By Elizabeth A. Murray, Mount St. Joseph University
When learning about musculoskeletal anatomy, one might feel defeated thinking, “We have to learn about 206 bones?” Well, there are some conveniences to it: For one thing, there are a lot of repeating themes in the body, like 24 individual vertebrae within the spine, which have many similar features, and 12 pairs of ribs, that likewise have much in common with each other.
General Rules When Learning Anatomy
There are 56 bones called phalanges that make up our fingers and toes and have great similarities, and those 56 are over a fourth of the typical 206 bones right there. We also have bilateral symmetry in our favor, so because the right and left sides of the body are basically mirror images, once you learn one side, you’ve learned the other side, too. Finally, due to our four-limbed, tetrapod ancestry, the upper limb and lower limb have much in common.
In terms of general principles, one of the things that’s often taught in a standard anatomy and physiology course is the classification of bones by shape: The four shape categories are long bones, like the femur and humerus of the limbs; flat bones, like some in the skull; short bones, which are smaller, boxy-bones, like the carpals in the wrist; and irregular bones, like vertebrae, which don’t really fit any of the other categories well.
One general concept used is the contrast between the axial part of the skeleton and the appendicular skeleton. The axial bones are those that make up the main longitudinal axis of the skeleton. These include the 22 bones of the skull, the 6 tiny ossicles in the ears, the single hyoid bone in the neck, the 26 bones of the vertebral column—the 24 individual vertebrae, plus the sacrum and coccyx, or tailbone as it’s called, the 24 ribs, and the sternum. That’s a total of 80 bones.
The appendicular skeleton, on the other hand, includes the 30 bones in each upper limb, the 30 bones in each lower limb, as well as the two clavicles and two scapulae of each pectoral girdle, and the pair of pelvic bones that attach our lower limbs to the axial skeleton, so the appendicular total is 126 bones. If we’ve done the math right, that’s 206, when the appendicular and axial totals are combined.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Remembering Specific Terms
Another general concept has to do with bony landmarks: There are some standard terms used for bone features—such as foramen, tubercle, condyle—and then adjectives are used to specify those on a given bone. An overarching scheme of bony landmarks would boil down to three main categories: projections, depressions, and openings.
Depressions and projections are typical of muscle attachment sites and joint surfaces, while openings will transmit arteries, nerves, and veins. Learning the general bony landmark terms in advance will help prevent confusion, since numerous bones have tubercles, notches, heads, facets, and so forth.
So, without understanding, these are rather generic terms. Keep in mind that some of the specific landmarks also use anatomical directional terms like lateral, medial, superior, and inferior. Learning the types of bony landmarks—condyles, foramen, and facets—will make a good foundation for learning the names of specific bone features.
Stress Affects Bones
So, where do these bony landmarks come from? People usually answer that the landmarks are there so that muscles can attach to them. But that’s not exactly the case.
To some extent, these projections—trochanters, tubercles, processes—are there because muscles attach to them. That might sound like double-talk, or a fine point, but really, it’s not. The landmarks don’t develop to facilitate muscle attachment; they grow because bones’ reaction to stress is to build more bone matrix.
The matrix is composed of the collagen fibers surrounded by calcium phosphate salts. That addition of more bone matrix in response to stress strengthens the bone. Essentially, this relates to a concept in anatomy known as Wolff’s law, which states that bone will adapt to the loads under which it is placed.
This is why stress like weight-bearing exercise is healthy for bones—within reason, of course. It is also why inactivity causes bone atrophy—whether it’s astronauts on the space station, a bedridden patient, or a person in a cast for six weeks.
Bones Aren’t Static
Human genetics lays down bone in predictable patterns in the skeleton. Genetics also causes muscles to attach in the same places in all of us. But from the outset, the fetal skeleton has long bones that are very simple in shape—they look like tiny sticks—and lack the typical landmarks of adult bones.
As babies begin to use their muscles, the muscles pull on the bone underlying their attachments, and by Wolff’s law, the stimulation actually helps build the bony landmarks typical of the adult skeleton. Most people think of the skeleton as static, but it is changing and responsive throughout life in subtle ways.
Common Questions about General Tips for Learning Anatomy More Easily
Learning the names of different bones in anatomy can become easier by classifying them into different groups such as long, flat, short, and irregular; understanding the regular patterns in the body where bones are similar; and learning where the general terms in anatomy and their respective adjectives are used instead of memorizing them.
Bones can change through a combination of genetics that defines the pattern of both bone structure and muscle attachments. The use of these muscles leads to the typical landmarks we’re familiar with in anatomy.
Wolff’s law is a concept in anatomy that states bone will adapt to the load under which it is placed. Weight-bearing exercise is deemed healthy exactly for this reason.