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Home , Facial muscles, Greater petrosal nerve, Levator veli palatini

The Course of Facial Innervation for the Levator

Veli Palatini Muscle

KAORU IBUKI, D.D.S., Ph.D. TOKUZO MATSUYA, D.D.S., Ph.D. JUNTARO NISHIO, D.D.S., Ph.D. YASUSHI HAMAMURA, D.D.S. TADASHI MIYAZAKI, D.D.S., D.Med.Sc. Osaka, Japan

The present study was designed to determine the motor nerve pathway of the to the levator veli palatint muscle. The experiments were carried out on 10 anesthetized rhesus monkeys. Recorded and analyzed were evoked EMG responses of the and the orbicularis oris muscles by electrical stimulation to both the facial nerve and its branch within the cranium. 4 Muscle action potentials (M-waves) from the two muscles could be recognized on stimulating the facial nerve at the petrosal area of the . On stimulating the greater petrosal nerve, M-waves from the levator muscle could be elicited. By cutting off the greater petrosal nerve at the , M-waves from the levator muscle completely disappeared on stimulating the facial nerve at the petrosal area. ' Results indicated that the course of the facial nerve for the levator veli palatini muscle is through the greater petrosal nerve.

KEY WORDS: Levator veli palatini muscle, Facial nerve, Greater petrosal nerve, Evoked EMG, Rhesus monkey.

Since Meckel (1748) reported the possibility gators could not reach specific conclusions of facial nerve innervation to the , concerning the motor nerve supply to the numerous investigators have discussed the levator, a muscle which is essential to velo- motor nerve supply to the muscles of the pharyngeal closure. Podvinec (1952), Brodal velopharynx. A better understanding of motor (1967), and Sedlackova, et al. (1973) sug- supply to this area is essential to a complete gested that the levator veli palatini muscle understanding of the physiological mecha- had double innervation from the facial nerve nisms on velopharyngeal movements. and branches of the pharyngeal plexus de- Turner (1889), Rethi (1893), Druner rived from the glossopharyngeal and vagus (1896), and Rich (1920) revealed that the . Further, Nishio, et al. (1976a, 1976b), tensor veli palatini muscle was innervated by in studies of evoked EMG and fiberscopic the . However, these investi- observations on rhesus monkeys, indicated that the facial nerve innervated the levator The authors are affiliated with the 1st Department of veli palatini muscle and regulated movements Oral & Maxillofacial Surgery, Osaka University Dental similar to those found in man during phona- School, Osaka, Japan. Dr. Ibuki is a staff member, Dr. tion. Matsuya an associate professor, Dr. Nishio a staff mem- There is, however, no general agreement as ber, Dr. Hamamura a staff member, and Dr. Miyazaki a professor. . yet on the pathway of the facial nerve to the This article is based on a paper presented at the 3rd levator veli palatini muscle. Futamura (1906) International Congress for Cleft Palate and Other Cran- published a study based on the embryological iofacial Anomalies in Toronto, Canada, June, 1977. findings of human and nerves Some of the material in this article has been published in the Journal of Osaka University Dental Society, Vol- and suggested that the stapedius and the lev- ume 22, No. 1, June, 1977. ator veli palatini muscles were developed from 209 210 Cleft Palate Journal, July 1978, Vol. 15 No. 3 the second branchial arch and that the course (1972) and consisting of isonaled platinum of the facial nerve went through the greater wire (Consolodated Reactive Metal Co. Ltd., petrosal nerve. Moritz (1939) suggested that U.S.A.) 50y in diameter with Imm bare tip, the route to the levator muscle passed through was inserted perorally into the levator veli the facial nerve, the , and the palatini muscle to record its action potentials . Nick]! (1950) supported the con- (Fritzel, 1969). The recording electrode of the tention of Moritz that the facial nerve innerv- levator veli palatini muscle was placed 2-3mm ated the levator muscle through the chorda mesial to the hamular process and about tympani. 10mm posterior-superiorly (Dickson, 1974). The present investigation utilized evoked The electrode was also placed percutaneously EMG to determine which branch of the facial in the as a control. nerve within the cranium innervates the lev- The inter-electrode distance was 2mm in ator veli palatini muscle. all cases. In addition, the tip resistance of the recording electrode was adjusted to 10 # 1 Materials and Methods KQ in normal saline. The experimental animals used in this in- As the second step, the middle cranial fossa vestigation were ten rhesus monkeys, weigh- approach of House (1961) was adapted to ing approximately 3.0 to 8.0 Kg. After the expose the greater petrosal nerve at the pe- trachea was canulated under pentobarbital trosal area of the temporal bone. After appro- sodium anesthesia (35mg/Kg., iv.), the ani- priate skin preparation and draping, an inci- mal was kept under artificial respiration. The sion was made just anterior to the at the was mounted on the stand of a stereo- level of the zygomatic arch to the top of the taxic instrument in which the ear rods had attachment. A round crani- been converted in order not to rupture the otomy of 5cm in diameter was made superior tympanums of the animals. and anterior to the external auditory canal, As the first step, after trepaning and incis- and the dura was elevated from the floor of ing the dura of the occipital region partial the middle fossa. The fibers of the greater decerebellum was carried out to expose the petrosal nerve, usually found on the under- facial nerve at the petrosal area of the tem- surface of the dura, were separated from the poral bone (Nishio, et al., 1976a). After the dural attachment, and then a bipolar plati- facial nerve was dissected as centrally as pos- num wire electrode was also placed to stimu- sible, a bipolar platinum wire electrode, 2004 late the peripheral stump of the nerve electri- in diameter, was placed on the peripheral cally (Figure 2). The facial and the greater stump of the nerve (Figure 1). A twin needle petrosal nerve were stimulated by square electrode, previously devised by Mimura wave pulses of 0.5msec in duration generated

