Question

1)AV block refers to a condition where there is a longer-than normal conduction delay at the AV node. There are different degrees of AV block. Sometimes conduction is only slightly delayed, and sometimes conduction is blocked entirely. Which of the following will not be observed in someone with AV block (of any severity).

incorrect answer i selected)Atrial and ventricular systole occur at the same time.

correct answer )Atrial contraction rate is slower than ventricular contraction rate.

2)Which of the following statements about the Neuromuscular Junction (NMJ) is CORRECT:

incorrect answer i selected)Blocking the actions of acetylcholine esterase (AChE) will prevent the opening of ACh receptor channels and reduce intracellular [Na+] in muscle cells.

correct answer ) In healthy muscle, an action potential in a motor neuron will always be followed by action potentials in the muscle fibers that are innervated by that motor neuron.

Can you please explain to me why the answer i selected is incorrect and why the correct answer is right for the both questions. Please explain.

Answer 1

1.AV nodal block
AV nodal blockage may occur as an incomplete heart block (which includes first degree and second degree heart blocks) or complete heart block (third degree heart block).
First degree AV nodal block. First degree AV nodal (or
heart) block is characterized by the slowing of conduction
at the level of AV node. Though all the atrial impulses reach the ventricles but the PR interval is abnormally long, i.e. more than 0.21 s .

Second degree AV nodal block. In second degree AV
nodal block not all atrial impulses are conducted to ventricles. It is usually associated with organic
heart diseases.

2. Action acetylcholinesterase is to break down the acetyl choline and that means it hydrolyses the acetyl choline . It helps opening receptors and there is influx of Na ions . But this doesnt happen at NMJ . The purpose of Acetylcholine  is to open ach receptors and cause the sodium ions from ECF enter the neuromuscular junction through these channels. And there, sodium ions alter the resting membrane potential and develops the electrical potential called the endplate potential.