Anatomical organization and sensory receptor content of soft tissues surrounding upper cervical vertebrae in the cat.

Abstract

The anatomical organization of joints and soft tissues investing upper cervical vertebrae were examined both by microdissection of vertebral columns and by histological analysis of 4 vertebral columns, which were decalcified, serially sectioned and stained with Ag and collagen methods. The distribution of encapsulated receptors throughout soft tissues was mapped. Vertebrae are interconnected by a complex series of small muscles. All intervertebral muscles contained large numbers of muscle spindles, most commonly located in deep muscle regions near intramuscular tendons. Golgi tendon organs (GTO) were common at musculotendinous interfaces in spindle-rich muscle regions. Between 25 and 75% of GTO in different intervertebral muscles were associated in dyad with one or more muscle spindles. The organization of connective tissues around intervertebral joints varied from 1 region to another. Plane joints between articular processes of C2-C5 were enclosed in thin but highly structured capsules, which were largely composed of fibrous connective tissue. The pivot joint between C1 and C2 was enclosed in a looser, kidney-shaped capsule whose cytological composition varied in its ventral, lateral and dorsal regions. Layers of connective tissue also covered the external surfaces of fibrocartilagenous disk regions. All these connective tissues contained paciniform corpuscles, but no other encapsulated receptors could be identified. Paciniform corpuscles were found both in circumscribed regions of muscle near tendons and in fibrous connective tissues. Most paciniform corpuscles were located in the fibrous outer layers of intervertebral joint capsules. Proprioceptive information from tissues around cervical vertebrae originates from receptors in both muscles and joints. A role for the unusually large numbers of muscle spindles and GTO must be considered when defining the mechanisms of position sense for the vertebral column.