Lecture 5 (Mechanisms Underlying Normal Heart Rate Changes)

Question 1

Sinus means

Answer 1

All wave forms are present in right sequence (P-QRS-T)

Question 2

R-R interval is typically used to measure

Answer 2

Heart rate

Question 3

A sinus rhythm is defined as being present if the following conditions are met

Answer 3

Every P wave is followed by a QRS wave
Every QRS is preceded by a P wave
The P wave is upright in leads I, II, and III

Question 4

Pacemaker currents

Answer 4

Funny current - Na and K
Slow calcium current
Fast calcium current
Potassium current
 - delayed rectifier
Background inward current
 - Na

Question 5

3 factors determining SA node rate of depolarization

Answer 5

Maximum negative potential reached (diastolic potential)
- longer time to get back to threshold
Rate of phase 4 spontaneous depolarization
- probability that a certain number of Na+ channels open at a given level of depolarization
Threshold potential for Ca++ influx
- less negative, increases time of threshold slows rate

Question 6

Muscarinic receptor binding decreases

Answer 6

Probability of Na+ and Ca++ channels to open

Question 7

Muscarinic receptors increase

Answer 7

K+ channel open probability

Question 8

Normal sinus arrhythmias

Answer 8

Fluctuations in heart rate due to changes in pulmonary afferent input to the medulla
Activated by inspiration, increased afferent inputs inhibits vagal outflow