APD Cardiac Physiology & Action Potential (Lecture 26)

SA node

Depolariztion of the heart starts at the (AV/SA) node.

SA node

What is the heart pacemaker?

60-100

The SA node has ____________ beats per minute.

AV node

Depolarization of the SA node then travels through the atria to the _____________.

bundle of His; Purkinje

After the AV node, the signal travels in the _____________________ to the _____________ fibers, which ultimately signals the ventricles.

gap junctions

Propogation of action potentials occurs through ____________________.

Phase 0

What phase of the action potential includes depolarization via calcium and/or sodium ions?

Phase 1; Inactivation of sodium and/or calcium channels

What action potential phase occurs in atrial/ventricular muscles and Purkinje fibers and includes rapid repolarization? What causes this rapid repolarization?

Phase 2; Atrioventricular/Atrial muscle and Purkinje fibers

What action potential phase serves as the plateau phase, which includes maintained opening of some calcium & sodium channels? Where does this phase occur in solely?

Phase 3

What action potential phase includes repolarization of the heart due to opening of potassium channels?

Phase 4

What action potential phase is responsible for pacemaker activity through depolarization of SA & AV nodes & Purkinje cells?

Calcium

During SA/AV node action potential phase 0, what ion causes depolarization?

Calcium; potassium

During phase 3 of SA/AV node action potentials, what ion channels progressively close? What ion channel slowly opens?

K+; Ca2+; HCN

During phase 4 of SA/AV node action potentials, only a few ____ channels remain open. ______ channels reopen at -55 mV. ___________ channels slowly activate, causing Na+ & some K+ to move inward.

False--not the same!

True/False: HCN channels are synonymous to sodium channels.

Na+ & Ca2+; depolarization

During atrial/ventricular muscle action potential phase 0, what ion(s) open? This causes ________________ to occur.

Vm; K+; repolarization

During atrial/ventricular muscle action potential phase 1, some Na+ & Ca2+ channels close due to a more positive ______ (less +). Special outward ____ channels may also be open during this phase. This causes _______________ to occur.

remain constant

During phase 2 of the atrial/ventricular muscle action potential (plateau phase), Na+ and Ca2+ channels (open/close/remain constant).

K+ channels; Na+ & Ca2+ channels; hyperpolarization/repolarization

During phase 3 of the atrial/ventricular muscle action potential, what channels begin to open slowly? What channels progressively close? This causes _______________.

Na+ & Ca2+; K+ channels

During phase 4 of atrial/ventricular muscle action potential, what channels remain closed? What few channels remain open?

Na+; K+

For action potentials in the heart, due to an increase in relative Ca2+ & Na+ outside the cell, ____ & _____ will move inward when the channels open.

Na+

What ion is responsible for phase 0 in the atrial/ventricular muscles & Purkinje fibers, but NOT the AV/SA node?

Na+; repolarization

At positive membrane potential, what channels slowly close? What part of the action potential does this cause?

plateau phase

Na+ channels that remain open cause the __________________.

Ca2+

What ion is present in all cardiac myocytes?

L-type

What is the main channel of calcium?

Ca2+

What ion is mainly responsible for depolarization in the SA/AV nodes?

contraction

Ca2+ leads to a delay in atrial & ventricular _____________ due to slower depolarization of nodal fibers.

Ca2+

What ion works with sodium in ventricular muscle & Purkinje fibers?

Ca2+

What ion channel reopens during phase 4 within AV/SA node & Purkinje fibers and aids in depolarization in pacemakers?

Ca2+

What ion helps prolong the plateau phase in ventricular muscle & Purkinje fibers?

K+

What ion channel opening repolarizes all cardiac monocytes?

Early outward potassium current

What potassium current is responsible for phase 1 of action potentials in the heart?

G-protein activated potassium channel

What potassium current is muscarinic, slows conduction, and is the GIRK channel in SA & AV nodes?

SA node; AV node; Purkinje fibers

Pacemaker current is found in the _________________, ______________, & _________________.

HCN channels

Allows cations (Na+ & K+) to enter the cell while hyperpolarized

K+; Ca2+

In addition to the pacemaker current producing the depolarizing current after phase 3, ______ & ______ ions also help.

Calcium, HCN, potassium

What are the 3 main channels of the sinoatrial (SA) node?

SA node

What node is associated with maximum diastolic pressure?

Ca2+; HCN channels

During a maximum diastolic potential, what channels rapidly open after -55 mV? What channels are inactivated upon depolarization?

Ca2+, HCN, & K+ channels

The atrioventricular node depends on what ion channels?

1. Na+
2. Ca2+
3. K+

What three channels does atrial muscle depend on?

False

True/False: The AV node cannot sustain a reliably driven heart rate like the SA node can.

Bachman's bundle

What bundle is responsible for SA node to left atrium?

1. Na+
2. Ca2+
3. K+

What are the 3 main currents of ventricular muscle?

Na+ & Ca2+

The action potential from AV node opens what channels in ventricular muscle?

effective (absolute)

During a/an __________ refractory period, no action potential can be generated.

relative

During a/an _____________ refractory period, more signal is required to achieve an action potential.

tertiary

In Purkinje fibers, a ________ pacemaker has all of the different types of channels--K+, Ca2+, Na+ & HCN channels.

