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Stretch-sensitive mechanoreceptors in the frog sartorius muscle
1Department of Physiology, Monash University, Clayton, Victoria 3168, Australia.
Neuroscience Letters
|July 17, 2009
Summary
Frog sartorius muscles have two mechanoreceptor types: muscle spindles and high-threshold extrafusal receptors. Extrafusal receptors, unlike spindles, show weak, variable responses and no resting discharge, suggesting a nociceptor-like function.
Area of Science:
- Neuroscience
- Comparative Physiology
- Muscle Biology
Background:
- The frog sartorius muscle is a model for studying muscle mechanoreceptors.
- Muscle spindles and tendon organs are well-characterized proprioceptors in vertebrate skeletal muscle.
Purpose of the Study:
- To investigate the properties of mechanoreceptors in the frog sartorius muscle.
- To characterize the afferent fiber conduction velocities and response properties of different receptor populations.
Main Methods:
- Electrophysiological recordings from afferent nerve fibers innervating the frog sartorius muscle.
- Stimulation of the muscle via stretch and contraction under varying tension levels.
Main Results:
- Two distinct populations of mechanoreceptors were identified: muscle spindles and extrafusal receptors.
- Muscle spindles were innervated by fast-conducting afferents (24-42 m/sec).
- High-threshold extrafusal receptors had slower afferent conduction velocities (14-22 m/sec), lacked resting discharge, and exhibited weak, variable responses to stretch and contraction.
Conclusions:
- Extrafusal receptors in the frog sartorius muscle possess unique properties distinct from muscle spindles and tendon organs.
- These extrafusal receptors share characteristics with high-threshold pressure receptors and nociceptors found in mammalian muscle.
- The findings suggest a role for these receptors in detecting potentially damaging stimuli rather than proprioception.
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