Skeletal System: Parts, Function, and 5 Fascinating Facts

Have you ever wondered why can’t I rotate my head 270 degrees like an owl or how our body stands upright without collapsing on itself like a jellyfish?

Well, the answer to all these questions is your skeletal system. It is the framework that gives your body its shape. To know the answer to these questions above, keep reading as in the following sections, we will discover our skeletal system together. We will talk about the different components of the skeletal system, its function, and how to keep it healthy. At the end of this article, you will find 5 fun facts about your skeletal system.

Table of content:

The Components of the Skeletal System

Your skeletal system is made up of bones, cartilage, ligaments, and tendons. In the following sections, we are going to briefly talk about each component of your skeletal system, and then we will talk about your skeleton in detail.

Bones

A bone is composed of 4 main layers from the outside inward:

  • Periosteum: this tough membrane is the most outer layer of a bone. It works as a protective cover layer.
  • Compact bone: this layer lies just under the periosteum. It is hard and white. It supports the inner layer of the bone.
  • Spongy bone: It is also called cancellous bone. It lies just under the compact bone layer. It is softer and thinner than compact bone. It is full of trabeculae (a meshwork and hence is called spongy). It contains bone marrow inside its trabeculae, which produces all blood cell types.
  • The medullary cavity. This is the innermost layer of your bone. It also contains bone marrow.
Bone parts. Skeletal system.

Want to know more about your bones and how they work? Check out this article. You can also watch this video on how bones work.

Cartilage

At the end of each long bone, you will find a soft and rubbery substance that covers the end of that bone where it meets another bone. This layer works as a cushion for your bones. It protects the bone from damage when friction occurs during movement. Unfortunately, this protective layer degenerates as you age by wear and tear.

Ligaments

These are tough bands of connective tissue that hold your bones together. Some of the most important ligaments in your body are found at your knee joint. Your knee joint is held in place by four strong ligaments. These are:

  • The medial collateral ligament.
  • The lateral collateral ligament.
  • The anterior cruciate ligament.
  • The posterior cruciate ligament.

Do you know that ligaments are not just connecting one bone to another? They are also present deep inside your body to support your internal organs and keep them in place. Some of the internal organs that are supported and held in place by ligaments are:

  • The liver.
  • The stomach.
  • The colon.
  • The female uterus.

Tendons

These are tough bands that lie at the end of each skeletal muscle. They connect your muscles to the underlying bone. One of the most famous tendons in your body is Achilles tendon. This tendon connects your calf muscles to the heel bone.

So you can tell now that one of the main differences between a tendon and a ligament is the structures they connect.

  • A ligament connects one bone to another bone.
  • A tendon connects a muscle to a bone.
Tendon vs ligament.

Now, after knowing the components of your skeletal system, we need to talk about the human skeleton. Your skeleton contains 206 bones which are classified into two main categories:

Your Skeleton

  • The axial skeleton
  • The appendicular skeleton
The skeletal system.
A human skeleton diagram with titled main parts of the skeletal system.

The Axial Skeleton

This is the part of your skeleton that lies in the midline of your body. It contains 80 bones that form your skull, vertebral column, rib cage and other small bones.

The Skull

You may think for a while that your skull is only one big bone. But it is made up of about 22 bones tightly attached to each other. These bones, however, fuse together as you age, except for your mandible (the lower jaw).

The infant skull is soft, and its bones are separated from each other to allow the brain to grow and expand. You can even feel a hollow area at the front of a baby’s head, so be careful not to press on it.

These 22 bones of your skull are further classified into two groups:

  • The facial bones: Fourteen bones are present in the front of your head (your face). They play an important role in your face shape and support your eyes, nose, and mouth. These bones include 6 paired and 2 unpaired bones. The first two bones below are the unpaired ones. They are:
    • The mandible.
    • The vomer.
    • Maxilla.
    • Zygomatic bone.
    • Nasal bone.
    • The inferior nasal conchae.
    • Palatine bone.
    • Lacrimal bone.
  • The cranial bones: lie at the back and upper part of your head and are 8 in number. They protect your brain from injury. They are named as follows;
    • One frontal bone.
    • Two parietal bones.
    • Two temporal.
    • One occipital bone.
    • One sphenoid bone.
    • One ethmoid bone.
Human skull.
Side view of the human skull

The Vertebral Column

Your vertebral column is made up of 33 bones. These bones are named according to the region they are present at in your body.

