Muscle cells

Question 1

What are ion channels

Answer 1

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

Question 2

What are pumps

Answer 2

ATP-dependent and voltage-independent membraneimbedded
proteins responsible for the movement of ions
against a chemical gradient (and possibly an electrical
gradient).

Question 3

what are exchangers

Answer 3

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)

Question 4

What is the ion channel state

Answer 4

reprimed → activated → inactivated →
reprimed. The inactivated state is essential for the proper functioning of cells/tissues

Question 5

What is the brief explanation of a pump

Answer 5

Pumps move ions against their chemical gradient at the expense of ATP

Question 6

What is the brief explanation of an exchanger

Answer 6

Exchangers move ions against their gradient using the potential of the chemical gradient of
another ion that drives the exchanger

Question 7

What causes cardiac output increase

Answer 7

Cardiac output increase is the product of a change in heart rate and stroke volume

Question 8

What is the ringer solution

Answer 8

there are a critical concentration of ions in the extracellular fluid that
are required for the heart to work

Question 9

What are the 3 special structures of cardiac tissue

Answer 9

intercalated discs (adjacent cardiac cells are interlocked),
desmosomes (structures that anchor membranes together),
gap junctions (allow ions to move between cells)

Question 10

Where might no gap junctions be found in cardiac muscle cells

Answer 10

No gap junctions between atrial and ventricular cells

Question 11

What is autorhythmicity

Answer 11

the heart generates action potentials itself

Question 12

what are the 2 types of cells in the myocardium

Answer 12

contractile cells (most of cardiac cells) - mechanical work
 conducting & autorhythmic cells (~1%) - APs

Question 13

What determines the waveform of an action potential

Answer 13

by the species of ion channels are
within its membrane and become permeant during the phases of the AP

Question 14

What is involved in the cardiomyocyte action potential

Answer 14

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)

Question 15

What overlaps with The long depolarization phase of the cardiomyocyte

Answer 15

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.

Question 16

What is the major difference between The phases of the APs in SA node and contractile cells

Answer 16

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.

Question 17

What is Einthoven’s Triangle

Answer 17

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)

Question 18

What is the order of APs

Answer 18

SA node -> AV node -> Bundle Branches -> Purkinje fibres

Question 19

What is the order of waves on an ECG

Answer 19

P wave -> Q wave -> R wave -> S wave -> T wave

Question 20

What is systole and diastole

Answer 20

Systole is contraction (ejection of blood)
Diastole is relaxation (filling with blood)

Question 21

What controls the pacing of the heart

Answer 21

The Autonomic Nervous System controls the pacing of the heart. (It also controls contractility)

Question 22

What does the parasympathetic nervous system do to the heart

Answer 22

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

Question 23

What does The sympathetic nervous system do to the heart

Answer 23

The PNS accelerates inactivation of K+ channels, to speed up the
rate that the pacemaker cells reach the threshold for AP generation

Question 24

what does the SA node do

Answer 24

The SA node overall increases pacemaker activity therefore increases heart rate

Question 25

What does the AV node do

Answer 25

The AV node increases conduction velocity which results in a short AV delay

Question 26

What does Atrial & ventricular contraction cause

Answer 26

It increases
Ventricular conduction which leads to increased excitability, velocity

Question 27

How do cells sense charge

Answer 27

Ca2+ signals

Question 28

What are the 6 steps in excitation‐contraction (EC) coupling

Answer 28

1. Action potential propagation along
   surface membrane.
2. Activation of the voltage sensor (VS) in
   the t‐system membrane.
3. Mechanical activation of the
   sarcoplasmic reticulum (SR) Ca2+
   release channel by the VS.
4. SR Ca2+ is rapidly released into the
   cytoplasm of the cell, increasing the
   [Ca2+] 100 times in a few milliseconds.
5. Ca2+ binds to contractile proteins and
   causes filaments to slide passed each
   other&raquo_space; force!!
6. Ca2+ is pumped from the cytoplasm
   back into the SR. Ca2+ unbinds from
   the contractile proteins&raquo_space; relaxation!!

Question 29

What is a major difference between cardiac and skeletal muscle EC coupling

Answer 29

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

Question 30

What is Starlings Law

Answer 30

increasing stretch of the heart wall increase sarcomere length and the
sensitivity of the heart to Ca2+ and increase force generation