The proprioceptive reflex control of the intercostal muscles during their voluntary activation.
TL;DR: A quantitative study has been made of the reflex effects of sudden changes in mechanical load on contracting human intercostal muscles during willed breathing movements involving the chest wall.
Abstract: 1. A quantitative study has been made of the reflex effects of sudden changes in mechanical load on contracting human intercostal muscles during willed breathing movements involving the chest wall. Averaging techniques were applied to recordings of electromyogram (EMG) and lung volume, and to other parameters of breathing.
2. Load changes were effected for brief periods (10–150 msec) at any predetermined lung volume by sudden connexion of the airway to a pressure source variable between ± 80 cm H2O so that respiratory movement could be either assisted or opposed. In some experiments airway resistance was suddenly reduced by porting from a high to a low resistance external airway.
3. Contracting inspiratory and expiratory intercostal muscles showed a ‘silent period’ with unloading which is attributed to the sudden withdrawal from intercostal motoneurones of monosynaptic excitation of muscle spindle origin.
4. For both inspiratory and expiratory intercostal muscles the typical immediate effect of an increase in load was an inhibitory response (IR) with a latency of about 22 msec followed by an excitatory response (ER) with a latency of 50–60 msec.
5. It was established using brief duration stimuli (< 40 msec) that the IR depended on mechanical events associated with the onset of stimulation, whereas stimuli greater than 40 msec in duration were required to evoke the ER.
6. For constant expiratory flow rate and a constant load, the ER of expiratory intercostal muscles increased as lung volume decreased within the limits set by maximal activation of the motoneurone pool as residual volume was approached.
7. The ER to a constant load increased directly with the expiratory flow rate at which the load applied, also within limits set by maximal activation of the motoneurone pool.
8. For a given load, the ER during phonation was greater than that occurring at a similar expiratory flow rate without phonation when the resistance of the phonating larynx was mimicked by an external airway resistance.
9. It is argued that the IR is due to autogenetic inhibition arising from tendon organs and that the ER is due to autogenetic excitation arising from intercostal muscle spindles.
10. The initial dominance of inhibition in this dual proprioceptive reflex control was not predicted by the servo theory. It is proposed that the reflex pathways subserving autogenetic inhibition are under a centrifugal control which determines in relation to previous experience (learning) the conditions under which autogenetic facilitation is allowed.
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TL;DR: Vocalization, in contrast to completely innate vocal reactions, needs the intactness of the forebrain and needs a facilitatory input from the periaqueductal grey of the midbrain and laterally bordering tegmentum in order to be able to produce vocalizations.
780 citations
TL;DR: The sections in this article are: Methodological Considerations, General Summary and Epilogue, Ascending Pathways that Monitor Segmental Interneuronal Activity, and Evidence That Ascending FRA Pathways Monitor Activity in interneurons of Reflex Pathways.
Abstract: The sections in this article are:
1
Methodological Considerations
1.1
Selective Stimulation of Primary Afferents
1.2
Stimulation of Central Motor Systems
1.3
Methods for Investigation of Convergence at Interneuronal Level
2
Spinal Neuronal Circuits Used in Common by Segmental Afferents and Supraspinal Motor Centers
2.1
Recurrent Inhibition
2.2
Pathways From Ia-Afferents and Their Control by γ-Motoneurons
2.3
Reflex Pathways From Group Ib Tendon Organ Afferents
2.4
Reflex Pathways From Cutaneous and Joint Afferents and From Groups II and III Muscle Afferents
2.5
Propriospinal Neurons
2.6
Presynaptic Inhibition of Transmission From Primary Afferents
3
Reticulospinal Inhibition of Segmental Reflex Transmission
3.1
Dorsal Reticulospinal System
3.2
Ventral Reticulospinal Pathways
3.3
Monoaminergic Reticulospinal Pathways
3.4
Decerebrate Preparation
4
Direct Projections of Descending Pathways to α-Motoneurons
5
Ascending Pathways that Monitor Segmental Interneuronal Activity
5.1
Evidence That Ascending FRA Pathways Monitor Activity in Interneurons of Reflex Pathways
5.2
Information Via Ascending Collaterals of Interneurons
5.3
Ventral Flexor Reflex Tracts
5.4
Ventral Spinocerebellar Tract
6
General Summary and Epilogue
6.1
General Summary
6.2
Epilogue
662 citations
TL;DR: It is confirmed that most subjects can suppress triggered reactions when the instruction calls for no intervention, leaving an unmodified reflex response, which implies the existence of and compensation for nonlinear muscle mechanical properties.
