Recruitment and Frequency Coding of Diaphragm Motor Units During Ventilatory and Non-Ventilatory Behaviors
The motor unit, comprised of an alpha motoneuron and the muscle fibers it innervates, is the final common pathway by which the nervous system controls muscle contractions. Since the pioneering studies of Sherrington (13), it has been recognized that the central nervous system controls the force generated by a muscle by changing the number of activated motor units (recruitment coding) or by modifying the discharge frequency of recruited units (frequency coding). In mixed muscles, motor units display a variety of contractile and fatigue properties (2). Thus, to accomplish different motor behaviors, the nervous system has a repertoire of units from which to select, For example, under conditions requiring prolonged force production, the nervous system might select to recruit only those units that are fatigue resistant. Under other conditions requiring shorts bursts of force, unit fatigue resistance might not be an important determinant in unit recruitment. Instead, more fatigable units, which typically generate greater forces might be selectively recruited. The nervous system might also select to increase force by increasing the discharge rate of those units already active.
KeywordsFatigue Catheter Lactate Cage Respiration
Unable to display preview. Download preview PDF.
- 1.Agostini, E. and J. Mead. Statics of the respiratory system. In: Handbook of Physiology, edited by W.O. Fenn and H. Rahn. Baltimore, MD: Williams and Wilkins, 1964, Vol. I, sect. 3, pp. 387–409.Google Scholar
- 2.Burke, R.E. Motor units: Anatomy, physiology, and functional organization. In: Handbook of Physiology, The Nervous System, Motor Control, edited by J. M. Brookhart and V.B. Mountcastle. Bethesda, MD: Am. Physiol., Soc., 1981, Vol. II, Part 1, sect. 1, pp. 345–422.Google Scholar
- 8.Fournier, M. and G.C. Sieck. Topographical projections of phrenic motoneurons and motor unit territories in the cat diaphragm. In Respiratory Muscles and Their Neuromotor Control, edited by G.C. Sieck, S.C. Gandevia, and W.E. Cameron. New York, NY: Alan R.Liss, 1987, pp. 215–226.Google Scholar
- 9.Henneman, E. and L.M. Mendell. Functional organization of motoneuron pool and its input. In: Handbook of Physiology, The Nervous System, Motor Control, edited by J.M. Brookhart and V.B. Mountcastle. Bethesda, MD: Am. Physiol. Soc., 1981, Vol. II, part 1, sect. 1, pp. 423–507.Google Scholar