Cardiovascular and Nervous System

Acetylcholine is the main vagal neurotransmitter. The vagus nerve controls the heart rate by electrical impulses to the SA node of the heart in which acetylcholine release slows down the pulse rate and decreases the blood pressure. Thus the correct answer is option A.

The central nervous system includes brain and spinal cord. It integrates and stores the sensory information from external and internal sense organs and commands different organs to respond accordingly.

The autonomous nervous system controls the heart beat rate via cardioregulatory centre in the medulla oblongata. The emergency conditions activate the sympathetic motor nerve and make the adrenal medulla release epinephrine and norepinephrine which in turn increase the heart beat rate. Hence, the nerve which increases heart beat is part of autonomic and sympathetic nervous system. The central nervous system includes brain and spinal cord only. The peripheral nervous system includes all cranial and spinal nerves; the 12 pairs of cranial nerves, except Vagus nerve, are part of the peripheral nervous system and are mostly concentrated in head, neck and facial region of the body. Vagus nerve conducts the parasympathetic motor impulses which in turn slow down the heart beat rate by the effect of acetylcholine; a neurotransmitter released by the parasympathetic nervous system. 

The human heart allows the complete separation of the deoxygenated and oxygenated blood. It has four chambers, the upper two atria and the lower two ventricles. The right side chambers (right atrium and right ventricle) are concerned with the deoxygenated blood. The right atrium receives the deoxygenated blood from the body and the right ventricle pumps it to the lungs. This is the pulmonary circulation. It completes when the left side chamber of the left atrium receives it. So, the left side chambers are concerned with oxygenated blood. The left ventricle then transports it to the rest of the body in the systemic circulation. So, the pulmonary and the systemic circulation maintained by the human heart constitute the double circulation of the blood.

Vaso means vessels and constriction means narrowing, therefore, narrowing of blood vessels results in vasoconstriction. Normally, it is done due to the shrinking of smooth muscles of vessels to react according to the environment by raising blood pressure for stabilization, prevent loss of heat, control blood flow in body, transfer nutrients and prevent from blood and fluid loss but in some cases it can also be a severe health problem leading to hypertension or high bp.

The Human circulatory system consists of a muscular four-chambered heart, a network of closed branching blood vessels and blood, the fluid which is circulated. The heart is a  4 chambered muscular organ present in the thoracic cavity in between the lungs. it does not have any bones. The chambers(spaces) of blood are filled with blood.T he muscular action of heart walls pump blood throughout the body through blood vessels. Hence the pumping 

The average resting heart rate for a healthy adult is typically between 60 and 100 beats per minute, with 72 beats per minute being the commonly cited average.

An ECG records the electrical activity of the heart over time, which allows clinicians to assess the heart rate and the regularity of the cardiac rhythm.

The human circulatory system consists of a muscular four-chambered heart, a network of closed branching blood vessels and blood, the fluid which is circulated. The heart is mesodermal in origin. It is situated in the thoracic cavity, in between the two lungs. The heart is slightly tilted towards the left side because the right lung is larger than the left lung. This condition provides the heart with enough space to function properly and pump blood efficiently to different parts of the body.

Nodes of Ranvier are the periodic gaps in the myelin sheath of medullated (myelinated) nerve fibers. They allow for saltatory conduction of nerve impulses.

The cardiac cycle consists of a period of relaxation called diastole, during which the heart fills with blood, followed by a period of contraction called systole. The total duration of the cardiac cycle, including systole and diastole, is the reciprocal of the heart rate. For example, if heart rate is 72 beats/min, the duration of the cardiac cycle is 1/72 beats/min about 0.0139 minutes per beat, or 0.833 second per beat.

This sequential event in the heart which is cyclically repeated is called the cardiac cycle. Each cardiac cycle consists of systole and diastole of both the atria and ventricles. Each cardiac cycle represents one heartbeat. The number of heart beats per minute in resting person is called as normal heart rate. The normal heart rate is about 72 beats per minute. The heart rate is same as pulse rate because the contractions of the heart cause an increase in blood pressure in arteries that leads to noticeable pulse. Hence each heartbeat generates one pulse in the arteries.

The cardiac output of a normal adult healthy person at rest is almost 5 litres. The volume of blood pumped out of the left ventricle in one beat is called the stroke volume. It is 70 ml.

When at rest, the body's metabolic demand decreases, but the heart rate typically stabilizes at a resting rate rather than increasing or decreasing indefinitely.