Skeletal/smooth muscle phys Flashcards
differentiate myofibril, myofiber, myofilament
myofiber= biggest, same as the muscle cell/fiber
myofibril= unit w/i myofiber made up of actin and myosin myofilaments
sarcomere
functional unit of the myofiber, demarcated by Z line- contains overlapping thick and thin myofilaments
myofiber triad
T tubule w/ SR terminal cisternae on either side, for Ca++ release
NMJ
synapse b/w somatic motor neuron and skeletal muscle fiber
motor unit
all muscle fibers innervated by one motor neuron (each fiber innervated by only one neuron, one neuron can innervate multiple fibers)
motor endplate
post synaptic region of skeletal muscle cell
endplate response to ACh from somatic motor neuron
nicotinic ACh receptors open to Na and K, graded EPP produced and initiates AP w/ voltage gated Na channels in sarcolemma
location of ACh receptors on endplate
top of junctional folds
location of voltage gated Na channels on endplate
bottom of junctional folds and on longitudinal sarcolemmal surface
muscle triad response to muscle AP at end plate
depolarization down into T-tubules, opens DHP/L-type Ca++ channels which mechanically opens ryanodine receptors on SR, Ca++ moves into cytosol from SR and binds troponin
how is Ca++ release from SR different in skeletal muscle?
single AP enough to bind all troponin, maximize cross bridging
SR directly linked to T tubules
SERCA
SR Ca++ ATPase- lowers cytosolic Ca++ by bringing it into SR, facillitates relaxation
major histological differences w/ smooth
spindle shaped, myofilaments arranged diagonally (reason for no striations), no Z bands, contraction causes ballooning outward (for shrinking a lumen)
vascular smooth muscle regulation
does not fire APs, under involuntary control (hormones, NTs)
mutiunit smooth muscle
not much electrical coupling b/w cells, fine motor control w/ independent contraction (eg iris)
single unit smooth muscle
extensive electrical coupling, coordinated contraction as in visceral organ lining
walk thru steps of smooth muscle contraction beginning w/ Ca++ release from SR
- Ca++ binds calmodulin
- Ca-Calmodulin activates Myosin light chain kinase
- MLCK phosphorylates MLC= contraction
role of MLC phosphatase
dephosphorylates MLC, causing relaxation of smooth muscle
active constitutively
characteristics of smooth muscle contraction compared w/ skeletal
slow and energy effecient compared to skeletal muscle, can be graded contraction dependent on Ca++
synthesis of NO
NO synthase w/ NADPH and L-Arginine, occurs in endothelial cells
fn of NO
potent vasodilator: stimulates cGMP production in smooth muscle which activatetes Protein kinase Gā more reuptake of cytosolic Ca++ and opening of K+ channels
less Ca++ and MLCK activity= relaxtion
