The TMJ consists of three bony parts:
Glenoid fossaOval depression in the temporal
bone that articulates with the mandibular
Articular eminenceRamp-shaped segment of
the temporal bone located anterior to the glenoid
CondyleThe knuckle-shaped portion of the
mandibular ramus found on the end of the
condyloid process. It is positioned underneath
the glenoid fossa and makes up the hinge joint of
MUSCLES OF THE HEAD
The muscles of the head can be classified into two
groups, muscles of facial expression and muscles of
mastication. How muscles work and function depends
on the action of each muscle (movement), the type of
joint it is associated with, and the way the muscle is
attached on either side of the joint. Muscles are usually
attached to two places: one end being joined to an
immovable or fixed portion, and the other end being
joined to a movable portion on the other side of a joint.
The immovable portion is called the origin of the
muscle, and the movable portion is called the insertion.
When muscles of the head contract, the insertion end is
pulled toward the origin.
MUSCLES OF FACIAL EXPRESSION
The muscles that are underneath the skin of the
face are responsible for helping communicate our
feelings through facial expression. The muscles of the
mouth help us express surprise, sadness, anger, fear,
and pain. Table 3-3 lists the muscles of facial
expression and figure 3-15 illustrates these muscles.
MUSCLES OF MASTICATION
Mastication is defined as the process of chewing
food in preparation for swallowing and digestion. Four
pairs of muscles in the mandible make chewing
movements possible. These muscles can be grouped
into two different functions. The first group includes
three pairs of muscles that elevate the mandible to
close the mouth as in biting down. The last group
includes one pair that can depress the mandible (open
the mouth), make grinding actions side to side, and can
make the mandible go forward in a protruding motion.
Table 3-4 lists the muscles of mastication and figure
3-16 illustrates these muscles.
ORAL STRUCTURES OF THE MOUTH
The oral cavity (mouth) contains various
structures that aid in the digestion process of food and
also serves as an organ of speech and sensory
Figure 3-15.Anatomy of muscles of facial expression.