Cardiac Muscle and Myogenic Heart Flashcards
What are the 3 types of muscular tissues?
Skeletal, Cardiac, Smooth
Describe characteristics of skeletal muscle?
voluntary, long and multinucleated
Describe the characteristics of cardiac muscle?
involuntary, short, branched, and contain intercalated discs
Describe the characteristics of smooth muscle?
involuntary, short, tapered ends
List the 7 characteristics of the cardiac muscle cell?
- cardiac myocytes
- intercalated discs
- gap junctions
- less sarcoplasmic reticulum
- larger T tubules
- longer plateau in action potential
- Na+ leak channel (causing depolarization automatically and rhythmically)
Describe cardiac myocytes?
short, thick, branched cell, and only one centrally placed nucleus
Contain especially large mitochondria that depend almost exclusively on aerobic respiration to make ATP
Describe function of intercalated discs found in cardiac muscle?
Myocytes are joined end to end by thick connections called intercalated discs
What are the 3 distinct features of intercalated discs?
Integrating folds (interlock) Mechanical junctions (desmosomes) Electrical junctions (gap junctions)
Describe gap junctions?
Electrical junctions for cell to cell communication = syncition (allows them to work as one, fire together)
Connects all the cardiac muscle cells together causing heart to work as one giant cell (coordinating)
If depolarize one cardiac cell, action potential spreads (moves) to all cardiac cell
Describe the difference in SR between cardiac and skeletal muscle?
Both skeletal and cardiac SR (sarcoplasmic reticulum) b=need Ca2+ for contraction.
However, SR of heart is less developed than in skeletal muscle
Describe the size of T tubules in cardiac muscle and their function?
The T tubules are much larger than in skeletal muscle
Larger T tubule allow extracellular Ca2+ to get in faster
*Extracellular Ca2+: in heart = 20% and in skeletal = 0%
Describe the reason for longer plateau in action potential regarding cardiac muscle cell?
Because the Ca2+ channels of the SR are slow to close or because the SR is slow to remove Ca2+ from the cytosol
Describe the Na+ leak channel in regard to the cardiac muscle cell?
Like a molecular pinhole, sodium leaks , resulting in the cell reaching threshold
Causing depolarization to occur automatically and rhythmically
What does the conduction system of the heart do?
It controls the rout and timing of electrical conduction to ensure that the four chambers of the heart are coordinated with each other
What is the pathway of the cardiac conduction system?
- SA node fires
- Excitation spreads through atrial myocardium
- AV node fires
- Excitation spreads down AV bundle
- Purkinje fibers distribute excitation through ventricular myocardium
Describe the SA node?
Located just under Epicardium near superior vena cava
Considered to be the pacemaker of the heart: initiates heartbeat, determines the heart rate
(*the cells that create the rhythmical impulses are called the pacemaker cells, and they directly control HR)
Excites myocytes and stimulates the 2 atria to contract simultaneously
Describe the AV node?
Located near the right AV valve at lower end of interatrial septum
Electrical gateway to ventricles, fibrous skeleton acts as an insulator
From SA node to AV node: 0.06 sce (thru AV node)
In Av node, signal delays for 0.1 sec (because of thinner myocytes and fewer gap junctions) which gives ventricles time to fill with blood before contracting.
Describe the path from the AV bundle to the bundle branches?
AV bundle is also called bundle of his.
Forks into left and right bundle branches
Enters the interventricular septum and descends toward the apex
Order of depolarization: interventricular septum - apex - base (0.06 sec)
Describe the purkinje fibers?
Nerve like processes that arise from the lower end of the bundle branches
Turn upward to spread throughout the ventricular myocardium
Distribute the electrical excitation to the myocytes of the ventricles
Form a more elaborate network in the left ventricle than right.
What is the time interval of conduction pathway?
SA Node to AV Node = 0.06 sec
Thru AV Node = 0.1 sec
AV Node to Ventricle = 0.06 sec
Total = 0.22 sec
