Tuesday, January 24, 2006

Wrinkles and folds on the brain

One of the first things people notice about the human brain is how convoluted its surface is. Instead of being smooth and nearly featureless like a kidney or spleen, the cerebral cortex (the thin layer of gray matter forming the outer surface of the brain) is chock-full of wrinkles and folds. Click on the image above for a larger view.

Technically, each crevice is called a sulcus (pl. sulci) and each ridge between the crevices is called a gyrus (pl. gyri). Sulci and gyri are simply a way of increasing the surface area of the cerebral cortex (and therefore the number of neurons) without greatly expanding the size of the skull. Good thing, too - if our skulls were much bigger, they wouldn't be able to squeeze through the birth canal and C-sections would become the norm. Not to mention that those enormous heads would make us look like Hollywood aliens.

There are perhaps 30 or so named sulci and gyri, but learning to identify them - a time-honored task of every medical student - isn't as easy as it might sound. It isn't true that if you've seen one brain, you've seen them all. Although the total surface area of the cortex is roughly the same in all people, there are large variations in the size of particular areas. Whether these differences in area are related to differences among individuals in various skills and functional capacities is largely unknown (but there have been a few intriguing studies, such as this one and this one).

For the sake of all those sleep-deprived med students, why can't we have a brain that looks more like, say, a howler monkey's?

So nice and smooth, almost no sulci or gyri to memorize. Actually, we humans start out wrinkle-free early in development. Check out this brain from a fetus at 22 weeks:

As neurons continue to divide, grow, and migrate, the cortex folds in on itself, forming a recognizable but unique pattern of bumps and grooves. Unless you happen to have lissencephaly. Children born with lissencephaly (which means "smooth brain") are severely retarded and many die before the age of 2.

So we should be happy with our brain wrinkles. As I've often pointed out to my students, it could be worse. We could be dolphins:

Finally, here's a quiz. Compare the brain below to the brain at the top of this post. What's wrong with it?

Answer: nothing, if you're a chimpanzee. Clearly, there are anatomical differences between a chimpanzee brain and a human brain, particularly in the size of the prefrontal cortex (the front part of the cerebral hemispheres). But the similarities in brain anatomy, like the similarities in DNA, are striking.

All but one of the brains shown here belong to the University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. I modified the first and last images slightly to make them easier to compare. The fetal brain came from humanpath.com.

Monday, January 23, 2006

A portrait of janiceps

Over the weekend I decided to seize the moment and take pictures of the remarkable preserved specimen that I mentioned in my first post. These little conjoined twins - both female - have evoked a sense of wonder and melancholy in me ever since I first discovered them in a dusty glass jar.

The most complete name for their unfortunate condition is cephalothoracopagus janiceps disymmetros. "Cephalothoracopagus" means that the fetuses are joined at the head and chest; "janiceps disymmetros" means that there are two similar faces, each facing in opposite directions like the Roman god Janus. For me the most curious thing about janiceps is that each face is formed seamlessly from two half-faces, one from each individual! You have to see it to believe it.

The first four photos show the twins from different angles. Click on each image for a larger version. In the position photographed, the specimen measures about 14 cm (5.5 inches) from the top of the head to the bottom of the feet. Below the chest everything looks basically normal except for a little tail on one twin. Unfortunately no other data are available - the specimen belongs to a very old collection that was never properly catalogued.

The next two photos are close-up views of the two faces. The eyelids are barely visible and cannot be opened. To use a clinical euphemism, janiceps is "incompatible with life" - these fetuses most likely died in the womb. A handful of case studies have been reported in the medical literature: for details do a search on "janiceps" at PubMed.

Friday, January 20, 2006

My uvula trick

Drumroll please. You are about to witness my most popular anatomical party trick. In fact, years from now, it will likely be the only thing that my former students remember about me.

The image above shows my uvula (better known as "that thing dangling in the back of your mouth") in its relaxed, more-or-less normal configuration. Now, watch what happens when I tighten up my soft palate...

It's pointing straight forward like a little pistol. Impressive, eh? I've met only one other person who could do it. It appears to be a congenital anomaly, not a trait you can develop through practice.

Anatomically, the uvula is basically an extension of the soft palate. Using my lesser known uvula trick -- touching my uvula with the tip of my tongue -- I've confirmed that the uvula is indeed remarkably soft. Like the soft palate, it even has its own named muscle: the musculus uvulae, which shortens the uvula when it contracts.

Functionally, I doubt the uvula serves any important purpose, but I could be wrong. A popular anatomy text book says that the uvula "assists in closing the nasopharynx during swallowing." This makes me wonder if people without uvulas are more likely to have milk come out their nose when they laugh. It's a testable hypothesis, since there are, in fact, a number of people who have their uvulas removed surgically as a treatment for excessive snoring or sleep apnea (e.g. laser-assisted uvulopalatoplasty). Anyone have some good anecdotal evidence?

