Summary
Volume conduction measurements were carried out on the brachial biceps, tibialis anterior and deltoid, in normal human subjects. Attenuation constant K and time constant t of the muscle tissue transfer function were measured, and the average electrode uptake area calculated for the three muscles. The average number of muscle fibres in the motor unit, i.e., the innervation ratio, was calculated from the electrode uptake area, data on the motor unit territory, and measurements of fibre density. The innervation ratios for the brachial biceps, tibialis anterior and deltoid were 209, 329, and 239 fibres, respectively. It was found that the anatomical scatter of fibres belonging to the same motor unit was smaller in brachial biceps than in tibialis anterior, whereas the electrophysiological “fibre density” was higher in tibialis anterior. The implications of these findings for the interpretation of normal and abnormal electromyographic findings are discussed.
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References
Bors J (1926) Über das Zahlenverhältnis zwischen Nerven und Muskelfasern. Anat Anz 60: 415–416
Brandstater ME, Lambert EH (1969) A histochemical study of the spatial arrangement of muscle fibres in single motor units within rat tibialis anterior muscle. Bull Am Assoc EMG Electrodiagn 82: 15–16
Broman H, Lindström L (1974) A model describing the power spectrum of myoelectric signals. Part II. Technical report. Res Lab Electr 8: 74
Brooke, MH, Engel WK (1969) The histographic analysis of human muscle biopsies with regard to fiber types. Neurology (Minneap) 19: 221–233
Buchthal F (1960) The general concept of the motor unit. In: Adam RD, Eaton LM, Shy GM (eds) Neuromuscular disorders. Williams and Wilkins, Baltimore, pp 3–30
Buchthal F, Erminio F, Rosenfalck P (1959) Motor unit territory in different human muscles. Acta Physiol Scand 45: 72–87
Buchthal F, Guld C, Rosenfalck P (1955) Propagation velocity in electrically activated muscle fibres in man. Acta Physiol Scand 34: 75–89
Burke RE, Levin DN, Zajac FE, Tsairis P, Engel WKL (1971) Mammalian motor units. Physiological-histochemical correlation in three types in cat gastrocnemius. Science 174: 709–712
Christensen E (1959) Topography of terminal motor innervation in striated muscles from stillborn infants. Am J Phys Med 38: 65–78
Clarke DE (1931) Muscle counts of motor units. Study in innervation ratios. Am J Physiol 96: 296–304
Feinstein, B, Lindegard B, Nyman E, Wholfart G (1955) Morphologic studies of motor units in normal human muscles. Acta Anat (Basel) 23: 127–142
Gath I, Stålberg E (1975) Frequency and time domain characteristics of single muscle fibre action potentials. Electroencephalogr Clin Neurophysiol 39: 371–376
Gath I, Stålberg E (1977) On the volume conduction in human skeletal muscle: in situ measurements. Electroencephalogr Clin Neurophysiol 43: 106–110
Gath I, Stålberg E (1978) The calculated radial decline of the extracellular action potential compared with in situ measurements in the human brachial biceps. Electroencephalogr Clin Neurophysiol 44: 547–552
Gath I, Stålberg E (1979) Measurements of the uptake area of small-size electromyographic electrodes. IEEE Trans Biomed Eng 26: 374–376
Ishimaru A (1978) Wave propagation and scattering in random media, vol I. Academic Press, London
Jennekens FGI, Tomlinson BE, Walton JN (1971) The sizes of the two main histochemical fibre types in five limb muscles in man. J Neurol Sci 13: 281–292
Kugelberg, E (1973) Properties of the rat hind-limb motor units. In: Desmedt JE (ed) New developments in electromyography and clinical neurophysiology, vol 3. Karger, Basel, pp 234–241
Kugelberg, E, Edström L (1968) Differential histochemical effects of muscle contractions on phosphorylase and glycogen in various types of fibres. Relation to fatigue. J Neurol Neurosurg Psychiatry 31: 415–423
Rexed B, Therman PO (1948) Calibre spectra of motor and sensory nerve fibres to flexor and extensor muscles. J Neurophysiol 11: 133–139
Sherrington CS (1925) Remarks on some aspects of reflex inhibition. Proc R Soc Lond [Biol] 97: 519–545
Stålberg E (1966) Propagation velocity in human muscle fibres in situ. Acta Physiol Scand [Suppl] 287: 1–112
Stålberg E, Thiele B (1975) Motor unit fibre density in the extensor digitorum communis muscle. J Neurol Neurosurg Psychiatry 38: 874–880
Stålberg, E, Schwartz MS, Thiele B, Schiller HH (1976) The normal motor unit in man. A single fibre EMG multielectrode investigation. J Neurol Sci 27: 291–301
Tergast P (1813) Über das Verhältnis von Nerven und Muskeln. Arch Mikr Anat 9: 36–49
Wray SH (1969) Innervation ratios for large and small limb muscles in the baboon. J Comp Neurol 137: 227–250
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Gath, I., Stålberg, E. In situ measurement of the innervation ratio of motor units in human muscles. Exp Brain Res 43, 377–382 (1981). https://doi.org/10.1007/BF00238380
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DOI: https://doi.org/10.1007/BF00238380