Muscle Receptor Organs in the Crayfish Abdomen: A Student Laboratory Exercise in Proprioception

Abstract

The primary purpose of this experiment is to demonstrate primary sensory neurons conveying information of joint movements and positions as proprioceptive information for an animal. An additional objective of this experiment is to learn anatomy of the preparation by staining, dissection and viewing of neurons and sensory structures under a dissecting microscope. This is performed by using basic neurophysiological equipment to record the electrical activity from a joint receptor organ and staining techniques. The muscle receptor organ (MRO) system in the crayfish is analogous to the intrafusal muscle spindle in mammals, which aids in serving as a comparative model that is more readily accessible for electrophysiological recordings. In addition, these are identifiable sensory neurons among preparations. The preparation is viable in a minimal saline for hours which is amenable for student laboratory exercises. The MRO is also susceptible to neuromodulation which encourages intriguing questions in the sites of modulatory action and integration of dynamic signals of movements and static position along with a gain that can be changed in the system. Video LinkThe video component of this article can be found at http://www.jove.com/video/2323/ Protocol 1) INTRODUCTIONProprioceptors are neurons that detect joint position, direction, speed, and muscle stretch. Proprioception is a unique sensory modality, because proprioceptors are interoceptors and sense stimuli within the body instead of from the outside world.In the vertebrate system, it appears that many of the joint and tension receptors are not necessary to detect gross proprioceptive information. The annulospiral and flowerspray (sensory nerve endings) receptors on muscle fibers have been shown by ablation as well as vibratory and anesthetic studies to be the two essential receptor groups needed for proprioception (Burgess et al. for a review, 1982). However, it is notable that there is redundant information gathered by other receptors, such as those in the joints, that are used for fine control of movements. Arthropods like vertebrates have articulated appendages. Therefore, it is not surprising that the proprioceptors described for vertebrates have their counterparts in arthropod limbs and joints.The anatomical arrangement of chordotonal organs in crabs allows the analysis of each individual neuron according to function. In addition, developmental questions can be addressed as the animal grows or when the animal regenerates a limb (Cooper and Govind, 1991; Hartman and Cooper, 1993). Some joint chordotonal organs in crabs contain hundreds of primary sensory neurons (Cooper, 2008) and these neurons monitor aspects in the range fractionation in movements and positions of the joint. A less complex proprioceptive system of monitoring joint movements and positions is the muscle receptor organs (MROs) in the abdomen of crayfish (Eckert, 1961a,b; McCarthy and MacMillan, 1995). The mechanoreceptors in crayfish abdomen MROs transduce a stretch stimulus in the sensory...

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