Human Frontalis Muscle Innervation and Morphology

Due to its clinical importance and due to a suggestion regarding the afferent innervation, the microscopic appearance of the frontalis muscle was investigated. METHODS: From seven human cadavers, serial sections of the frontalis muscle were studied using light microscopy. Immunhistochemistry was performed using antibodies against collagen XXII and neurofilament. RESULTS: The macroscopic appearance of the muscle was in accordance with the literature. At both insertion sides, the muscle fiber endings expressed collagen XXII, a marker for myotendinous junctions, although no tendons were present at the origin side. Neuromuscular junctions were seen in the middle part of the muscle belly (insertion of the nerve fibers of the facialis nerve) and in the cranial part toward the galea aponeurotica (possible afferent fibers?). CONCLUSIONS: This study summarizes the microscopic appearance of the frontalis muscle. It is a first example that collagen XXII can be expressed even without tendon formation. It confirms the absence of corpuscular afferent neuronal structures within the muscle.