week 3 cardiovascular system 2

Question 1

Cardioacceleratory center

Answer 1

sends signals through the sympathetic trunk to increase both the rate and force
* Stimulates SA and AV nodes, heart muscle, and coronary arteries

Question 2

Cardioinhibitory center

Answer 2

parasympathetic signals via vagus nerve to decrease rate
* Inhibits SA and AV nodes via vagus nerves

Question 3

Sequence of excitation

Answer 3

Cardiac pacemaker cells pass impulses, in following order, across heart in ∼0.22 seconds
1. Sinoatrial node →
2. Atrioventricular node →
3. Atrioventricular bundle →
4. Right and left bundle branches →
5. Subendocardial conducting network (Purkinje fibers)

Question 4

medulla

Answer 4

is a muscle that connects the spinal cord and the brain

Question 5

Action Potentials of Contractile Cardiac Muscle Cells

Answer 5

Depolarization opens fast voltage-gated
Na+ channels; Na+ enters cell
* Positive feedback influx of Na+ causes rising phase ofAP (from −90 mV to +30 mV)

Depolarization by Na+ also opens slow Ca2+ channels
* At +30 mV, Na+ channels close, but slow Ca2+ channels remain

open, prolonging depolarization – Seen as a plateau
After about 200 ms, slow Ca2+ channels are closed, and voltage- gated K+ channels are open

• Rapid efflux of K+ repolarizes cell to RMP
• Ca2+ is pumped both back into SR and out of cell into extracellular space