Cardiovascular and Nervous System

ECG stands for Electro Cardio Gram, which records the electrical activity of the heart over time. It's a diagnostic tool that helps detect heart rhythm problems and other cardiac conditions.

The normal resting heart rate for adults is 60-100 beats per minute, with 72 bpm being a commonly cited average. The range 71-80 bpm is within the normal healthy range and represents the most accurate choice among the options given.

The sixth week is correct. The human heart begins beating around day 22-23 of embryonic development (approximately 3 weeks), but it becomes detectable and more rhythmic by the sixth week. The heart is one of the first organs to function in the embryo. The first heartbeat occurs in the third week, but by the sixth week it's clearly established and can sometimes be detected via early ultrasound.

Tachycardia is the medical term for a heart rate that exceeds the normal resting rate (over 100 beats per minute). Bradycardia is the opposite - an unusually slow heart rate. A heart murmur is an abnormal sound, not a rate issue.

Pulse pressure is the difference between systolic and diastolic blood pressure. It reflects the force that the heart generates each time it contracts. Normal pulse pressure is around 30-50 mmHg.

Purkinje fibers are specialized cardiac muscle fibers located in the ventricles. They form the conduction pathway that rapidly transmits electrical impulses from the AV bundle to the ventricular myocardium, ensuring coordinated ventricular contraction. They are not in auricles or striated muscle generally.

Stroke volume is the correct term for the amount of blood ejected by the left ventricle during each heartbeat. In a healthy adult at rest, this is approximately 70-80 mL. Cardiac output is the total blood pumped per minute (stroke volume × heart rate). Ejection fraction is the percentage of blood pumped out relative to the total blood in the ventricle. 'Threshold output' is not a standard cardiac term.

The terminal sulcus is a groove in the right atrium of the heart. The terminal sulcus marks the separation of the right atrial pectinate muscle from the sinus venarum. The terminal sulcus extends from the front of the superior vena cava to the front of the inferior vena cava

The atrioventricular node, located in the wall between the right atrium and the right ventricle. Here, the impulses are delayed for about 0.1s before spreading to the walls of the ventricle.

Third heart sound is physiologic in children but pathological in adults. The four heart sound is a result of the atrial systole and vibration of the AV valves, due to blood rush during atrial systole. It is inaudible neither in adults nor in children.

The left ventricle is the pumping chamber for the systemic circulation. Because a greater blood pressure is required to pump blood through the much more extensive systemic circulation than through the pulmonary circulation, the left ventricle is larger and its walls are thicker than those of the right ventricle.

It is a V shaped groove diffentiating the anterior two thirds of the tongue from the posterior third and containing the circumvallate papillae.

The sinoatrial (SA) node is a section of nodal tissue that is located in the upper wall of the right atrium. The SA node is also referred to as the pacemaker of the heart.

Third heart sound is physiologic in children but pathological in adults. The four heart sound is a result of the atrial systole and vibration of the AV valves, due to blood rush during atrial systole. It is inaudible neither in adults nor in children.

Lithium iodide, or LiI, is a compound of lithium and iodine. When exposed to air, it becomes yellow in colour, due to the oxidation of iodide to iodine. It is used as an electrolyte for high temperature batteries. It is also used for long life batteries as required, for example, by artificial pacemakers. The solid is used as a phosphor for neutron detection.