Muscle Physiology Flashcards
where do action potentials in muscles propagate?
sarcolemma
Triad Junction
- T tubule w/ 2 terminal cisternae, which are specialized regions of sarcoplasmic reticulum
what is happening when the muscle shortens?
it means it’s contracting and producing tension
where can we find ryanidine receptors?
skeletal and cardiac muscles
sarcomere
repeating unit b/w adjacent Z disks/lines
smallest functional unit of skeletal muscle
proteins tethered to z disk of skeletal muscles
actin
nebulin
titin
alpha actinin
alpha actinin
crosslinks antiparallel thin filaments at z disk
helps to anchor myofibrillar actin filaments
titin
connects myosin to z disk
stretch sensing and signal communication to nucleus of skeletal muscle
titin, nebulin
a filament that forms internal support and attachment for actin
nebulin
what is the back bone of thin filament?
F-actin
structure of F-actin
right-handed, two-stranded helix of non-covalently polymerized actin molecules
what is another calcium-binding protein that is closely related to troponin C?
calmodulin
Troponin T binds to…
a single molecule of tropomyosin
Troponin I
binds to actin and inhibits contraction
what enhances myosin cross-bridge interactions?
phosphorylation of RLC (myosin regulatory light chain) by myosin light chain kinases
myosin light chain phosphatase function
dephosphorylates regulatory light chain of the motor protein myosin II
how do calcium ions exert their effect in muscle contraction?
they bind to regulatory proteins rather than directly interacting w/ contractile proteins
myosin II
responsible for ATP-dependent force generation in all types of myocytes
location of the 2 high affinity sites on skeletal muscles
c lobe of TNNC2 (troponin C subtype)
location of 2 low affinity sites on skeletal muscle
n lobe of TNNC2
how many molecules of ATP are consumed after one round of cross-bridge cycle?
only one ATP molecule
what is the most important mechanism for the termination of muscle contraction?
calcium ion reuptake by SR via the SARCOPLASMIC ENDOPLASMIC RETICULUM Ca-ATPase.
calreticulin
- a calcium binding protein that is found in smooth muscles in high concentration
calsequestrin
calcium-binding protein in SKELETAL MUSCLES
buy may also be present in cardiac and smooth muscle
minor mechanism in termination of muscle contraction
NCX or PMCA
na-ca exchanger or plasma membrane ca-atpase
what determines the amount of tension developed?
degree of overlap between actin and myosin filaments
how is the shortening velocity affected with higher loads?
velocity is slower because more cross-bridges are simultaneously active.
relationship b/w load and velocity
they’re INVERSELY PROPORTIONAL
what structures interconnect cardiac myocytes from end to end?
intercalated disks
what is an absolute requirement for cardiac muscle contraction?
influx of Ca++ through the L-type calcium channels
what type of junction is made b/w single terminal cisterna of SR and t-tubule?
dyad junction
what is needed IOT pump calcium back into SR?
ATP
what maintains Na+ gradient during EC coupling in cardiac muscle?
Na-K ATPase
In skeletal muscle, how many calcium ions bind to TNNC2 subtype?
4 calcium ions
In cardiac muscle, how many calcium ions bind to TNNC2 subtype?
3 calcium ions
what inhibits SR calcium pump?
PHOSPHOLAMBAN
nerve bundles that release NTs in smooth muscles
varicosities (close to postsynaptic membrane of smooth muscle cell)
smooth muscles don’t have synaptic clefts
multiunit smooth muscle
each SM cell receives its own synaptic input
iris, walls of blood vessels
unitary smooth muscle
only a few cells receive direct synaptic input
hollow organs
function of gap junctions in smooth muscles
permit coordinated contraction
why is the rate of rising of action potential lower in smooth muscles?
calcium channels open much slower than Na+ channels in cardiac and skeletal muscles.
purpose of fast, voltage Na+ channels in smooth muscles
hasten activation of voltage-gated Ca++ channels, which contribute to faster rate of depolarization
what causes spontaneous electrical activity in smooth muscles?
regular, repetitive oscillations in Vm and contractions (SLOW WAVE POTENTIAL)
what can activate contract in smooth muscles?
both extracellular and intracellular calcium ions
2 proteins that tonically inhibit interaction b/w actin and myosin
caldesmon and calponin
tonically inhibit actin-activated ATPase activity of myosin
caldesmon
tonically inhibits ATPase activity of myosin
calponin
