Tag: biology

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.

Angiotensinogen produced by the liver is broken into angiotensin I by renin which us an enzyme produced by the kidney. This angiotensin I is the precursor of angiotensin II which often plays a role in the constriction of glomerular arterioles, increase blood flow and blood pressure. 

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

Berger waves, also called as $\alpha$-waves are neural oscillations in the frequency range of 7.5-12.5 Hz. $\alpha$-waves are called as Berger waves in the memory of the founder of EEG.
$\alpha$-waves are one type of brain waves detected either by either EEG, electroenccephalography or magnetoencephalography (MEG) and predominantly originate form the occipital lobe during wakeful relaxation with closed eyes.
Thus, the correct answer is option (C), 'Brain'.

Magnetoencephalography or MEG is a non-invasive technique for investigating human brain activity. It allows the measurement of the ongoing brain activity on a millisecond-by-millisecond basis and it shows where in the brain activity is produced. So, it is helpful in shocked patients.
So, the correct answer is option C.

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.

The cardiac activity is controlled by the sympathetic nervous system through the epinephrine. It fastens the heartbeat and the cardiac output so that more concentration of oxygen can be supplied to the body parts.