title: Searching for proprioceptors in human facial muscles.
abstract: The human craniofacial muscles innervated by the facial nerve typically lack muscle spindles. However these muscles have proprioception that participates in the coordination of facial movements. A functional substitution of facial proprioceptors by cutaneous mechanoreceptors has been proposed but at present this alternative has not been demonstrated. Here we have investigated whether other kinds of sensory structures are present in two human facial muscles (zygomatic major and buccal). Human checks were removed from Spanish cadavers, and processed for immunohistochemical detection of nerve fibers (neurofilament proteins and S100 protein) and two putative mechanoproteins (acid-sensing ion channel 2 and transient receptor potential vanilloid 4) associated with mechanosensing. Nerves of different calibers were found in the connective septa and within the muscle itself. In all the muscles analysed, capsular corpuscle-like structures resembling elongated or round Ruffini-like corpuscles were observed. Moreover the axon profiles within these structures displayed immunoreactivity for both putative mechanoproteins. The present results demonstrate the presence of sensory structures in facial muscles that can substitute for typical muscle spindles as the source of facial proprioception.
authors.affiliation: Departamento de Morfología y Biología Celular, Grupo SINPOS, Sección de Anatomía y Embriología Humana, Universidad de Oviedo, Oviedo, Spain; Servicio de Cirugía Máxilofacial, Hospital Universitario Central de Asturias, Oviedo, Spain.
authors.forename: Juan L
authors.initials: JL
authors.lastname: Cobo
authors.affiliation: Dipartimento di Science Veterinarie, Sezione di Anatomia, Università di Messina, Messina, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Abbate
authors.affiliation: Servicio de Cirugía Máxilofacial, Hospital Universitario Central de Asturias, Oviedo, Spain; Departamento de Cirugía y Especialidades Médico-Quirúrgicas, Área de Odontología, Universidad de Oviedo, Oviedo, Spain.
authors.forename: Juan C
authors.initials: JC
authors.lastname: de Vicente
authors.affiliation: Departamento de Cirugía y Especialidades Médico-Quirúrgicas, Área de Odontología, Universidad de Oviedo, Oviedo, Spain; Instituto Asturiano de Odontología, Oviedo, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Cobo
authors.affiliation: Departamento de Morfología y Biología Celular, Grupo SINPOS, Sección de Anatomía y Embriología Humana, Universidad de Oviedo, Oviedo, Spain; Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Santiago de Chile, Chile. Electronic address: javega@uniovi.es.
authors.forename: José A
authors.initials: JA
authors.lastname: Vega
mesh_terms: D062565:Acid Sensing Ion Channels / Q000378:metabolism; D000368:Aged; D002610:Cheek / Q000033:anatomy & histology / Q000294:innervation; D005152:Facial Muscles / Q000033:anatomy & histology / Q000294:innervation* / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008465:Mechanoreceptors / Q000378:metabolism*; D008875:Middle Aged; D011434:Proprioception; D050916:TRPV Cation Channels / Q000378:metabolism
chemical_list: C568424:ASIC2 protein, human; D062565:Acid Sensing Ion Channels; D050916:TRPV Cation Channels; C416986:TRPV4 protein, human
keywords: Facial muscles; Mechanoproteins; Proprioceptors; Sensory corpuscle-like structures