Cardiovascular and Nervous System

Systolic pressure is measured in the arteries when the heart contracts and is 120 mm of Hg in a normal condition.

A sphygmomanometer is an instrument, attached to an inflatable air bladder cuff and used with a stethoscope, for measuring blood pressure in an artery. Systolic pressure is identified with the first of the continuous korotkoff sounds. Diastolic pressure is identified at the moment the korotkoff sounds disappear. 

Hypertension is generally defined as blood pressure consistently at or above 130/80 or 140/90 mm Hg. Among the choices, 140/100 represents a hypertensive reading.

In a blood pressure reading of 120/80, the top number (120) is the systolic pressure, which is the pressure during heart contraction. The bottom number (80) is the diastolic pressure.

Pulse pressure is calculated as the difference between the systolic pressure and the diastolic pressure. Here, 120 - 80 = 40 mm Hg.

The pulse pressure is the difference between systolic and diastolic pressure. For a standard 120/80 reading, the difference is 120 - 80 = 40 mm Hg.

A blood pressure reading of 140/90 mm Hg is considered elevated and is classified as hypertension. Normal is typically 120/80.

When the heart beats, it contracts and pushes blood through the arteries to the rest of the body. This force creates pressure on the arteries. This is called as systolic blood pressure. A normal systolic blood pressure is 120 mm hg. The diastolic blood pressure indicates the pressure in the arteries when the heart rests between beats. A normal diastolic blood pressure number is 80 mm hg.

Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. When blood vessels constrict, the flow of blood is restricted or decreased, thus increasing vascular resistance causing a reduction in blood flow. Thus, vasoconstriction usually results in an increase in systemic blood pressure.

The involuntary nature of cardiac muscles is the major quality that makes them contract and relax continuously without pausing or without experiencing any fatigue like the rest of the muscles of our body. The parasympathetic nervous system has effects antagonistic to those of the sympathetic nervous system. The parasympathetic stimulation oh cardiac muscles, however, cannot change the involuntary nature of the cardiac musculature.

Sympathetic neural signals, adrenal medullary hormones (like epinephrine), and thyroxine all increase heart rate. Parasympathetic signals and acetylcholine decrease heart rate, while the vagus nerve carries parasympathetic signals.

A refractory period is a period of time during which an organ or cell is incapable of repeating a particular action. 

The tenth cranial nerve (X) is the vagus nerve. It is the longest cranial nerve. (Its name means "wanderer"). It supplies most of the organs in the thoracic and abdominal cavities. This nerve also contains motor fibers to the larynx (voice box) and pharynx, and to glands that produce digestive juices and other secretions. The vagus nerve is responsible for such varied tasks as heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech. Parasympathetic innervation of the heart is partially controlled by the vagus nerve and is shared by the thoracic ganglia. To be specific, vagal and spinal ganglionic nerves mediate the lowering of the heart rate. 

Heart beat is initiated by the nodal cells of the SA node. It starts the heart beat. The electrical impulse is then carried by the nerves to the AV node and the Purkinje fibres. Thus the nerves help to spread the impulse throughout the heart. Hence the rate and rhythm of heart beat is controlled by the impulses travelling through the nerves.