Video Transcript
In this video, we will learn to
describe the structure of the human axial skeleton. We will learn about the function of
the spinal column, the skull, and the thoracic cage. And we will learn about the types
of joints most commonly found in the axial skeleton.
The adult human skeletal system
consists of 206 bones, as well as all of the joints that connect them. The skeletal system is a feature of
some organisms called vertebrates. Specifically, mammals, reptiles,
birds, amphibians, and some fish have bony skeletons similar to ours. The skeletal system is adapted to
serve a number of functions. Our bones are the site of blood
cell production and they play a role in our immune system. They store certain ions and
minerals, and, maybe most importantly, the skeleton is the internal support and
framework of our bodies. The bones of the skeleton give the
body shape, allow movement, and protect our most delicate and important organs.
The human skeletal system is often
divided into two sections: the axial skeleton and the appendicular skeleton. The appendicular skeleton contains
the bones of the appendages. In humans, those are the arms and
the legs. The appendicular skeleton also
contains the bones that are responsible for connecting these appendages to the
torso. The axial skeleton contains the
bones found along the vertical axis of the body. The axial skeleton contains the
skull; the thoracic cage, also called the rib cage; and the vertebral column, also
referred to as the spine.
Let’s take a closer look at the
anatomy of the axial skeleton. We’ll start with the skull. The human skull is a structure
composed of 22 different bones. The large round portion of the
skull is called the cranium. The main function of the cranium is
to protect the brain. The cranium contains several
plate-like bones that are particularly hard and strong. Some of these bones are the frontal
bone in the forehead, the occipital bone in the rear of the skull, the parietal
bones that cover the largest lobes of our brain, and the temporal bones found near
our ears. The bottom of the cranium has an
opening called the foramen magnum. The word foramen refers to a
natural opening in a bone. The foramen magnum allows the
spinal cord to connect to the brain.
The front of the skull contains
several irregularly shaped bones called facial bones. Some of the facial bones are the
bones found in the orbit or socket of the eye, the zygomatic or cheekbones, and the
two small nasal bones found in our nose. The facial bones support and anchor
all of the muscles of the face that allow us to speak, blink, and communicate using
many different nuanced facial expressions. Attached to the bottom of the front
of the skull is the jawbone, also called the mandible.
Within the jaw, we find our
teeth. The teeth are often considered to
be a part of our skeletal system, but teeth are not made of bone. Teeth are harder and more rigid
than bones. They are also not able to repair
and mend themselves when broken the way that our bones do. The skull can also be divided into
an anterior and a posterior portion. Posterior is a word that means rear
or behind. An anterior means front or
forward. The term posterior skull typically
refers to the bones of the cranium, and anterior skull typically refers to the
facial bones and mandible.
Next, let’s take a look at the
bones of the thoracic cage, or rib cage. The thoracic cage is also commonly
called the rib cage. The thoracic cage serves several
different functions. It connects and supports the bones
and muscles of the arms and upper body. It surrounds and protects the
delicate tissue of the lungs and the heart, as well as other vital organs, like the
liver and kidneys. It also connects and supports the
diaphragm and intercostal muscles, which allow us to breathe. The thoracic cage consists of the
bones of the ribs, the sternum, and the thoracic vertebrae. The ribs are 12 pairs of curved,
flat bones. They stretch from the spine in the
posterior of the torso to the sternum in the anterior part of the chest.
The ribs are connected to the
sternum by a special type of cartilage called costal cartilage. The bottom two pairs of ribs are
shorter than the others. They are referred to as floating
ribs because they do not connect to the sternum at all. The sternum is also commonly called
the breastbone. It not only attaches to 20 of your
24 ribs but also serves as a point of attachment for the arms through the two
clavicle or collarbones. The thoracic vertebrae are the 12
bones of the spine that connects to the ribs. Now that we reviewed the anatomy of
the thoracic cage, let’s move on to review the anatomy of the spinal column.