FIGURE 1. Diagram of the stimulation of the facial FIGURE 2. Diagram of the stimulation of the greater nerve. 1. For. Ovale; 2. Greater petrosal nerve; 3. For. petrosal nerve. 1. Bipolar electrode; 2. For. Ovale; 3. lacerum; 4. Facial nerve; 5. ; 6. Greater petrosal nerve; 4. For. lacerum; 5. Facial nerve; Bipolar electrode. 6. Vestibulocochlear nerve; 7. For. juglare.

Ibuki, et al., FACIAL NERVE INNERVATION 211 by an electrical stimulator (Nihonkohden served from the orbicularis oris muscle. Figure SEN-1101). The minimum intensity of a stim- 4, shows an example of simultaneous recorded ulus necessary to elicit a muscle action poten- muscle action potentials (intensity; 6.5V). tial was defined as threshold. In this experi- Amplitudes and latencies of action potentials ment, the intensity levels of stimulation were at maximum stimulation in the levator mus- converted consecutively from threshold to its cles ranged from 380 to 1100uV and from 1.5 maximum which revealed no further change to 1.9 msec, respectively. in amplitude. However, as the case may be, In Group B, when the peripheral stump of the intensity levels were increased beyond the facial nerve in the petrosal area was stim- maximum stimulation; le., supramaximum ulated, muscle action potentials were recorded stimulation. To prevent spread of electrical from both the levator veli palatini and the current and drying, each nerve was sur- orbicularis oris muscles on the stimulated side rounded by cotton, and bathed in mineral (Figure 5). Amplitudes of action potentials at water. The reactions to the motor nerve stim- maximum stimulation ranged from 320 to uli were ascertained through muscle action 830 uV in the levator and from 560 to 1220uV potentials, M-waves, from the levator and the in the orbicularis oris muscles. Latencies at orbicularis oris muscles. maximum stimulation in the levator and the Hence, the experimental monkeys were di- orbicularis oris muscles ranged from 1.6 to vided into three groups as follows: Group A 1.I9msec and from 1.7 to 2.0msec respectively. (Subjects 1, 2, 3, and 4), stimulating the In Group C, with sustained stimulation, greater petrosal nerve at the upper petrosal intensity of 2.0 V, to the peripheral stump of portion of the temporal bone. Group B (Sub- the facial nerve at the petrosal area, the jects 5, and 6), stimulating the facial nerve just before it entered the internal auditory ol meatus. Group C (Subjects 7, 8, 9, and 10), -A - |I | transecting the greater petrosal nerve at the | i floor of the middle fossa, with sustained stim- | | ulation to the facial nerve. | After the examinations, the monkeys were sacrificed to acertain the positions of the re- cording electrodes in the muscles. Action po- tentials from both the levator and the orbi- cularis oris muscles were simultaneously dis- played on an oscilloscope (Nihonkohden, VC- FIGURE 3. Analysis of evoked EMG. A. Latency; B. 7A) through the R-C coupled preamplifiers Amplitude. and recorded on film when necessary. In gen- eral, intensity levels of thresholds in a study M. orbicularis oris —\4,\A_fi -\\’—_ of evoked EMG are affected by individual 6.5V 1mV variations in experimental monkeys and by

