The Skeletal System

Summary

This script offers an in-depth exploration of the human skeleton, highlighting its two main parts: the axial skeleton, consisting of the skull, vertebral column, and thoracic cage, and the appendicular skeleton, comprising the limbs. It details the skull's 22 bones, the spine's 26 vertebrae, and the thoracic cage's ribs and sternum. The limbs are dissected, from the clavicle and scapula to the intricate bones of the hands and feet, emphasizing the skeleton's complexity and function in supporting and protecting the body.

Takeaways

• 🦴 The human skeleton consists of around 206 bones, cartilage, joints, and ligaments, making up approximately 20% of an adult's body mass.
• 💀 The skull is made of 22 different bones, divided into cranial bones that protect the brain and facial bones that structure the face.
• 🔒 The cranium's bones are connected by sutures, including the coronal, sagittal, lambdoid, squamous, and occipitomastoid sutures.
• 🕳️ The skull features foramina, such as the foramen magnum, which allows the passage of the spinal cord.
• 🦷 The mandible is the lower jawbone, and the maxillary bones form the upper jaw and part of the face.
• 📐 The vertebral column, or spine, is composed of 26 irregular bones, divided into cervical, thoracic, lumbar, sacral, and coccygeal sections.
• 🌈 The spine supports the body in an S-shape, with intervertebral discs acting as shock absorbers.
• 🏗️ The thoracic cage includes the sternum and ribs, with costal cartilage connecting them to the spine.
• 🦾 The appendicular skeleton includes the limbs, pectoral girdle, and pelvic girdle, providing attachment and mobility.
• 🤲 The upper limb has the humerus in the arm, radius and ulna in the forearm, and multiple bones in the wrist and hand.
• 🦵 The lower limb features the femur in the thigh, tibia and fibula in the leg, and tarsals, metatarsals, and phalanges in the foot.

Q & A

How many bones are there in the adult human skeleton?

There are around two hundred and six bones in the adult human skeleton.

What are the main components of the skeletal system besides bones?

Besides bones, the skeletal system also includes cartilage, joints, and ligaments, which together make up around twenty percent of a person’s body mass.

What are the two main sections of the human skeleton?

The two main sections of the human skeleton are the axial skeleton and the appendicular skeleton.

What are the functions of the cranial bones in the skull?

The cranial bones in the skull serve to protect the brain, while the facial bones provide structure to the face.

How many bones make up the cranium and what are some of their names?

The cranium is made up of eight bones: the frontal bone, two parietal bones, the occipital bone, two temporal bones, the sphenoid bone, and the ethmoid bone.

What is the function of the sutures in the skull?

Sutures are the lines where most of the bones in the skull are connected, allowing for growth and providing some flexibility.

What is the vertebral column made up of and what is its general shape?

The vertebral column, also known as the spine, is made up of twenty-six irregular bones that form a flexible, curvy S-shape structure.

How many sections can the spine be divided into and what are they?

The spine can be divided into five sections: cervical vertebrae (7), thoracic vertebrae (12), lumbar vertebrae (5), sacrum, and coccyx.

What is the function of the intervertebral discs in the spine?

The intervertebral discs act as shock absorbers between each vertebra, providing cushioning during movement.

What is the composition of the thoracic cage and its role?

The thoracic cage is composed of the sternum, ribs, and costal cartilage. It provides protection for the organs in the thorax and contributes to the respiratory process.

What are the two main components of the appendicular skeleton and their functions?

The appendicular skeleton is mainly composed of the limbs and the pectoral and pelvic girdles, which attach the limbs to the axial skeleton and provide support and mobility.

How many bones are there in each hand and foot, and what are their types?

Each hand has 27 bones: 8 carpals, 5 metacarpals, and 14 phalanges. Each foot has 26 bones: 7 tarsals, 5 metatarsals, and 14 phalanges.

What is the significance of the foramen magnum in the skull?

The foramen magnum is a large hole at the base of the skull through which the spinal cord passes to connect with the brain.

