Anatomy And Physiology

Anatomy Physiology

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Flat irregular bones that protect the brain make up the bones of the cranium. It consists of a base that sits beneath part of the brain, and a vault that provides covering. Within these bones are a number of perforations that allow for the passage of nerves, and a variety of blood and lymph vessels.

When the skull growth is complete, the bones become fixed together by fibrous tissue known as sutures. These can be thought of as dividing lines within and between bones.

The bones of the cranium are made up of:

1 Frontal bone

2 Parietal bones

2 Temporal bones

1 Occipital bone

1 Sphenoid bone

1 Ethmoid bone

Frontal Bone

This makes up the forehead and forms the upper part of the orbital cavities (eye sockets) and the ridges above the eyes, the area where the eyebrows grow. These are known as the supraorbital margins. Just above the supraorbital margins and within the bone, sinuses are located and these open into the nasal cavities. The frontal bone is connected to the parietal bones, the sphenoid, the ethmoid as well as some of the facial bones by the coronal suture. The frontal bone itself is divided into two halves by the frontal suture.

Parietal Bones

The inner surfaces of these bones are concave. They form the top and the highest sides of the skull vault, and are joined at the sagittal suture. This continues on from the frontal suture and travels towards the back of the skull where it divides into two and then forms the lambdoidal suture. It is the squamous sutures, one either side, that divide the parietal bones from the temporal bones.

Temporal Bones

These bones are located one on each side of the skull beneath the parietal bones and in front of the occipital bone. The temporal bones form part of the vault and a part of the skull base. There are four parts to each of the temporal bones.

1 The largest section makes up what is known as the squamous part. This is thin and flat and is joined to the parietal bone.

2 Just behind the ear there is a part of the bone named the mastoid process. It is here that many tiny air sinuses are located. These are necessary for the proper functions within the middle ear.

3 The section of the bone that makes up part of the skull base is known as the petrous portion. Internal structures within the ear are contained within this area.

4 A thin protrusion of bone known as the zygomatic process joins to the zygomatic bone (cheek bone) and the space between the zygomatic bone. The forward facing part of the temporal bone forms what is known as the zygomatic arch.

The lower part of the temporal bones join with the mandible (jaw bone) and this is the only movable joint of the skull, it is known as the temporomandibular joint.

Occipital Bone

This is found at the back of the head and forms part of the skull base. The occipital bone is joined to the parietal, temporal and sphenoid bones. Its inner surface is extremely concave and within this space the occipital lobe of the brain and the cerebellum are located.

Sphenoid Bone

The sphenoid bone is located at the centre at the base of the skull. It joins with the temporal, parietal and frontal bones. It is a wing-shaped bone that contains a depression known as the hypophyseal fossa and it is here that the pituitary gland is located. The sphenoid bone also consists of large sinuses that open into the nasal cavities.

Ethmoid Bone

This is found in the front section of the skull base. It forms part of the orbital cavities in the parts nearest to the nose, the nasal septum, and the nasal cavities. This is a delicate bone that contains numerous sinuses that open into the nasal cavities.

These bones together make up the bones of the cranium. The entire skull consists of many more, the majority of which comprise of the facial bones.

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