Muscle Tissue Flashcards
(19 cards)
What is the difference between epi, endo, and perimyseum?
Epimysium - covers entire muscle (made of dense CT)
Perimysium - covers muscle fascicles (bundles of muscle fibers); this is similar to marbling seen in steaks
Endomysium - covers individual muscle fiber (type III reticular)
Epi > Peri > Endo
What is the hierarchy of muscle fibers, from large to small, in diameter?
Muscle > Fascicle > muscle fiber > myofibril > myofilaments
Name 2 important contractile cells and their functions? (not muscle)
- Myoepithelial cells - squeeze schmutz out of glandular tissues
- Myofibroblast - involved in wound healing
Explain the main differences between White and Red muscle fibers?
- Red Fiber - Type I
- Mitochondria dense
- slow twitch
- O2 dependent energy (OxPhos)
- Ex: Postural muscles (eg. erector spinae) for long, sustained contraction
- White Fiber - Type IIa or IIb
- Fewer mitochondria
- Glycolytic pathway for energy
- Fast twitch
- eg. extra-ocular muscles
- most muscles are a mix of both types
What do the following represent:
- Z line
- M line
- A band
- H band
- I band
- Z line - splits the I band in half; represents the boundaries of the sarcomere
- M line - the MIDDLE of the sarcomere (houses c protein and myomesin); located within the H band
- A band - length of thick and thin filaments (anisotropic - light does not go through); there is overlap with thick and thin filaments (1 thick filament per 6 thin filaments) - this length does NOT change during contraction
- H band - thick filament only (essentially the A band without any of the thin filament overlap)
- I band - thin filament only (isotropic = light goes through)
Best way to remember: “Zee Intelligent Animal Has Muscle”
How is the nerve impulse communicated within the sarcoplasm?
The Triad is the site of excitation-contraction coupling
(in cardiac muscle, there is a diad)’
Triad = 1 Transverse Tubule + 2 Terminal CIsternae of Junctional SR
Diad = 1 TT + 1 SR
- Sarcoplasmic Reticulum - modified endoplasmic reticulum
- Transverse Tubules - the “meat” in the TC sandwich of the triad; the Ca++ enters through the transverse tubule from outside the sarcolemma
What physical changes happen to the sarcomere during contraction?
A band (thick + thin) undergoes NO change
I band (thin only) and H band (thick only) - shrink
Thus, you can see that the area of overlap btw the thin and thick is greatly INCREASING
Name the 4 main components of the thin filament, including the 3 accessory proteins
- F-actin - filamentous actin (looks like twisted mardi gras beads; the G-actin is just the component “beads”)
- Tropomyosin - lies in the groove of F actin
- Tropomodulin - binds both actin and tropomyosin (looks like a golf club)
- Troponin Complex (T, C, l) - troponin binds to calcium
What are the 2 components of the thick filament?
On which component does the actin bind?
- Tail - 2 intertwined heavy chains
- Head - 4 light chain “heads” that have ATP and actin binding sites
Name 2 “anchoring proteins in each sarcomere and their functions.
Titin - anchors thick filament (myosin II)
Nebulin - anchors thin filament (F actin, troponin, tropomodulin, and tropomylosin)
What are the 4 stages of the sliding filament theory?
- Attachment - myosin head bound to actin (no ATP = rigor bc myosin and actin are bound)
- Release - conformational change occurs in myosin+ATP complex, releasing myosin head
- Bending - ADP + Pi causes myosin head to “bend” toward the Z line
- Force Generation - excess Pi gets released which causes head to return to original state (power stroke)
- Reattachment - myosin binds to actin molecule as in stage 1
What is the function of the muscle spindle apparatus and what are its contents (specifically 2 fibers)?
How does it differ from a Golgi Tendon Organ?
- Specialized stretch receptor fibers located within skeletal muscle to detect changes in length of muscle
- Contain specialized fibers within spindle apparatus (Intrafusal fibers)
- Contain normal fibers, outside of spindle apparatus (extrafusal)
- Golgi Tendon Organ - only contains *afferent *fibers
- Respond when muscle is being contracted
- ie play devil’s advocate and counteract action of muscle fibers
- Necessary so muscle is not over-contracted and rips off the bone
- Respond when muscle is being contracted
What are the differences between ventricular and atrial cardiomyocytes?
- Ventricular - short fibers, mostly binucleated
- Atrial - obvious granules containing atrial natriuretic factor (used to for bp regulation)
Explain the difference composition of lateral vs. transverse components of intercalated discs.
- Transverse - Fascia Adherens, tight junctions consisting of IF
- Lateral (shelves) - GAP junctions, which allow communication between cardiac cells
Macula adherens is present mostly on lateral, but is also visible on transverse
How does the excitation/contraction coupling mechanism differ in smooth muscle vs. skeletal?
- Ca++ is stored in caveolae (NO T SYSTEM)
Explain the Ca++ - Calmodulin - MLC Kinase System
- Ca++ enters cell following depolarization
- Ca++ binds to calmodulin, forms a complex which binds to form an active MLC kinase
- Active MLC kinase phosphorylates MLC enabling active contraction to begin through the crossbridge cycle
Active - MLC phosphorylated, myosin tails released, and actin binding site opens
Relaxed - actin sites closed, myosin tail is coiled
How do smooth and skeletal muscle differ in thick filament orientation
- Bipolar thick filament - Z line is drawn from either side of the M Line
- Side Polar - chains slide over each other in opposite directions (no z-line visible)
What are dense bodies and what role do they play in smooth muscle contraction?
- Dense bodies are cytoplasmic densities that are rich in alpha-actinin protein
- They help to anchor intermediate filaments (desmin, vimentin), that are the scaffolding for the myosin actin/complexes
What is a motor unit
A motor unit is a single motor neuron and the muscle fibers that it innervates
