Skeletal Muscle Flashcards
alpha-actinin
actin-binding protein; comprises the Z disk
A-band
where actin and myosin overlap
actin
thin filaments
H band
band with myosin but no actin
I band
actin but no myosin, attaches so Z disk
M line
where myosin attaches; middle of sarcomere
nebulin
regulates actin filament length during sarcomere assembly
titin
helps maintain resting length of sarcomere
Z disk
where actin attaches
transverse tubule
invaginations of the plasma membrane that is open to the outside; where AP travels to release calcium
What type of channel is located on the T tubule?
L-type Ca++ channel; opens due to chemical stimulation
skeletal muscle contraction
AP travels down T tubule –> binds the L-type Ca++ channel and opens it –> L-type channel mechanically opens the Ca++ release channel on the SR –> calcium exits the SR and activates troponin C
tropomyosin
regulates the binding of myosin head to actin –> troponin binds this to move it out of way
troponin T
binds tropomyosin
troponin C
binds calcium
troponin I
binds to actin and inhibits contraction
alkali light chains of myosin
stabilize the head region
regulatory light chains of myosin head
regulate ATPase activity of myosin
When does TnI cover the myosin binding site?
in the absence of Ca++
phosphate release
power stroke
cross bridge cycle
myosin head forms a cross bridge with actin (ADP and Pi are attached) –> myosin head bends, releasing ADP and Pi for the power stroke –> new molecule of ATP binds, causing myosin to detach –> ATP hydrolyzes to ADP and Pi, which returns myosin to cocked position
termination of contraction
requires re-uptake of Ca++
re-uptake of Ca++
calcium is stored in the SR via the Ca++/H+ pump (primary active); PMCA pump on membrane extrudes calcium (primary active); Na+/Ca++ pump on membrane extrudes calcium (secondary active)
isotonic
same tension
isometric
same length
temporal summation
stimulation before complete relaxation causes a greater contraction (more tension)
tetanus
no relaxation, plateau of tension
motor unit
a single muscle neuron and the muscle fibers that it innervates
motor neuron pool
all the motor neurons that innervate a single muscle
skeletal synapses are _
chemical
electrical synapse
directly link cytoplasm of adjacent cells; connexon channels of gap junctions
chemical synapse
NTs synthesized and packaged in vesicles –> AP arrives at presynaptic terminal –> VG-Ca++ channels open and Ca++ enters –> rise of Ca++ causes fusion of synaptic vesicles with presynaptic membrane –> transmitter molecules diffuse across synaptic cleft and bind to receptors on postsynaptic cell
action potential stimulation
Na+ enters cell and depolarizes it
end of action potential
K+ exits cell for repolarization
ionotropic receptors are _
skeletal; stimulate muscle contraction
metabotropic receptors are found in _
heart; can inhibit muscle contraction with Ach binding
