(2005) to help bring these interesting, fun and pedagogically rich student activities into greater classroom and outreach use. We offer suggestions for updating and quantifying the qualitative exercises of Keating et al. Specifically, for the set of activities described here, inappropriate muscle spindle firing can produce distortions in perception of arm position and correct standing posture ( Proske and Gandevia, 2012). A distorted perception of limb position or body movement (kinesthetic illusion) can be caused by artificially altering the action potential firing rate of muscle spindles as they report muscle length information to the brain ( Proske and Gandevia, 2012). The focus of the exercise is the role muscle spindles play in providing correct positional information of body parts to the CNS for awareness of limb position and maintenance of standing posture. (2005) to adapt their student lab exercise on the perception of body position and movement (kinesthesia) for an active learning session in a freshman physiology course at Cornell University, and to present our version of this exercise at the 2017 FUN Workshop at Dominican University. A broader context for the activities could include postural adaptations at sea and upon return to land, postural illusions experienced by astronauts and the postural and locomotor problems they experience upon return to Earth, and the effects of aging and disease on the proprioceptive control of limb position and posture. They lead directly to discussions of sensory physiology, central pathways for integration of sensory information and spinal pathways to execute motor commands. These activities are open for continued student-designed exploration. Although descriptive data can suffice to engage students in these activities, we suggest quantitative measurements to add further depth. This creates an illusion of limb position or standing posture change. We use a percussion stimulator to vibrate muscle spindles in several muscle groups, causing an artificially incorrect message to the CNS that a muscle has lengthened. We focus on the muscle spindle contribution to limb positional sense and standing postural maintenance. It has been established that this is not the case by direct visual observation of intrafusal contraction in isolated living spindles, by intracellular recording from intrafusal fibres, and by light and electron microscopy of cat muscle spindles.This article describes three simple activities we presented at the 2017 FUN Faculty Workshop at Dominican University that demonstrate how proprioceptive information contributes to our mental image of physical self, and how artificially altering this information creates kinesthetic illusions. Complete resolution of the problem was delayed until 1980 because the glycogen depletion technique suggested that static γ axons frequently innervated the bag₁ fibre (Fig. The other one, the 'bag₁ fibre', is separately controlled by dynamic axons (Fig. One of them, the 'bag₂ fibre', is controlled by static γ axons which sometimes share this innervation with the nuclear chain fibres. The controversy was to a large extent resolved by the discovery in the early 1970s that there were two types of nuclear bag fibres which are structurally and mechanically quite different. Barker and colleagues maintained that the same motor axon frequently terminated on both types of intrafusal fibre. Boyd maintained that two types of intrafusal muscle fibre, nuclear bag fibres and nuclear chain fibres, were separately innervated by different types of small γ motor axons. The controversy in the 1960s about the motor innervation of mammalian muscle spindles is described.
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