What are the main ligaments in the spine and their functions?

The main ligaments in the spine include the anterior and posterior longitudinal ligaments, which run down the front and back of the column, and shorter ligaments that connect adjacent vertebrae. They help to hold the vertebrae together and provide stability.

What is the difference between true ribs and false ribs in the thoracic cage?

True ribs are the first seven pairs that attach directly to the sternum via costal cartilage. False ribs are the remaining five pairs, with three attaching indirectly to the sternum and the last two, the floating ribs, not attaching to the sternum at all.

Outlines

00:00

💀 Human Skeleton Overview

The script introduces the human skeleton, emphasizing its composition of around 206 bones, cartilage, joints, and ligaments accounting for 20% of body mass. It distinguishes between the axial and appendicular skeletons, with the axial skeleton consisting of the skull, vertebral column, and thoracic cage, and the appendicular skeleton comprising the limbs. The skull's structure is highlighted, with 22 bones divided into cranial bones that protect the brain and facial bones that give structure to the face, connected by sutures. The vertebral column's role in supporting the body's weight and its division into cervical, thoracic, lumbar, sacral, and coccygeal regions is also discussed.

05:05

🦴 Detailed Anatomy of the Skull and Spine

This paragraph delves deeper into the skull's anatomy, describing the cranial bones, their connections via sutures, and the presence of foramina for nerves and blood vessels. It also covers the facial bones, including the mandible, maxillary bones, and others, with a special mention of the hyoid bone. The vertebral column is then explored in detail, explaining the structure and function of individual vertebrae, their processes, and variations across different regions of the spine. The paragraph also discusses the thoracic cage, including the sternum and ribs, and distinguishes between true ribs, false ribs, and floating ribs.

10:12

🤲 Appendicular Skeleton and Joints

The final paragraph focuses on the appendicular skeleton, starting with the pectoral girdle and moving through the upper limb, detailing the bones of the arm, forearm, and hand, including the carpals, metacarpals, and phalanges. It then describes the pelvic girdle and lower limb, highlighting the femur, tibia, and fibula, and their respective features. The foot's structure is also outlined, with the tarsals, metatarsals, and phalanges of the toes. The paragraph concludes by setting the stage for a discussion on joints, which are critical for the skeleton's function and mobility.

Keywords

💡Skeletal System

The skeletal system is the framework of bones, cartilage, joints, and ligaments that provide support and structure to the human body. It is the main focus of the video, which discusses its composition and function. The script mentions that it is comprised mainly of bones, around two hundred and six in an adult, and includes cartilage, joints, and ligaments making up approximately twenty percent of a person’s body mass.

💡Axial Skeleton

The axial skeleton is one of the two main sections of the human skeleton, which includes the skull, vertebral column, and thoracic cage. It forms the central axis of the body and is crucial for protecting vital organs such as the brain and heart. The script elaborates on the components of the axial skeleton, starting with the skull made of twenty-two different bones.

💡Cranial Bones

Cranial bones are the bones that form the skull and protect the brain. They are part of the axial skeleton and are connected by sutures. The script specifies that there are eight cranial bones, including the frontal bone, parietal bones, occipital bone, and others, which together form the cranial cavity housing the brain.

💡Vertebral Column

The vertebral column, also known as the spine, is a flexible structure made up of twenty-six irregular bones. It supports the body, allowing for movement and protection of the spinal cord. The script describes the spine's division into cervical, thoracic, lumbar, sacral, and coccygeal regions, each with specific characteristics and functions.

💡Intervertebral Discs

Intervertebral discs are cushion-like structures located between each vertebra, acting as shock absorbers and allowing for flexibility in the spine. They consist of a nucleus pulposus and an anulus fibrosus. The script mentions their role in the spine's functionality, emphasizing their importance in movement and protection against impact.