Abstract: 1. The stretch reflex in the elbow flexor musculature was studied in 23 human subjects. The subjects were required to establish an initial force equivalent to 10% maximum at a prescribed initial length; mechanical disturbances delivered at random times increased load force to 15% or reduced it to 5%. We measured arm force, displacement, and EMG (usually biceps); acceleration was calculated from displacement, and average responses from sets of 10 like trials. 2. Modification of the stretch reflex was studied by comparing average responses obtained with different instructions, but with the same disturbance. The usual introductions were "compensate for arm deflection" and "do not intervene voluntarily". The initial response did not depend on instruction; changes in response that depended on instruction began abruptly after a latent period which ranged from 70 to 320 ms (measured from force and acceleration), depending on conditions and subject. The latency became longer (10-50 ms) and more variable when the subject did not know the direction of disturbance in advance. This and other observations indicate that modifications of the stretch reflex are not produced by servo actions. They are produced by triggered reactions, which occur at both short and long latencies and which have properties resembling the movements produced in a reaction-time task. 3. We confirmed that most subjects can suppress triggered reactions when the instruction calls for no intervention, leaving an unmodified reflex response. This response consists of a compliant deflection of the arm in the direction of the disturbance. 4. The compensatory actions associated with unmodified stretch (and unloading) reflexes were assessed from EMG responses of biceps. During a 300-ms transient phase, EMG changes were notably asymmetric when responses to symmetric disturbances were compared. Increased force stretched biceps and produced a prominent increase in EMG, whereas decreased force allowed biceps to shorten and produced either an EMG decrease of smaller magnitude or an actual increase. These asymmetric reflex actions produced quite symmetric mechanical responses (arm displacements and forces), which implies the existence of and compensation for nonlinear muscle mechanical properties. This result is discussed in relation to the hypothesis that the function of the stretch reflex is to compensate for variations in muscle properties, thus maintaining stiffness. 5. Effective control of muscle length or joint position does not result from servo action by the stretch reflex. Errors in position are corrected only when triggered reactions are superimposed on the reflex response.
644 citations
TL;DR: In this paper, the authors used the pre-and post-stimulus time (PPST) histogram to detect synchronized firing among groups of intercostal motoneurones discharging in response to their natural synaptic drives.
Abstract: 1. The hypothesis is advanced that the joint occurrence of unitary excitatory post-synaptic potentials e.p.s.p.s) evoked in motoneurones by branches of common stem pre-synaptic fibres causes short-term synchronization of their discharge during the rising phases of the unitary e.p.s.p.s. 2. This hypothesis was tested using the pre- and post-stimulus time (PPST) histogram to detect synchronized firing among groups of intercostal motoneurones discharging in response to their natural synaptic drives. 3. Motor nerve action potentials were recorded monophasically from nerve filaments of the external intercostal muscles of anaesthetized, paralysed cats maintained on artificial ventilation. 4. Computer methods were used to measure peak spike amplitude, spike amplitude, spike interval and filament identification for simultaneous recordings from four filaments. The spike amplitude histograms were derived for each filament and groups of spikes were selected for analysis. 5. With spikes of one group designated as 'stimuli' (occurring at zero time) and those of a second as 'response' the PPST histogram was computed with different time bin widths. 6. With bin widths of 100 and 10 msec the central respiratory periodicity was apparent in the PPST histogram. With 1.0 msec bins the PPST histogram showed a narrow central peak extending to +/- 3.0 msec at its base. This 'short-term synchronization' supports the hypothesis of joint firing due to common presynaptic connectivity. 7. It was shown that detection of short-term synchronization was critically dependent on a sufficient quantity of data but that provided a simple criterion of adequate counts per bin in the PPST histogram was met, short-term synchronization could be detected between intercostal motoneurones of the same and adjacent segments.
411 citations
TL;DR: The sections in this article are:Respiratory Homeostasis and Control of Respiratory Movements, Exercise—An Example of an Integrated Response, and Conclusion.
Abstract: The sections in this article are:
1
Respiratory Homeostasis and Control of Respiratory Movements
1.1
Effectors of Ventilation
1.2
Respiratory Muscles and Their Innervation
1.3
Summary
2
Central Location of Respiratory Controller
2.1
Historical Background
2.2
Summary
2.3
Modern View
2.4
Brain Stem Anatomy
2.5
Classification of Respiratory Neurons
2.6
Connections Between Respiratory Neurons
2.7
Location and Mechanisms for Generation of Respiratory Patterns
2.8
Production of Respiratory Pattern
2.9
Central Pattern Generation and Respiration
2.10
Hypothesis for Role of Dorsal and Ventral Respiratory Groups in Generating Respiratory Pattern
3
Sensors
3.1
Time Course of Responses to Respiratory Afferent Stimulation
3.2
Integrated Responses to Changes in Carbon Dioxide
3.3
Integrated Responses to Changes in Oxygen
3.4
Summary
4
Mechanoreceptors
4.1
Pulmonary Stretch Receptors
4.2
Summary
5
Exercise—An Example of an Integrated Response
5.1
Critique
6
State Dependence
7
Conclusion
390 citations