Cardiac Muscle Cheat Sheet C.Forsythe

Human Blood Circul­ation
Double pump action
Two circuits
Pulmonary arteries
Carry oxygen­-poor blood from hearts right half to capillary beds in lungs
Pulmonary veins
Return oxygenated blood to heart's left half
Systemic circuit
Oxygenated blood is pumped from the heart’s left half into body’s main arteries
Aorta
Blood flows to smaller arteries then capillary beds

Lies in thoracic cavity between sternum anteriorly and the vertebrae poster­iorly
Apex lies to the left of the sternum and base lies to the right
Atria
Receive blood returning to heart and transfer to lower chambers
Ventricles
Pump blood from the heart
Veins
Return blood from tissues to the atria
Arteries
Carry blood away from the ventricles to the tissues
Septum
Continuous muscular partition that prevents blood mixing from the two sides of the heart

Right Half
Right atrium
-Receives deoxyg­enated blood from head and arms and trunk and legs
Right ventricle
-Receives deoxyg­enated from right atrium from AV valve
-Pumps into pulmonary artery
-Carries to lungs
Left Half
Left atrium
-Receives blood from right and left pulmonary veins
-Well oxygenated
Left ventricle
-Receives oxygenated blood from atrium through left AV valve
-When contracted blood moves into aorta and is then pushed throughout major arteries of body
-Condu­ction of electrical signals
-Causes heart to contract
-Begins at SA node (sinoa­trial node)
-Found near Right atrium
Pacemaker
Spreads through both atria and causes it to contract
Spreads then to AV node
Relays impulse to bundle of HIS
Charge is distri­buted
Cardiac myocytes
Mechanical pumping
Autorh­ythmic cells
Initiate and conduct electrical impulses
Pacemaker activity
Fire action potential

Blood returning from systemic circul­ation enters right atrium via two large veins:
Venae cavae
-Returning blood from above and the other returning blood from below heart level
-Deoxy­genated blood flows from right atrium into right ventricle
-Pumps out through pulmonary artery
Pulmonary veins
-Blood returning to left atrium from both lungs

Atriov­ent­ricular Valves between the Atria and Ventricles
AV valves are positioned between atrium and ventricle on the right and left sides
Let blood flow from atria into the ventricles during ventri­cular filling
Prevent backflow of blood
Right AV valve
Tricuspid valve
3 cusps or leaflets
Left AV valve
Bicuspid valve
2 cusps

Semilunar Valves between the Ventricles and Major arteries
Aortic and pulmonary valve
-Forced open when left and right ventri­cular pressures exceed the pressure in the aorta and pulmonary artery during ventri­cular contra­ction and emptying

Heart walls
Endoth­elium
-Thin, inner layer
-Unique type of epithelial tissues that lines entire circul­atory system
Myocardium
-Middle layer
-Composed of cardiac muscle and consti­tutes bulk of heart wall
Epicardium
-Thin, external layer
-Covers the heart
Interc­alated discs
Desmosomes
-Adhering junction that mechan­ically holds cells together
Gap junctions
-Areas of low electrical resistance that allow action potentials to spread from one cardiac cell to adjacent cells
Perica­rdial sac
Membranous sac that encloses heart
Double­-walled
Two layers
Tough, fibrous covering
Attaches to the connective tissue partition that separates the lungs
Secretory lining
Thin perica­rdial fluid
-Provides lubric­ation to prevent friction between the layers as they glide with heart beats

Sinoatrial node (SA node)
Small, specia­lized region in the right atrial wall near the opening of the superior (upper) vena cava
Controls pacemaker potential
Atriov­ent­ricular node (AV node)
Small bundle of specia­lized cardiac muscle cells located at the base of the right atrium near the septum, just above the junction of the atria and ventricles
Bundle of His/At­rio­ven­tri­cular bundle
Tract of specia­lized cells that originates at the AV node and enters the septum between the ventricles
Divides to form the right and left bundle branches that travel down the septum, curve around the tip of the ventri­cular chambers, and travel back toward the atria along the outer walls
Purkinje fibers
Small terminal fibers that extend from the bundle of His and spread throughout the ventri­cular myocar­dium, much like small twigs of a tree branch

The spread of cardiac excitation is coordi­nated to ensure efficient pumping
Atrial excitation and contra­ction should be complete before the onset of ventri­cular contra­ction
Excitation of cardiac muscle fibers should be coordi­nated to ensure that each heart chamber contracts as a unit to pump effici­ently
Fibril­lation
Random, uncoor­dinated excitation and contra­ction of cardiac cells
The pair of atria and pair of ventricles should be functi­onally coordi­nated so that both members of the pair contract simult­ane­ously
Atrial Excitation
The intera­trial pathway extends from the SA node within the right atrium to the left atrium
The internodal pathway extends from the SA node to the AV node
Ventri­cular Excitation
Impulse travels rapidly down the septum via the right and left branches of the bundle of His and throughout the ventri­cular myocardium via the Purkinje fibers

The action potential of cardiac contra­ctile cells shows a charac­ter­istic plateau
A long refractory period prevents tetanus of cardiac muscle
Rapidly repetitive stimul­ation that does not let the muscle fiber relax between simula­tions results in a sustained, maximal contra­ction known as tetanus
In contrast, cardiac muscle has a long refractory period because of the prolonged plateau phase of the action potential
Cardiac muscle cannot be restim­ulated until contra­ction is almost over, precluding summation of contra­ctions and tetanus of cardiac muscle