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Cardiac Muscle - NPB 101 Cheat Sheet (DRAFT) by

Key things to know about cardiac muscle!

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Key Anatomy of the Heart

4 Chambers:
Right Atria & Right Ventricle (Respo­nsible for pumping oxygen­-poor blood to the lungs.)
Left Atria & Left Ventricle (Respo­nsible for pumping oxygen­-rich blood to the body tissues.

Types of Valves

The Flow of Blood

Deoxyg­enated blood flows into right atrium from the body.
Then from the right atrium, deoxyg­enated blood flows into the right ventricle via the atriov­ent­ricular valve (AV valve)
From right ventricle the blood flows to the lungs to become oxygenated via the pulmonary valve
Oxygenated blood is then pumped into the left atrium where it can then flow into the left ventricle via another AV valve
From left ventricle the oxygenated blood is then pumped through the aortic valve into rest of body

Diagram of Ventricles

(Blue = oxygen­-poor blood, Red = oxygen­-rich blood)

Diagram of Blood Flow Through the Heart

  

Structure of Heart Walls

Endoca­rdium - thin layer of endoth­elial tissue that lines the inside of each chamber
Myocardium - middle layer of heart wall consisting of desmosomes and gap-ju­nctions
Desmosomes help hold things together so the heart doesn't rip apart, Gap-Ju­nctions allow the cardiac muscle to form a functional syncytium
Epicardium - thin external membrane that covers the heart and filled with perica­rdial fluid to prevent friction.
Fun Fact!
99% of cardiac cells are contra­ctile and require an outside source to activate an action potential. While 1% of the remaining cardiac cells are auto-r­hythmic and initiate their own action potent­ials!

Comparison of 2 Types of Cardiac Action Potentials

Action Potentials in Pacemaker Cells

3 Channel Types
If = Funny Channels
T = Transi­ent­-type (short time) Ca2+ channels
L = Long-l­asting Ca2+ channels
Pacemaker Activity
Resting Potential = -60mV
K+ Channels are closed and If channels allow for concen­tration of Na+ to increase in the cell. (Na+ in)
T channels open and Ca2+ is let into the cell, allowing the potential to reach threshold. (Ca2+ in)
Once threshold is reached, L channels open to create the action potential. (More Ca2+ in)
At the peak of the action potential, K+ channels open, and L channels close, creating the falling phase. (K+ out)
Cycle repeats
 

Pacemaker Cells

Electrical Activity within the Heart

Nodes - groups of specia­lized cardiac cells capable of pacemaker activity
Different Types of Nodes
Sinoatrial (SA) Node
Located in wall of right atrium, exhibits an autorh­yth­micity of 70 AP/minute. This is the fastest node and it leads the activity of other pacemaker struct­ures.
Atriov­ent­ricular (AV) Node
Located at base of the right atrium, exhibits autorh­yth­micity of 50 AP/minute.
Bundle of His
Tract of specia­lized, cardiac pacemaker cells. Starts at AV Node and divides into the left and right ventri­cles.
Purkinje Fibers
Terminal fibers that extend from bundle of His and spreads throughout the ventri­cular myocar­dium.

Sequence of Current Flow Through the Heart Wall

SA Node -> AV Node -> Bundle of His -> Right & Left Bundle of His Branches -> Purkinje Fibers

Action Potentials in Cardiac Cells

Threshold = -70mV
Resting Potential = -90mV
Fast Na+ channels open, creating a fast rising phase. (Na+ in fast)
Na+ channels inactivate and transient K+ channels open. L-type Ca2+ channels open and K+ channels (transient & leaky) slowly close. (K+ out fast, Ca2+ in slow)
Voltag­e-Gated K+ channels open and L-type Ca2+ channels close resulting in a rapid falling phase. (K+ out fast)
Resting potential maintained by closing of VG K+ channels and opening of leaky K+ channels