cardiac muscle Flashcards
properties of cardiac muscle
small, branched cells joined by intercalated discs
striated
does cardiac muscle have troponin
yes
does cardiac muscle have sarcomeres
yes
are cardiac cells electrically coupled
yes
3 components of intercalated discs
interdigtating folds- in folds at the end of cells that increase the surface area of cell-cell connection
mechanical junction-2 types: fascia adherens and desmosomes
electrical junctions- electrically coupled by gap junctions. Enables each cell to stimulate the next
gap junctions
present in intercalated discs of adjacent cells
low-resistance pathway between cells
cell-cell conductance by electrical coupling
description of blood supply in cardiac muscle
requires continuous O2 for mitochondria to produce ATP
rich capillary supply
short diffusion distance for O2 and waste
2 types of electrical activity
pace maker potential and prolonged cardiac action potential
3 ion conducting mechanisms
progressive reduction in K+ permemability- K+ channels that open at repolarisation and close at negative potentials Funny channel (F current) = Na+ permeable ion channel that opens at negative potentials (unlike most VGCs). These depolarise the membrane T-type calcium channels: VGCCs that contribute to final depolarisation boost of the pacemaker potential
what is contraction in cardiac muscle cells in response to
membrane action potential that propagates through the T-tubules
L type Ca 2+ channels
(long lasting current)
Modified DHP receptors that act as the voltage sensor in skeletal muscle excitation-contraction coupling
Enable depolarization of the cell due to influx of extracellular Ca2+
VGCs
Where does Ca2+ for contraction come from
entering Ca2+ through L type channels not only depolarises the membrane and increases cytosolic Ca2+, it also triggers release of much more Ca2+ from the sarcoplasmic reticulum. This is because ryanodine receptors on external surface of sarcoplasmic reticulum are Ca2+ channels, and not opened by voltage as in skeletal muscle, instead by bindng of trigger Ca2+ in the cytosol
Any differences between skeletal muscle filament activation, cross bridge cycling etc and in cardiac muscle
No
when does contraction end
when cytosolic Ca2+ concentration restores to its low value by Ca2+ ATPase pumps in the sarcoplasmic reticulum and sarcolemma (cell membrane of muscle cell)
Sequence of excitation-contraction coupling
Membrane depolarizzed by Na+ as an AP begins
Depolarisation opens L-type channels in T tubules
Trigger Ca2+ enters cytosol, contributing to cell depolarisation. Binds to and opens ryanodine receptor
Ca2+ flows into cytosol, cross bridge cycling occurs
Once Ca2+ has been restored to same level, membrane is repolarized when K+ exits the cell to end the action potential
