No abstract

Silver-stained sections have been examined from the five dorsal neck muscles splenius, biventer, cervicis, complexus, rectus capitis major, and occipitoscapularis. Every serial section was examined for at least one muscle of each type so that a complete description of the spindle distribution and morphology could be made. With the exception of occipitoscapularis (whose prime function is probably in scapula rotation and not in head movement), neck muscles have a remarkably high spindle density. Occipitoscapularis has a spindle density similar to that of hindleg locomotor muscles (13-19 per gram), but splenius has a density of 46-66 per gram, biventer cervicis 74-96 per gram, complexus 71-107 per gram, and rectus capitis major 48-84 per gram. Such high densities have only previously been seen in small muscles whose total spindle population is not large. Because of the relatively large size of some neck muscles, individual muscles with a spindle content of up to 254 spindles have been found.

No abstract

1. Single-fiber recording was used to examine the properties of 107 spindle endings in cat biventer cervicis (BC) and complexus (CM) muscles. Responses of receptors were examined following muscle contraction and ramp and hold stretch. Twenty-two endings in splenius (SP) were also examined, but their responses could not be quantitated because the anatomy of SP prevented the application of appropriate stretches. 2. Conduction velocitites of spindle afferents ranged from 13 to 90 m/s. Endings with primary response patterns usually had faster conduction velocities than secondary endings, but there was overlap in the conduction velocity ranges of the two subgroups. 3. Most neck spindle afferents could be classified as either primary or secondary by a constellation of physiological criteria including dynamic response pattern, dynamic index, and variability of resting discharge frequency. However, 22 of 107 endings from BC and CM had responses with characteristics intermediate between primary and secondary responses. The possible sources of these characteristics are discussed. 4. Despite the similarity in properties between spindles of different neck muscles, the length sensitivities of CM spindles were high compared to those of BC spindles. CM spindles showed length-related modulation of firing frequency over a more restricted range of initial muscle lengths than did BC spindles. 5. Eight Golgi tendon organs (GTO) were identified by their characteristics responses. Conduction velocities obtained for five GTO afferent nerves ranged from 50 to 67 m/s. Recordings were also made from receptros in deep muscles surrounding the vertebrae. These receptors had properties characteristic of muscle spindles.

No abstract