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. 2022 May;240(5):936-940.
doi: 10.1111/joa.13604. Epub 2021 Dec 10.

Muscle spindles in the rhesus monkey platysma

Christian Albrecht May  1 , Kerstin Mätz-Rensing  2 , Daniel Aschoff  2 , Silvia Bramke  1
Affiliations

Muscle spindles in the rhesus monkey platysma

Christian Albrecht May et al. J Anat. 2022 May.

Abstract

The platysma of the rhesus monkey consists of two parts: a platysma myoides located similar to the human platysma, and a platysma cervicale passing the dorsal cervical region and being in contact with the cheek pouch. Our investigation showed that the muscle fiber morphology was comparable in both parts. Muscle spindles were only present in regions connected to the cheek pouch and contained only nuclear chain fibers. It is tempting to speculate that they sense the filling of the cheek pouch rather than mimic activities.

Keywords: cheek pouch; muscle spindle; platysma; rhesus monkey; striated muscle.

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Figures

FIGURE 1
FIGURE 1
Macroscopic appearance of a left in situ (a) and extracted (b) platysma (7‐year‐old male rhesus monkey): note the compact platysma cervicale (double‐headed arrow) covering partly the cheek pouch (asterisk). The platysma myoides (white arrowheads) forms single muscle bundles separated by connective tissue strands
FIGURE 2
FIGURE 2
Microscopic appearance of the platysma cervicale (Plat) and the epithelium (Ep) and genuine muscle (asterisks) of the cheek pouch (HE stain). (a) Note a lymph follicle (L) and next to it mucous glands in the lamina propria between the epithelium and the cheek pouch muscle. (b) The variability in muscle fiber orientation of the cheek pouch muscle (asterisks) is clearly seen. The arrowhead marks a muscle spindle within the platysma cervicale
FIGURE 3
FIGURE 3
Microscopic appearance of the platysma myoides (HE stain). Note single muscle fiber bundles (Plat) separated by connective tissue. At places, the connective tissue shows densifications (arrowheads) without forming a continuous epimysium
FIGURE 4
FIGURE 4
Microscopic appearance of a muscle spindle within the platysma cervicalis (HE stain). (a) At the termination of the muscle spindle, only two intrafusal muscle fibers (arrowheads) can be detected. (b) At the polar zone the spindle contains five intrafusal muscle fibers (arrowheads); the surrounding connective tissue sheath is tenuous. (c) At the equatorial zone, only single nuclei can be seen within the intrafusal muscle fibers (arrowheads) characterizing all fibers as nuclear chain fibers. N = entering nerve fibers
FIGURE A1
FIGURE A1
Immunohistochemical staining of monkey tissue with two human antibodies: S46 (a) and A4.74 (b and c). (a) There was no staining of the extrafusal (asterisks) and intrafusal (arrow) platysma muscle fibers. (b) There was some background, but no specific staining in most of the extrafusal (asterisks) and intrafusal (arrow) platysma muscle fibers. Single extrafusal muscle fibers of the platysma stained positive (data not shown). (c) All small muscle fibers of the cheek pouch muscle stained positive defining them possibly as type 2a/2x fibers.
See this image and copyright information in PMC

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