"Should we reconsider these terms in medicine?"
Erasistratus and his colleague Herophilus (2nd century B.C.), at School of Anatomy at Alexandria, performed first dissections and are credited with the origin of many a nomenclature that exists even today. Brain was dissected and the terms such as cerebrum and cerebellum (‘small brain’) were advocated. A part was named as per its appearance; for instance, cortex ~ bark of a tree. Trachea (windpipe), pneuma (lung), veins & arteries were researched upon.
Field of biology and medicine has evolved since. As our knowledge, well-aided by technological revolution, made advances, many old theories were given a go-by. In some instances, the old hypotheses were replaced by diametrically opposite newer ones. There was a time when use of cold milk was advocated in GERD or acidity. Then, with the finding of rebound acidity, cold milk got replaced by warm milk. If last century was the century of antibiotics, this century is likely to be the century of probiotics!! In summery, this field was never static; it progressed with time, making amendments to its own principles.
Some terms, however, have stayed the course. No changes were suggested for these terms, though the terms are either confusing or downright improper. Let us consider some examples (and also consider their reconsideration).
(1) Dead space:- The trachea and the first 16 generations of the respiratory tree; the space is termed “dead” with reference to gas exchange. Howsoever it may be true to the context, no space in the living body should be called ‘dead’. This so-called dead space performs many important functions – humidification of the inspired air, defense function, and so on. It can be called ‘non-respiratory’ space. Then, the types of this dead space create some confusion – anatomic & physiologic dead space. Anatomic dead space is anatomically ‘dead’ because of lack of the epithelium that can allow gas exchange. It means there won’t be the primary ‘function’ of gas exchange here. That be the case, why should we use the term ‘physiologic’ dead space, which is suggestive of another space which (also) is ‘functionally’ dead? The terms ‘anatomic’ & ‘physiologic’ sound mutually exclusive, which they are not. In fact, anatomic dead space is ‘functionally’ dead, and physiologic (functionally) dead space includes the ‘anatomic’ dead space. Physiologic dead space can be simply called ‘total’ dead space that includes anatomically and functionally ‘no-gas-exchange’ areas.
(2) Basal ganglia:- A group of nerve cells outside the CNS is termed ganglion; a collection of nerve cells in the brain is referred to as nucleus. Thus, the masses of grey matter at the base of the brain could have been called basal ‘nuclei’. Also, they are 5 discreet masses contributing to the same function(s), assisting the motor cortex in selecting and performing an appropriate desired motor activity. Should they be addressed in singular or pleural? (Basal ganglia ‘is’, or basal ganglia ‘are’?!. Until World War I, United states ‘were’, and then they came to be known as United States ‘is’….) Probably the basal ganglia is/are referred to as ‘ganglia’ (and not nuclei) because a ganglion or a nucleus is a relay station; the basal ganglia, though they are collections of nerve cells, do not act like relay stations in the conventional sense. Another point to be noted is, their constituent parts are called as nuclei (caudate, lentiform), and the wholesome structure is basal ‘ganglia’.
Substantia nigra is named so due to its staining properties. To avoid using the ‘N’ word, can we call it substantia melanina or something?
(3) Tetanus, tetany: Again a certain amount of confusion using these terms. Tetanus, in Physiology, is used to denote a high-frequency stimulation. For a skeletal muscle, such a high frequency stimulation results in a sustained state of contraction (failure to relax). There is accumulation of Ca++ INTRACELLULARLY. The common experience of tetanus is while writing an exam; the hand muscles go into sustained state of contraction for some time. Also, post-tetanic potentiation occurs in the CNS synapses. This too results from accumulation of Ca++ in the presynaptic neuron, caused by high-frequency stimulation. It’s the basis for short-term memory. Tetanus, in medicine, denotes the disease caused by Clostridium tetani. Then there is hypocalcemic tetany. Decreased ECF Ca++ makes the sodium channels in the nerve membrane unstable, resulting in a volley of impulses to the muscle and a sustained contraction of the muscle. Tetanus literally means ‘I stretch’; it’s been used as a common term for all the aforementioned phenomenon because the underlying mechanism for all of them is a high-frequency stimulation of nerves/muscles. However, increased ICF Ca++ (tetanus), decreased ECF Ca++ (tetany), and a toxin inhibiting the release of glycine and GABA and thereby causing excess activity in the motor neurons (tetanus) could have been denoted by different terms. Just to avoid confusion…..
Dr. Vivek Nalgirkar