💡Pectoral Girdle

The pectoral girdle is a part of the appendicular skeleton that connects the upper limbs to the axial skeleton. It is composed of the clavicle and scapula, providing support and mobility to the arms. The script describes the pectoral girdle's structure and its role in attaching the limbs, highlighting the clavicle's connection to the manubrium and the scapula's attachment to the clavicle.

💡Appendicular Skeleton

The appendicular skeleton includes the limbs and their associated structures, such as the pectoral and pelvic girdles. It is responsible for movement and interaction with the environment. The script explains that the appendicular skeleton is mainly the limbs but also includes other components like the pectoral girdle, which is crucial for upper limb attachment and movement.

💡Pelvic Girdle

The pelvic girdle is the lower counterpart to the pectoral girdle, attaching the lower limbs to the axial skeleton. It provides stability and supports the weight of the upper body. The script details the pelvic girdle's composition, which includes the sacrum and two hip bones, and its role in the stability and support of the lower limbs.

💡Femur

The femur, or thigh bone, is the longest, strongest, and heaviest bone in the human body. It plays a critical role in supporting the body's weight and facilitating movement. The script describes the femur's features, such as the head, greater and lesser trochanters, and condyles, which are essential for the thigh's function in locomotion.

💡Joints

Joints are the points where bones meet and allow for movement. They are critical to the function and mobility of the skeleton. The script indicates that while joints are not the primary focus of the initial explanation, they are essential for understanding the full functionality of the skeletal system and will be discussed later in the video.

💡Foramina

Foramina are openings in bones that allow for the passage of nerves, arteries, and veins. They are important for the circulation and sensory functions of the body. The script specifically mentions the foramen magnum, a large opening at the base of the skull through which the spinal cord passes, illustrating the concept of foramina in the context of the skull's structure.

Highlights

The skeletal system consists of around 206 bones, cartilage, joints, and ligaments, making up approximately 20% of an adult's body mass.

The human skeleton is divided into the axial and appendicular skeletons.

The axial skeleton includes the skull, vertebral column, and thoracic cage.

The skull is composed of 22 bones, including cranial and facial bones, with most being flat and connected by sutures.

The cranium has a vault and a base, divided into anterior, middle, and posterior cranial fossae, forming the cranial cavity for the brain.

There are eight main cranial bones, including the frontal, parietal, occipital, temporal, sphenoid, and ethmoid bones.

The vertebral column, or spine, is made up of 26 irregular bones forming a flexible, S-shaped structure.

The spine is divided into cervical, thoracic, lumbar, sacral, and coccygeal sections, with vertebrae increasing in size to support more weight.

Each vertebra has a body, vertebral arch, and various processes like the spinous process and transverse processes.

The thoracic cage includes the sternum, ribs, and costal cartilage, providing protection for vital organs.

The appendicular skeleton comprises the limbs and other components like the pectoral and pelvic girdles.

The pectoral girdle consists of the clavicle and scapula, attaching the upper limbs to the axial skeleton.

The upper limb includes the humerus, radius, ulna, and numerous bones in the wrist (carpals), palm (metacarpals), and fingers (phalanges).

The pelvic girdle provides stability and attaches the lower limbs to the axial skeleton, with the sacrum and hip bones.

The lower limb features the femur, tibia, and fibula in the thigh and leg, and the foot includes the tarsals, metatarsals, and toes' phalanges.

Joints are critical for the function and mobility of the skeleton, and will be discussed following the overview of bones.

Transcripts

Professor Dave again, let’s look at the human skeleton.

Now that we’ve learned about the structure of bones, we are ready to take a look at how

they are assembled in the body.

The skeletal system is comprised mainly of bones, around two hundred and six of them

in an adult to be specific, but there is also a good amount of cartilage, joints, and ligaments,

which all together make up around twenty percent of a person’s body mass.

We will get to joints a little bit later, first let’s check out all the different

bones in the body.

As we recall, there are two sections to the human skeleton, those being the axial skeleton,

made of the skull, vertebral column, and thoracic cage, and the appendicular skeleton, made

more or less of just the limbs.