Thursday, January 19, 2006

What do chiropractic adjustments do to your anatomy?

Last week I visited a chiropractor for the first time since moving to Vermont. I went to him because, for several years now, I've experienced varying degrees of pain or discomfort at various levels of my vertebral column: lower cervical, mid-thoracic, lower lumbar, all on the left side. I have to say, I'm kind of annoyed by the left side of my body. Sure, it carries its weight most of the time, but it doesn't seem to be happy about it. Tingling in the sole of my left foot when I'm wearing certain boots, iliotibial band syndrome (or something like it) in my left lower limb, left gluteal muscles that don't agree with extended periods of sitting. Nothing that prevents me from running or downhill skiing or any of the activities of daily living, but just enough to make me think, "Maybe I should do something about this."

The most annoying problem area is mid-thoracic. Every few months when I least expect it, I have a back attack: sharp yet hard-to-pinpoint pain in my back and lower neck that makes it hurt to turn my head, sit, stand, or really any activity that requires me to be upright. Mercifully the acute phase typically lasts an hour or less, eventually morphing into a more tolerable burning pain that flares up only if I flex my neck too far or turn my head too far to the left. What triggers the back attack is usually a mystery. Sleeping in a bad position? Leaning over a cadaver table in the anatomy lab? Maybe, but more often than not the attack seems unrelated to anything. Stretching, massaging, and ibuprofen can ease the pain, but mostly it's a matter of waiting for the body to heal itself, a "self-limiting" injury as the clinicians like to say. And the discomfort never disappears completely.

So did the chiropractor make a difference? Yes, at least in the neck and midback (the jury is still out on the lumbar region). I notice an increase in neck mobility, especially in turning to the left. I notice substantially reduced pain when I lower my head as far as it can go. I notice that my left arm isn't bothering me now when I run. And I hasten to add that I'm not a chiropractic True Believer. In fact, I'm automatically skeptical of just about everything that comes out of my chiropractor's mouth. Chiropractic seems to have a foundation that is still primarily anecdotal and philosophical, not scientific. That's not to say that it's all baloney. I know there are studies that support its effectiveness for certain conditions in certain patient populations. Whatever. I don't want to get mired here in the devisive "chiropractic vs. allopathic" debate. What I've started wondering is more specific: What exactly happens to your anatomy (joints, muscles, nerves, etc.) during a chiropractic adjustment (or any similar sort of spinal manipulation)?

It turns out that there are a number of reasonable working models and at least a trickle of supporting data. One place to start is a 2002 review article in the Annals of Internal Medicine. It's by William Meeker, DC, MPH, and Scott Haldeman, DC, PhD, MD, FRCPC. Scott Haldeman, a neurologist in Irvine, California, may very well be the only person on Earth with that combination of letters after his name. According to the authors, there are at least five mechanical, anatomical, and/or neurological things that chiropractic manipulations may do (I'm paraphrasing):

  1. Release part of a joint capsule that has become entrapped in facet joints, joints between pairs of vertebrae that have been shown to be very sensitive to pain.
  2. Reposition part of an intervertebral disc (the rubbery disc between successive vertebrae).
  3. Loosen fibrous tissue that formed in a previous injury.
  4. Inhibit overactive reflexes in muscles of the spine or limbs.
  5. Reduce the compression or irritation of nerves.
They also cite studies suggesting that chiropractic adjustments increase the range of joint motion, increase pain tolerance, increase muscle strength, and so on. Lest you get too excited about chiropractic, they also discuss the issue of serious complications from spinal manipulations. Nasty things like vertebral artery dissection and cauda equina syndrome. Such complications are rare but they do happen, and so far there is no way to predict who might have an increased risk.

Probably the most compelling study I've seen so far is one called The Effects of Side-Posture Positioning and Spinal Adjusting on the Lumbar Z Joints (which, coincidentally, was also published in 2002). With funding from the National Center for Complementary and Alternative Medicine, the authors recruited healthy young volunteers to undergo MRI scans before and after a lumbar manipulation on one side. Data analysis (and rather striking images like the one below) show that the adjustments produced increased separation of the facet joints (also called zygapophysial joints or Z joints). Of course, whether that's good or bad is a matter of debate, one that will hopefully be illuminated by more data.

Two MRI cross-sections of the lumbar spine in the same individual. The bottom of the image is towards the back of the person. R = right; L = left; L5 = fifth (lowest) lumbar vertebra. The first image (c) was taken before the left lumbar side-posture spinal adjustment; the second (d) is after. Notice that the gap of the left facet joint (i.e., the white space between the two dark hamburger-bun shapes directly above the L) is larger after the adjustment. Figure copied from Cramer, et. al (2002). The Effects of Side-Posture Positioning and Spinal Adjusting on the Lumbar Z Joints. Spine 27: 2459-2466.

