Video Transcript
In this video, we will learn to
name and identify the bones of the upper and lower appendages. We will learn about the types of
joints found in the appendicular skeleton. And we will learn about the
structures within these joints.
The adult human skeletal system
consists of 206 individual bones and all of the joints in between them. Bones are strong, rigid organs made
mostly of a special type of connective tissue called osseous tissue. Osseous is a word that means
related to bones. Bones serve many functions,
including producing red and white blood cells in our bone marrow, storing minerals,
also called salts or ions. They protect some of our most
important and delicate organs. And they provide the support and
structure that our bodies need in order to be able to move.
Interestingly, human infants
possess more bones than human adults. Humans possess about 300 bones at
birth. And their skeletons contain much
more of a different less rigid connective tissue called cartilage. Cartilage is different from bone
tissue because cartilage is softer and more flexible. Additionally, cartilage does not
possess a network of blood vessels, while bone tissue does. Over time, the nonvascular
cartilage in the baby’s skeleton develops into vascular bone tissue. And several of the baby’s bones
will fuse together. And this explains how humans start
with 300 bones but end up with only 206.
The skeletal system is often
divided into two different sections: the axial skeleton and the appendicular
skeleton. The axial skeleton consists of the
bones of the skull, the spine, and the rib cage. These are bones found along the
vertical axis of the body. The appendicular skeleton consists
of the bones of the arms and the legs, as well as the bones that connect the arms
and the legs to the axial skeleton. The arms and legs are also referred
to as appendages, which is where the appendicular skeleton gets its name.
Next, let’s investigate the anatomy
of the upper appendages, or arms. The human arm is the upper
appendage. It’s specially adapted for throwing
accuracy and for precise movement and manipulation. The upper arm is attached to the
rib cage by two bones: the scapula and the clavicle. The scapula, sometimes called the
shoulder blade, is a flat triangular bone found on the back of the upper torso. The clavicle is sometimes called
the collarbone, and it’s an S-shaped bone located near the base of the neck.
The scapula is actually not
attached to the bones of the back but instead floats above them. The scapula is attached to the
torso by its connection with the clavicle. The scapula is also attached to the
bone of the upper arm, called the humerus. The humerus extends from the
shoulder to the elbow.
The part of the arm found between
the elbow and the wrist contains two long bones. The bone that extends from the
elbow to the wrist on the side of the thumb is called the radius. The bone that extends from the
elbow to the wrist on the side of the pinky finger is called the ulna. I like to remember the difference
between these two bones by recalling that the pinky finger is the smallest of your
four fingers and that the ulna is the shorter of the two names, having only four
letters.
The bones of the wrist are called
carpals. The name of these bones comes from
the Greek and Latin words for wrist, which is karpós or carpus. There are eight small, irregularly
shaped carpal bones in the wrist. The bones of the palm of the hand
are called metacarpals. Meta- is a word part that can mean
next to or after, and we already know that carpal means wrist. The bones of the fingers are called
phalanges. Each finger contains three
phalanges, called proximal, which is another word for near, middle, and distal,
which is another word for far. The thumb only contains two
phalanges: a proximal phalanx and a distal phalanx. The word phalanx is the singular
form of the word phalanges.
Now we’re familiar with the bones
of the arm, from the scapula in our shoulder all the way to the farthest
phalanx. Next, we will investigate the
anatomy of the leg.
Humans evolved over many millions
of years to have specialized upper and lower appendages. Our distant ancestors were
four-legged organisms called tetrapod, whose forelimbs were nearly identical to the
hind limbs. We can see this evolutionary
history reflected in the fact that the bones of the human arm are homologous to the
bones of the human leg. This means that the arms and the
legs have bones in similar arrangements, even though our arms and legs carry out
different functions.
The scapula and clavicle are
sometimes referred to as the shoulder girdle or the pectoral girdle. The pelvic bones carry out a
similar function in the lower appendages and are also sometimes called the pelvic
girdle. The pelvic bones are two large,
irregular, flat bones with a shape that reminds some people of a human ear. The upper part of the pelvic bone
is called the ilium. You might be able to feel your
iliac crest if you press down on the upper outer part of your hips.