Let’s go through the axial skeleton first, starting at the top with the skull.

The skull is a fascinating structure, made of twenty two different bones.

Cranial bones are the ones that protect the brain, and facial bones are the ones that

give structure to the face.

Most of the bones in the skull are flat bones, and in the cranium these are connected at

serrated lines called sutures.

The cranium is made of a vault, as well as a base, and we should note that the base is

divided into the anterior, middle, and posterior cranial fossae.

Together, these produce the cranial cavity, where the brain sits.

There are also ear cavities and nasal cavities, as well as orbits, which house the eyes.

All together there are eight cranial bones.

There is the frontal bone, two large parietal bones, the occipital bone, two temporal bones,

the sphenoid bone, and the ethmoid bone.

The cranial bones are connected, as we said, by sutures, and those have specific names

as well.

These are the coronal, sagittal, lambdoid, squamous, and occipitomastoid sutures.

We should also mention the foramina, which are holes that nerves and arteries and veins

pass through, most notably the foramen magnum at the base of the skull through which the

spinal cord passes.

Moving on to the facial bones, of which there are fourteen, we can start with the mandible,

which is the lower jawbone.

Then there are maxillary bones, which form the upper jaw and part of the face.

Next we have two zygomatic bones which are the cheekbones, nasal bones which make up

the bridge of the nose, lacrimal bones, palatine bones, the vomer, and inferior nasal conchae.

Lastly, technically not part of the skull, there is also the hyoid bone, which sits just

below the mandible, and does not connect with any other bone.

Next up in the axial skeleton is the vertebral column, also called the spinal column, or

simply the spine.

This is comprised of twenty six irregular bones that come together to form a flexible

structure in a curvy S-shape, and this supports everything from the skull to the pelvis.

The spine can be divided into five sections.

At the top we have the cervical vertebrae, which are the first seven.

The next twelve are called the thoracic vertebrae.

The remaining five are called the lumbar vertebrae.

We should note that the vertebrae get larger as we go down, in order to support more and

more weight.

Below the vertebrae we can find the sacrum, which is actually five vertebrae fused together,

and lastly, below the sacrum there is the coccyx, otherwise known as the tailbone, which

is made of a few tiny vertebrae fused together.

Of course there is much more to the spine than just the vertebrae.

There are lots of ligaments keeping everything together.

The main ones are the anterior and posterior longitudinal ligaments, running down the front

and back of the column from the neck to the sacrum.

There are also shorter ligaments that connect adjacent vertebrae, as well as intervertebral discs.

These are cushiony pads made of a nucleus pulposus, which is the more elastic part,

surrounded by an anulus fibrosus, with lots of collagen.

These are found in between each vertebra, acting as shock absorbers when we run and jump.

Now let’s look a little closer at an individual vertebra.

These all have a body and a vertebral arch.

The hole is called the vertebral foramen, and the spinal cord passes through here, which

we will discuss later.

The vertebral arch is made of two pedicles and two laminae, and from these project various

processes.

These are the spinous process, two transverse processes, as well as the superior and inferior

articular processes.

The vertebrae vary slightly depending on where they are found in the column.

Cervical vertebrae have a spinous process that is very short, a vertebral foramen that

is large, and an additional transverse foramen to accommodate vertebral arteries.

Thoracic vertebrae have a spinous process that is long and points down, and they also

exhibit structures called demifacets which connect to the ribs.

Lumbar vertebrae, being much larger, have pedicles and laminae that are short and thick,

as well as other slight discrepancies.

The last part of the axial skeleton is the thoracic cage.

This is essentially comprised of the sternum and the ribs, as well as a lot of costal cartilage.

The sternum is a flat bone right in the middle of the thorax, and it is made from three smaller

bones that have fused together.

From top to bottom these are the manubrium, the body, and the xiphoid process.

Then there are twelve pairs of ribs that project from the vertebrae.

The first seven pairs attach directly to the sternum via sections of costal cartilage,

and these are called true ribs.

