• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of jphysiolThe Journal of Physiology SiteMembershipSubmissionJ Physiol
J Physiol. Apr 1993; 463: 307–324.
PMCID: PMC1175345

Matching between motoneurone and muscle unit properties in rat medial gastrocnemius.

Abstract

1. Electrical and contractile (isometric) properties were studied for sixty-six motoneurone-muscle unit combinations from rat medial gastrocnemius (MG). The animals were anaesthetized with pentobarbitone. 2. The muscle units were classified into S (slow) and F (fast) on the basis of measurements of speed and fatigue resistance: the 'slow' category comprised units with an initial twitch contraction time exceeding those found among fatigue-sensitive units (border value 20 ms). 3. Twitch speed was assessed by three different measures: (i) contraction time (time to peak, range 11.4-28.0 ms), (ii) half-relaxation time (8.4-56.5 ms), and (iii) total twitch duration (34-116 ms). All three measures were mutually highly correlated and their respective values showed a continuous and unimodal distribution across the unit population. 4. The motoneurones were investigated with regard to their time course and amplitude of post-spike after-hyperpolarization (AHP; range of total durations 30-116 ms, amplitudes 0.9-8.0 mV), rheobase (0.8-17.1 nA), input resistance (0.8-5.1 M omega) and axonal conduction velocity (33-85 m/s). 5. Motoneurones of slow-twitch muscle units (type S) had, on average, a significantly slower time course of AHP, a smaller rheobase, a higher input resistance and more slowly conducting axons than those innervating fast-twitch muscle units. 6. Across the whole neuronal sample, input conductance (reciprocal of input resistance) correlated well with rheobase (r = 0.74). However, the differences in rheobase did not seem to be caused exclusively by the associated differences in input conductance. 7. Throughout the sampled population, the relative slowness of AHP showed a continuous and highly significant correlation with the relative slowness of the corresponding unit twitch. The absolute duration of AHP was close to that of the twitch. In the Discussion it is argued that this 'speed match' between motoneurone and muscle unit would help ensure that barely recruited motoneurones start firing at a frequency that is optimally suited for the subsequent rate gradation of force. 8. AHP amplitude was, on average, significantly smaller for fast-twitch than for slow-twitch motoneurones. Calculations indicated that these differences were almost completely caused by the associated differences in input resistance; the computed value for the conductance change underlying the AHP was nearly the same for fast- and slow-twitch motoneurones. 9. A simple neurone model was used to calculate the consequences of the differences in AHP amplitude and duration for repetitive discharge properties of fast and slow cell categories.(ABSTRACT TRUNCATED AT 400 WORDS)

Full text

Full text is available as a scanned copy of the original print version. Get a printable copy (PDF file) of the complete article (2.2M), or click on a page image below to browse page by page. Links to PubMed are also available for Selected References.

