biology zoology blog benno meyer rochow sneeze

The Science behind Sneezing

Have your handkerchief handy

Have you noticed that most of the words related to the “nose” start with the letters ‘n’ and ‘sn’? Apart from nose, nares, nostril, and nasal you’d find snot, snort, sniff, snuff, snore, snooze, snub-nosed and, of course, sneeze. The most common reason advanced for why people (and other animals) sneeze is that the act of sneezing removes an irritant or obstruction in the nasal passage. Suffering from hayfever (my children used to have fun chasing me around in the garden with flowers in their hands) I once counted that I was sneezing forty times in a row  – and that was not at all because of an obstruction in my nasal passages (or looking into the sun, which is said to trigger sneezing in some people). So, what goes on?

The allergic reaction to pollen like the one that made me sneeze is probably one of the commonest reasons of sneezing in humans. But it’s complicated, for it involves an oversensitivity reaction in which substance P (cf., my earlier blog) is increased in the nasal epithelium together with other neuropeptides like, for example, calcitonin (cf. also old blog). These and the release of antibodies and histamine by the body’s immune system to the perceived threat posed by the inhaled pollen, lead to the hypersensitivity reactions (e.g. nose and eye itch). All these in conjunction with neurotrophic factors stemming from the allergy, target neuronal fibres like chemo- and pain receptors and those sensing itch, which then send the information to the trigeminal ganglion. The trigeminal nerve that serves also the cheek and orbital region of the face then instructs the sneezing centre in the brain’s medulla to take action.

Action means that effector neurons should become active. Those involved with breathing make sure that deep inspirations occur prior to the sneeze and that the eyes and the glottis close, before through an increase of the pressure in the lungs the glottis suddenly opens and releases in an explosive action air and fluid droplets through mouth and nose. The pressures involved in a sneeze can be 176 mm Hg, which would be one tenth of the pressure of a tyre of a small car or one third of the pressure penguins generate to poop. During a sneeze thousands of tiny droplets of liquid are released up to a metre and sounds accompanying a sneeze can vary from faint to deafening.

People who own a dog or a cat know that their pets may occasionally sneeze spontaneously or when you tickle their nose or when they smell irritating chemicals. The same holds true for humans and I for one avoid the perfume sections of the department store because the odours there could make me sneeze. The sneezing that accompanies a cold is usually related to a mucus build-up in the nasal passages that the sneeze tries to remove. The Galapagos iguana and some marine birds sneeze to remove salt crystals that have accumulated in the nasal passage and need to be flushed out.  All vertebrate animals with lungs and a connection between the nose and the pharynx (that excludes the fish) are said to have ‘choanae’ (= internal nares) and can sneeze. The nose of a fish consists of two nasal openings for the inflow and two for the outflow of the water. Located between in and outflow nares is the olfactory epithelium with its odour sensitive cells. Thus, looking at the head of a fish you will see 4 nasal openings and not just two as in all terrestrial vertebrates. Sneezing in fish is therefore not possible.

Antarctica is a good place for people with pollen allergies. Although you can get cold there, you are not likely to ‘catch a cold’ there, but on one of my trips to the icy continent my friend and colleague Taka Hariyama sneezed (dust does exist in some areas of Antarctica). He sneezed once and seemed happy, exclaiming joyfully “only once!”. I was puzzled why he stressed “only once”, until I learned that ‘sneezing once’ suggests to a Japanese that someone is saying good things about the ‘sneezer’, but that sneezing twice means the opposite. Yet, what it means to sneeze 40 times in a row I don’t want to know.

© Dr V.B. Meyer-Rochow and, 2021.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content. 

Stinging and Injection Devices of Animals

Cases of convergent evolution

What qualifies as a sting and what had better be called a bite is not always clear and most people say they’ve been bitten by a mosquito while some refer to the “bite” as a “sting”. If the sharply pointed end of a structure is pushed into the tissue of another individual, I think we should call it a sting  –  and stinging animals abound. The stinging devices in animals are amazingly diverse and although we tend to think immediately of the defensive stings of bees and wasps, stinging is also used to deposit, for example in female parasitic wasps, their eggs into caterpillar or spider hosts on whose tissue the larval baby wasps can feed. Injecting venom can be the fastest way to immobilise prey and some stinging animals like, for example the fish-eating slowly moving cone shells or some spiders and snakes that inject venom into their victims, make use of their stinging devices in this way. To obtain oxygen under water without having to come up to the surface, the larvae of the mosquito Mansonia spp. impale the air-containing cavities in the stems of underwater plants with their syringe-like “stinging” syphons.

Venomous snakes, depending on the species, have two ways of delivering the venom to their victims. In those with venom glands connected with teeth at the back of the mouth, the teeth are not hollow, but possess a narrow groove on their inner side, in which the venom runs along. More dangerous are the hollow front teeth of some snakes. These teeth are normally folded up and tucked away under the roof of the mouth when not used, but when needed they point forward to strike the prey and to deliver the venom through tiny pores at their tips. The bite is carried out with a considerable force and the venom is forced from its storage glands into the wound of the victim. A rather similar method is employed by spiders, which also inject venom through a canal inside their two oral appendages, known as chelicerae. The chelicerae have very pointy tips with a hole at the end and the venom stems from the glands at the base of the chelicerae or from deeper in the head. How a droplet of the liquid venom can be pressed through the very narrow tube in the hollow chelicerae and then leave through the tiny pore at the end is something for scientists interested in fluid mechanics and involves some knowledge of the viscosity of the venomous liquid. In most web-building spiders the two chelicerae work like pincers, but in the often much bigger mygalomorph spiders the chelicerae work in parallel striking prey like 2 axes from above.

