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| The lateral pterygoid muscle (in purple above)
is responsible for moving the lower jaw from side to side
when the right or left lateral pterygoid is active
separately. Contraction of the right lateral pterygoid
muscle moves the jaw to the left, and contraction of the
left draws the jaw to the right. It is also responsible, in combination with the digastric muscle for opening the lower jaw during the
translation phase of opening. It
is shaped a bit like a partly unfolded fan. |
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The wide end of
the fan, it's origin, originates from a small, finlike projection
under the skull called the lateral pterygoid plate. The narrow end
of the fan inserts into the anterior surface of the coronoid process.
Notice that the lateral pterygoid has two bellies. The
light colored object projecting downward between the two bellies is the
mandibular nerve on its way toward the mandibular foramen. The upper belly
of the lateral pterygoid is attached primarily to the articular disk while the
lower belly is attached to the neck of the condyle. The two bellies may work independently, but
usually in concert to keep the articular disk
always situated between the closest points of contact between the condyle
and the glenoid fossa during both the rotational phase of jaw opening and
the translational phase. In pathologic conditions, the
two bellies can contract at different rates which causes the articular disk to
be pulled ahead of the condyle during transulatory movements. This can
tear the cartilage damaging the joint and allowing the condyle to snap up
against the glenoid fossa. This is what causes the clicking that TMJ
patients notice when opening or closing their mouths.
The medial pterygoid muscle (in red) arises from the medial (inside) surfaces
of the lateral pterygoid plate which is attached to the undersurface of
the temporal bone. In lay terms, the attachment is on the
undersurface of the skull just behind the last upper tooth. The fibers
of the medial pterygoid are directed downward and backward, just like
the masseter (pictured above), only on the inside of the mandible.
The insertion of this muscle is to the inside of the lower border and
angle of the mandible. The masseter and medial pterygoid act like a contractile
"hammock" in which the lower jaw rests. These two
muscles are more or less "twins", the masseter acting on the
outside of the lower jaw and the medial pterygoid on the inside.
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Copyright 2000
by Doctor Martin S. Spiller, DMD
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