The last lecture in this section is going to look at the different types of bones and structural features of bones. So before we go any further, I want to talk a little bit about the skeletal system. The skeletal system consists of 206 total bones, and they're divided into two groups.
You have your axial skeleton, which is your head and torso, basically. your skull, your ear bones, the bones in your throat, your hyoid, your ribs, your sternum, and your vertebra. And that's a total of 80 bones. Then you have the appendicular skeleton, and that's 126 bones.
These are the bones of your upper and lower limbs or your extremities and the girdles that connect them to the axial skeleton. So the next section, we'll look at the axial skeleton. Then section eight, we'll look at the appendicular skeleton.
And then we'll finish out this unit looking at joints. So almost all of your bones can be classified into one of five types. You have long bones.
And we looked at that when we did bone tissue. These are called long bones because they look like long bones. And these are the typical ones you think about, you know, Fido carrying his bone. Then you have short bones.
Short bones are so-called short bones because they're short. Um, many of them are somewhat cubicle in shape. Um, but these are examples of short bones.
Uh, then you have flat bones, like your sternum here is a flat bone. Uh, then you have irregular bones, like your vertebra means they don't really fall into any shape. They're not long. They're not short. They're not flat.
They just look funky. Um, so those are irregular bones. And then finally you have sesamoid bones like your patella or your kneecap. And these are shaped like a sesame seed. Also, we have sutural bones.
Sutural bones are extra bones that are located between the cranial bones. These don't have names because there's different numbers of them in everybody. But at birth, you have cranium bones that are separated by what are known as soft spots or fontanelles.
We'll talk about that as we go, but they're flexible areas to allow the baby's head to move through the birth canal at birth. And then within the first 18 months or so, those begin to harden or your fontanelles begin to close. As they close, you form sutural bones.
So the areas where these bones in the cranium are connected, so you see pink, blue, orange here, these are different. cranial bones that we'll talk about in axial skeleton, but they fuse together in what we call sutures. And then sometimes you have small bones that form between the sutures and they're called sutural bones.
Now, when we talk about surface features of bones, some things we want to look at are projections, things that stick out and then indentions or openings or depressions that you see that form in. And we're going to look at each of them. individually. So bones have those two types of markings and they would be depressions or openings and the point of depressions or openings is to allow soft tissues like tendons for example or nerves to pass through and also to help form joints to hold bones together.
And then you have processes. Processes or projections are things that stick out from a bone. And these are also for attachment of ligaments and tendons that help form your joints.
Now to distinguish, ligaments are connective tissue that run bone to bone. Tendons are connective tissue that run from a muscle to a bone. So a ligament connects two bones together.
A tendon connects a muscle to a bone, right? So the first example is a fissure. A fissure is a narrow slit.
usually for blood vessels or nerves to pass through. And here's an example here, your superior orbital fissure. That's where your optic nerve passes from your orbital canal back into the brain through the cranial nerves.
And that's a fissure. A foramen is a big hole. The foramen magnum here at the base of the skull is where your spinal cord passes from your brain into your vertebral column.
It's the biggest foramen in the body. So it's called the foramen magnum. but there are many foramen you can see one right there and those are just holes for blood vessels nerves or ligaments to pass through a bone and the hole in the bone or the opening is called the foramen A fossa is a shallow depression.
It looks almost like somebody took their thumb and pressed it into the bone to create this little indention. And there's one, your mandibular fossa, that's where the mandible attaches at the base of the skull. But a fossa is just a shallow depression.
And you can also see a couple right here. A sulcus is a furrow for a blood vessel, nerve, or tendon. You can see right here on the femur near the head. You can see this little sulcus.
It's similar to a fissure, but it's not a full opening. It's just a little indention, almost like a valley. Then you can have a meatus, like your external auditory meatus. It's almost like a hole in a bone, but it's not a foramen because it goes all the way through the bone, more like a tunnel than a hole. So it's a tube-like opening.
A condyle. is a rounded projection. So here on your mandible is the condylar process. And this is what sticks in that, uh, faucet, that depression I showed you on the base of the skull.
Uh, you can see how this rounded area looks very much like a thumb and would fit right in that thumbprint or that depression in the skull. Um, so it's a rounded projection that has a smooth surface and it's called an articular surface because it articulates with another bone. It's where one bone meets another bone. A facet is a articular surface as well, but it's flat.
And so this is a facet here on your vertebra. Head and neck, some of your bones kind of wrap around like this or have projections. And the head is at the end and it's connected to the body of the bone by the neck. This is a rib.
And you can see depressions, fossa here, and facets as well. A crest is a prominent ridge. So here's the medial sacral crest in the back of the pelvis, the base of the spinal cord.
And you can see that ridge right there. And that's what we call a crest. You can also see several foramen right here. An epicondyle is a roughened projection on a condyle.
So you've got a condyle here and then if you feel on the edge here, it's very bumpy. And that's called an epicondyle. The reason it's bumpy is because you're attaching tendons and ligaments here. So if the bone were super smooth, it would be difficult to attach those. So it's more like a roughened edge for attachment.
Then you can have a line, and that's similar to a crest, but it's smoother. A crest is going to be very prominent. A line is more like a small bump, and you can see those in the back of the skull here.
A spinous process is only seen in your spine. If you feel down someone's back and you feel the bumps, those are the spinous process, but it's a narrow slender projection from a bone. A trochanter applies only to the femur. You can see the head of the femur here where it attaches in the pelvis, but on the outside here, you have a trochanter.
The trochanter is like an epicondyle. You have a lesser one here. So it's a very bumpy edge here. And that's where you attach all those ligaments and tendons that are going to hold your leg together at the hip. And then a tubercle is a rounded projection.
And you can see that tubercle here, similar to a line, but much smaller. See, the line goes very long across the bone. The tubercle is very small. Tuberosity is another type of bumpy surface. And you can see that here on the sacrum here.
And that's for attachment of ligaments and tendons.