Summary
Excitatory postsynaptic potentials (e.p.s. p.s) elicited by impulses in single muscle spindle afferent fibers from the medial gastrocnemius (m.g.) muscle were recorded intracellularly from homonymous and heteronymous motoneurons in order to study factors that influence the amplitudes of such responses. Impulses in large afferent fibers elicited larger single-fiber e.p.s.p.s than those in smaller afferents. Mean e.p.s.p. amplitudes were related exponentially to afferent conduction velocities of both Ia and spindle group II fibers. The closer a motoneuron was to the spinal entry point of an afferent fiber, the larger was the mean e.p.s.p. amplitude evoked in it. Impulses in the same afferent fiber elicited larger e.p.s.p.s in small than large motoneurons when the two cells were located at the same craniocaudal levels. Other factors being equal, the single-fiber e.p.s.p.s evoked in homonymous and heteronymous motoneurons were approximately equal in amplitude. Relatively simple morphological and topographical explanations for the findings were advanced and their functional significance for orderly recruitment in partitioned and unpartitioned reflexes was described.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Burke RE (1968) Group Ia synaptic input to fast and slow twitch motor-units of cat triceps surae. J Physiol (Lond) 196: 605–630
Clamann HP, Henneman E, Lüscher H-R, Mathis J (1985) Structural and topographical influences on functional connectivity in spinal monosynaptic reflex arcs in the cat. J Physiol (Lond) 358: 483–507
Cohen LA (1953) Localization of stretch reflex. J Neurophysiol 16: 272–285
Cullheim S (1978) Relations between cell body size, axon diameter and axon conduction velocity of cat sciatic alpha-motoneurons stained with horseradish peroxidase. Neurosci Lett 8: 17–20
Fleshman JW, Munson JB, Sypert GW (1981) Homonymous projection of individual group Ia-fibers to physiologically characterized medial gastrocnemius motoneurons in the cat. J Neurophysiol 46: 1339–1348
Gelfan S, Rapisarda F (1964) Synaptic density on spinal motoneurons of normal dogs and dogs with experimental hindlimb rigidity. J Comp Neurol 123: 73–95
Gustaffson B, Pinter MJ (1984) Relations among passive electrical properties of lumbar motoneurones of the cat. J Physiol (Lond) 312: 455–470
Harrison PJ, Taylor A (1981) Individual excitatory post-synaptic potentials due to muscle spindle Ia afferents in cat triceps surae motoneurones. J Physiol (Lond) 312: 455–470
Henneman E, Lüscher H-R, Mathis J (1984) Simultaneously active and inactive synapses of single Ia fibres on cat spinal motoneurones. J Physiol (Lond) 352: 147–161
Ishizuka N, Mannen H, Hongo T, Sasaki S (1979) Trajectory of group Ia afferent fibers stained with horseradish peroxidase in the lumbosacral spinal cord of the cat: from serial sections. J Comp Neurol 186: 189–211
Jack JJB, Redman SJ, Wong K (1981) The components of synaptic potentials evoked in cat spinal motoneurones by impulses in single Ia afferents. J Physiol (Lond) 321: 65–96
Kernell D (1966) Input resistance, electrical excitability and size of ventral horn cells in cat spinal cord. Science 152: 1637–1640
Kernell D, Zwaagstra B (1981) Input conductance, axonal conduction velocity and cell size among hindlimb motoneurones of the cat. Brain Res 204: 311–326
Liddell EGT, Sherrington C (1924) Reflexes in response to stretch (myotatic reflexes). Proc R Soc Lond [Biol] 96: 212–242
Lucas SM, Binder MD (1984) Topographic factors in distribution of homonymous group Ia-afferent input to cat medial gastrocnemius motoneurons. J Neurophysiol 51: 50–63
Lucas SM, Cope TC, Binder MD (1984) Analysis of individual Iaafferent EPSPs in a homonymous motoneuron pool with respect to muscle topography. J Neurophysiol 51: 64–74
Lüscher H-R, Ruenzel P, Fetz E, Henneman E (1979) Postsynaptic population potentials recorded from ventral roots perfused with isotonic sucrose: connections of group Ia and II spindle afferent fibers with large populations of motoneurons. J Neurophysiol 42: 1146–1164
Lüscher H-R, Ruenzel P, Henneman E (1980) Topographic distribution of terminals of Ia and group II fibers in spinal cord, as revealed by postsynaptic population potentials. J Neurophysiol 43: 968–985
Lüscher H-R, Vardar U (1989) A comparison of homonymous and heteronymous connectivity in the spinal monosynaptic reflex arc of the cat. Exp Brain Res 74: 480–492
Mendell LM, Henneman E (1971) Terminals of single Ia fibers: location, density and distribution within a pool of 300 homonymous motoneurons. J Neurophysiol 34: 171–187
Munson JB, Sypert GW (1979) Properties of single fibre excitatory postsynaptic potentials in triceps surae motoneurones. J Physiol (Lond) 296: 329–342
Noven SV, Hamm TM, Stuart DG (1986) Partitioning of monosynaptic Ia excitatory postsynaptic potentials in the motor nucleus of the cat lateral gastrocnemius muscle. J Neurophysiol 55: 569–586
Scott JG, Mendell LM (1976) Individual EPSPs produced by single triceps surae Ia afferent fibers in homonymous and heteronymous motoneurons. J Neurophysiol 39: 679–692
Ulfhake B, Kellerth J-O (1981) A quantitative light microscopic study of the dendrites of cat spinal α-motoneurons after intracellular staining with horseradish peroxidase. J Comp Neurol 202: 571–583
Westbury DR (1982) A comparison of the structures of α-and γ-spinal motoneurones of the cat. J Physiol (Lond) 325: 79–91
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Lüscher, H.R., Stricker, C., Henneman, E. et al. Influences of morphology and topography of motoneurons and muscle spindle afferents on amplitude of single fiber excitatory postsynaptic potentials in cat. Exp Brain Res 74, 493–500 (1989). https://doi.org/10.1007/BF00247351
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00247351