Wednesday, January 18, 2006

Muscles to smile, muscles to frown

A long time ago I heard the adage that it takes something like 43 muscles to frown but only 17 muscles to smile, ergo, we should just smile because it's easier. It wasn't until my first anatomy class in college that I realized these numbers couldn't possibly be right. As far as I can tell, there are only about 36 named muscles of facial expression, and they're not all involved in smiling and frowning. Here they are in alphabetical order (a "2" in parentheses means the muscle is bilateral, "1" means it's unpaired):

Auricularis anterior (2)
Auricularis posterior (2)
Auricularis superior (2)
Buccinator (2)
Corrugator supercilii (2)
Depressor anguli oris (2)
Depressor labii inferioris (2)
Depressor septi nasi (1)
Frontalis (1)
Levator anguli oris (2)
Levator labii superioris (2)
Levator labii superioris alaeque nasi (2)
Mentalis (1)
Nasalis (2)
Orbicularis oculi (2)
Orbicularis oris (1)
Platysma (1)
Procerus (1)
Risorius (2)
Zygomaticus major (2)
Zygomaticus minor (2)

So which ones are responsible for smiling and/or frowning? I could hazard a guess, but I'll defer to Dr. David Song, a plastic surgeon and Associate Professor at the University of Chicago Hospitals, who was interviewed for a Straight Dope article: Does it take fewer muscles to smile than it does to frown? Counting only the muscles that make significant contributions, he concludes that smiling takes one more muscle than frowning (12 vs. 11). That doesn't necessarily mean that smiling is harder to do. Maybe it is, maybe it isn't. I suppose you could compare the masses of "smiling muscles" vs. "frowning muscles" to get a rough estimate of energy consumption (assuming the muscles all consume energy at the same rate per unit mass). In the meantime, check out Happiness Is Only Grin Deep at the always enlightening and entertaining Urban Legend Reference Pages.

Tuesday, January 17, 2006

How much sodium in a pint of blood?

Updated June 2010

That's what I was wondering as I sat in the blood donation center yesterday with a large-bore needle in my cephalic vein, having finally succumbed to the nagging of my conscience (and the nagging of the American Red Cross).

The answer, as far as I can tell, is about 1.5 grams. That's less than I thought. It's only about 60% of the "daily value" (2.4 g). However, it is more than the amount of sodium in one can (340 mL) of V8 (880 mg), one serving (1/2 cup) of Campbell's Chicken Noodle soup (890 mg), or one large Vlasic pickle (880 mg). So next time you finish drinking a bottle of apple juice after donating blood, you should slap yourself in the forehead and say, "I could've had a V8!"

For the curious, here's how I came up with 1.5 grams. One pint of blood is 473 mL. The normal concentration of sodium in the blood is 135-145 mEq/L (according to this handy site). I picked the mean, 140 mEq/L, which is equivalent to 140 mmol/L (since sodium is a monovalent ion). There are 23 grams of sodium in one mole (information you find on a periodic table), so 140 mmol/L = 3.22 g/L. Multiply by 473 mL and there you go (1.52 grams).

Here's another way to put it. One pint of blood has 1.52 grams of sodium, which is the amount found in 3.8 grams (or 0.8 teaspoons) of table salt (sodium chloride). Assuming you have 5 liters (5.3 quarts) of blood in your body, you have a total of 16.1 grams of sodium in your blood, which is the amount found in 8.5 teaspoons of salt.

Bottom line: you have about 8.5 teaspoons of table salt in your blood. In reality you have more sodium ions than chloride ions in your blood, but I think my estimate is good enough for cocktail party conversation.

Monday, January 16, 2006

Kitten with one eye

Cy, short for Cyclopes, a kitten born with only one eye and no nose, is shown in this photo provided by its owner in Redmond, Oregon, on Wednesday, Dec. 28, 2005. The kitten, a ragdoll breed, which died after living for one day, was one of two in the litter. Its sibling was born normal and healthy. (AP Photo/Traci Allen)

OK, so this entry isn't about human anatomy, but the condition called cyclopia can occur in humans, too. Cyclopia is a variety of holoprosencephaly, a congenital malformation of the forebrain and parts of the skull and face. Fortunately (for them), babies with cyclopia don't survive for long. IMO the most astonishing congenital anomaly is cephalopagus (or janiceps) conjoined twins, in which the twins have a single skull with two faces looking in opposite directions (like the Roman God Janus). Although the faces may look normal, each face is actually composed of two fused half-faces, one from each twin! A few years ago I stumbled across a janiceps specimen in an old embryology collection in our anatomy department. Given that the incidence is something like 1 in 3,000,000 births (according to a recent case report), these specimens must be extraordinarily rare. I plan to photograph it before I leave this summer (update: here are the photographs).

Here's an article written by the AP in response to the initial skepticism about the one-eyed kitty photo: One-Eyed Cat Had Medical Condition. I'm not sure how long the article is going to remain online so I'll keep a copy in my (offline) archives.