electrical activity of the heart

what are the conducting cells of the heart?

bundle of His, bundle branches, Purkinje fibers

what are the contracting cells of the heart?

cardiac myocytes

what is the function of the conducting cells of the heart?

generate and deliver action potentials to the myocardium

what is the function of the contracting cells of the heart?

contract in response to arrival of electrical signal from the conduction system or neighboring cardiac muscle cell

how do electrical activity spread across the heart?

through gap junctions

what is firing frequency?

rate at which a cell/tissue fires action potentials ( # action potentials/min)

what is conduction velocity?

how fast the action potential moves from one cell to the next

what is the pathway of the conduction system?

SA node --> internodal pathway --> aV node --> Bundle of His,--> left and right bundle branches -->purkinje fibers

what is the role of the SA node?

pacemaker of the heart

what is the role of the internodal pathway?

conduct action potentials from SA node to the atrial muscle, then onto the AV node

what is the role of the AV node?

delay conduction of action potential to the bundle of HIS

what is the role of the bundle of HIS?

carries signals from the AV node to the L and R bundle branches

what is the role of the left and right bundle branches?

carries action potential to the purkinje fibers

what is the role of the purkinje fibers?

synchronous contraction of ventricles

where are action potentials initiated at in the heart?

SA node

why is the SA node the pacemaker?

it has the fastest AP firing frequency

what can take over if the SA node is lost?

AV node

what can take over if the AV node is lost?

purkinje fibers

why do ventricles contract after the atria?

the AV node transmits action potentials slowly so that the atria are finished contracting before the ventricles start

how does electrical activity spread?

left to right septum --> apex to base --> endocardium to epicardium

what is the pacemaker potential?

it is the result of the inability of the cell membrane to maintain a resting membrane potential, as soon as the membrane potential repolarizes, it immediately begins to depolarize again

what occurs during depolarization?

SA node is depolarized, AV node produces an INFLUX of calcuim

what occurs during repolarization?

SA node is repolarized, AV node produces an EFFLUX of potassium

how are voltage gated calcium channels opened?

depolarization

what are two types of calcium channels?

T-type(short time) and L-type(long-lasting)

how are voltage potassium channels opened?

depolarization, but a delayed response

what is the HCN channel?

permeable to any cation (mainly lets in sodium), opened due to hyperpolarization, movement of positive charge into SA/AV node through the HCN channel

what is the plateau phase?

slow repolarization

what occurs during cardiac muscle depolarization?

sodium channels are open and an INFLUX of sodium occurs

what occurs during cardiac muscle transient repolarization?

a brief opening of select potassium channel and an EFFLUX of potassium occurs

what occurs during the cardiac muscle plateau phase?

L-type calcium channels are open and there is an INFLUX of calcium channels. potassium channels are altered

what occurs during the cardiac muscle repolarization?

calcium channels close and potassium channels open, EFFLUX of potassium

what channel is responsible for the upstroke phase of the pacemaker potential in nodal cells?

HCN channels

what is an ECG?

a recording of the electrical activity of the heart

what does the QRS wave represent?

ventricular depolarization

what does the P wave represent?

atrial depolarization

what does the PR interval represent?

AV conduction time

what does the ST segment represent?

plateau phase of ventricular contraction

what does the T wave represent?

ventricular repolarization

what does the U wave represent?

late ventricular repolarization