Electrical activity of the Heart

Question 1

pericardium

Answer 1

Double-layered sac covering of the heart. Allows the heart to beat without friction, room to expand and resists excessive expansion

Question 2

Parietal pericardium

Answer 2

• Outer, tough, fibrous layer of CT
• Pericardial cavity:
  Filled with pericardial fluid
• Lubricating fluid in pericardial space (between layers) reduces friction

Question 3

Visceral pericardium:

Answer 3

• epicardium of heart wall
• Inner, thin, smooth, moist serous layer
• Covers heart surface

Question 4

what are the 3 layers of the heart wall?

Answer 4

1. epicardium
2. myocardium
3. endocardium

Question 5

Epicardium (visceral pericardium)

Answer 5

• Outside layer
• Connective tissue layer
• Serous membrane covers heart

Question 6

Myocardium

Answer 6

• Thick muscular layer
• Network of collagenous and elastic fibers
• Provides structural support and attachment for cardiac muscle
• Important in coordinating contractile activity

Question 7

Endocardium

Answer 7

Smooth inner lining of epithelial cells

Question 8

what separates heart muscle cells in the myocardium?

Answer 8

intercalated discs

Question 9

Interlaced discs made up of two specialized cellular connections

Answer 9

1. Desmosomes that provide anchorage
2. Gap junctions that permit rapid exchange of ions and other things

Question 10

Cardiac muscle

Answer 10

• Individual cells connected electrically via the intercalated discs
• Enables coordinated contraction

Question 11

The electrical conduction system of the heart

Answer 11

• Transmits signals generated by the sinoatrial node to cause contraction of the heart muscle

Question 12

4 specialized cardiac muscle fibers

Answer 12

1. Sinoatrial node (SA node)/ pacemaker
2. Atrioventricular node (AV node)
3. Bundle of His
4. Purkinje fiber

Question 13

what is the heart’s rhythm controlled by? And what is it made up of?

Answer 13

SA node, which is made up of specialized myocardial cells called nodal cells

Question 14

Sinoatrial (SA) node

Answer 14

• 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

Question 15

Electrical activity of the heart

Answer 15

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

Question 16

Automatic nature of the heartbeat is referred to as __________?

Answer 16

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

Question 17

what are 2 types of specialized autorhythmicity cardiac muscle cells?

Answer 17

1. Autorhythmic cells (1%)
2. Contractile cells (99%)

Question 18

Autorhythmic cells (1%)

Answer 18

• Membrane potential “never rests” pacemaker potential
• Do not contract
• Specialized for initiating and conducting action potentials responsible for contraction of working cells

Question 19

Contractile cells (99%)

Answer 19

• Do mechanical work of pumping
• Normally do not initiate own action potentials

Question 20

How does the electrical signal travel throughout the heart?

Answer 20

• 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

Question 21

Generation of action potential/pacemaker potential

Answer 21

• 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)

Question 22

Cardiac muscle action potential

Answer 22

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

Question 23

Concept of heartbeat

Answer 23

• 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

Question 24

Action potentials in autonomic neurons are needed to start heartbeat

True
False

Answer 24

false

Question 25

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

Answer 25

Bundle of His and its branches

Question 26

SA node is located on:

Right atria
Right ventricles
Left atrium
Left ventricle

Answer 26

right atria