Question

Heart-beat is initiated by-
a) Sinu-auricular node
b) Atria- ventricular node
c) Sodium ion
d) Purkinje’s fibers

Answer 1

Heart is a muscular and important organ or major organ of the body. It comes under the circulatory system as its function is to pump blood throughout the body. If a heart stops working the person could die. It is that essential organ. The heart is about the size of our fist located behind and slightly left of the breastbone. Functions of the heart includes pumping oxygenated blood to the other body parts. Hormones and other essential compounds also receive deoxygenated blood and metabolic products from the body in different parts of the body.

Complete answer:
Option a) Sino-auricular node- Sino-atrial node is a mass of nodal tissue which is found in the upper part of the right auricle. It generates the nerve impulses which is responsible for starting the contraction of the heart. It controls the rhythm of the heart contraction. It is therefore known as the natural heart pacemaker.
So, option a is correct.
Option b) Atria-ventricular node- the atria-ventricular node is the part of the electrical conduction system of the heart that coordinates the top of the heart. It leads from the atrium to the ventricles the normal electrical impulse.
Option b is incorrect.
Option c) sodium ion- sodium ion is nowhere related to the heart beat initiation as it controls the gradient pump which acts in the gated channels for the maintenance of ion channels as sodium is a major ion required in body for the influx and outflux of osmotic regulation in body.
So, option c is incorrect.
Option d) Purkinje’s fibers- Purkinje’s fibers are specialized conducting fibers composed of electrically fibers composed of electrically excited cells. They are myofibrils with mitochondria which conducts cardiac action potentials more quickly and efficiently than any other cells in the heart.
So, option d is incorrect.

Hence, Option a is the correct answer.

Note:
The walls of the heart are made up of three layers- epicardium, myocardium and endocardium. The human heart is situated in the middle mediastinum. The upper part of the heart is located as the attachment point of several large blood vessels- the vena cava aorta and pulmonary trunk. The lower tip of heart apex lies to the left of the sternum between the junction of fourth and fifth ribs near their articulation with the costal cartilages. The heart has four chambers as we know, two upper atria the receiving chambers and two lower ventricles the discharging chambers.