HIST - Muscle Flashcards
1
Q
THREE TYPES OF MUSCLE
A
Skeletal Muscle (SkM)
- Striated, multinucleated
- Elongated nuclei lie along the periphery
- In a cross section, cells look angular
Cardiac Muscle (CM)
- Striated
- Intercalated discs
- Uni/multinucleated, lie in center
Smooth Muscle (SM)
- No striations
- Elongated, fusiform cells
- One, centrally located nucleus per cell
- Density depends on amount of extracellular CT
- Cross-section = Highly cellular
2
Q
CHARACTERISTICS OF ALL MUSCLE
A
- All muscle is derived from primitive mesenchymal cells of the mesoderm
- EXCEPT the iris –> derived from the ectoderm
- All muscle cells have microfilaments: actin and/or myosin
3
Q
GROWTH OF SKELETAL MUSCLE
A
- Muscle cells grow unorganized during embryogenesis
- Become oganized into fibers later (by unnamed proteins)
- **myoblasts **fuse to form myotubes which form a mature muscle that can act as syncytium
- Breakdown:
- Muscle
- Fasicles
- Muscle fibers (cells)
- Myofibrils
- Myofilaments
- Actin/myosin
- Myofilaments
- Myofibrils
- Muscle fibers (cells)
- Fasicles
- Muscle
4
Q
ORGANIZATION OF SKELETAL MUSCLE
A
Surrounded by CT sheaths that
- Allow transmission of force
- Allow tranmission of nerves and vasculature
-
Sarcolemma = PM, around cell/fiber
-
Endomysium = around each muscle fiber
-
Perimysium = around fasicle
- Epimysium = around muscle
-
Perimysium = around fasicle
-
Endomysium = around each muscle fiber
5
Q
SKELETAL MUSCLE FACTS
A
- # of muscle fibers fixed at puberty b/c myostatin inhibits new fiber development
-
Myostatin = cytokine produced by muscle cells
- Circulates as a hormone after puberty (12-14 y/o)
- Regulates muscle development
- inhibits myoblast differentiation and hypertrophy
- Athletes/strong people often have mutant myostatin
- Many ilicit drugs inhibit myostatin
-
Satellite cells = muscle progenitor cells
- Differentiate into myoblasts
- Function in new muscle fiber growth until puberty (12-14 y/o)
- Function in injury muscle
-
Can regenerate (ish)
- Trauma –> fibrosis (fibroblasts replace dead SkM with CT)
-
Hypertrophy = increased in muscle fiber size
- Caused by repeated exercise
- **Hyperplasia **= increase in number of fibers
- May be induced by stressful exercise (weight lifting)
Muscle growth from exercise = increase in size of fibers and increase in CT surrounding fibers
6
Q
SARCOMERE
A
- Banding
- Z line to Z-line = sarcomere = functional unit of SkM
- I band = actin, thin; isotropic (allows polarized light); 7 nm
- A band = myosin, thick, and actin; anisotropic properties from myosin; 15 nm
- H band = myosin
- Muscle fiber = repeating units of sarcomeres
-
T-tubule = triad
- Invagination + SR (smooth ER) on either side
- Ca2+ release and storage from SR’s terminal cisternae
-
Sliding filament model
- I and H bands shorten
- A bands unchanged
- Z discs move closer
7
Q
SKELETAL MUSCLE CONTRACTION
A
- Voluntary, by nerve innervation at motor end plate
- Capped by a Schwann cell (protects)
- Synaptic cleft = neuromuscular junction
- Stimulated by ACh
- All or none rule
- Ca2+ release regulates contraction
8
Q
CARDIAC MUSCLE
A
- Striated
- Intercalated discs
- 1-2 centrally located nuclei
- Bifurcating and anastomosing
-
Atrial granules = vesicles that secrete ANP
- Atrial naturetic peptide = acts on the kidney to regulate BP by changing sodium/water reabsorption
- Heart contraction occurs in a wringing motion from atria to ventricles
- Cannot regenerate
9
Q
ORGANIZATION OF CARDIAC MUSCLE
A
-
Endocardium (epithelial cells)
-
Myocardium (CM)
-
Epicardium/visceral pericardium (mesothelium)
- Secretes pericardial fluid into the pericardial cavity
- Parietal pericardium (mesothelium) (Also secretes pericardial fluid)
- Secretes pericardial fluid into the pericardial cavity
-
Epicardium/visceral pericardium (mesothelium)
-
Myocardium (CM)
-
CS –> cardiac tamponade, increase in fluid, pressure on ventricles
- Causes irregular contractions
-
T-tubule = diad
- Invagination + SR network
- Ca2+ storage and release
- No cisternae
- TONS of mitochondria in CM
10
Q
TYPES OF CARDIAC CELLS
A
CARDIOCYTES
- Contractile cardiomyocytes = CM
- Nodal cardiocytes = SA, AV nodes
- **Myoendocrine cardiocytes **= in atria, secrete ANP
-
Purkinje fibers = conduct from AV node
- Derived from cardiomyocytes (have straitions)
- Lie directly under endocardium
- Full of glycogen
11
Q
INTERCALATED DISCS
A
- Step-like arrangement of CM fibers
- Vertical = FA (specialized ZA) and MA (desmosomes)
- Horizontal = GJs
- Function: help CM act in syncytium
- Contraction = spontaneous; involuntary
- Internal pacemaker
- Modulated by ANS
- Rhythmic, all-or-none
12
Q
SMOOTH MUSCLE
A
- Relaxed = elongated, fusiform
- Contracted = corkscrew
- Have cytoplasmic dense bodies/plaques (sarcolemma) = Z discs
- Actin and myosin myofilaments
- No striations
- External basal lamina
- GJs (LOTS of them)
- No T-tubules –> caveolae = Ca2+ storage and release
- One, central nucleus per cell
- Involuntary contractions, modulated by ANS
- Parasympathetic/Sympathetic ANS
- Hormones (ex: oxytocin)
- Drugs
-
Cross-section =
- Inner circular layer
- Outer longitudinal layer
- Can regenerate
13
Q
SMOOTH MUSCLE CONTRACTION
A
- Cytoplasmic dense bodies/plaques are pulled together by myofilaments
- Crumples into a ball
- Isotonic contraction
- Not “all-or-none” can be partial
14
Q
SMOOTH MUSCLE CLASSIFICATION
A
-
Single Unit
- Can contract individually
- Act in syncytium
- Ex: intesine, urethra, ureter
-
Multi Unit
- Can contract individually because each has its own innervation.
- Not one nerve to one cell, but each cell is stimulated by a nerve, not by other cells
- Via **en passant **axonal swellings/projections into each muscle fiber = motor end plate
- One nerve can innervate many SM cells
- Ex: iris, trachea, esophagus
-
Vascular
- Blood vessels
- Mix of single and multi unit properties