Skeletal, Cardiac, and Smooth Muscle

Question 1

Developing Skeletal Muscle

Answer 1

Myoblasts -[differentiation]-> Myocytes -[Migration Adhesion]-> Nascent Myotubules -[Fusion]-> Mature Myotubules -[Fusion with myotubules]> myofibers

Question 2

Sarcomere Structure

Answer 2

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)

Question 3

Identifying Skeletal Muscle

Answer 3

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

Question 4

Skeletal Muscle Cell Structure

Answer 4

Myotubules, glycogen granules, sarcoplasmic reticulum, and mitochondria

Question 5

Triad

Answer 5

T-tubule which releases Ca2+

Question 6

Accessory

Answer 6

Titin anchor thick filaments to Z line
Actinin: bundles think filaments and anchored at Z-line
Dystofin: links actin to the extracellular external laminin

Question 7

Speed of muscle contraction

Answer 7

Fast!

Question 8

Muscle Cell: Visualizing the triad

Answer 8

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

Question 9

Myotendinous junction

Answer 9

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

Question 10

Junction between tendon and bone

Answer 10

Tendon attaches to bone across a functionally graded fibrocartilaginous transition site
Tendon -> tendon proper -> fibrocartilage -> mineralized fibrocartilage -> bone

Question 11

Muscle Spindle

Answer 11

Regulates muscle contraction, length, and coordination

Question 12

Smooth Muscle Structure

Answer 12

no sarcomeres, but contraction through dense bodies (calcium allows for contractions)

Question 13

Smooth Muscle nervous system controls

Answer 13

Stimuli in digestive tract and autonomic nervous system feed into sympathetic (A), parasympathetic (A), and enteric (A & Stimuli in DT) nervous systems

Question 14

Multi-unit smooth muscle cell

Answer 14

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

Question 15

Single-Unit smooth cells

Answer 15

fibers become excited and contract as single unit, cells are linked by gap junctions (electrically)
Found in: intestinal lining

Question 16

Smooth Muscle Structure

Answer 16

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

Question 17

Dense bodies

Answer 17

Analogous to Z-lines of skeletal muscle (visualized by TEM)
- contain actinin which binds to thin filaments and cytoskeleton (desmin and vimentin)

Question 18

Other Smooth Muscle Structures

Answer 18

Sarcoplasmic reticulum: not as regularly arranged at SkMCs
Gap junctions - functional syncytium
Glycogen: dark particles
Dense bodies: desmin, vimentin, and alpha actinin

Question 19

Speed of smooth muscle contractions

Answer 19

slower biochemical process

Question 20

Smooth Muscle Sarcoma

Answer 20

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

Question 21

Cardiac Muscle

Answer 21

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

Question 22

Cardiac Structure at EM level

Answer 22

• myofibrils of the cardiac muscle pass around their nuclei
• gap junctions - lateral component of disc
• adherens - transverse component of disc