Component Parts of the Head

Skull

The many bones of the head collectively form the skull . Most of these bones are interconnected by sutures, which are immovable fibrous joints.

In the fetus and newborn, large membranous and unossified gaps (fontanelles) between the bones of the skull, particularly between the large flat bones that cover the top of the cranial cavity , allow:
the head to deform during its passage through the birth canal; and
postnatal growth.

Most of the fontanelles close during the first year of life. Full ossification of the thin connective tissue ligaments separating the bones at the suture lines begins in the late twenties, and is normally completed in the fifth decade of life.

There are only three pairs of synovial joints on each side in the head. The largest are the temporomandibular joints between the lower jaw (mandible) and the temporal bone. The other two synovial joints are between the three tiny bones in the middle ear, the malleus, incus, and stapes.

Cervical vertebrae
The seven cervical vertebrae form the bony framework of the neck.
Cervical vertebrae (Fig A) are characterized by:

• small bodies;
• bifid spinous processes; and
• transverse processes that contain a foramen (foramen transversarium). 

Together the foramina transversarium form a longitudinal passage on each side of the cervical vertebral column for blood vessels (vertebral artery and veins) passing between the base of the neck and the cranial cavity.
The typical transverse process of a cervical vertebra also has anterior and posterior tubercles for muscle attachment. The anterior tubercles are derived from the same embryological elements that give rise to ribs in the thoracic region. Occasionally, cervical ribs develop from these elements, particularly in association with the lower cervical vertebrae.

The upper two cervical vertebrae (CI and CII) are modified for moving the head (Fig. B-E).

Hyoid bone

The hyoid bone is a small U-shaped bone (Fig. A) oriented in the horizontal plane just superior to the larynx, where it can be palpated and moved from side to side.
The body of hyoid bone is anterior and forms the base of the U.
The two arms of the U (greater horns) project posteriorly from the lateral ends of the body.

The hyoid bone does not articulate directly with any other skeletal elements in the head and neck.

The hyoid bone is a highly movable and strong bony anchor for a number of muscles and soft tissue structures in the head and neck. Significantly, it is at the interface between three dynamic compartments:

• superiorly, it is attached to the floor of the oral cavity;
• inferiorly, it is attached to the larynx;
• posteriorly, it is attached to the pharynx

Muscles
The skeletal muscles of the head and neck can be grouped on the basis of function, innervation, and embryological derivation.

In the head
The muscle groups in the head include:

• the extra-ocular muscles (move the eyeball and open the upper eyelid);
• muscles of the middle ear (adjust the movement of the middle ear bones);
• muscles of facial expression (move the face);
• muscles of mastication (move the jaw-temporomandibular joint);
• muscles of the soft palate (elevate and depress the palate); and
• muscles of the tongue (move and change the contour of the tongue).

In the neck
In the neck, major muscle groups include:

• muscles of the pharynx (constrict and elevate the pharynx);
• muscles of the larynx (adjust the dimensions of the air pathway);
• strap muscles (position the larynx and hyoid bone in the neck);
• muscles of the outer cervical collar (move the head and upper limb); and
• postural muscles in the muscular compartment of the neck (position the neck and head).

Sources :

- Gray's Anatomy for Students, 2nd Edition ( 800 – 801 – 802 – 803 - 804 ) .

By Richard Drake PhD , A. Wayne Vogl PhD , Adam W. M. Mitchell MB 

Copyright © 2009 by Churchill Livingstone