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The awe of similars

Nature is famously conservative. If it does something right, it repeats the plan.

Sometimes, it’s obvious: The fractal patterns of river deltas, human kidneys and trees or the camouflaged stripes of tigers and chameleons.

Sometimes, technology reveals less obvious or unseen similarities. More fanciful, perhaps, but stunning nonetheless. Above are two images: One is a bright-field micrograph of a meadow buttercup floral bud, taken by Stephen S. Nagy, an honorable mention winner in the 2006 Nikon Small World microscopy contest. The other is a multi-photon fluorescence micrograph depicting intestinal villi of a mouse, taken by Thomas Deerinck at the National Center for Microscopy and Imaging Research, which took 8th place in Nikon’s 2005 contest.

Which is which? Answer below.

Answer: Flower bud top; intestine below.

Skin deep

The average person is covered by 16 to 21 square feet of skin. It’s the largest organ in (on?) the human body. A key role of skin (aside from simply helping keep us all together) is to serve as a physical barrier to our surrounding environment and its assorted, myriad pathogens.

Indeed, our skin (or more particularly, its outer layer called the epidermis) is home to its own ecosystem of microorganisms, including yeasts and bacteria that cannot be removed by any amount of cleaning. On average, it’s estimated that roughly 50 million microbes inhabit each square inch of epidermis, though that number varies greatly by location. Oily or moist skin, such as under the arm or between the toes, harbors higher numbers than a similarly sized patch of forearm.

The scanning electron micrograph above, created by Thomas Deerinck at UC San Diego’s National Center for Microscopy and Imaging Research, depicts a patch of skin. The epidermis contains no blood vessels, receiving all of its nutrients via diffusion from capillaries in the underlying dermis layer.

The bottom layer of the epidermis contains proliferating cells, which divide to form keratinocytes. These daughter cells migrate up through the epidermis and eventually die as their nutrient supply dwindles. The keratinocytes lose their cytoplasm, which is replaced with keratin, a structural protein that forms tough, insoluble filaments similar to those found in your hair and nails.

After 27 days or so, the dead keratinocytes reach the surface of the skin and are sloughed off.  It’s estimated humans shed about 600,000 particles of skin per hour, about 1.5 pounds a year or 105 pounds of skin by the time they are 70 years old. This translates to an entirely new outer layer of skin cells every 27 days, almost 1,000 new skins in an average lifetime.

River of Dreams

The cortex is the brain’s outermost layer, visually characterized by its notable sulci or deep folds, which allow the brain to cram more neurons into limited space. When you look at a human brain, you see only about one-third of its surface, the other two-thirds are hidden in the folds. The more wrinkly the brain surface, the greater the ability to think, generally speaking. 

The cortex is where much of our brain’s higher executive functions occur, from interpreting sensory input and controlling voluntary movement to generating thoughts and forming memories. Naturally, doing all of that work requires a large and steady supply of oxygen and other nutrients.

Above is wide-field confocal micrograph by Tom Deerinck at the National Center for Microscopy Imaging and Research at UC San Diego. The image depicts the in situ superficial vasculature (blood vessels) of a rat cerebral cortex, whose brains are very similar to humans in basic structure and function. It was made using 50 optical sections.

Memorable pictures

The hippocampus is a major component of the brains of humans and other vertebrates, playing critical roles in the consolidation of information from short-term memory to long-term memory and in spatial navigation. Damage to the hippocampus, whether from oxygen starvation, diseases such as encephalitis or epilepsy or physical trauma can result in memory loss and disorientation, including anterograde amnesia – the inability to form or retain new memories.

The hippocampus is also among the first regions of the brain to be affected by Alzheimer’s disease.

The hippocampus is a many-layered splendor, as these false-color confocal micrographs of a rat hippocampus by Thomas Deerinck of the National Center for Microscopy and Imaging Research at UC San Diego brilliantly show, layer upon lovely layer of pyramidal neurons, support cells and neuronal fibers.

Padded muscle

Skeletal muscle attaches to joints and long bones and is under the control of the conscious brain. As you read this blog, occasionally typing on your keyboard, it’s skeletal muscle directing your fingers through their finely-tuned tap dance.

(FYI: Aside from skeletal, there are two other major muscle types in your body: smooth and cardiac. Smooth is involuntary and non-striated. Generally, it’s either fully contracted or fully relaxed. Your urinary bladder, lungs and the irises of your eyes are controlled by smooth muscle. Cardiac muscle is also involuntary – doing its job automatically – but striated, meaning parts of it are able to contract while other parts do not. Your heart is composed of cardiac muscle.)

In this confocal fluorescent light micrograph by Thomas Deerinck at the National Center for Microscopy and Imaging Research at UC San Diego, you’re looking at a cross-section of parallel skeletal muscle fibers (stained red due to the presence of the proteins actin and myosin) sheathed in a sugar-protein complex (green). Cell nuclei are stained blue.

There are roughly 700 muscles in the body, in all shapes and sizes. The biggest single muscle is the Gluteus maximus, one of three muscles that comprise each buttock. Our big butts help make it possible for us to stand, move upright and run. Indeed, a 2006 paper by Harvard and University of Utah researchers suggested giant glutes make humans the undisputed best long-distance runners in the history of life on Earth.

The widest skeletal muscle in the human body is the Lastissimus dorsi, which is Latin for “wide back.” It’s the muscle that begins at the spine, fans out and attaches at the other end to the upper arms.

The longest muscle is the Sartorius, which begins at the outside of the hip, runs down the upper leg and terminates inside the knee. The name Sartorius means “tailor,” so-called because this muscle allows one to cross one’s legs, purportedly a common position assumed by working tailors. The Sartorius also assists in flexing the knees and hips.

The Gluteus maximus often is dubbed the strongest muscle because it works to keep the entire body upright, but there are many ways to measure strength:

The muscles of the uterus, for example, must be strong enough to push a baby through the birth canal.

The heart beats continuously for as long as you live – more than 3 billion times in a person’s life, pumping approximately 2,500 gallons of blood every day.

Similarly, the muscles of the eyes are constantly repositioning them. In an hour of reading, the external muscles of the eyes will make nearly 10,000 coordinated movements.

And let’s say something for the tongue, which is a bundle of tireless muscles. While eating, it moves around mixing food to aid digestion. It binds and contorts to make speech. Even when you’re asleep, it’s constantly pushing saliva down the throat.

But arguably the strongest muscle, at least based upon its weight, is the masseter or primary jaw muscle. When all of the muscles of the jaw are working together, humans can apply a bite force up to 55 pounds on the incisors and more than 200 pounds on the molars.

That’s nothing compared to the maximum chomping power of Tyrannosaurus rex (12,800 pounds), of course, but it still would hurt.

Cells afire

Appearances aside, the image above, produced by Tom Deerinck at the National Center for Microscopy and Imaging Research at UC San Diego, does not actually depict cells in flames.

Rather, the red, fire-like projections are filopodia – microscopic filamentous bundles that serve multiple cellular functions. For example, they act as sensory antennae, probing the cell’s surrounding microenvironment. Motile or migratory cells commonly sport filopodia, which aid in their movement. Fibroblasts use filopodia to migrate to wounds and close them. Filopodia also help direct the growth of dendrites in neurons.

Filopodia are even used by some bacteria to move between cells, helping them evade the host immune system.