Results M. levator _W\'~— ‘NNP—l—(flr-{lsec In Group A, when the peripheral stump of FIGURE 5. Examples of muscle action potentials on the greater petrosal nerve at the floor of the stimulating the facial nerve at the petrosal area. To compare with Figure 4, these were recorded at supra- middle fossa was stimulated, action potentials maximum stimulation (intensity: 6.5V) which revealed were recorded from the levator muscle on the no more change in amplitude. These were recorded from stimulated side, but no potentials were ob- subject 5. 212 Cleft Palate Journal, July 1978, Vol. 15 No. 3 greater petrosal nerve was transected at the through the ear drum on the same side in 60 floor of the middle fossa. As illustrated in per cent of his patients. However, it was not Figure 6, muscle action potentials from the clear if he tried to stimulate the nerve electri- orbicularis oris muscle continued after tran- cally as peripherally as possible after blocking section, while those of the levator muscle van- the connection between the brain and the ished. Moreover, evoked EMG from the lev- chorda tympani. Nickl's experimental results ator muscle could not be elicited by increasing appeared to be unreliable when we considered the intensity level of stimulation up to 6.5 V. that he disregarded the inter-connections among the facial, the glossopharyngeal, the Discussion vagus, and the trigeminal nucleuses in the medulla oblongata. Algaba's study (1972) in In order to identify which branch of the cats showed that evoked EMG responses from facial nerve within the temporal bone innerv- the levator muscle were not recognized with ates the levator veli palatini muscle, an ex- chorda tympani stimulation. periment using evoked EMG procedures was On the other hand, Futamura (1906) in the carried out on 10 Rhesus monkeys. embryological study of facial nerves and mus- Numerous investigators have recognized cles in human embryos, reported that both that the facial nerve supplies the motor fibers the levator veli palatini muscle and the of the velopharyngeal muscles (Futamura, greater petrosal nerve originated from the 1906; Moritz, 1939; Nickl, 1950; Prodvinec, second branchial arch and joined together in 1952; Sedlackova, et al., 1973). Nishio, et al. an early stage of facial nerve development. (1976a, 1976b) also ascertained that action Hence, he provided the course of facial nerve potentials from the levator muscles were rec- innervation for the lavator veli palatini mus- ognized ipsilaterally by electrical stimulation cle was as follows: facial nerve-geniculate of the facial nerve at the front of the internal ganglion-greater petrosal nerve-pterygo- auditory meatus. The present study coincided palatine ganglion-minor palatine nerve- with these previous studies. levator veli palatini muscle. Gasser (19672, Still unsettled, however, was which branch 1967b), in the study of facial nerve embryol- of the facial nerve was concerned with move- ogy in human and Baboon embryos, sup- ments of the levator veli palatini muscle. ported Futamura's idea that the greater pe- Moritz (1939) analyzed velar disabilities in trosal nerve developed from the second bran- patients with facial paralysis and assumed chial arch. that the pathway of the facial nerve to the The most important problem left, then, was levator muscle was as follows: facial nerve- learning whether or not the greater petrosal chorda tympani-otic ganglion-internal nerve contained motor fibers from the facial sphenoidal nerve-greater petrosal nerve- nerve. Druner (1896) and Brubacker (1916) minor palatine nerve-levator veli palatini denied that the greater petrosal nerve com- muscle. The hypothesis of Moritz was sup- prised the motor axons. Baumel (1974), on ported by Nickl (1950), who reported that reviewing the clinical reports of patients with contraction of the velum was found on elec- facial paralysis, suggested that the motor trical stimulation of the chorda tympani route of the greater petrosal nerve, by way of communication with the pterygopalatine and the otic ganglions, provided the aberrants of M. orbicularis oris “WWW—- % accessory pathways to the facial musculature 2.0V of the second and the third divisions of the trigeminal nerve. 1mV On the other hand, histological studies of M. levator e Rabl (1887) and Kure (1936) indicated that omsec 6.5V the greater petrosal nerve of the mammalian contained the motor route of the facial nerve. FIGURE 6. Examples of muscle action potentials on Foley (1947), on the degeneration study of the stimulating the facial nerve at the petrosal area after cutting off the greater petrosal nerve. These were re- facial nerve, decided that the proportions of corded from subject 8. motor axons in the greater petrosal nerve were Ibuki, et al., FACIAL NERVE INNERVATION 213 from 51 to 85 per cent in cats and 72 per cent nerve have already been described by Nish10, in dogs. Therefore, it can be seen that the et al., (1976a). The results obtained from the greater petrosal nerve plays a greater role in present study revealed similar data to those. movements of facial muscles originating from However, the present study seems to be the the second branchial arch. first to indicate motor nerve innervation of The discrepancies in every study described the greater petrosal nerve to the levator mus- above might be species differences between cle by evoked EMG. humans and the other experimental animals. Figure 7 illustrates the result of the present With respect to those problems, Gasser study as well as the diagram of the greater (1967b) reported that the arrangement of the petrosal nerve and its connections (Larsell, intercranial part of the facial nerve in mon- 1928; Stewart, 1930; Brodal, 1967; Vidic, keys was quite similar to that found in man. 1967, 1968). In this study, evoked EMG re- May (1973) also stated that the anatomy of sponses from the levator muscle were recog- the facial nerve in the cat and in man showed nized by the electrical stimulation of the a close resemblance. Accordingly, it was greater petrosal nerve at the upper portion of thought that the detailed anatomy of the the temporal bone on the same side. This facial nerve in the temporal bone in cats result demonstrates that the greater petrosal and/or monkeys should have direct clinical nerve was comprised of the motor fibers from application. the facial nerve as previously reported by Amplitudes and latencies of responses from Foley (1947) and others, while it had a bene- the levator muscle on stimulating the facial ficial effect upon movements of the levator