These are divided as follows:

  • Seven cervical vertebrae: found in the head and neck region.
  • Twelve thoracic vertebrae: found in your upper back.
  • Five lumbar vertebrae: found in your lower back.
  • One sacral bone: found below your lumbar vertebrae.
  • One coccygeal bone: is also called the tailbone and is the lowermost bone of your spine.

But if you do the math (7 + 12 + 5 + 1 +1), you will get a total sum of 26. So, where are the rest of these bones?

Well, that is because your sacrum is composed of 5 vertebrae fusing together to form only one bone. Your coccyx is also composed of 4 vertebrae that fuse together at the end of your spine.

The correct calculation should be (7 + 12 + 5 + 5 + 4), and there you get a total of 33.

The Thoracic Cage

Also known as your rib cage. It is made up of the following bones:

  • The sternum (also known as the breastbone).
  • Twelve pairs of ribs.
  • Twelve thoracic vertebrae.
Rib cage. Skeletal system.

These ribs are then classified according to their attachment to the sternum into:

  • True ribs: these are the first seven pairs of ribs. They are called true because they have their own costal cartilage band that allows them to attach to the sternum directly.
  • False ribs: these include the last five ribs. Ribs number 8, 9, and 10 are connected to the sternum through the costal cartilage of the previous rib (rib number 7). They do not have their own costal cartilage, which is why they are called “false”.

The last two ribs are so unique. Besides being false ribs, they do not have any attachment point at all to the sternum. And that is why they are called “floating ribs”. They are attached to the muscles of the abdominal wall instead.

But do you know why these ribs are designed as such, and why do we have floating ribs at the end of our rib cage?

Well, that is so vital for your body as this design gives your chest more freedom to expand during inspiration. It also allows your internal organs that lie just below the diaphragm (like your stomach and liver) to expand easily without causing discomfort or injury to these organs.

Just imagine how it would be difficult and restraining for you to take a deep breath if your rib cage encircled you to the end.

Other Small Bones

These include:

  • The Hyoid bone: a small U-shaped bone that lies just below your lower jaw. It works as an attachment point for some muscles and ligaments in your neck.
  • The auditory ossicles. These are 3 tiny bones located deep in your skull’s temporal bone (especially in each one of your middle ears). They work together to transmit the sound waves your outer ear receives to the inner ear. They also play a significant role in the amplification of sound. They are called:
    • The malleus (also known as the hammer).
    • The incus (also called the anvil).
    • The stapes (stirrup).

The Appendicular Skeleton

This part of your skeleton lies in the periphery and has a bigger number of bones. It has 126 bones that form your shoulder, pelvis, legs and arms.

The Shoulder (Pectoral) Girdle

Your arms get attached to your axial skeleton through the shoulder girdle.

Your shoulder girdle is composed of the following two bones:

  • The clavicle (the collarbone).
  • The scapula (the shoulder blade).

The Upper Limbs

Your upper limb is a term used to describe your arm, forearm, and hand. Each limb contains around 30 bones.

These bones are:

  • The humerus: a bone that is present in your arm.
  • The radius: one of the two bones that are present in your forearm.
  • The ulna: the second bone found in your forearm.
  • Carpal bones: eight bones found in your wrist area.
  • Metacarpal bones: five bones seen in your hand.
  • Phalanges: fourteen bones that make up your five fingers. Each finger in your hand has 3 phalanges except for the thumb, which has only two.

The upper part of your humerus and the scapula make up the shoulder joint. At the same time, the lower part of your humerus, together with the upper part of your ulna and radius, make up the elbow joint.

See the diagram of the skeleton above to get a clear picture of the bones mentioned above.

The Pelvic Girdle

Your legs get attached to your axial skeleton through the pelvic girdle. It is made up of the hip bone, which in turn is made up of three bones fused together.

These bones are:

  • The ileum.
  • The ischium.
  • The pubis.

The Lower Limbs

Like the upper limb, the number of bones in each one of your lower limbs is 30.

These bones are:

  • Femur: a bone that is seen in your thigh (upper leg).
  • Tibia: one of the two bones seen in your lower leg. It forms the main support for your lower leg.
  • Fibula: the second bone that forms your lower leg skeleton. It is thinner and smaller than your tibia.
  • Patella: this is your kneecap.
  • Tarsal bones: seven bones that make up your ankle.
  • Metatarsal bones: five bones that are found in your foot.
  • Phalanges: fourteen bones that are seen in your toes. They have the same distribution as in your fingers.

The upper part of your femur, together with the hip bone, makes the hip joint, while the lower part of your femur, the patella and the upper part of your tibia make up the largest joint in your body; the knee joint.

Want to play with a 3d interactive diagram of your skeleton and other body systems? Check out this website.

