Phrenic motor unit recruitment during ventilatory and non-ventilatory behaviors

Carlos B. Mantilla, Gary C. Sieck

Research output: Contribution to journalReview article

61 Scopus citations

Abstract

Phrenic motoneurons are located in the cervical spinal cord and innervate the diaphragm muscle, the main inspiratory muscle in mammals. Similar to other skeletal muscles, phrenic motoneurons and diaphragm muscle fibers form motor units which are the final element of neuromotor control. In addition to their role in sustaining ventilation, phrenic motor units are active in other non-ventilatory behaviors important for airway clearance such as coughing or sneezing. Diaphragm muscle fibers comprise all fiber types and are commonly classified based on expression of contractile proteins including myosin heavy chain isoforms. Although there are differences in contractile and fatigue properties across motor units, there is a matching of properties for the motor neuron and muscle fibers within a motor unit. Motor units are generally recruited in order such that fatigue-resistant motor units are recruited earlier and more often than more fatigable motor units. Thus, in sustaining ventilation, fatigue-resistant motor units are likely required. Based on a series of studies in cats, hamsters and rats, an orderly model of motor unit recruitment was proposed that takes into consideration the maximum forces generated by single type-identified diaphragm muscle fibers as well as the proportion of the different motor unit types. Using this model, eupnea can be accomplished by activation of only slow-twitch diaphragm motor units and only a subset of fast-twitch, fatigue-resistant units. Activation of fast-twitch fatigable motor units only becomes necessary when accomplishing tasks that require greater force generation by the diaphragm muscle, e.g., sneezing and coughing.

Original languageEnglish (US)
Pages (from-to)57-63
Number of pages7
JournalRespiratory Physiology and Neurobiology
Volume179
Issue number1
DOIs
StatePublished - Oct 15 2011

Keywords

  • Diaphragm muscle
  • Henneman size principle
  • Motor unit
  • Muscle fiber type
  • Recruitment order

ASJC Scopus subject areas

  • Neuroscience(all)
  • Physiology
  • Pulmonary and Respiratory Medicine

Fingerprint Dive into the research topics of 'Phrenic motor unit recruitment during ventilatory and non-ventilatory behaviors'. Together they form a unique fingerprint.

  • Cite this