Abstract
The mammalian external ear houses extrinsic and intrinsic auricular muscles. There are three extrinsic auricular muscles—the posterior, superior, and anterior auricular muscles—and six intrinsic muscles—the helicis major and minor, tragicus, anti-tragicus, transverse and oblique muscles. These muscles have been considered vestigial in humans. However, numerous therapeutic and diagnostic wearable devices are designed to monitor and alleviate the symptoms of neurological disorders, brainstem injuries, emotional states, and auditory functions, by making use of the neural networks of the auricular muscles and their locations, which are easily accessible for ergonomic wearable biomedical devices. They can also serve as a bio-controller of human neuroprosthetics. The functionality of these auricular muscles remains elusive and requires further experimentation for a more in-depth understanding of their anatomy. The aims of this review are (1) to provide a detailed account of the neural networks of the extrinsic and intrinsic auricular muscles, (2) to describe diagnostic and therapeutic functions of these muscles as demonstrated in the current literature, and (3) to outline existing and potential neuroprosthetic applications making use of the auricular muscles and their neural networks.
Highlights
The auricle of humans and other mammals contains three extrinsic and six intrinsic muscles [1, 2]
The aims of this review are [1] to provide a detailed account of the neural networks controlling the extrinsic and intrinsic auricular muscles, [2] to summarize the diagnostic and therapeutic functions of these muscles as described in the current literature, and [3] to outline existing and potential future neuroprosthetic applications based on the auricular muscles and their neural networks
Three extrinsic auricular muscles—the superior auricular muscle (SAM), AAM, and posterior auricular muscle (PAM)—arise from the temporal aspect of the cranium and insert into the auricular cartilage (Figure 1A). They hold the auricles in place and are responsible for the reinforcement, positioning, and angle of the auricle [1, 8]. They are innervated by the temporal (SAM and AAM) and PAM branches of the facial nerve [3, 9], and vascularized by the superficial temporal, posterior auricular, and occipital arteries [10]
Summary
The auricle of humans and other mammals contains three extrinsic and six intrinsic muscles [1, 2]. The extrinsic muscles are the posterior auricular muscle (PAM), superior auricular muscle (SAM), and anterior auricular muscle (AAM), whereas the intrinsic muscles are the helicis major (HMJM) and minor (HMNM), tragicus (TR), anti-tragicus (ATR), transverse auricular muscle (TAM), and oblique (OAM) muscles These muscles have been considered vestigial in humans, though it has been suggested that during development in the womb they may exert forces on the cartilage and affect the shaping of the ear [2, 3]. The neural connections of the auricular muscles with the brainstem and other deep brain structures are intact [5,6,7], and these muscles are accessible for wearable neuroprosthetics They have been used as targets for numerous existing and potential future neuroprosthetic applications, for the diagnosis and treatment of a large range of diseases and health conditions, including neurological disorders, brainstem injuries, emotional states, and auditory functions. They have been used as a bio-controller for assistive devices
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