Muscle cells Flashcards
What are ion channels
voltage-dependent membrane-imbedded proteins
that pass a particular ion, usually selectively, in one direction
(dependent on the electrical and chemical gradients) or can be
activated by a ligand
What are pumps
ATP-dependent and voltage-independent membraneimbedded
proteins responsible for the movement of ions
against a chemical gradient (and possibly an electrical
gradient).
what are exchangers
voltage-independent & ATP-independent
membrane-imbedded proteins that pass usually two different
species of ions, uni- or bi-directionally (affected by chemical
and electrical gradients)
What is the ion channel state
reprimed → activated → inactivated →
reprimed. The inactivated state is essential for the proper functioning of cells/tissues
What is the brief explanation of a pump
Pumps move ions against their chemical gradient at the expense of ATP
What is the brief explanation of an exchanger
Exchangers move ions against their gradient using the potential of the chemical gradient of
another ion that drives the exchanger
What causes cardiac output increase
Cardiac output increase is the product of a change in heart rate and stroke volume
What is the ringer solution
there are a critical concentration of ions in the extracellular fluid that
are required for the heart to work
What are the 3 special structures of cardiac tissue
intercalated discs (adjacent cardiac cells are interlocked),
desmosomes (structures that anchor membranes together),
gap junctions (allow ions to move between cells)
Where might no gap junctions be found in cardiac muscle cells
No gap junctions between atrial and ventricular cells
What is autorhythmicity
the heart generates action potentials itself
what are the 2 types of cells in the myocardium
contractile cells (most of cardiac cells) - mechanical work
conducting & autorhythmic cells (~1%) - APs
What determines the waveform of an action potential
by the species of ion channels are
within its membrane and become permeant during the phases of the AP
What is involved in the cardiomyocyte action potential
a long plateau phase. This phase is determined by the
L‐type Ca2+ channel, which inactivates slowly. The long depolarization keeps the Na+
channel, which initially depolarized the cell and inactivated rapidly (2‐3 ms), inactivated for
this whole period. The Na+ channel reprimes as the membrane potential returns to resting
state. This is critical as it means secondary APs cannot be initiated until the L‐type Ca2+
channels have inactivated (>200 ms)
What overlaps with The long depolarization phase of the cardiomyocyte
the contractile response
of the tissue, ensuring that the ventricles relax after a single AP. This prevent tetani and
ensure normal beats of the heart.
What is the major difference between The phases of the APs in SA node and contractile cells
an unstable baseline that makes the pacemaker
autorhythmic. There is a funny current and no voltage‐activated Na+ channel but L‐type
Ca2+ channel for the faster depolarization phase.
What is Einthoven’s Triangle
Lead 1 is Right arm (RA) -> Left arm (LA)
Lead 2 is Right arm (RA) -> Left Leg (LL)
Lead 3 is Left Arm (LA) -> Left Leg (LL)
What is the order of APs
SA node -> AV node -> Bundle Branches -> Purkinje fibres
What is the order of waves on an ECG
P wave -> Q wave -> R wave -> S wave -> T wave
What is systole and diastole
Systole is contraction (ejection of blood)
Diastole is relaxation (filling with blood)
What controls the pacing of the heart
The Autonomic Nervous System controls the pacing of the heart. (It also controls contractility)
What does the parasympathetic nervous system do to the heart
It slows the close of K+ channels in the SA node to
increase the time it take for the cell to reach threshold for AP generation
What does The sympathetic nervous system do to the heart
The PNS accelerates inactivation of K+ channels, to speed up the
rate that the pacemaker cells reach the threshold for AP generation
what does the SA node do
The SA node overall increases pacemaker activity therefore increases heart rate
What does the AV node do
The AV node increases conduction velocity which results in a short AV delay
What does Atrial & ventricular contraction cause
It increases
Ventricular conduction which leads to increased excitability, velocity
How do cells sense charge
Ca2+ signals
What are the 6 steps in excitation‐contraction (EC) coupling
- Action potential propagation along
surface membrane. - Activation of the voltage sensor (VS) in
the t‐system membrane. - Mechanical activation of the
sarcoplasmic reticulum (SR) Ca2+
release channel by the VS. - SR Ca2+ is rapidly released into the
cytoplasm of the cell, increasing the
[Ca2+] 100 times in a few milliseconds. - Ca2+ binds to contractile proteins and
causes filaments to slide passed each
other»_space; force!! - Ca2+ is pumped from the cytoplasm
back into the SR. Ca2+ unbinds from
the contractile proteins»_space; relaxation!!
What is a major difference between cardiac and skeletal muscle EC coupling
the physical interaction
of the voltage‐sensor/DHPR/L‐type Ca2+ channel protein with the ryanodine receptor
(RyR)/Ca2+ release channel of the sarcoplasmic reticulum for the release of Ca2+ in skeletal
muscle but the lack of physical interaction between the voltage‐sensor/DHPR/L‐type Ca2+
channel protein with the ryanodine receptor/Ca2+ release channel of the sarcoplasmic
reticulum in cardiac. In cardiac, Ca2+ enters the cytoplasm from the t‐system to bind to the
ryanodine receptor to open it. This is Ca‐induced Ca release. This is the same Ca2+ influx that
controls the long plateau phase of the cardiomyocyte AP
What is Starlings Law
increasing stretch of the heart wall increase sarcomere length and the
sensitivity of the heart to Ca2+ and increase force generation
