Standard Article

Functional Organization of Motoneuron Pool and its Inputs

Handbook of Physiology, The Nervous System, Motor Control

  1. Elwood Henneman1,
  2. Lorne M. Mendell2

Published Online: 1 JAN 2011

DOI: 10.1002/cphy.cp010211

Comprehensive Physiology

Comprehensive Physiology

How to Cite

Henneman, E. and Mendell, L. M. 2011. Functional Organization of Motoneuron Pool and its Inputs. Comprehensive Physiology. 423–507.

Author Information

  1. 1

    Department of Physiology, Harvard Medical School, Boston, Massachusetts

  2. 2

    Department of Physiology, Duke University Medical Center, Durham, North Carolina

Publication History

  1. Published Online: 1 JAN 2011

Abstract

The sections in this article are:

  • 1
    Morphological Considerations
    • 1.1
      Columnar Arrangement of Motoneuron Pool
    • 1.2
      Dimensions of α-Motoneurons and Distribution of Cell Size
    • 1.3
      Scaling of Motoneurons
    • 1.4
      Initial Segment of α-Motor Axons
    • 1.5
      Axon Collaterals of α-Motoneurons
    • 1.6
      Recurrent Inhibitory Feedback from Motoneurons
    • 1.7
      Direct Synaptic Interconnections Between Spinal Motoneurons
    • 1.8
      Species of Motoneurons
    • 1.9
      Terminals of Motoneurons in Muscle
    • 1.10
      Morphology of Neuromuscular Junctions
    • 1.11
      Matching the Properties of Motoneurons and the Muscle Fibers They Supply
    • 1.12
      Concluding Comments
  • 2
    Firing Patterns of Individual Motoneurons and Motor Units
    • 2.1
      Functional Significance of Size of Motoneurons
    • 2.2
      Measurement of Total Output of Motoneuron Pools
    • 2.3
      Critical Firing Levels of Motoneurons
    • 2.4
      Relation of Critical Firing Level to Axon Diameter and Motoneuron Size
    • 2.5
      Effects of Inhibitory Inputs on Critical Firing Level and Rank Order During Repetitive Firing
    • 2.6
      Recruitment of Motor Units in Humans
    • 2.7
      Evidence Regarding Alternative Patterns of Recruitment
    • 2.8
      Evidence Regarding Voluntary Selective Control of Motor Units
    • 2.9
      Size Principle in Other Species
    • 2.10
      Modulation of Firing Rate
  • 3
    Organization of Input to Motoneuron Pools
    • 3.1
      Anatomical Studies
    • 3.2
      Techniques Used to Study EPSPs Elicited by Impulses in Single Afferent Fibers
    • 3.3
      Amplitudes of EPSPs Elicited by Impulses in Single Fibers
    • 3.4
      Boutons of Ia-Fibers on Motoneurons
    • 3.5
      Physiology of Ia-Terminals
    • 3.6
      Distribution of Ia Excitation to Motoneuron Pools
    • 3.7
      Comparison of Projections to Homonymous and Heteronymous Motoneurons
    • 3.8
      Correlations Between Morphology and Function
    • 3.9
      Latency of EPSPs
    • 3.10
      Other Examples of Divergence in Inputs to Motoneurons
    • 3.11
      Ia-Projections to Motoneurons Controlling Other Parts of the Body
    • 3.12
      Group II Input From Secondary Endings in Muscle Spindles
    • 3.13
      Inhibitory Inputs to Motoneurons
    • 3.14
      Group Ib Input From Golgi Tendon Organs
    • 3.15
      Monosynaptic Input From Descending Pathways
    • 3.16
      Topographic Factors Governing Development of Connections of Ia-Fibers to Motoneurons
    • 3.17
      Concluding Comments
  • 4
    Nonuniformity of Motoneurons
    • 4.1
      Early Classification of Tonic and Phasic Types of Motoneurons
    • 4.2
      Significance of Nonuniformity of Muscle Fibers
    • 4.3
      Motoneuron Properties Independent of Size
    • 4.4
      Differential Responses of Motoneurons to Injected Currents
    • 4.5
      Influence of Muscle on Developing and Mature Motoneurons
    • 4.6
      Evidence From Human Disease
    • 4.7
      Concluding Comments
  • 5
    How Size of Motoneurons Determines their Susceptibility to Discharge
    • 5.1
      Properties of Motoneurons That Influence Susceptibility to Discharge
    • 5.2
      Role of Input in Determining Susceptibility to Discharge
  • 6
    Some Principles Underlying Organization of Motoneuron Pools
    • 6.1
      How Sensitivity in Gradation of Tension is Achieved
    • 6.2
      Basis for Relation Between Motoneuron Size and the Force Its Motor Unit Develops
    • 6.3
      Actual Sensitivity in Grading Muscular Tension
    • 6.4
      Mathematical Derivation of a “Principle of Maximum Grading Sensitivity”
    • 6.5
      Recruitment Order and Minimum Energy Principle
    • 6.6
      Collective Action of Motoneuron Pool: Role of Input
    • 6.7
      The Size Principle in Ia and Group II Sensory Fibers
    • 6.8
      How Does the Central Nervous System Use the Motoneuron Pool?