Question

On contraction of alary muscles, the size of the pericardial sinus
A) Increase
B) Decrease
C) Remain same
D) There is no relation between two

Answer 1

Alary muscles are analogous to the SA node of the heart of mammals. As the frequency of activation of the SA node directly depends on the blood flowing into and out of the heart.

Complete answer:
Pericardial sinus is the covering of the heart. Alary muscles are described as parts of the cardiac system in different arthropods. Alary muscles are the muscles found in the heart or pericardial sinus of arthropods. There are twelve pairs of alary muscles found in cockroaches. Alary muscles are triangular/fan/delta shaped muscles related to the heart and circulation in arthropods. Alary muscles are also called muscles of the dorsal diaphragm because alary muscle is one of the components of the dorsal diaphragm of the heart. The dorsal diaphragm separates the pericardial sinus from the perivisceral sinus. Contraction of alary muscles causes blood to flow from the perivisceral sinus to the pericardial sinus and then into the heart. The alternate contraction and relaxation of alary muscles lead to the fall and rise of the dorsal diaphragm resulting in blood flow from the perivisceral sinus to pericardial sinus and finally in the heart as it beats. The contraction of alary muscles increases the pumping force of the heart of cockroaches. The contraction of alary muscles enlarges the pericardial space so that the blood from the perivisceral sinus flows into the pericardial space. When the alary muscles relax the blood is pushed out through Ostia into the heart.
In arthropods, the dorsal vessel in the abdomen is considered as the heart. It is divided into chambers that are separated by valves also called Ostia to ensure a one-way flow of haemolymph (blood). A pair of alary muscles are attached to the lateral walls of the chamber and circulate hemolymph.
Therefore, the contraction of alary muscles increases the size of the pericardial sinus.

Hence option ‘B’ is the correct answer.

Note: The clavicle fracture is a break in the bone connecting the breastbone and shoulder. It can result in swelling and increased pain when moving the shoulder.