Topography of corpuscular mechanoreceptors in the shoulder joint region ofmonodelphis domestica

The topography and structure of corpuscular mechanoreceptors in the shoulde r joint capsule and periarticular connective tissue of a small laboratory m arsupial (monodelphis domestica) were studied using light and electron micr oscopy. This animal is known to use its upper extremities for a wide range of activities like climbing and manipulating food. Thus, the shoulder joint of this animal species has a similar wide range of movement as the human s houlder joint, but is small enough for serial sectioning in its entirety. S ilver stained serial paraffin sections were examined under the light micros cope and the distribution of the different types of mechanoreceptors was re constructed using three-dimensional image processing. In addition, selected mechanoreceptors were studied electron microscopically. Approximately 100 small lamellated corpuscles were found in the dense connective tissue of th e joint capsule close to the insertion on the scapula and in the thickening of the joint capsule close to the glenoid labrum. Ruffini corpuscles were found in much smaller numbers in the moderately dense connective tissue of the axillary region. Only very few Vater-Pacinian corpuscles were seen in t he soft periarticular connective tissue. The large number and localization of mechanoreceptor corpuscles in the shoulder joint capsule especially clos e to the glenoid labrum suggests, that these specialized nerve endings are likely to play an important role in control of joint movement. They can ind uce protective reflexes during extreme movements in the shoulder joint prev enting shoulder luxation by increasing the tone of muscles pressing the hum erus head into the glenoid cavity. Anat Rec 263: 35-40, 2001. (C) 2001 Wile y-Liss, Inc.