3D Anatomy of the Quail Lumbosacral Spinal Canal-Implications for Putative Mechanosensory Function.

Viktoriia Kamska,Alexander Badri-Spröwitz,Monica Daley

doi:10.1093/iob/obaa037

Abstract

SynopsisBirds are diverse and agile vertebrates capable of aerial, terrestrial, aquatic, and arboreal locomotion. Evidence suggests that birds possess a novel balance sensing organ in the lumbosacral spinal canal, a structure referred to as the “lumbosacral organ” (LSO), which may contribute to their locomotor agility and evolutionary success. The mechanosensing mechanism of this organ remains unclear. Here we quantify the 3D anatomy of the lumbosacral region of the common quail, focusing on establishing the geometric and biomechanical properties relevant to potential mechanosensing functions. We combine digital and classic dissection to create a 3D anatomical model of the quail LSO and estimate the capacity for displacement and deformation of the soft tissues. We observe a hammock-like network of denticulate ligaments supporting the lumbosacral spinal cord, with a close association between the accessory lobes and ligamentous intersections. The relatively dense glycogen body has the potential to apply loads sufficient to pre-stress denticulate ligaments, enabling external accelerations to excite tuned oscillations in the LSO soft tissue, leading to strain-based mechanosensing in the accessory lobe neurons. Considering these anatomical features together, the structure of the LSO is reminiscent of a mass-spring-based accelerometer.

Highlights

Birds are diverse vertebrates with exceptional ecological range, occupying many habitats on Earth
We suggest an alternative mechanosensing hypothesis based on the anatomical features and Schroeder’s observations (Schroeder and Murray 1987)—the inertial load of the glycogen body may act to tune and amplify localized oscillations of the spinal cord neural tissues, resulting in stress and strain in the denticulate ligaments which stimulate the accessory lobes to sense body motion (De Gennaro 1982; De Gennaro and Benzo 1987; Polak-Krasna 2019)
We report the morphometric data of the spinal cord hemispheres, the glycogen body, the denticulate ligaments, the cerebrospinal fluid (CSF), and the spinal canal, for use in the development of physical models of the mechanosensing process

Summary

Introduction

Birds are diverse vertebrates with exceptional ecological range, occupying many habitats on Earth. Despite the diversity in body size and limb proportions (Gatesy and Middleton 1997; Heers and Dial 2015), birds share a consistent body plan, with a similar basic arrangement of bones and joints This suggests that it is not innovations in body form that has been critical to the exceptional agility and locomotor diversity of birds. The fused lumbosacral vertebrae form an enclosed and enlarged space, substantially larger than the spinal neural tissues contained within. Along with this ß The Author(s) 2020.

Objectives

Methods

Results

Discussion

Conclusion