Then there are five pairs of false ribs, three of which attach to the sternum indirectly,

with costal cartilage joining the cartilage from ribs above, and then the last two are

called floating ribs, because they don’t attach to the sternum at all.

Ribs are flat bones that get longer going from pair one to seven, and then shorter again

from eight to twelve.

With the axial skeleton complete, let’s move on to the appendicular skeleton.

While this is mainly just our limbs, there are other components to mention as well.

Let’s start with the pectoral girdle.

This is comprised of the clavicle, or collarbone, and the scapula, or shoulder blade, which

together give structure to the shoulder, thereby attaching the upper limbs to the axial skeleton.

The clavicle has a sternal end where it attaches to the manubrium, and an acromial end, which

joins the scapula.

The scapula is a thin, flat bone, roughly triangular, and it has three borders, the

superior, the medial or vertebral, and the lateral or axillary.

From here, we move on to the upper limb.

This consists of the arm, forearm, and hand.

Though colloquially we think of this whole thing as an arm, when speaking in terms of

anatomy, it is just this upper portion that we call the arm, so let’s start there.

In the arm we find the humerus, a typical long bone, with its greater and lesser tubercle,

radial groove, medial and lateral epicondyle, radial and coronoid fossa, trochlea, and capitulum.

Moving on to the forearm, we now see two bones, the radius and the ulna.

These are connected all the way down by the interosseous membrane, a flexible ligament.

The ulna is slightly longer, with its olecranon and coronoid process.

The radius goes from wide to thin the other way, with a thin head, the radial tuberosity,

and a radial styloid process.

From there we see the hand, which has many separate bones.

The carpus, or wrist, is made of eight short bones called carpals.

These are the scaphoid, lunate, triquetrum, pisiform, and then the trapezium, trapezoid,

capitate, and hamate.

Next we see the five metacarpals, which make up the palm of the hand, and they are simply

named one through five, from thumb to pinky.

These connect to the phalanges, which are the bones that make up your fingers.

There are fourteen of these bones per hand, three per finger, which are the distal, middle,

and proximal phalanges, except the thumb which has two, as it has no middle phalanx.

Moving back over to the torso, we see the pelvic girdle.

This attaches the lower limbs to the axial skeleton just like the pectoral girdle did

for the upper limbs, although this one has far less mobility and far more stability than

the other.

This girdle starts at the sacrum we described earlier, and continues with two hip bones.

These are made of three separate bones at birth, which fuse to become one by adulthood,

but we still describe the regions of the hip bone as being the ilium, ischium, and pubis.

Lastly, the lower limb contains very thick bones, allowing us to run and jump effectively.

The thigh is made of a single bone just like the arm, and this one is called the femur,

which is the largest bone in the body.

Here we see the head, with a small pit called the fovea capitis.

Then the greater and lesser trochanter, the intertrochanteric crest, the gluteal tuberosity,

linea aspera, medial and lateral condyles, and epicondyles, intercondylar fossa, and patella.

From there, we go to the leg, which like the forearm, contains two bones, the tibia and

the fibula.

Again, we see an interosseous membrane between them.

In the larger tibia, we see the medial and lateral condyles, the intercondylar eminence,

tibial tuberosity, anterior border, medial malleolus, and fibular notch.

The fibula is much thinner, with its head and lateral malleolus.

Then we get to the foot, which is similar to the hand.

We see the tarsus, made of seven bones called tarsals.

The biggest two, the talus and calcaneus, make up the ankle.

Then there is the cuboid, the navicular, and the medial, intermediate, and lateral cuneiform bones.

Next we see the metatarsus, with five long metatarsals, again numbered one through five.

Also like the hand, we see fourteen phalanges, three per toe, except two for the big toe,

also known as the hallux.

So that wraps up our basic tour of the human skeleton, at least from the standpoint of

the bones, which are the primary component.

But there are other structures that are critical to the function and mobility of the skeleton,

and these are called joints, so let’s move forward and learn about these now.