Skeletal, Cardiac, and Smooth Muscle Flashcards
Week 3
Developing Skeletal Muscle
Myoblasts -[differentiation]-> Myocytes -[Migration Adhesion]-> Nascent Myotubules -[Fusion]-> Mature Myotubules -[Fusion with myotubules]> myofibers
Sarcomere Structure
Thin and thick filament
- A band (anisotropic): thick (dark), bisected by H-band (lighter)
- M-line: darker (middle)
- I band (isotropic): thin (light filaments), bisected by Z-line (darker)
Identifying Skeletal Muscle
Nucleli to the side, striated, associated with dense connective tissue, column-shaped, even structure, high in protein
Connective tissue (negative staining) pulls myofibers tightly together
Capillaries in white space
Skeletal Muscle Cell Structure
Myotubules, glycogen granules, sarcoplasmic reticulum, and mitochondria
Triad
T-tubule which releases Ca2+
Accessory
Titin anchor thick filaments to Z line
Actinin: bundles think filaments and anchored at Z-line
Dystofin: links actin to the extracellular external laminin
Speed of muscle contraction
Fast!
Muscle Cell: Visualizing the triad
Contractions driven by Ca2+ availability
Sarcoplasmic reticulum extends from one end of A band to the other (A-I junction)
Terminal Cisterna: localized gated Ca2+ channel
T-tubule: brings action potential into interior of muscle fiber
Myotendinous junction
Force generated in the muscle is transmitted through the tendon
Muscle fibers end as numerous finger-like projections to increase contact area between muscle and tendon
Basal Lamina of muscle cells attach to collagen fibers of the dense connective tissue
Junction between tendon and bone
Tendon attaches to bone across a functionally graded fibrocartilaginous transition site
Tendon -> tendon proper -> fibrocartilage -> mineralized fibrocartilage -> bone
Muscle Spindle
Regulates muscle contraction, length, and coordination
Smooth Muscle Structure
no sarcomeres, but contraction through dense bodies (calcium allows for contractions)
Smooth Muscle nervous system controls
Stimuli in digestive tract and autonomic nervous system feed into sympathetic (A), parasympathetic (A), and enteric (A & Stimuli in DT) nervous systems
Multi-unit smooth muscle cell
Consists of discrete units simulated by nerves
Found in:
- in walls of large blood vessels
- in large airways to lungs
- in muscle of eye that adjusts lens for near/far vision
- in iris of eye
- at base of hair follicles
Single-Unit smooth cells
fibers become excited and contract as single unit, cells are linked by gap junctions (electrically)
Found in: intestinal lining
Smooth Muscle Structure
Spindle-shaped (fusiform) cells (generally arranged as bundles or sheets) with tapered ends
Connected by gap junctions (functions syncytium)
Centrally located nucleus - smooth pink cytoplasm with H&E
Dense bodies
Analogous to Z-lines of skeletal muscle (visualized by TEM)
- contain actinin which binds to thin filaments and cytoskeleton (desmin and vimentin)
Other Smooth Muscle Structures
Sarcoplasmic reticulum: not as regularly arranged at SkMCs
Gap junctions - functional syncytium
Glycogen: dark particles
Dense bodies: desmin, vimentin, and alpha actinin
Speed of smooth muscle contractions
slower biochemical process
Smooth Muscle Sarcoma
Leiomyoma: smooth muscle tumor
Benign tumor of smooth muscle most commonly found in uterus but also vessels and digestive tract
Stains vimentin positive
More rounded nuclei
Whirled appearance
Cardiac Muscle
No columns, centered nuclei, striated
Intercalated discs: resemble stairway - highly specialized attachment sites between cells - gap junctions
Functional Syncytium: numerous cylinders stacked end to end
- no triad; diad - still has t-tubule
Cardiac Structure at EM level
- myofibrils of the cardiac muscle pass around their nuclei
- gap junctions - lateral component of disc
- adherens - transverse component of disc
