Question

part A. The steep repolarization phase of the action potentials of myocardial contractile cells is due to which ion(s)?

Ca²⁺

K⁺

Na⁺

Ca²⁺ and K⁺

Ca²⁺ and Na⁺

^{Part B:}

The common pathway of coagulation begins with?

a.the sticking of platelets to damaged tissue.

b.the activation of a proenzyme exposed to collagen.

c.the release of tissue factor by damaged endothelium.

d.the activating of a clotting factor that converts prothrombin to thrombin.

part c

The term myogenic refers to the fact that the signal that initiates contraction of cardiac muscle cells comes from?

a.the heart muscle itself.

b.the efferent nerves of the heart.

c the brain region controlling the heart rate.

d.the endocrine system component controlling the heart rate.

e. the brain and endocrine system components controlling the heart rate.

Answer 1

1. Answer: Option B is correct
Explanation:
The repolarization step is the phase-3 of the action potential.
It occurs due to an increase in potassium ion (K+) permeability.
The K+ permeability can be further increased at the SA node by vagal stimulation.

2. Answer: Option D is correct
Explanation:
The common pathway of coagulation begins with the production of Factor Xa from factor X.
The factor Xa converts prothrombin to thrombin.

3. Answer: Option A is correct
Explanation:
Myogenic = The signal for the contraction heart arises within the heart muscles (Cardiomyocytes).

Neurogenic = The signal is initiated by the nerves derived from the brain