Heart Anatomy & Blood Flow
What valve separates the left atrium from the left ventricle?
Mitral/bicuspid valve
What are intercalated disks made of? What do these do?
1. Desmosomes: are strong cell-adhesion protein structures that hold adjacent cells together
2. Gap junctions: allow direct and rapid spread of ions between cells
Which node acts as a backup pacemaker if the SA node fails?
The atrioventricular (AV) node
Which node in the heart normally serves as the primary pacemaker that starts the heartbeat?
SA node (sinoatrial node)
What is it called when the heart is beating too slowly?
Bradycardia
Which side of the heart is responsible for pulmonary circulation?
Right side.
What ion influx is responsible for triggering contraction in cardiac muscle after an action potential?
Calcium (Ca2+)
What ion’s voltage-gated channels cause repolarization in pacemaker cells, and how is this similar to neurons?
Voltage-gated K⁺ channels; they repolarize the membrane just like in neurons.
What type of cell–cell connection allows the spread of positive ions from the SA node into neighboring cells to propagate the action potential?
Gap junctions in intercalated discs
What do the P wave, QRS complex, and T wave represent?
P wave: atria depolarize
QRS complex: ventricles depolarize
T wave: ventricles repolarize
Select all situations in which a heart valve would close:
A)Patrium>Pventricle
B)Pventricle>Patrium
C)Partery>Pventricle
D)Pventricle>Partery
B)Pventricle>Patrium
C)Partery>Pventricle
Describe how the crossbridge cycle allows cardiomyocytes to contract. (Hint: Skeletal muscles)
1. Current spreads to cardiomyocytes via gap junctions
2. AP travels along the plasma membrane & T tubules
Ca + channels open in plasma membrane & sarcoplasmic reticulum
Ca2+ induces Ca2+ release from sarcoplasmic reticulum
Ca2+ released from SR binds to troponin >> exposes myosin binding sites
Crossbridge cycle begins as actin binds to myosin
Power stroke
ATP unbinds actin and myosin >> crossbridge cycle over
Ca2+ actively transported back to SR and extracellular fluid
Where in the heart are pacemaker cells concentrated?
SA node in the right atrium and AV node between the atria and ventricles
Where does depolarization spread to, after the conducting fibers in the ventricles (Purkinje fibers)?
The contractile cells of the ventricles (cardiomyocytes)
True or False: Is an ECG/EKG a representation of an intracellular action potential?
BONUS: Why/why not?
False.
An intracellular action potential measures the voltage changes across the membrane of a single heart muscle cell, while an ECG is an extracellular recording that measures the collective electrical activity of the entire heart from the surface of the skin.
List the correct pathway of blood in the heart given the following:
lungs, aorta, right atrium, right ventricle, left atrium, left ventricle, vena cavae, pulmonary veins
Vena cavae → right atrium →right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta
Which ion (Na+, K+, Cl-, Ca2+) is responsible for the prolonged depolarization of the cardiomyocyte after VGNaCh inactivation?
BONUS: explain the direction the ion will travel and what process is occurring intracellularly during prolonged depolarization.
Ca2+ is responsible for the prolonged depolarization of the cell
BONUS: Ca2+ will travel into the cell from VGCaCh channels and T tubules >> Ca2+ binds to troponin so that myosin binding sites will be exposed and actin and myosin can begin the crossbridge cycle.
Why do pacemaker cells generate their own action potentials?
They do not have a steady resting membrane potential because after an AP they depolarize again
Funny channels (IF) → cational channels open at hyperpolarized potentials and Na+ ions enter the cell through the funny channels to cause a depolarization. This causes the cell to reach the AP threshold due to the opening of vgCach
What prevents the heart muscle from contracting in an uncoordinated fashion?
The orderly spread of electrical signals via gap junctions and conduction pathways ensures synchronization
A patient arrives at the emergency room suffering from a heart attack and ventricular fibrillation. The medical team immediately begins defibrillation in an effort to restore normal heart function. How does defibrillation help bring the heart back to its normal rhythm?
Defibrillation works by delivering a controlled electric shock to the heart, which temporarily stops all electrical activity. This allows the heart's natural pacemaker to reset and reestablish a normal, coordinated rhythm.
A blood clot blocks the pulmonary artery, how would this affect the blood flow through the heart?
Blood cannot travel from the right ventricle to the lungs, leading to reduced or blocked pulmonary circulation and back-up of blood in the right side of the heart.
If calcium (Ca²⁺) could not enter a cardiac muscle cell from outside the cell, what would most likely happen?
A. The heart would stop sending electrical signals.
B. The heart would keep beating, but contractions would be weaker.
C. The heart cells would not stick together anymore.
D. The heart would make stronger contractions.
B. The heart would keep beating, but contractions would be weaker. Autorhythmic cells can still create a heartbeat without Ca2+/make their own AP.
Explain why Funny Channels (If) are unique in comparison to other voltage gated channels
They open when the cell is hyperpolarized, unlike most channels that open upon depolarization
Explain how the SA node initiates the trigger of a heart contraction
The SA node depolarizes, and positive ions spread into adjacent cells through gap junctions. The depolarization from the SA node brings the nearby contractile cells to threshold to fire the action potential. This electrical signal from the AP would spread through the contractile cells in the atria, then to the AV node, through the conducting fibers in the ventricles, and then to the contractile cells in the ventricles.
In the ECG/EKG of Mobitz Type I Heartblock shown below, where is there an interruption in the heart’s electrical conduction system?
DOUBLE: explain why
AV Node.
You can see that the SA node is healthy because the P waves are firing at regular intervals. The lengthening intervals between the P wave and QRS complex (aka the PR interval) point to an electrical blockage in the AV node (because it is not depolarizing at regular intervals)