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Ariano MA, Armstrong RB, Edgerton VR. Hindlimb muscle fiber populations of five mammals. J Histochem Cytochem. 1973 Jan;21(1):51–55. [PubMed]
  • Barrett EF, Barrett JN, Crill WE. Voltage-sensitive outward currents in cat motoneurones. J Physiol. 1980 Jul;304:251–276. [PMC free article] [PubMed]
  • Burke RE, Levine DN, Tsairis P, Zajac FE., 3rd Physiological types and histochemical profiles in motor units of the cat gastrocnemius. J Physiol. 1973 Nov;234(3):723–748. [PMC free article] [PubMed]
  • Burke RE, Strick PL, Kanda K, Kim CC, Walmsley B. Anatomy of medial gastrocnemius and soleus motor nuclei in cat spinal cord. J Neurophysiol. 1977 May;40(3):667–680. [PubMed]
  • Carp JS, Powers RK, Rymer WZ. Alterations in motoneuron properties induced by acute dorsal spinal hemisection in the decerebrate cat. Exp Brain Res. 1991;83(3):539–548. [PubMed]
  • Dum RP, Kennedy TT. Physiological and histochemical characteristics of motor units in cat tibialis anterior and extensor digitorum longus muscles. J Neurophysiol. 1980 Jun;43(6):1615–1630. [PubMed]
  • Emonet-Dénand F, Hunt CC, Petit J, Pollin B. Proportion of fatigue-resistant motor units in hindlimb muscles of cat and their relation to axonal conduction velocity. J Physiol. 1988 Jun;400:135–158. [PMC free article] [PubMed]
  • Fleshman JW, Munson JB, Sypert GW, Friedman WA. Rheobase, input resistance, and motor-unit type in medial gastrocnemius motoneurons in the cat. J Neurophysiol. 1981 Dec;46(6):1326–1338. [PubMed]
  • FRANK K, FUORTES MG. Stimulation of spinal motoneurones with intracellular electrodes. J Physiol. 1956 Nov 28;134(2):451–470. [PMC free article] [PubMed]
  • Gardiner PF, Kernell D. The "fastness" of rat motoneurones: time-course of afterhyperpolarization in relation to axonal conduction velocity and muscle unit contractile speed. Pflugers Arch. 1990 Mar;415(6):762–766. [PubMed]
  • Grottel K, Celichowski J. Division of motor units in medial gastrocnemius muscle of the rat in the light of variability of their principal properties. Acta Neurobiol Exp (Wars) 1990;50(6):571–587. [PubMed]
  • Gustafsson B, Pinter MJ. An investigation of threshold properties among cat spinal alpha-motoneurones. J Physiol. 1984 Dec;357:453–483. [PMC free article] [PubMed]
  • Harada Y, Takahashi T. The calcium component of the action potential in spinal motoneurones of the rat. J Physiol. 1983 Feb;335:89–100. [PMC free article] [PubMed]
  • Hashizume K, Kanda K, Burke RE. Medial gastrocnemius motor nucleus in the rat: age-related changes in the number and size of motoneurons. J Comp Neurol. 1988 Mar 15;269(3):425–430. [PubMed]
  • Kanda K, Hashizume K. Changes in properties of the medial gastrocnemius motor units in aging rats. J Neurophysiol. 1989 Apr;61(4):737–746. [PubMed]
  • Kanda K, Hashizume K. Factors causing difference in force output among motor units in the rat medial gastrocnemius muscle. J Physiol. 1992 Mar;448:677–695. [PMC free article] [PubMed]
  • Kernell D. The repetitive impulse discharge of a simple neurone model compared to that of spinal motoneurones. Brain Res. 1968 Dec;11(3):685–687. [PubMed]
  • Kernell D. Rhythmic properties of motoneurones innervating muscle fibres of different speed in m. gastrocnemius medialis of the cat. Brain Res. 1979 Jan 5;160(1):159–162. [PubMed]
  • Kernell D. Functional properties of spinal motoneurons and gradation of muscle force. Adv Neurol. 1983;39:213–226. [PubMed]
  • Kernell D. Organization and properties of spinal motoneurones and motor units. Prog Brain Res. 1986;64:21–30. [PubMed]
  • Kernell D, Eerbeek O, Verhey BA. Motor unit categorization on basis of contractile properties: an experimental analysis of the composition of the cat's m. peroneus longus. Exp Brain Res. 1983;50(2-3):211–219. [PubMed]
  • Kernell D, Eerbeek O, Verhey BA, Donselaar Y. Effects of physiological amounts of high- and low-rate chronic stimulation on fast-twitch muscle of the cat hindlimb. I. Speed- and force-related properties. J Neurophysiol. 1987 Sep;58(3):598–613. [PubMed]
  • Kernell D, Monster AW. Threshold current for repetitive impulse firing in motoneurones innervating muscle fibres of different fatigue sensitivity in the cat. Brain Res. 1981 Dec 14;229(1):193–196. [PubMed]
  • Kernell D, Monster AW. Motoneurone properties and motor fatigue. An intracellular study of gastrocnemius motoneurones of the cat. Exp Brain Res. 1982;46(2):197–204. [PubMed]
  • Kernell D, Zwaagstra B. Input conductance axonal conduction velocity and cell size among hindlimb motoneurones of the cat. Brain Res. 1981 Jan 12;204(2):311–326. [PubMed]
  • Kernell D, Zwaagstra B. Dendrites of cat's spinal motoneurones: relationship between stem diameter and predicted input conductance. J Physiol. 1989 Jun;413:255–269. [PMC free article] [PubMed]
  • McDonagh JC, Binder MD, Reinking RM, Stuart DG. Tetrapartite classification of motor units of cat tibialis posterior. J Neurophysiol. 1980 Oct;44(4):696–712. [PubMed]
  • Moore J, Appenteng K. The membrane properties and firing characteristics of rat jaw-elevator motoneurones. J Physiol. 1990 Apr;423:137–153. [PMC free article] [PubMed]
  • Pinter MJ, Curtis RL, Hosko MJ. Voltage threshold and excitability among variously sized cat hindlimb motoneurons. J Neurophysiol. 1983 Sep;50(3):644–657. [PubMed]
  • Tötösy de Zepetnek JE, Zung HV, Erdebil S, Gordon T. Motor-unit categorization based on contractile and histochemical properties: a glycogen depletion analysis of normal and reinnervated rat tibialis anterior muscle. J Neurophysiol. 1992 May;67(5):1404–1415. [PubMed]
  • Zengel JE, Reid SA, Sypert GW, Munson JB. Membrane electrical properties and prediction of motor-unit type of medial gastrocnemius motoneurons in the cat. J Neurophysiol. 1985 May;53(5):1323–1344. [PubMed]

Articles from The Journal of Physiology are provided here courtesy of The Physiological Society

Formats:

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...

Links

  • MedGen
    MedGen
    Related information in MedGen
  • PubMed
    PubMed
    PubMed citations for these articles

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...