9.2 Action Potentials and EKG

Neurogenic hearts beat under ________________________ and are found in some ______________

control of the nervous system; crustaceans

Myogenic hearts have contractions ___________ within the heartt and the nerves going to the heart only regulate the _____ of heartbeat. these hearts are found in __________

initiated; rate; all other organisms

Intercalated discs are in cardiac muscle cells and allow for ____ __________ which allow for uniform _______________ of the heart muscle

gap junctions; depolarization

The hear is autorhythmic meaning

heart stimulates itself to contract at regular intervals

____________ cells in the SA node have a specialized PM that allow for ____, ___, and ___ ions to cross and trigger electrical impulses

Pacemaker; Na+, K+, and Ca2+

The cells in the sinoatrial (SA) node spontaneously depolarize, resulting in contractions abt _____ times per minute

100

The very fast rate of SA depolarization is monitored by activity in the _____________ and ____________ nerve fibers so that the avg resting heartrate is about ____ beats per minute

sympathetic and parasympathetic; 70

What are cardiomyocytes?

heart muscle cells

What is the order of heart contraction starting with excitation of the SA node?

1. SA node spontaneously generates APs

2. APs travel rapidly through atria to AV node

3. transmission through AV node is slow and travels to Bundle of His

4. Bundle of His goes to left and right bundle branches

5. signal then travels to Purkinje fibers and AP is delivered very rapidly

The only way to send signals from the atria to the ventricles is through ____________ __________ with ________ diameters. This diameter causes APs to be transmitted ________

conducting fibers; small; slowly

Why do we want APs to go through the atria to ventricles slowly?

do not want atria and ventricles to pump at same time so ventricles can fill with blood

In the slow rise of SA node depolarization, K+ channels are ____________, Funny channels are _______ and let in _____, and transient calcium channels let Ca2+ ______

closing; open; Na+; in

In the quick rise of SA node depolarization what kind of channels are open and what are they letting in?

Long lasting calcium channels are open and letting calcium in

In the repolarization of the SA node, what channels are open and what is flowing out?

Potassium channels open, letting K+ flow out

What type of channel responds to low membrane potential and open and close quickly? What type of channel responds to higher membrane potentials and open and close slowly

T-type channels (transient); L-type channels (long)

T-type Calcium channels are important in ____________ APs while L-type calcium channels are important in ____________ APs

initiating; sustaining

Funny channels are activated by __________ or _______ and allow ____ and ____ ions through

voltage or cAMP; Na+ and K+

What is the sympathetic effect?

norepi increases membrane permeability to Na+ and Ca2+ so slow depolarization occurs faster so rate of APs increase

What is the parasympathetic (vagus) effect?

acetylcholine decreases membrane permeability to Ca2+ and Na+ and increases permeability to K+, so depolarization takes longer

The AP in cardiac muscle is ___________ than AP in skeletal muscle

longer

Why is the AP in cardiac muscle long?

longer refractory period so ventricles can contract --> relax --> contract, NO SUMMATION

The cardiac muscle AP in ventricular muscle starts with a rapid increase in ____ and ____ channels are closed

Na+; K+

In the AP for ventricular muscle contraction, after Na+ influxes rapidly, ____ channels close and ______________________ channels open, letting in ___

Na+; L-type calcium; Ca2+

In ventricular muscle contraction, the opening of the potassium channels is ____________ which results in a slow repolarization of the AP

delayed

The L-type calcium channels opening allows for the small ___________ seen in the cardiac muscle AP

plateau

The long refractory period in cardiac muscle AP makes it so _________ is not possible

tetanus

In cardiac muscle, AP opens voltage sensitive calcium channels on the membrane in __ ______________. Ca flows into cytosol and binds to receptors on the surface of the ___________ _______________. More Ca2+ flows into the cytosol and a contraction occurs

T tubules; sarcoplasmic reticulum

EKG measures electrical activity that can be measured at the _____________ of the body

surface

Electrodes are conductive ______ that make an electrical circuit with the electrocardiograph

pads

A lead provides a comparison between _________

electrodes

Different placements of leads gives ______________ EKG results

different

Insert EKG wave

What does the P wave represent?

depolarization that spreads from SA node to atria

What is the flat region between the P wave and the QRS wave?

time when the impulse travels within the AV node and Purkinje fibers

The QRS wave represents?

ventricles contracting

What is the flat region between S and T?

ventricles are completely depolarized

What is the Q-T interval?

ventricular depolarization and repolarization

What would happen to EKG if the spread of AP through the AV node was slower?

insert pic

What would happen to EKG if ventricular AP had a shorter duration

insert pic