The spinal column, also called the
vertebral column, stretches from the base of the skull to beneath the pelvis. The spinal column supports and
protects the delicate spinal cord, which is responsible for relaying messages to and
from the brain. The bones of the spinal column are
called vertebrae, and there are 24 individual vertebrae in the spinal column. The top seven vertebrae are called
cervical vertebrae. Cervical is a word that means
referring to the neck. Beneath these, we find the 12
thoracic vertebrae. We’ve already learned that the
thoracic vertebrae each connects to a pair of ribs. Next, we have the five lumbar
vertebrae. These are the vertebrae of the
lower back.
Attaching the bones in the
posterior of the pelvis, we find the sacrum, also sometimes called sacral
vertebrae. The sacrum is a plate of five fused
vertebrae that are generally considered to be one bone. Dangling beneath the sacrum is the
coccyx, also sometimes called the coccygeal vertebrae. The coccyx is a set of four tiny
fused vertebrae, also commonly referred to as the tailbone. Each vertebra has a unique
shape. The vertebrae become larger and
thicker as you travel down the spine, and they’re thinner and more delicate near the
top. This is because the lower vertebrae
support more of our body weight than the upper ones do. Even though each vertebra has a
unique shape, they all have some features in common.
This diagram shows one thoracic
vertebra viewed from the top. Towards the anterior side of the
bone, each vertebra has a section called the body that stacks together with the
vertebrae above and below it. Each vertebra has an opening called
the vertebral foramen, which is the space that the spinal cord passes through. And in the posterior of the bone,
each vertebra has at least one extension called a process. These are the anchor points for
tendons and ligaments that support the body and allow movement.
Joints are what we call the
connections between two or more bones. There are three major types of
joints in the human skeletal system, and some are more flexible or movable than
others. The three major joint types are
synovial joints, cartilaginous joints, and fibrous joints. Synovial joints are highly
movable. These joints are cushioned and
lubricated by a special type of fluid called synovial fluid. In the axial skeleton, you will
find synovial joints where the skull meets the spinal column and where the jawbone
attaches to the skull. Cartilaginous joints are partially
movable or mostly immovable joints. The bones in these joints are
connected to each other by cartilage. Some examples of cartilaginous
joints in the axial skeleton are the connections of the ribs to the costal cartilage
and the joints between each of the vertebrae.
Fibrous joints are immovable joints
and tend to have very little flexibility. These joints are held together by
tough fibers. Some examples of fibrous joints
found in the axial skeleton include the suture joints between the platelike bones of
the cranium. These stiff and tough joints stitch
the bones of the skull together into one rigid protective structure that houses our
delicate and important brain. The joints of the axial skeleton
generally tend to be less movable than the joints you find in the appendicular
skeleton.
Now that we’ve learned about the
anatomy of the axial skeleton as well as the types of joints we find between these
bones, let’s try a practice question.
What are the components of the
axial skeleton? (A) The pectoral and pelvic girdles
and the bones of the arms and the legs. (B) The vertebral column, the limb
bones, and the pectoral girdle. (C) The skull and the pelvic
girdle. Or (D) the vertebral column, the
skull, and the thoracic cage.
This question is about the skeletal
system. And it’s asking us to recall the
components or parts that are in the axial skeleton, which is a part of the skeletal
system. The adult human skeletal system
consists of 206 bones, as well as all of the joints that hold them together. The skeletal system is often
divided and described in two sections: the axial skeleton and the appendicular
skeleton.
The appendicular skeleton consists
of the human appendages, which we call arms and legs. The appendicular skeleton also
contains the bones that attach the appendages to the torso. And that includes our pelvic
girdle, as well as the pectoral girdle. The axial skeleton contains the
bones that fall along and around the central axis of the human body. This includes the bones of the
skull, the bones of the thoracic cage, also called the rib cage, as well as the
bones of the vertebral column, which we also call the spinal column. This means that the components of
the axial skeleton are the vertebral column, the skull, and the thoracic cage.
Let’s wrap up our lesson by taking
a moment to review some of what we’ve learned. In this video, we learned about the
structure and the function of the axial skeleton. The axial skeleton consists of the
bones of the skull, which are the bones that protect the brain, the thoracic cage,
which protects the heart, lungs, and other vital organs, as well as the bones of the
vertebral column, also called the spinal column. These bones protect the spinal
cord.