Nucleus salivatoriu superior

Porus acoustics

Nucleus tractus solitariu \

12 Levator M. Stapedius M, §

/!Lz Internal carotid - N. r" Glossopharyngeal N.

For. stylomastoideum FIGURE 7. Diagram of the greater petrosal nerve and its connections. Solid line indicates the motor- route of the facial nerve to the levator veli palatini muscle obtained from this study, while dotted line reveals the author's hypothesis. 1. ; 2. Greater petrosal nerve; 3. ; 4. Stapedius nerve; 5. Chorda tympani; 6. R. communicans cum nerve zygonatico; 7. Rr. nasales posterior; 8. Arnold's nerve; 9. Minor petrosal nerve; 10. Lesser ; 11. Tympanic plexus; 12. Deep petrosal nerve.

214 Cleft Palate Journal, July 1978, Vol. 15 No. 3

muscles without the intervention of the GASSER, R. F., and HENDRICKx, A. G., The development of the famal nerve in Baboon embryos, (Papio sp)", J. branch derived from the tympanic plexus. Comp. Neur., 129, 203-218, 1967. Moreover, it was recognized that M-waves House, W. F ., Surgical exposure of the internal auditory from the levator muscle completely disap- canal and its contents through the middle cranial fossa, peared when the greater petrosal nerve was Laryngoscope, 71, 1363-1385, 1961. cut off and the facial nerve was stimulated KURE, K., and SANO, T., Faserarten in Nervus facialis und die funktionelle Bedeutung des Ganglion geniculi, electrically. It was clear that there was no Zsch. Zell. Mirco. Anat., 23, 495-509, 1936. branch from the facial nerve sending out mo- LARSELL, O., and FENTON, R. A., The embryology and tor fibers to the levator muscle other than the neurohistology of sphenopalatine ganglion connec- greater petrosal nerve. Therefore, considering tions; A contribution to the study of otalgia, Lanryngo- the special viseral efferent fibers of the facial scope, 38, 371-389, 1928. May, M., Anatomy of the facial nerve (Spatial Orienta- nerve originating in the facial nucleus, the tion of fibers in the temporal bone), Laryngoscope, 83, authors arrived at the conclusion that the 1311-1329, 1973. course of facial nerve innervation for the lev- MECKEL, J. F., De Quinto pare Nervorum GCerebri, Got- ator veli palatini muscle was as follows: facial lingen, 1748; from Broomhead, I. W., The nerve supply of the muscles of the soft palate, Brit. J. Plast. Surg., 4, nucleus-geniculate ganglion-greater pe- 1-5, 1951. trosal nerve-pterygopalatine ganglion-lev- MImUrRA, T., An electromyographic study on muscle ator veli palatini muscle. functions of the soft palate during pharyngeal closure, Hence, it remains to be determined what J. Osaka Univ. Dent., 17, 1-16, 1972. MORITZ, W., Uber die Funktion und Innervation der part of the facial nucleus in the pons dis- Muskulatur des weichen Gaumens, Zsch. Anat., 109, charges the motor neurons involving velopha- 197-206, 1939. ryngeal movements. It is also obscure as to NICKL, V. E., Uber die Innervation des Muskulus Leva- how the facial nerve