Study on Distribution of Terminal Branches of the Facial Nerve in Mimetic Muscles (Orbicularis Oculi Muscle and Orbicularis Oris Muscle)

Abstract

There have been many anatomical reports to date regarding the course of the facial nerve to the mimetic muscles. However, reports are relatively scarce on the detailed distribution of the terminal branches of the facial nerve to the mimetic muscles. In this study, we performed detailed examination of the terminal facial nerve branches to the mimetic muscles, particularly the branches terminating in the orbicularis oculi muscle and orbicularis oris muscle. Examination was performed on 25 Japanese adult autopsy cases, involving 25 hemifaces. The mean age was 87.4 years (range, 60-102 years). There were 12 men and 13 women (12 left hemifaces and 13 right hemifaces). In each case, the facial nerve was exposed through a preauricular skin incision. The main trunk of the facial nerve was dissected from the stylomastoid foramen. A microscope was used to dissect the terminal branches to the periphery and observe them. The course and distribution were examined for all terminal branches of the facial nerve. However, focus was placed on the course and distribution of the zygomatic branch, buccal branch, and mandibular branch to the orbicularis oculi muscle and orbicularis oris muscle. The temporal branch was distributed to the orbicularis oculi muscle in all cases and the marginal mandibular branch was distributed to the orbicularis oris muscle in all cases. The zygomatic branch was distributed to the orbicularis oculi muscle in all cases, but it was also distributed to the orbicularis oris muscle in 10 of 25 cases. The buccal branch was not distributed to the orbicularis oris muscle in 3 of 25 cases, and it was distributed to the orbicularis oculi muscle in 8 cases. There was no significant difference in the variations. The orbicularis oculi muscle and orbicularis oris muscle perform particularly important movements among the facial mimetic muscles. According to textbooks, the temporal branch and zygomatic branch innervate the orbicularis oculi muscle, and the buccal branch (or the buccal branch and marginal mandibular branch) innervates the orbicularis oris muscle. In this study, we performed dissection of the terminal facial nerve branches that terminate in the orbicularis oculi muscle and orbicularis oris muscle and performed detailed examination of their courses. The results revealed 5 multiple anomalies not in conventional books, and the movements of the muscles might be compensated.

Lagophthalmos of the upper eyelid after rhinoplasty: A case report

“… 8 While according to the references, most of the surgeons think that the upper orbicularis oculi muscle innervated by temporal branch of facial nerve, 10 there is conflicting evidence about the innervation of orbicularis oculi muscle fibers in the upper eyelid region as well as the course of buccal branch of the facial nerve. 11 , 12 According to these precise anatomical studies the terminal fibers of buccal branch of facial nerve, coursing from lateral parts of the bony pyramid of nose are responsible for innervating the medial part of upper eyelid orbicularis muscle. The course of these fibers is compatible with lateral nasal osteotomy site.…”

Variability in facial‐muscle innervation: A comparative study based on electrostimulation and anatomical dissection

“…Orbicularis oculi function is spared following frontal branch injury as the muscle receives dual innervation in the form of a second nerve supply from the zygomatic branch, but this seems to be limited to the inferior region. Mitsukawa et al () examined the branches of the terminal facial nerve and the mimetic muscles in detail in 25 Japanese adult autopsies. They reported that the temporal branch (they did not separate the frontal and temporal branches) was connected to the orbicularis oculi muscle in all cases and that the marginal mandibular branch was always connected with the orbicularis oris muscle.…”

Relationship between buccal branches of the facial nerve, parotid duct, buccal fat pad and Zuker’s point

“…There is a large diversity regarding the number of BB which has been reported to be composed of 1 to 5 branches. [1,3,4,16,[19][20][21] Only a single BB has been reported to be found 2.5% to 85%, two branches 15% to 50%, three branches 48.6% and four branches 5.7%. [11,[22][23][24] In the present study, the mean number of BB was identified as 2.40±0.62 (range: 1-4) branches proximally and 4.03±1.03 (range: 2-6) branches distally.…”

“…Deep twigs of the BB innervate the zygomaticus major and minor, levator labii superioris, levator anguli oris, levator labii superioris alaeque nasi, small nasal muscles, buccinator and orbicularis oris muscles. [1][2][3][4] Zygomatic branches of the facial nerve (ZB) cross the zygomatic bone towards lateral canthus and innervate orbicularis oculi muscle. These branches may also con-tribute innervation of the muscles which are innervated by the BB.…”