The lower part of the pelvic bone,
the part you sit on, is called the ischium. The pelvic bones are attached at
the hip joint to the femur. The femur is the largest, strongest
bone in the human body. The femur plays a role similar to
the humerus in the arm. It stretches from the hip to the
knee. Like the lower part of the arm, the
lower part of the leg possesses two bones. The larger of these two bones is
called the tibia, and it’s also sometimes referred to as the shinbone. The smaller bone found on the outer
side of the lower leg is called the fibula.
The knee joint possesses a bone
that has no equivalent in the arm. In the front of the knee, there’s a
small, round bone called the patella. We also sometimes call this bone
the kneecap. The patella helps to make sure that
our knee joint bends in one direction and not in the other. The tarsals in the foot are similar
to the carpals in the wrist. The tarsals are seven irregularly
shaped bones that make up the ankle, the heel, and the proximal part of the
foot. Extending from the tarsals, we find
the metatarsals. These five long bones make up the
main part of the arch of each foot. At the end of the metatarsals are
the phalanges. Just like your fingers, four of
your toes possess three phalanges each, while the big toe only possesses two.
These are all of the bones of our
legs from our hips all the way down to our toes. Our bones provide support and
structure to the body. But we couldn’t move without the
joints that are found between them. Joints are the connections between
bones. There are three main types of
joints in the human skeletal system. They are fibrous, cartilaginous,
and synovial. Fibrous joints are generally found
between bones that are in very close contact with each other. And these bones are connected by
fibrous tissue. A cartilaginous joint is when two
bones are joined by cartilage. Finally, synovial joints are freely
moving joints. They are cushioned and lubricated
by a special fluid called synovial fluid.
Fibrous joints tend to be immovable
joints, and cartilaginous joints can be immovable or slightly movable. Synovial joints are adapted to
allow a wide range of motions. These are the most common type of
joint found in your highly articulated or movable appendicular skeleton. This diagram shows a cross section
of a simplified synovial joint. In yellow, we see the synovial
cavity that is filled with the synovial fluid. Synovial fluid is very
slippery. It lubricates the joints and
reduces friction.
The ends of these bones would also
be coated with a thin layer of articular cartilage. Articular cartilage also decreases
friction within joints. The bones are attached to each
other by fibrous organs called ligaments. Ligaments function to connect bones
to other bones.
Pictured in red, we see two
muscles. The muscles are what cause the
joint to move. When this upper muscle contracts,
the joint will straighten. When this lower muscle contracts,
the joint will bend further.
The muscles are connected and
anchored to the bone by a fibrous organ called a tendon. Tendons serve the function of
connecting muscles to other body parts, often bones. Almost all of our most movable
joints are synovial joints similar to this one. This includes our shoulders, hips,
knees, elbows, wrists, and ankles. This also includes the joints
between the phalanges in our fingers and the phalanges in our toes. The pivot joint in our neck and the
hinge joint in our jaw are also examples of synovial joints.
Now that we’ve learned about the
bones of the appendicular skeleton as well as the joints that connect them, let’s
try a practice question.
Which bodily structure’s bones are
made up of the carpals, metacarpals, and phalanges?
This question provides us with the
names of three different sets of bones. And then it asks us to recall which
bodily structure these bones belong to. Well, phalanges is the scientific
name for the bones in our fingers and the bones in our toes. So we can narrow our answer choices
down to either the hand or the foot.
Here, I’ve drawn a simplified
diagram of the bones of the hand and the bones of the foot. We’ve already recalled that the
fingers and toes are called phalanges. In the foot, the bones of the ankle
and heel are called tarsals and the bones of the arch of the foot are called
metatarsals, while in the hand the bones of the wrist are called carpals and the
bones of the palm of the hand are called metacarpals. So the bodily structure that’s
bones are made up of the carpals, metacarpals, and phalanges are the hands.
Let’s wrap up our lesson by taking
a moment to review what we’ve learned. In this video, we learned about the
anatomy of the appendicular skeleton. We learned to name and identify the
bones of the shoulder girdle, the pelvic girdle, the arm, the leg, the hand, and the
foot. We learned about the structure of
synovial joints as well as the functions of tendons and ligaments.
