Cardiac Function

Question 1

what are intrinsic factors that affect cardiac activity

Answer 1

cardiac pacemaker activity

Question 2

what are extrinsic factors that affect cardiac activity

Answer 2

autonomic control

Question 3

what does sympathetic NS do to cardiac activity

Answer 3

increase HR
increase contractile force
increase regularity of contraction

Question 4

what does parasympathetic NS do to cardiac activity

Answer 4

decrease HR

decrease regularity of contraction

Question 5

Cardiac Electrophysiology

Answer 5

Cardiac muscle cells undergo rhythmic contractions that do not require input from the CNS or PNS

Myocardial cell contraction is dependent on action potentials similar to those in neural cells

The contraction of pacemaker cells sets the rhythm of overall heart contraction

Question 6

The Path of Electrical Conduction Through the Heart

Answer 6

1. SA node
2. Atrium
3. AV node
4. Bundle of His
5. Purkinje fibres

Question 7

what is the cardiac tissue composed of

Answer 7

Pacemaker (SA/AV)

+ Contractile Cells (Nonpacemaker Cells)

Question 8

Cardiac Ventricular Contractile Cell Potential

Answer 8

(non pacemaker)
0. fast depolarisation: FAST NA+ channels open

1. Partial repolarisation: Na+ channels close / FAST K+ channels open
2. Plateau: L-type (long refractory period) Ca2+ channels open; K+ channels partially close Ca2+ influx =K+ efflux
3. Resting potential: DELAYED RECTIFIER K+ channels open / L-type channels close

Question 9

Cardiac Nodal Cell Potential

Answer 9

(pacemaker cells)
1. Pacemaker potential: F-type (If) Na+ channels open, SLOW K+ channels close

2. T-type(transient) Ca2+ channels open, slow K+ channels continue to close
3. L-type Ca2+ channels open, slow K+ channels open

Question 10

what does ECG patterns do

Answer 10

provide a measure of cardiac conductance

Question 11

Abnormal ECG Causes

Answer 11

• Genetic Factors (Ion channel deficiencies)
• Disease/Injury
• Drugs

Question 12

Cardiac Arrhythmias 1

Answer 12

change in rate:
A. tachycardia - increased rate

B. bradycardia-decreased rate

Question 13

Cardiac Arrhythmias 2

Answer 13

source of arrhythmias:

A. supraventricular

B. ventricular

Question 14

Delayed After-Depolarization

Answer 14

• Calcium build-up in cardiac cells due to low-level stimulus from sympathetic NS
• Enough calcium accumulates until threshold reached and T-type channels open
• Causes premature contraction
• Can lead to tachycardia

Question 15

Ectopic Pacemakers

Answer 15

Non-pacemaker cells can take on spontaneous pacemaker activity as a result of:

1. Excessive sympathetic stimulation (treat with drugs that block cardiac adrenergic receptors or enhance parasympathetic activity)
2. Partial depolarization caused by ischemia (treat with drugs that increase flow of blood through coronary arteries)

Question 16

Heart Block

Answer 16

• A block in conducting pathways as a result of tissue damage
• In a complete heart block the atria and ventricles can beat independently of each other
• Treatment often involves implantation of artificial pacemaker

Question 17

Heart Problems

Answer 17

.Arrhythmias
.Ischemic Heart Disease “Angina” (blockage of coronary arteries)
.Myocardial Infarct (blood clot -arteries blocked)
.Congestive Heart Disease
Causes of these conditions include: atherosclerosis “coronary artery disease”, chronic hypertension, and congenital or infection-induced damage to heart valves or cardiac muscle tissue

Question 18

how can you recognize tachycardia on an ECG

Answer 18

increased stimulus rate = increased action potentials in time + plataue

Question 19

cardiac abnormalities that give rise to arrhythmias

Answer 19

1. delayed after depolarisation
2. re-entry (re-entrant circuit)
3. ectopic pacemaker activity
4. heart block

Question 20

re-entrant circuit

Answer 20

electrical conductivity of pathway altered = backward flow of electrical current - irregular contraction