A&P II Lecture (BIOL 2302) Exam 2 Review (CH. 17, 18, &
19) Questions | 2026/2027 | Answers Correct | With
Complete Solutions
Three Parts of a Cardiac Action Potential
1. Pacemaker Potential: K+ channels are closed, but slow Na+
channels are open, causing interior to become more positive
2. Depolarization: Ca2+ channels open (around −40 mV),
allowing huge influx of Ca2+, leading to rising phase of action
potential
3. Repolarization: K+ channels open, allowing efflux of K+, and
cell becomes more negative
Sinoatrial (SA) Node
-Pacemaker of heart in right atrial wall
-Generates impulses about 75×/minute
-Impulse spreads across atria, and to AV node
Atrioventricular (AV) Node
-In inferior interatrial septum
-Delays impulses approximately 0.1 second
AV Bundle (Bundle of HIS)
-In superior interventricular septum
-Only electrical connection between atria and ventricles
AV Bundle Branches
-Two pathways in interventricular septum
-Carry impulses toward apex of heart
,Purkinje Fibers
-Complete pathway through interventricular septum into apex
and ventricular walls
-More elaborate on left side of heart
Arrhythmias
-irregular heart rhythms
-Uncoordinated atrial and ventricular contractions
Fibrillation
-rapid, irregular contractions
-Heart becomes useless for pumping blood, causing circulation
to cease; may result in brain death
-Treatment: defibrillation interrupts chaotic twitching, giving
heart "clean slate" to start regular, normal depolarizations
Ectopic Focus
an abnormal pacemaker that takes over pacing
Junctional Rhythm
-occurs if the AV node takes over
-40-60 beats/minute
Extrasystole
-ectopic focus of small region of heart that triggers impulse
before SA node can, causing delay in next impulse
-Heart has longer time to fill, so next contraction is felt as thud
as larger volume of blood is being pushed out
-Can be from excessive caffeine or nicotine
,Cardioacceleratory System
-sends signals through sympathetic trunk to increase both rate
and force
-Stimulates SA and AV nodes, heart muscle, and coronary
arteries
Cardioinhibitory Center
-parasympathetic signals via vagus nerve to decrease rate
-Inhibits SA and AV nodes via vagus nerve
Differences between contractile muscle fibers and skeletal
muscle fibers
-AP in skeletal muscle lasts 1-2 ms; in cardiac muscle it lasts
200 ms
-Contraction in skeletal muscle lasts 15-100 ms; in cardiac
contraction lasts over 200 ms
Electrocardiograph
can detect electrical currents generated by heart
Electrocardiogram (ECG/EKG)
-a graphic recording of electrical activity
-Composite of all action potentials at given time; not a tracing of
a single AP
-Electrodes are placed at various points on body to measure
voltage differences
P Wave of an EKG
depolarization of SA node and atria
, QRS Complex of an EKG
ventricular depolarization and atrial repolarization
T Wave of an EKG
ventricular repolarization
P-R Interval of an EKG
beginning of atrial excitation to beginning of ventricular
excitation
S-T Segment of an EKG
entire ventricular myocardium depolarized
Q-T Interval of an EKG
beginning of ventricular depolarization through ventricular
repolarization
What problems can be detected with an EKG?
-Enlarged R waves may indicate enlarged ventricles
-Elevated or depressed S-T segment indicates cardiac ischemia
-Prolonged Q-T interval reveals a repolarization abnormality
that increases risk of ventricular arrhythmias
-Junctional blocks, blocks, flutters, and fibrillations can also be
detected
Systole
period of heart contraction
Diastole
period of heart relaxation
19) Questions | 2026/2027 | Answers Correct | With
Complete Solutions
Three Parts of a Cardiac Action Potential
1. Pacemaker Potential: K+ channels are closed, but slow Na+
channels are open, causing interior to become more positive
2. Depolarization: Ca2+ channels open (around −40 mV),
allowing huge influx of Ca2+, leading to rising phase of action
potential
3. Repolarization: K+ channels open, allowing efflux of K+, and
cell becomes more negative
Sinoatrial (SA) Node
-Pacemaker of heart in right atrial wall
-Generates impulses about 75×/minute
-Impulse spreads across atria, and to AV node
Atrioventricular (AV) Node
-In inferior interatrial septum
-Delays impulses approximately 0.1 second
AV Bundle (Bundle of HIS)
-In superior interventricular septum
-Only electrical connection between atria and ventricles
AV Bundle Branches
-Two pathways in interventricular septum
-Carry impulses toward apex of heart
,Purkinje Fibers
-Complete pathway through interventricular septum into apex
and ventricular walls
-More elaborate on left side of heart
Arrhythmias
-irregular heart rhythms
-Uncoordinated atrial and ventricular contractions
Fibrillation
-rapid, irregular contractions
-Heart becomes useless for pumping blood, causing circulation
to cease; may result in brain death
-Treatment: defibrillation interrupts chaotic twitching, giving
heart "clean slate" to start regular, normal depolarizations
Ectopic Focus
an abnormal pacemaker that takes over pacing
Junctional Rhythm
-occurs if the AV node takes over
-40-60 beats/minute
Extrasystole
-ectopic focus of small region of heart that triggers impulse
before SA node can, causing delay in next impulse
-Heart has longer time to fill, so next contraction is felt as thud
as larger volume of blood is being pushed out
-Can be from excessive caffeine or nicotine
,Cardioacceleratory System
-sends signals through sympathetic trunk to increase both rate
and force
-Stimulates SA and AV nodes, heart muscle, and coronary
arteries
Cardioinhibitory Center
-parasympathetic signals via vagus nerve to decrease rate
-Inhibits SA and AV nodes via vagus nerve
Differences between contractile muscle fibers and skeletal
muscle fibers
-AP in skeletal muscle lasts 1-2 ms; in cardiac muscle it lasts
200 ms
-Contraction in skeletal muscle lasts 15-100 ms; in cardiac
contraction lasts over 200 ms
Electrocardiograph
can detect electrical currents generated by heart
Electrocardiogram (ECG/EKG)
-a graphic recording of electrical activity
-Composite of all action potentials at given time; not a tracing of
a single AP
-Electrodes are placed at various points on body to measure
voltage differences
P Wave of an EKG
depolarization of SA node and atria
, QRS Complex of an EKG
ventricular depolarization and atrial repolarization
T Wave of an EKG
ventricular repolarization
P-R Interval of an EKG
beginning of atrial excitation to beginning of ventricular
excitation
S-T Segment of an EKG
entire ventricular myocardium depolarized
Q-T Interval of an EKG
beginning of ventricular depolarization through ventricular
repolarization
What problems can be detected with an EKG?
-Enlarged R waves may indicate enlarged ventricles
-Elevated or depressed S-T segment indicates cardiac ischemia
-Prolonged Q-T interval reveals a repolarization abnormality
that increases risk of ventricular arrhythmias
-Junctional blocks, blocks, flutters, and fibrillations can also be
detected
Systole
period of heart contraction
Diastole
period of heart relaxation
