Electrical activity of the Heart Flashcards
pericardium
Double-layered sac covering of the heart. Allows the heart to beat without friction, room to expand and resists excessive expansion
Parietal pericardium
- Outer, tough, fibrous layer of CT
- Pericardial cavity:
Filled with pericardial fluid - Lubricating fluid in pericardial space (between layers) reduces friction
Visceral pericardium:
- epicardium of heart wall
- Inner, thin, smooth, moist serous layer
- Covers heart surface
what are the 3 layers of the heart wall?
- epicardium
- myocardium
- endocardium
Epicardium (visceral pericardium)
- Outside layer
- Connective tissue layer
- Serous membrane covers heart
Myocardium
- Thick muscular layer
- Network of collagenous and elastic fibers
- Provides structural support and attachment for cardiac muscle
- Important in coordinating contractile activity
Endocardium
Smooth inner lining of epithelial cells
what separates heart muscle cells in the myocardium?
intercalated discs
Interlaced discs made up of two specialized cellular connections
- Desmosomes that provide anchorage
- Gap junctions that permit rapid exchange of ions and other things
Cardiac muscle
- Individual cells connected electrically via the intercalated discs
- Enables coordinated contraction
The electrical conduction system of the heart
- Transmits signals generated by the sinoatrial node to cause contraction of the heart muscle
4 specialized cardiac muscle fibers
- Sinoatrial node (SA node)/ pacemaker
- Atrioventricular node (AV node)
- Bundle of His
- Purkinje fiber
what is the heart’s rhythm controlled by? And what is it made up of?
SA node, which is made up of specialized myocardial cells called nodal cells
Sinoatrial (SA) node
- Generates the action potential that initiates contraction
- Excites the right atrium, travels through Bachmann’s bundle to excite left atrium
- Impulse travels through internodal pathways in RA to the atrioventricular (AV) node
-From the AV node, the impulse travels through the bundle His and down the bundle branches, fibers specialized for rapid transmission of electrical impulses
- Right bundle branch (RBB): depolarizes the right
ventricle
- Left bundle branch (LBB): depolarizes the left
ventricle and interventricular septum
- Both bundle branches terminate in Purkinje
fibers
Electrical activity of the heart
The heart will beat without input from the nervous system and will continue to beat, even outside the body, as long as the cells are alive
Automatic nature of the heartbeat is referred to as __________?
automaticity: spontaneous electrical activity of the SA node
- Electrical impulses generated from the SA node spread through heart via a nodal tissue pathway that coordinates the vents of the cardiac cycle
what are 2 types of specialized autorhythmicity cardiac muscle cells?
- Autorhythmic cells (1%)
- Contractile cells (99%)
Autorhythmic cells (1%)
- Membrane potential “never rests” pacemaker potential
- Do not contract
- Specialized for initiating and conducting action potentials responsible for contraction of working cells
Contractile cells (99%)
- Do mechanical work of pumping
- Normally do not initiate own action potentials
How does the electrical signal travel throughout the heart?
- The electrical signal from the pacemaker cells spread to nearby cells via gap junctions
- Gap junctions are channels that are shared by two adjacent cell membranes
- When one heart cell fires and electrical signal, the signal quickly spreads to neighboring cells
Generation of action potential/pacemaker potential
- SA nodal cells produce spontaneous pacemaker potentials
- Unique ion channels found in these cells
- Once threshold is reached, action potential begins
- Overall duration is shorter than a ventricular AP (but much faster than skeletal muscle)
Cardiac muscle action potential
phase 4 (resting phase)
- Na+ and Ca+ channels are closed at resting TMP
phase 0 (depolarization)
- Threshold is reached = Na+ channels open, and rapid depolarization occurs
phase 1 ( early repolarization)
- Na+ channels close and the membrane begins to repolarize. K+ channels open
phase 2 (plateau phase)
- Closure of K+ channels = permeability decline; Ca++ channels open. Both slow or stop repolarization
phase 3 (repolarization)
- K+ channels open and Ca++ begin to close
- Ca++ entering the cell from intracellular fluid stimulates the release of Ca++ from the sarcoplasmic reticulum
Concept of heartbeat
- Chamber of the heart alternatively contract and relax in a rhythmic cycle
- During the period of contraction (systole), the heart pumps blood out through the arteries; during the period of relaxation (diastole), the heart fills with blood
- One complete sequence of filling and pumping out of blood is called a cardiac cycle, or heartbeat
Action potentials in autonomic neurons are needed to start heartbeat
True
False
false
The portion of the intrinsic conduction system located in the interventricular septum is the:
SA node
Purkinje fibers
Bundle of His and its branches
AV node
Interatrial pathway
Bundle of His and its branches
SA node is located on:
Right atria
Right ventricles
Left atrium
Left ventricle
right atria
