The Heart Pt. 2

Question 1

Describe cardiac muscle fibers. Length? Diameter? Transverse section? Branching?

Answer 1

Shorter in length, larger in diameter, square in transverse section. Exhibit branching

Question 2

Compare cardiac muscle fibers and skeletal muscles

Answer 2

Cardiac muscle fibers have the same arrangement of action and myosin, and same bands, zones and 2 discs as skeletal muscles

Question 3

Contrast cardiac muscle fibers and skeletal msucles

Answer 3

Cardiac muscle has less sarcoplasmic reticulum than skeletal muscles and require Ca2+ from extracellular fluid for contraction

Question 3

Cardiac muscle tissue forms how many functional networks in the heart

Answer 3

2

Question 4

What are the 2 functional networks in the heart that are formed from cardiac muscle fibers

Answer 4

atrial network and ventricular network

Question 5

Why are some cardiac muscle cells considered autorhythmic cells

Answer 5

They are self-excitable. They repeatedly generate spontaneous action potentials that then trigger heart contractions

Question 6

What are the components of the conduction system of the heart?

Answer 6

> sinoatrial (SA) node
atrioventricular (AV) node
atrioventricular bundle (bundle of His)
Right & Left bundle branches
Purkinje fibers (conduction myofibers)

Question 7

What is considered our body’s natural pacemaker?

Answer 7

The sinoatrial (SA) node

Question 8

Steps of an impulse in a ventricular contractile fiber

Answer 8

1) rapid depolarization
2) plateau
3) repolarization

Question 9

Describe the refractory period of a cardiac muscle fiber to the contraction itself

Answer 9

The refractory period is longer than the contraction itself

Question 10

What does cardiac muscle rely on for ATP production

Answer 10

aerobic cellular respiration

Question 11

What is another way cardiac muscle produces ATP

Answer 11

via creatine phosphate

Question 12

What does the presence of creatinine kinase indicate in the heart

Answer 12

Indicates a cardiac muscle injury caused by an MI

Question 13

What is an ECG?

Answer 13

electrocardiogram; a recording of the electrical changes that accompany each cardiac cycle (heartbeat)

Question 14

What is the purpose of an ECG/EKG?

Answer 14

> helps to determine if conduction pathway is abnormal
if heart is enlarged
if certain regions are damaged

Question 15

What does a normal ECG contain?

Answer 15

> P wave
QRS complex
T wave

Question 16

What does the P wave of an ECG mean?

Answer 16

atrial depolarization - spread of impulse from SA node over atria

Question 17

What does the QRS complex of an ECG mean?

Answer 17

ventricular depolarization - spread of impulse through ventricles

Question 18

What does the T wave of an ECG mean?

Answer 18

ventricular repolarization

Question 19

What does the P-Q (PR) interval represent?

Answer 19

the conduction time from the beginning of atrial excitation to the beginning of ventricular excitation

Question 20

What does the S-T segment represent?

Answer 20

the time when ventricular contractile fibers are fully depolarized, during the plateau phase of the impulse

Question 21

Describe the action potential propagation through the heart

Answer 21

1) Depolarization of atrial contractile fibers produces P wave
2) Atrial systole (contraction)
3) Depolarization of ventricular contractile fibers produces QRS complex
4) Ventricular systole (contraction)
5) Repolarization of ventricular contractile fibers produces T wave
6) Ventricular diastole (relaxation)