Nerve endings in mammalian muscle

SINCE Ruffini [1898] gave us his beautiful drawings of muscle spindles, and Sherrington [1894] showed that they were sensory end-organs, our knowledge of their function and importance has been steadily growing owing to the observations of physiologists in many parts of the world, and particularly to those of Sherriington and his co-workers. Until recent years our knowledge of the behaviour of the sense organs in muscle was obtained by inference and indirect observations. The only direct observations on mammalian proprioceptors made hitherto are those of Forbes, Campbell and Williams [1924], and Mc Couch, Forbes and Rice [1928], who, using a string galvanometer, were able to show that sensory action currents occurred after a muscle had contracted. But now the methods pioneered by Adrian have made direct observation of the response of these nerve endings possible, and it has only been necessary to adapt the technique to the pecularities of the problem for the behaviour of mammalian muscle spindles to be studied directly. A considerable amount of work has already been done oin the nerve endings in frog's muscle [Adrian and Zotterman, 1926a; Bronk, 1929a and b; Matthews, 1929b, 1931a and b], but the histology of the' nerve endings in mammalian muscle is far more complex than that of the muscle spindles in the frog, and does not justify the assumption that they behave in exactly the same way. The present work has been undertaken to see what can be learnt of these nerve endings by -direct observation, and this paper is a general survey of the subject, as the work has raised many new problems which have not as yet been fully examined. The tecbnique employed is essentially the same as that by which muscle spindles in the frog were studied [Matthews, 1931 a, b], but many modifications in details have been necessary.