phys cardiovascular part 3

what is the natural pacemaker of the heart?

the SA node

where is the SA node located

upper wall of the RA near the superior vena cava

what is the intrinsic firing rate of the SA node?

about 100 action potentials per min

what is the function of the AV node?

it delays electrical signal about 0.1 second so the ventricles can fill before they contract

where is the AV node located?

in the interatrial septum near the tricuspid valve

why is the AV node delay important

it allows the atria to finish contracting before the ventricles contract

what is the function of the fibrous skeleton?

it electrically insulates the atria from the ventricles making the AV node the only normal pathway for electrical signals

what is the bundle of HIS

a conduction pathway that carries electrical signals fromt he AV node down the interventricular septum

what do purkinje fibers do?

rapidly distribute electrical impulses through the ventricles causing them to contract from the apex upward

what makes pacemaker cells unique

they automatically generate action potentials and have no true resting membrane potential

which ion channels open first in pacemaker cells

funny (If) channels

what ion mainly enters through funny channels

sodium (Na+)

which calcium channels help pacemaker cells reach threshold

T-type calcium channels

which calcium channels cause rapid depolarization in pacemaker cells

L-type calcium channels

which ion is responsible for repolarization in pacemaker cells

potassium (K)

what ion causes rapid depolarization (phase 0) in contractile cardiac muscle cells

sodium (Na+)

what happens during the plateau phase (phase 2)

calcium enters the cell while potassium movements outward decreases

why is the plateau phase important

it prevents tetanus and allows the heart to relax and refill between beats

which ion causes depolarization in contractile cells

potassium (K)

what is the main difference between pacemaker and contractile cells

Pacemaker cells generate the heartbeat automatically, while contractile cells contract only after being stimulated.

what does an ECG measure

the electrical activity of the heart

what does P wave represent

atrial depolarization

what does QRS complex represent

ventricular depolarization

what electrical event is hidden within the QRS complex

atrial repolarization

what does the T wave represent

ventricular repolarization

what does the PR interval measure

the time it takes the electrical signal to travel from the atria through the AV node to the ventricles

what does the QT interval represent

the total time for ventricular depolarization and repolarization

what does the RR interval represent

one complete cardiac cycle (one heartbeat)

how do you calculate heart rate using the RR interval

heart rate = 60 / RR interval in seconds