Cardiac Muscle Flashcards
organization
organized into sarcomeres
intercolated discs join neighboring cells- contain desmosomes and gap junctions
Cellular properties
found almost exclusively in heart wall
striated
uni/bi nucleated
feature Y-shaped branching
join other cells at intercolated discs
autorythmic (does not require nerve stimulation)
under involuntary control
Cardiac action potential
- rapid depolarization due to opening of voltage gated Na channels
- plateau due to opening of more voltage gated slow Ca channels, and closing some k channels
- repolarization due to opening of more voltage gated K channels and blocking of Ca channels
Control
pacemaker cells
contractile cardiac myocytes
intercolated discs
pacemaker cells
autorhythmic
spontaneously active and set pace for heart rate
contractile cardiac myocytes
driven by pacemakers which fire Ca upstroke APs to direct cardiac myocyte beating
intercolated discs
help to spread the signal
pace can be altered
Autonomically (up/dow)
- sympathetic
- parasympathetic
- hormonally
Sympathetic alteration
norepinephrin
Up- regulates
parasympathetic alteration
acetylcholine
Down-regulates
hormonally
epinephrine/ thyroid hormone
usually up-regulates
Cardiac is like skeletal
striations
sarcomere structure
Na upstroke/k downstroke
-90 mV resting
Cardiac is unlike skeletal
shorter fibers
often branched/ gap junctions
uni/bi nucleated
Ca plateau
involuntary control
contraction takes longer
contraction happens during absolute refractory period
cannot summate AP/contraction (peak is during refractory period)
Excitation-Contraction coupling- skeletal
mechanically gates Ca release from SR
RyRs
RyRa opened by action of non-permeable L-type Ca Channels (DHP)
modified Ca receptors (DHP) in T-tubules
RyRs is mechanically gated
Excitation-Contraction coupling- cardiac
Ca-induced Ca release from SR and RyRs
AP induced Ca influx from sarcolemma: real voltage-gated Ca channels
Positive feedback
RyRs is ligand gated
