Muscle Spindles

Abstract

Based on a Dissertation presented to the Society on 6th November, 1964

The action of our muscles is controlled with a remarkable delicacy, and components of the nervous system at every level contribute to this. On the afferent side, the stretch receptors of muscle spindles are the most peripheral elements and have been known to histologists and physiologists for more than a century, Hassall must receive the credit for the discovery of muscle spindles in 1851, but the first systematic description was Weissmann’s in 1861. Each spindle consists of a parallel bundle of striated muscle fibres—intrafusal fibres. The bundle is 7 to 12 mm. long, and is surrounded by what Sherrington later called the lymph space, because he was able to inject it with dye via the lymph vessels: this space is enclosed by a thin fibrous capsule. The intrafusal fibres vary in their length and diameter, and are attached to one another at their ends; the ends of the longest fibres are attached to extrafusal endomysium. The spindle is supplied with nerves of various diameters terminating in different types of ending on the intrafusal fibres.