Similar fluid mechanical problems would apply to the venom delivery of wasp and bee stingers, for they resemble hypodermic needles. The honey bee stinger is barbed (a bit like that totally unrelated stinger of the stingray) and stays in the flesh of a stung human, leading to the death of the bee, but continues to pump venom by itself for some minutes. Wasp stingers and those of some powerfully venomous ants like the Australian bull ant are smooth and can be used repeatedly. Giant centipedes are feared because of their strong mandibles, sometimes referred to as ‘fangs’, which possess a canal through which a venom can be injected into a bitten individual. However, stingers delivering a potent venom that can kill are known not from centipedes, but scorpions. The most dangerous stinging animals in the sea are probably the already mentioned cone shells with their single hollow chitin tooth connected to a venom bulb, further the so-called stone fishes and some others with venomous fin rays as well as stingrays (the death of Steve Irwin comes to mind). The only “stinging mammal” is the male platypus with its venomous and hollow hind leg spurs. But who’d want to pet or even have a chance to pet a platypus?

© Dr V.B. Meyer-Rochow and, 2020.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content. 

biology zoology blog benno meyer wrinkle

“Wrinkle-wrinkle, au revoir”

How I wonder what you are

I have recently been reading about wrinkles. Not because I am worried about my wrinkles (I actually think wrinkles can make a face look more interesting than if it was “as smooth as a baby’s bottom”), but because so many people here in East Asia seem terrified of getting wrinkles and avoid an exposure to direct sunlight through face masks, parasols, summer hats, lotions, creams, etc. The scientific literature on wrinkles includes information on skin structure and function, biochemical and physiological reasons to develop wrinkles, but I couldn’t find anything about perhaps the most obvious reason: you get older, you shrink!  As we age, our height diminishes. During the time I passed university examination I was 184 cm tall; now I am 181 cm tall. People who have spent some time in the space station circling around our planet Earth under zero gravity conditions reverse that trend and are a little bit taller when they return to Earth. An apple that ages shrinks and becomes wrinkly. And humans  – how about us?

Wrinkles consist of more or less deep furrows and bulges and they usually develop along locations of microlines in the skin. The latter form a polygonal network of fine lines easily visible on the outer skin layer (the epidermis) with a magnifying glass. Under the epidermis lie the dermis and hypodermis with their stabilizing connective tissue component proteins collagen for structural integrity and elastin for flexibility and plasticity. And, not to forget, there is hyaluronic acid in the skin with its multiple functions. All the skin layers are associated with underlying lymphatic vessels along with perilymphatic and subcutaneous fat tissue, known as panniculus adiposus and p. carnosus. What is most damaging and a cause of the skin to age is oxidative stress, in other words free oxygen radicals. These radicals are highly reactive and may be produced by the breakdown of double-bond fatty acids following an exposure to UV-radiation. There are, of course, ways the skin tries to protect itself: a higher sebaceous gland density of the skin is correlated with shallower wrinkles, but as the pillars of the skin (like collagen and hyaluronic acid) slowly diminish and the skin becomes drier the decline in skin cell renewal of older people can only be slowed down with a nutrition that is rich in vitamins and anti-oxidants.

What matters also are the genetic factors and how rapidly a person ages. In addition, smoking and heat are often mentioned as wrinkle-promoting, and so is lack of sleep; in fact, anything that causes skin to become dehydrated. However, there is one cause that is related to facial expressions.  Grooves on the forehead during thinking, or wrinkles during laughter, or the vertical lines between your eyes during squinting to see more clearly: such lines can become permanently visible as expressive wrinkles. There is generally not terribly much that an ageing person can do to avoid getting wrinkles, but there is one dog breed (the “Shar-pei”), in which the wrinkles disappear with age. For other and much bigger animals with wrinkled skins, the wrinkles can actually be an advantage as they can hold moisture that can then evaporate from a larger surface area and in this way lead to the cooling of the wrinkled individual. This suggestion has often been advanced to explain the folds and wrinkles of the skins of elephants and rhinoceroses. However, fact is that any animal (other than a Shar-pei dog) develops wrinkles as it ages, especially around the joints. But because animals are covered in fur we tend to overlook their wrinkles  -with one exception: the beautiful, pain-free naked mole rats. Their incredibly wrinkled bodies help these subterranean, naked rodents to turn around in their narrow tunnels and navigate corners with ease.

To return to my earlier statement that we shrink as we age and that space travellers are taller when returning to Earth: my hypothesis is that they would not only be slightly taller but also less wrinkled (provided they got enough sleep and had good vitamin-rich food while at the space station). In any case: Every wrinkle has a story to tell and as for me, there will be a lot more stories when I’m older.

© Dr V.B. Meyer-Rochow and, 2020.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and with appropriate and specific direction to the original content.