Distribution of sensory receptors in joints of the upper cervical column in the laboratory marsupial Monodelphis domestica

In order to investigate the sensory innervation, the upper cervical spine o f a small laboratory marsupial (monodelphis domestica) was examined with se rial section light microscopy and re-embedding of selected sections for ele ctron microscopy. Large numbers of free nerve endings supplied by A delta- and C-fibres were found in the longitudinal ligaments and facet joint capsu les. Electron microscopically, areas of direct contact between axon and col lagen fibres of the surrounding connective tissue separated only by the bas al lamina were observed. Such structural adaptations suggest mechanorecepti ve or polymodal nociceptive functions. In addition, about 100 small lamella ted corpuscles were found in the longitudinal ligaments mainly concentrated around the first intervertebral disk. Electron microscopy shows finger-lik e processes extending from the axon terminal into the inner core lamellae. These are the likely sites of the mechanoelectric transduction process. Sma ller numbers of lamellated corpuscles were seen in the lower intervertebral disks and facet joint capsules. Lamellated corpuscles are known to functio n as rapidly adapting mechanoreceptors supplementing information supplied b y muscle spindles to the CNS about position and movement of the cervical sp ine.