Lecture 14 - Muscle Tissue Flashcards
(33 cards)
What are the different classifications of muscle tissues?
- skeletal (voluntary/striated)
- cardiac
- smooth (involuntary)
What are the histological characteristics of skeletal muscle?
- multinulceated syncytium formed by fusion of embryonic myotubes
- peripheral nuclei
- sarcomeric arrangement
- innervated by a single motor axon
- contains troponin C
- “all-or-none” contraction
- 50-60μm
What are the characteristics of Type I myofibers?
- intense staining for oxidative enzymes
- rich in NADH transferase and myoglobin
- many mitochondria
- primarily uses oxidative phosphorylation
- slow, continuous contractions
- “red” or “dark” fibers
What are the characteristics of Type IIA myofibers?
- intermediate staining for oxidative enzymes
- uses aerobic and anaerobic respiration
- contract more rapidly than Type I but slower than Type IIB
- resistant to fatigue
What are the characteristics of a Type IIB myofiber?
- light staining for oxidative enzymes
- utilize anaerobic respiration primarily
- rich in ATPase
- contract most rapidly
- fatigue quickly
- “white” or “light” fibers
What are the histological characteristics of smooth muscle?
- single, mononucleated cells
- no sarcomeric arrangement
- innervated by ANS
- no “all-or-none” response
- connected via gap junctions
What are the histological characteristics of cardiac muscle?
- single, mononucleated cells
- centrally located nuclei
- often branched
- sarcomeric arrangement
- connected via gap junctions (intercalated discs)
- not directly innervated
Describe the hierarchal structure of skeletal muscle (include connective tissue).
Myofilament (actin/myosin filaments that make up a sacromere) -> myofibril (chain of sarcomeres) -> myofiber (muscle cell containing many myofibrils) -> sarcolemma (cell membrane of myofiber) -> endomysium (connective tissue surrounding each myofiber) -> fascicle (bundle of myofibers) -> perimysium (connective tissue surrounding each fascicle) -> muscle (multiple fascicles) -> epimysium (connective tissue around each muscle
What are Z disks?
- separates adjacent sarcomeres
- anchor actin filaments
What are A bands?
- consist of both actin and myosin
- represents the length of myosin filaments
- flanked by I bands and contains H band
- does not change length
What is the I band?
- portion of actin filaments not overlapping with myosin
- in between A band and Z disc
- changes length
What is the H band?
- portion of myosin not overlapped by actin
- in the middle of the A band
- changes length
Describe thick myofilaments.
Myosin:
-dimeric protein with long tails and two heads
-two pairs of light chains
—essential light chains (stability of head?)
—regulatory (stability of myosin II and sites for PO4+ binding)
Heads contain:
- actin binding region
- ATP-binding region
- light-chain binding site
Describe thin myofilaments.
F actin:
- polymer of G actin
- two polymers wound in an alpha helix
- plus end inserts into Z-disk
Actin-associated molecules: -troponin —troponin I (inhibits binding of actin and myosin) —troponin C (binds calcium) —troponin T (binds tropomyosin) -tropomyosin —sits in groove of actin strands —spans 7 actin monomers
Where are T tubules located in the sarcomere in skeletal muscle?
-A-I junctions (two per sarcomere)
What is αβ-crystalline?
-heat shock protein that protects desmin from mechanical stress
What is dystrophin?
- links α-actinin/desmin complex to sarcolemma
- anchors actin to sarcolemma
- reinforces sarcolemma
What is the dystroglycan complex?
-links dystrophin (intracellular) to laminin-2 (extracellular)
What is α-actinin?
-attaches thin filaments to Z line
What is nebulin?
- extends from Z disc to end of actin filaments
- regulates length of actin filament
What is titin?
- large, fibrous protein
- extends from Z-disk to middle of H-band and connects ends of thick filaments to Z-line
- provides myosin elasticity
- centers thick filaments in the sarcomere
What is desmin?
- intermediate filaments
- framework of desmin filaments which surrounds Z disc
- links myofibrils laterally and to the sarcolemma
What is plectin?
-binds desmin filaments
What is muscular dystrophy?
- X-linked genetic disease resulting in progressive degeneration of skeletal muscles
- result of the absence of or abnormal dystrophin which anchors actin to the sarcolemma and stabilizes muscles during contraction
