The nerve to masseter passes through the mandibular notch to enter the muscle on its medial surface
The nerve to the masseter muscle is the masseteric nerve, which is a branch
of the mandibular nerve (CN V3), the largest division of the trigeminal nerve
(cranial nerve V). The masseter muscle is one of the muscles of mastication that
lifts the lower jaw, contributing to the action of biting and chewing.
The masseteric nerve originates from the anterior division of the mandibular
nerve and typically passes:
1. Deep to the medial pterygoid muscle: The medial pterygoid muscle is located
in the infratemporal fossa, which is the space deep to the zygomatic arch and
medial to the temporomandibular joint (TMJ). The masseteric nerve runs in a deep
position relative to the medial pterygoid muscle as it travels towards the
masseter muscle. This muscle is involved in the side-to-side movement of the
jaw, known as lateral excursion.
2. Posterior to the temporomandibular joint: The TMJ is the articulation between
the mandible and the temporal bone of the skull. It is a synovial joint that
allows for the hinge movement of the jaw, such as opening and closing the mouth.
The masseteric nerve passes behind the TMJ to reach the masseter muscle. This
nerve does not actually cross the joint itself but runs in a position posterior
to it.
3. Superior to the zygomatic arch: The zygomatic arch is the bony structure that
extends from the zygomatic process of the temporal bone to the zygomatic bone of
the skull. It forms the prominence of the cheek. The masseteric nerve runs
superior to the zygomatic arch to reach the masseter muscle. The arch serves as
a landmark for the nerve's course, and the nerve typically does not pass through
the arch itself.
4. Through the mandibular notch: This statement is not entirely correct. The
masseteric nerve does not pass through the mandibular notch, which is a
depression on the medial surface of the ramus of the mandible, but rather it
passes above (superior to) the notch. The mandibular notch is the location where
the masseteric nerve and the other branches of the mandibular nerve leave the
infratemporal fossa and enter the submandibular space to innervate the muscles
of mastication, including the masseter. The nerve then runs along the lateral
surface of the lateral pterygoid plate and enters the deep surface of the
masseter muscle.
In summary, the masseteric nerve passes deep to the medial pterygoid muscle,
posterior to the TMJ, and superior to the zygomatic arch. It does not pass
through the mandibular notch; instead, it runs superior to it before reaching
the masseter muscle. The anatomical pathway of this nerve allows it to
effectively innervate the masseter muscle, which is crucial for the function of
the muscle in mastication.
