Lecture 5-7 Flashcards
Myofilament
Actin and myosin filaments that make up a sarcomere
Myofibrils
A chain of sarcomeres w/in a myofiber
Myofiber
Individual multinucelated muscle cell
Sarcolemma
Cell membrane of muscle fiber
Endomysium
Delicate CT around each myofiber
Fascicle
A bundle of myofibers
Perimysium
CT surrounding individual Fascicle
Muscle
Made up of fascicles “bundle of sticks”
Epimysium
CT surrounding entire muscle
Z discs [lines]
Anchor actin filaments
Located at each end of a sarcomere
Z-between
I bands
Composed entirely of actin
Width changes during contraction
A bands
Actin and myosin
With doesn’t change during contraction
H bands
Composed entirely of myosin
Width changes during contraction
How many t-tubules to sarcomere?
2 t tubules to a sarcomere
Changes that occur during sarcomere contraction
HI changes
A band doesn’t change
Sliding filament mechanism events:
- AP at terminal end of nerve fiber
- Opening of voltage-gated Ca++ channels o nerve fiber ending
- Release of Ach from synaptic vesicles into synaptic cleft
- Opening of ligand-gated Na+ channels of sarcolemma
- Generation of AP on sarcolemma
- Voltage-gated channels on T tubules interact w/ ryanodine receptors on SR
- Opening of ryanodine-sensitive Ca+ ion release channels
- increase Ca++ [ ] in cytosol
- Activation of sliding filament mechanism
- released Ca+ binds to troponin.
- Tropomyosin uncovers myosin binding sites on actin.
- ATPase heads of myosin molecules split ATP and bind to actin.
- Stored energy in myosin head causes deformation so that thick /thin filaments slide past one another
- A 2nd ATP binds to myosin and causes it to release actin.
- Repeated over and over
- Contractions ends when ATP-dependent Ca+ pump gets Ca+ back to SR.
Does binding of myosin head or release of myosin head req’ ATP?
Release after the powerstroke
Describe role of SR and T tubules in muscle contraction:
T-tubules: When depolarizer by AP, conformational change in DHP receptor and ryanodine receptor= opening of ryanodine Ca+ channels
SR: Ca+ released after its ryanodine receptor is opened by DHP on T tubule
Role of Ca++ in muscle contraction
Ca+ binds to troponin which allows tropomyosin to uncover myosin binding sites on actin—–
Exposes active site
Function of SERCA
Sarcoplasmic reticulum Ca++ ATPase: recycles Ca++ against [ ] gradient…ATP-dependent.
Function of calsequestrin
Takes Ca+ out of sol’n makes job easier for SERCA…
Lessens the [] of Ca++gradient to lower resistance
Function of DHP
Voltage gated L-type calcium channels arranged in quadruplets
On sarcolemma of t tubules; conformational change results in opening of SR ryanodine channels allowing Ca++ into the cytosol
Function of ryanodine channels
Allow Ca+ to flow into cytosol to initiate muscle contraction…must be activated by DHP
Preload
load on a muscle in the relaxed state
Results: passive tension-stretching