Proprioceptors in extraocular muscles

Abstract

New Findings What is the topic of this review? This review aims to evaluate the literature on proprioceptors and particular nerve specializations (palisade endings) in mammalian extraocular muscles (EOMs) and to reconsider current knowledge of their structure and function. What advances does it highlight? Classical proprioceptors (muscle spindles and Golgi tendon organs) are absent in the EOMs of most mammals. Instead, palisade endings are present in most mammalian EOMs. For many years, palisade endings were considered to be sensory but recent studies show that they combine sensory and motor features. The functional significance of palisade endings is still debated. AbstractProprioception is the sense that lets us perceive the location, movement and action of the body parts. The proprioceptive apparatus includes specialized sense organs (proprioceptors) which are embedded in the skeletal muscles. The eyeballs are moved by six pairs of eye muscles and binocular vision depends on fine‐tuned coordination of the optical axes of both eyes. Although experimental studies indicate that the brain has access to eye position information, both classical proprioceptors (muscle spindles and Golgi tendon organ) are absent in the extraocular muscles of most mammalian species. This paradox of monitoring extraocular muscle activity in the absence of typical proprioceptors seemed to be resolved when a particular nerve specialization (the palisade ending) was detected in the extraocular muscles of mammals. In fact, for decades there was consensus that palisade endings were sensory structures that provide eye position information. The sensory function was called into question when recent studies revealed the molecular phenotype and the origin of palisade endings. Today we are faced with the fact that palisade endings exhibit sensory as well as motor features. This review aims to evaluate the literature on extraocular muscle proprioceptors and palisade endings and to reconsider current knowledge of their structure and function.

Additive Manufacturing Provides Infinite Possibilities for Self‐Sensing Technology

“…The concept of self‐sensing is based on the proprioceptors of organisms (Figure 1f ). [ 16 , 17 , 18 , 19 ] Proprioception, the human sense that enables us to perceive the movement of body parts, is responsible for involuntarily controlling the trunk and limbs. [ 19 ] It is achieved by the nervous system through the coordination between the tendon spindle, muscle spindle, ligament, and other skin senses and the adjustment of local joint and muscle tension (Figure 1f ).…”

“…[15] However, research on intelligent equipment has DOI: 10.1002/advs.202400816 focused on external sensors [16,17] to obtain more accurate information but less on internal sensing. [18,19] The absence of internal information can potentially lead to inaccurate data and inadequate self-evaluation, ultimately culminating in significant failures. Organisms have developed external receptors and high-performance internal proprioceptors (Figure 1f).…”

“…[23][24][25][26][27][28][29] The most important characteristic of self-sensing technology (SST) is the ability of the device to assess the stability of its structure and components. [16][17][18][19] This capability has a wide range of applications in construction, biomedical, aerospace, military, microelectronics, and other civilian fields. [23][24][25][26][27][28][29] In the early stages of self-sensing research, the focus was primarily on the exploration and development of self-sensing cement and its application in diverse structures, encompassing bridges, tunnels, skyscrapers, residential buildings, highways, and water conservancy facilities.…”

“…Organisms have developed external receptors and high‐performance internal proprioceptors (Figure 1f ). [ 16 , 17 , 18 , 19 ] External receptors are capable of detecting changes in the external environment in real time, whereas proprioceptors can assess the organism's condition in real‐time. The seamless integration of both external and internal receptors is essential for an organism to achieve lightness, agility, and vitality.…”

Experimental Physiology special issue: ‘Mechanotransduction, muscle spindles and proprioception’

“…Interestingly, the palisade endings also contain many clear vesicles and the molecular machinery for the calcium‐mediated exocytosis of acetylcholine (Blumer et al., 2020 ). These results suggest that palisade endings are more complex, that is, that they might not only provide sensory information from the eye to the brain but might also have motor features (Blumer et al., 2024 ).…”