AV node

The His-Purkinje system begins at the ____________ and splits into right and left bundle.

unreliable

Purkinje fibers are (reliable/unreliable) pacemakers.

SA node; AV node; AV node; His/Purkinje

In ventricular muscle, the __________ depolarizes with signal sent to the atria & _______. Only normal electrical access is via the _______ and _____________.

septum

In ventricular muscle, the ________ depolarizes left to right (AKA myocardium --> epicardium).

apex to base

Depolarization travels (apex to base/base to apex).

e, b, c, a, d

List the following structures in order of how an action potential travels within the heart:
a. Apex
b. Atria & AV node
c. Septum
d. Base
e. SA node

SA node; AV node

The _________ sends an action potential through the heart via _________ & atrial/ventricular muscle gap junctions.

Chronotropic

Changes rate

Inotropic

Changes force

autonomic nerves

What nerves regulate heart rate?

Norepinephrine

During sympathetic regulation of the heart, what neurotransmitter is released?

increased; tachycardia

Sympathetic regulation causes a/an (decreased/increased) heart rate/force, also known as _________________.

Norepinephrine & epinephrine

What neurotransmitters does the adrenal medulla release?

β1; chronotropic; inotropic

Positive hormone regulation activates ____ receptors and causes either a positive ______________ or ____________ response.

Positive chronotropic response

Increase contraction rate from positive hormone regulation

Positive inotropic response

Increase contraction force from positive hormone regulation

Calcium, thyroid hormone, caffeine

What substances increase intracellular calcium and partake in positive hormonal regulation?

catecholamines (norepinephrine, epinephrine)

High thyroid hormone levels increase sensitivity to ______________________.

1. Increase HCN channels
2. Increase calcium channel activation
3. Affect muscles (atria/ventricles)

Catecholamines modulate contraction by doing what three things?

positive; chronotropic

The increase in calcium channel activation during catecholamine modulation of contraction is a (positive/negative) (inotropic/chronotropic) effect.

positive; inotropic

The effect on muscles during catecholamine modulation of contaction is a (positive/negative)(inotropic/chronotropic) effect.

increased; greater; store

The effect on muscles during catecholamine modulation of contraction is due to a/an (increased/decreased) concentration of Ca2+, which in turn causes (lower/greater) sensitivity. This means there is more calcium available to ________.

more; more

In the heart, if we have more HCN function, we have (less/more) heart contraction. If we have more Ca2+, we have (less/more) force of contraction.

vagus; acetylcholine

Parasympathetic regulation is due to __________ nerve innervation. What neurotransmitter is released during parasympathetic regulation?

Bradycardia

Decreases heart rate/force

decreases

Parasympathetic regulation (increases/decreases) heart rate/force.

1. Metoprolol
2. Propranolol
3. Atenolol

What are 3 examples of β blockers?

adrenergic

β blockers are ____________ receptor blockers.

1. Betaxolol
2. Atenolol
3. Metoprolol

What are cardioselective β blockers?

negative

β blockers are involved in (positive/negative) hormonal regulation.

negative

Calcium channel blockers are involved in (positive/negative) hormonal regulation.

1. Diltiazem
2. Amlodipide
3. Verapamil
4. Nifedipine

What are 4 examples of calcium channel blockers?

Negative chronotropic

Decrease heart rate

Negative inotropic

Decrease force of contraction

Acetycholine; negative chronotropic; negative inotropic

At the nodes, what neurotransmitter slows conduction velocity which decreases heart rate? What type of hormonal regulation is this? This NT also decreases force of contraction. What type of hormonal regulation is this?

negatiev; chronotropic

Parasympathetic regulation has a (negative/positive) (chronotropic/inotropic) effect.

peripheral

Without calcium entry, there is no/les contraction of heart & _______________ blood vessels.

heart rate

Autonomics regulate ________________.

β 1&2

Propranolol affects what β receptor(s)?

1. Sinus tachycardia
2. Atrial fibrillation
3. Sinus arrhythmias

What are 3 cardiac arrhythmias?

Sinus tachycardia

--Faster than normal heart rate
--Seen in acute hyperthyroidism

sinus tachycardia

What type of cardiac arrhythmia is seen in acute hyperthyroidism?

Atrial fibrillation

--Leads to risk of stroke (blood thinners)
--Irregular (ineffective) contractions of atria

Atrial fibrillation

What type of cardiac arrhythmia leads to increased risk of stroke (blood thinners)?

clots

When blood is left with no where to go, it forms ________.

1. Abnormal anatomy
2. Depolarization

What are 2 forms of conduction arrhythmia?

Abnormal anatomy

--Conduction arrhythmia involving ectopic locus (abnormal pacemaker location)
--Pathway that bypasses AV node

Depolarization (heart block)

--Conduction arrhythmia involving partial conduction block
--Slowed conduction
--Atria & ventricles depolarize independently

Arrhythmia

Abnormal heart rate

Amiodarone

What is an example of potassium channel blockers used in the treatment for arrhythmia?

1. Potassium channel blockers
2. Calcium channel blockers (L-type)
3. β-adrenergic blockers
4. Sodium channel blockers

What are the 4 main categories of drugs used for arrhythmia treatments?