innervates the levator tor veli palatini durch den Nervus facialis, Arch. Psy- muscle after the greater petrosal nerve enters chiat. Neur., 184, 117-132, 1950. NisHIO, J., MaTsUYA, T., MACHIDA, J., and MIYAZAK1, the pterygopalatine ganglion. In addition, the T., The motor nerve supply of the velopharyngeal existence of afferent fibers from the levator muscles, Cleft Palate J., 13, 20-30, 1976a. muscle is as yet not known. NisH1O, J., MaTsUYA, T., IBUKI, K., and MIYAZAKI, T., This study revealed evidence that the func- Roles of the facial, glossopharyngeal and vagus nerves in velopharyngeal movement, Cleft Palate J., 13, tion of the levator veli palatini muscle was 201-214, 1976b. affected by motor fibers from the facial nerve PoDpVINEC, S., The physiology and pathology of the soft through the greater petrosal nerve. palate, /. Laryng, 66, 452-461, 1952. RABL, K., Uber das Gebiet des Nervus Facialis, Anat. References Anz 2, 219—227 1887. ALGABA, J., Experimental study of the innervation of the RETHI, L., Der periphere Verlauf der motorischen soft palate, Rev. Esp. Oto-Neuro-Oftalm., 30, 1-10, 1972. Rachen und Gaummennerven, Sitzungber. Ksl. Akad. BAUMEL, J. J., Trigeminal-facial nerve communications, Wiss., Wien, Mathem-naturw. Classe; Bd. C II, Abdth. Arch. Otolaryngol., 99, 34-44, 1974. 3., 199-220, 1893. BRODAL, A., Neurological Anatomy, ed. 2, Oxford Univ. RICH, A. R., The innervation of the tensor veli palatini Press., New York, 397-411, 1967. and levator veli palatini muscles, /ohns Hopk. Hosp. BRUBACKER, A. P., The innervation of the nasal cham- Bull., 31, 305-335, 1920. bers, Ann. Oto-Rhino-Laryng., 25, 607-617, 1916. SEDLACKOVA, E., LaSfOVKA, M., and SRAM, F., Con- DICKSON, D. R., and DICKSON, W. M., Velopharyngeal tribution to knowledge of soft palate innervation, Folia anatomy, /. Speech. Hear. Res., 15, 372-381, 1972. Phoniat., 25, 434-441, 1973. DRUNER, L., Uber die Muskulatur des Vesceralskelettes STEWART, D., and LAMBERT, V., The spheno-palatine der Urodeln, Anat. Anz., 23, 545-570, 1896. ganglion, J. Laryng. Oto., 45, 753-771, 1930. FoLEY, J. O., Functional components of the greater TURNER, W. B., On the innervation of the muscles of superficial petrosal nerve, Proc. Exp. Med., 64, 158-162, the soft palate, J. Anat., 13, 523-531, 1889. 1947. Vipic, B., and YOUNG, P. A., Gross and microscopic FRITZEL, B., The velopharyngeal muscles in speech, Acta. observations on the communicating branch of the fa- Oto-Rhino- Laryng (suppl), 250, 1-81, 1969. cial nerve to the lesser petrosal nerve 1, Anat. Rec., 158, FUTAMURA, R., Uber die Entwmklung der Facialismu- 257-262, 1967. skulatur des Menschen Anat. Hefte., 31, 434-516, 1906. ViDpIc, B., The origin and the course of the communicat- GASSER, R. F., The development of the facial nerve in ing branch of the facial nerve to the lesser petrosal man, Ann. Oto-Rhino-Laryng., 76, 37-56, 1967. nerve in man, Anat. Rec., 162, 511-516, 1968.