The histology of the heart superficially shows the following structures, $EXCEPT$:

Define/Explain: $(1)$ Semi-lunar valve.

Explain in short: $Lub$ and $Dub$ sounds.

If the heart of a mammal is injected with a $2\%$ $CaCl_2$ solution,then:

What is the membrane surrounding the heart called?

$SA$ node (Sinoatrial node) ke baare mein sahi kathan chuniye:
$I$. Located at the right upper corner of the right atrium.
$II$. Heart of heart.
$III$. It initiates the rhythmic contractile activity of the heart.
$IV$. It is called the pace-keeper of the heart.
$V$. It is called the pacemaker of the heart.
Which of the following options contains the correct statements?