Background: We investigated the pattern of distribution of corpuscular sensory nerve endings in the shoulder region of the laboratory mouse in relation to their functional properties.
Methods: Twelve adult female white NMRI-F2-mice were used. The topography of sensory nerve endings in the shoulder joint region was reconstructed by three-dimensional image processing by using serial silver-stained sections of paraffin-embedded samples. Semithin sections obtained from additional samples were used for light microscopy.
Results: Within the fibrous layer of the joint capsule, three types of mechanoreceptors were identified: small lamellated corpuscles of the Pacini type, Ruffini corpuscles, and Golgi tendon organs. Intracapsular small lamellated corpuscles of the Pacini type (in an average number of 29/joint) were found mainly in three areas: in the predominantly flaccid tissue of the axillary region, in the denser ventromedial parts of the capsule, close to the scapula, and in the tight texture of the fiber bundles near the glenoid labrum. Ruffini corpuscles were identified only in small numbers (2/joint) in the ventral aspect of the articular capsule of two animals. Golgi tendon organs (14 or 15 receptors/joint) were discovered predominantly in close vicinity to the joint capsule at the muscle tendon junction of the inserting rotator cuff muscles and in the biceps brachii and triceps brachii muscles.
Conclusions: In view of their location in the shoulder joint capsule and the glenoid labrum, corpuscular mechanoreceptors evidently play an important role in joint control by inducing protective reflex actions in phases of extreme or abnormal movement. The density of sensory receptors in distinct areas of the shoulder joint capsule appears to be related to zones that are subjected to increased biomechanical stress during physical activity.