natriuretic peptide and brain natriuretic peptide
- Intercalated disc are the dark staining bands
Describe smooth muscle structure
Elongated, fusiform cells with tapered cells
- generally organized into bundles or sheets
- No cross striated thus even staining with H & E staining
Usually arranged in sheets around the lumen of hollow organs
- Central nucleus
- often has a cork screw
How do lengths vary for different types of smooth muscle?
- about 20 um in walls of small blood vessels
- about 200 um in wall of intestine
- about 500 um in wall of uterus during pregnancy
Contrast skeletal, cardiac and smooth muscle
- Skeletal muscle- multiple nuclei peripherally located. Long cylindrical walls. Striations
- Cardiac muscle-intercalated discs, centrally located nucleus, branched cells, striations
- Smooth muscle- spindle shaped cells, centrally located nucleus
What are sarcomere ?
Light or I band
Dark or A band
Within these bands additional bands and lines can be observed
- I band: median dark Z line
- A band: median lighter H band which is transcribed in the middle by an M line.
What’s a sarcomere?
- The functional unit of the myofibrils and the basic unit of contraction
- It is defined as the segment of the myofibrils between two adjacent Z lines
