An electron microscopic study of the muscle spindle in the arytenoid muscle of the human larynx

We used transmission electron microscopy to examine a muscle spindle found in serial sections of the arytenoid muscle of the human larynx. Eight intrafusal fibers were observed at the equatorial region and contained two types of muscle fibers, nuclear bag fibers and nuclear chain fibers. The sensory nerve endings found on the nuclear bag fibers were annular or varicose in shape and contained numerous mitochondria. Another small sensory ending was composed of many vesicles and some dense granules. The fusimotor nerve endings found on the nuclear chain fibers had three types of endings with different sizes and complexities.