Anat Cell Biol.  2024 Dec;57(4):570-578. 10.5115/acb.24.094.

Striated muscle fiber crossings of the head and neck: a histological study using near-term human fetuses and elderly cadavers

• Kim JH
• Kitamura K
• Honkura Y
• Murakami G
• Abe Si

• KMID: 2562504
• DOI: http://doi.org/10.5115/acb.24.094

Abstract

Striated muscle fiber crossings at almost right angle are known to exist in the face, soft palate, pharyngeal wall and tongue. We aimed to identify a specific interface tissue at the crossing. We observed histological sections from 22 halfheads of 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). For comparison, we also observed tongue frontal sections from 5 elderly cadavers (75–85 years old). At the angle of mouth as well as in the soft palate and pharyngeal wall, a solitary striated muscle fiber (e.g., levator) consistently crossed a fiber bundle of the antagonist muscle (e.g., depressor), but a solitary-to-solitary fiber interdigitation was unlikely with the antagonist muscle. Near the external nasal orifice as well as in the tongue intrinsic muscle layer, at every section, there was a crossing with an endomysium-to-endomysium contact: the nasalis and platysma muscles and; the vertical and transverse (or inferior longitudinal) tongue muscles. Therein, the functional vectors crossed at almost right angle. Also in adult tongue, the vertical and transverse muscle fibers sometimes (0–2 sites per section) crossed with an endomysium-to-endomysium contact. At the muscle crossing with an endomysium contact, the endomysium and basement membrane seemed to receive a friction stress between two muscles. Although some crossings might disappear due to high muscle activity after birth, not a few of them were likely to maintain. To minimize the mechanical stress, a minute nervous control of the timing, duration and strength of muscle contraction seemed to be necessary.

Keyword

Striated muscle fibers; Facial muscles; Soft palate; Intrinsic tongue muscle; Mechanoreceptors

Figure

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  Fig. 1 Angle of mouth and the soft palate. H&E staining. Panels (A–C) (a fetus of 310 mm; a single frontal section) display the angle of mouth. Panels (D–F) (a fetus of 328 mm; a single sagittal section) exhibit the soft palate. Panels (B, C) (or E, F) are higher magnification views of squares in panel (A) (or D, E). The platysma muscle (PM) joins the levator angli oris muscle (LAOM) and, at the meeting site, a fibrous tissue appears to connect these muscle fibers (B). The levator muscle crosses the depressor angli oris muscle (DAOM), but a crossing of a solitary-to-solitary muscle fiber is unlikely because the depressor muscle fibers are bundled (C). Likewise, in the soft palate (D), a solitary muscle fiber of the uveae muscle (UM) crosses a bundled fibers of the levator veli palatini muscle (LVPM). (A, C–E) Scale bars=1 mm, (B, F) scale bars=0.1 mm. OOM, orbicularis oris muscle; PB, palatine bone.

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  Fig. 2 Lateral wall of the pharynx and the face including the external nasal orifice. H&E staining. Panels (A–C) (a fetus of 274 mm; a single horizontal section) display the lateral wall of the pharynx including the palatine tonsil. Panels (D, E) (a fetus of 334 mm; a single frontal section) exhibit the face including the external nasal orifice. Panels (B, C) are higher magnification views of squares in panels (A, B), respectively. A square in panel (D) is shown in panel (E) at the higher magnification. The stylopharyngeus muscle (SPM) inserts into the pharyngeal wall (A) and a solitary muscle fiber of the former crosses bundles of the constrictor pharynges superior muscle (CPSM) fibers (C). Near the external nasal orifice, a buccal stretch receptor (arrows in E) is embedded in the platysma, levator labii superioris and orbicularis oris muscles (PM, LLSM, OOM). (A, B, D) Scale bars=1 mm, (C, E) scale bars=0.1 mm. GN, glossopharyngeal nerve; ICA, internal carotid artery; PMM, pterygoideus medialis muscle; NM, nasalis muscle; NS, nasal septum.

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  Fig. 3 Nasalis and platysma muscles (NM, PM) near the external nasal orifice. H&E staining. A single frontal section of a fetus of 334 mm (a section 0.8 mm superficial to ). Panels (B, D, F) display higher magnification views of three squares in panel (A). Squares in panels (B, D, E) are shown in panels (C, E, G) at the higher magnification, respectively. The nasalis muscle fibers cross the platysma muscle fibers with no or few interface tissue. Panels (B, D, F) or panels (C, E, G) were prepared at the same magnification. (A) Scale bars=1 mm, (B, C) scale bars=0.1 mm. NS, nasal septum.

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  Fig. 4 Tongue intrinsic muscles at near-term. H&E staining. A single horizontal section of a fetus of 271 mm. Panels (B, D) display higher magnification views of squares in panel (A). Squares in panels (B, D) are shown in panels (C, E) at the higher magnification, respectively. The vertical muscle (VM) fibers cross muscle fibers of the inferior longitudinal muscle (ILM) at a manner between solitary-to-solitary muscle fibers with few tissue at the interface (C, E). These muscles also cross the transverse muscle (TM), but the latter muscle fibers are bundled (B, D). Panels (B, D) or panels (C, E) were prepared at the same magnification. (A) Scale bars=1 mm, (B, C) scale bars=0.1 mm.

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  Fig. 5 Tongue intrinsic muscles in adults. Azan staining. Two frontal sections from a 76 years old female (A–D) and an 82 years old male (E–G). Panel (B) displays a higher magnification view of a square in panel (A, C, D) correspond to squares in panel (B). Panels (F, G) are higher magnification views of circles in panel (E). The intrinsic vertical muscle (VM) fibers cross muscle fibers of the transverse muscle (TM) at a manner suggesting the endomysium-to-endomysium contact (D, F). The transverse muscle fibers appear to join in panel (C). The transverse muscle fibers appear to take a wavy course to avoid contact to the vertical muscle in panel (G). (A, B, E) Scale bars=1 mm, (C, D, F, G) scale bars=0.1 mm. SLM, superior longitudinal muscle.

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  Fig. 6 Schematic representations showing three types of muscle fiber crossing. The crossing is hypothesized between two muscles with quite different vectors (the vectors cross at almost right angle) such as seen in the levator and lateral tractor. A striated muscle fiber or muscle cell (black) is covered by the basal lamina and surrounded by the endomysium (orange). Usually, when two muscles cross, 1) muscle fibers are bundled by the perimysium (green) and the bundles cross or 2) a bundle crosses a solitary muscle fiber. However, in limited sites, a solitary muscle fiber is likely to cross another fiber with the endomysium-to endomysium contact.

Reference

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