The Functions of the Skeletal System

Your skeletal system is responsible for protecting the vital organs inside your body, besides other important functions.

The main functions of your skeletal system are:

  1. First, it supports your body and gives it its shape.
  2. Second, your joints allow you to move your body in different directions with a wide range of movement, especially in your limbs.
  3. Third, your skeleton provides attachment points for all your skeletal muscles.
  4. It also protects your internal organs from injuries:
    • The skull protects your brain inside it.
    • Your rib cage protects both your heart and lungs.
    • Your vertebral column protects the spinal cord.
  5. It acts as a mineral reservoir. Your bones have a massive amount of calcium, phosphorus, and other minerals that get released from your bone when your body needs them.
  6. It contains bone marrow. The bone marrow is responsible for producing all types of cells that are present in your blood: white blood cells (WBCs), red blood cells (RBCs), and platelets.

How to Keep Your Skeletal System Healthy

to keep your skeletal system healthy, you need to pay more attention to what you eat.

Here are 4 things to do to keep your skeletal system robust and fit.

  1. Make sure to get enough sun exposure. Doing so will give you an adequate amount of Vitamin D, which is essential for your bone health.
  2. Eat plenty of food containing calcium, like yoghurt, milk, and leafy vegetables like broccoli. It is also good for strong bones.
  3. Exercise regularly.
  4. Try reducing your weight to the most optimal and healthier range. Reducing your weight will lessen the pressure put on your bones to transmit your body weight. This will make running or doing any other kind of exercise so easy for you.

Conclusion

Now it’s time to tackle the question mentioned at the beginning of this article. Why can’t we, as humans, rotate our heads 270 degrees like owls? Check out this article to know why.

Time to finish this article with 5 fun facts about the skeletal system.

  1. The number of bones you have in your skeleton varies as you age. The number of bones in your skeleton as an adult is 206 bones. However, this number is higher in childhood. This is because as you age, some of your bones fuse together, making the number of bones you have as an adult fewer than a child.
  2. Male and female skeletons are different. You can identify the sex of a person from their bones after death. For example, the female pelvic bones are wider and shorter to make it easier for pregnancy and childbirth.
  3. The only movable bone in your skull is your mandible.
  4. Your hyoid bone is the only bone in your body that is not attached to another bone (it does not form a joint with any other bone). Instead, it is a free-floating bone under your jaw.
  5. The femur is the longest bone in your body, and the stapes (one of your auditory ossicles) is the smallest.

Want to test yourself out on the skeletal system? Check out the quiz below.

Q1. All of the following are parts of the axial skeleton except:

  1. The skull.
  2. The vertebrae.
  3. The sternum.
  4. The radius.

Q2. Which of these bones make up your knee joint:

  1. 10, 11, and 12.
  2. 17, 18, and 19.
  3. 4 and 5.
  4. 9 and 10.

Q3. The bone numbered 10 in the diagram is called:

  1. Humerus.
  2. Radius.
  3. Tibia.
  4. Femur.
skeletal system,skeleton LearningMole

Q4. Your bone marrow is responsible for the following:

  1. Produce RBCs.
  2. Produce WBCs.
  3. Produce platelets.
  4. All of the above.

Q5. Which one of the following is not a function of your skeletal system:

  1. Produces all blood cell types in the bone marrow.
  2. Supports your body.
  3. Controls your blood pressure.
  4. Allows you to move.

Q6. Which of the following is false about ligaments:

  1. They connect bones together.
  2. They are part of your skeletal system.
  3. They attach muscles to bones.
  4. They support some of your internal organs.

Q7. Which of the following statements is true regarding tendons:

  1. They are not part of your skeletal system.
  2. They support some of your internal organs.
  3. They cover the tip of your long bones.
  4. They attach your muscles to the underlying bones.

Q8. One of the following does not belong to your appendicular system:

  1. The skull.
  2. The scapula.
  3. The femur.
  4. The humerus.

Q9. Which of these ribs are called floating:

  1. Ribs 10 and 11.
  2. Ribs 8 and 9.
  3. Ribs 11 and 12.
  4. Ribs 1 and 2.

Q10. The number of your thoracic vertebrae is:

  1. Five.
  2. Seven.
  3. Four.
  4. Twelve.

The Correct Answers

Q1 – 4

Q2 – 1

Q3 – 4

Q4 – 4

Q5 – 3

Q6 – 3

Q7 – 4

Q8 – 1

Q9 – 3

Q10 – 4

And if you are interested in knowing how your heart works, check out this article.

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