Cranial Bones

What are the Cranial Bones

Out of the 22 bones that form the human skull, there are 8 bones that encase the brain. These bones are termed cranial bones, as they collectively form the cranium, also known as neurocranium, and braincase. Some of these bones are flat, while some are irregular. As stated, the cranium encloses and protects the brain, along with it also forms the shape of the head.

Where is the Cranium Located

The cranium is located at the top of the head. You can easily feel this structure by running your hands on the crown of your head.

How Many Cranial Bones are There in the Human Body

As mentioned, there are 8 cranial bones that are listed below:

  1. Frontal bone (Unpaired)
  2. Parietal bones (Paired)
  3. Temporal bones (Paired)
  4. Occipital bone (Unpaired)
  5. Sphenoid bone (Unpaired)
  6. Ethmoid bone (Unpaired)
Cranial Bones Labeled

Functions

As we know, all the cranial bones fuse to form the cranium. So, here are the functions of cranium:

  • It protects the brain from any external injury or shock.
  • Also, it provides a surface for the facial muscles to attach.
  • Along with these, it allows passage of the cranial nerves that are necessary for our day-to-day functioning, such as seeing, smelling, and chewing.

Anatomy of the Bones in the Cranium

The cranium is somewhat spherical, mostly resembling a baseball cap. Anatomically, the cranium is divided into two parts: cranial roof and cranial base.

Cranial Roof

Also known as calvarium, this part of the cranium is formed by the frontal, occipital, and two parietal bones.

Cranial Base

It is composed of the frontal, sphenoid, ethmoid, occipital, parietal, and temporal bones.

Now, let us discuss these individual bones in a bit detail:

1. Frontal Bone: It is an unpaired flat bone that makes up the forehead and upper part of the eye sockets.

2. Parietal Bones: This is a pair of flat bones located on either side of the head, just behind the frontal bone. It protects the brain lying underneath.

3. Temporal Bones: Another paired bone, located under each of the parietal bones. However, unlike the previous, these are irregular bones. These bones protect auditory nerves and a few ear structures that control hearing and balance.

4. Occipital Bone: It is an unpaired flat bone found at the back of the skull. It has an opening through which the spinal cord passes and connects to the brain.

5. Sphenoid Bone: An unpaired irregular bone located just below the frontal bone. It forms a large part of the skull base, as it spans the width of the skull.

6. Ethmoid Bone: Another unpaired irregular bone located in front of the sphenoid bone that forms a part of the nasal cavity.

These bones are held together by unique, immovable joints, called sutures. Sutures are made of thick connective tissue and are irregularly shaped to allow all these uniquely shaped cranial bones to join. These sutures do not fuse until adulthood, which allows the brain to continue its growth from childhood till adolescence.

Cranial Bones Mnemonic

Here are some sentences that will help you to remember the names of these cranial bones:

  1. Eight Osseous Parts Form The Skull.
  2. Ethan’s Fried Spanish Pasta Tempted Octavia

Another easy phrase would be ‘STEP OF 6’, where the 6 stands for six types of cranial bones.

The bold letters in these sentences and phrase correspond to each cranial bone’s name. Here’s what it looks like:

E: Ethmoid bone

O: Occipital bone

P: Parietal bones

F: Frontal bone

T: Temporal bones

S: Sphenoid bone

Development of the Cranial Bones

The cranial bones are developed in the mesenchymal tissue that surrounds the head end of the notochord.

FAQs

Q.1. What are the three cranial bones that contain sinuses?

Ans. The three cranial bones that contain sinuses are the frontal, ethmoid, and sphenoid bones.

References

    1. Bones of the Skull – Teachmeanatomy.info
    2. The Skull – Courses.lumenlearning.com
    3. Axial Skeleton – Training.seer.cancer.gov
    4. Skull Cranial Bones – Getbodysmart.com
    5. Cranial Bones: Parts, Location and Function – Study.com