PMID- 7776236
OWN - NLM
STAT- MEDLINE
DCOM- 19950712
LR  - 20190512
IS  - 0022-3751 (Print)
IS  - 1469-7793 (Electronic)
IS  - 0022-3751 (Linking)
VI  - 483 ( Pt 1)
IP  - Pt 1
DP  - 1995 Feb 15
TI  - Responses of human masseter motor units to stretch.
PG  - 251-64
AB  - 1. The reflex responses to stretch were studied in single motor units and the 
      surface electromyogram in human masseter. 2. Controlled stretches of the 
      isometrically contracting jaw-closing muscles evoked short-latency (10-15 ms) and 
      long-latency (35-70 ms) excitatory reflex responses in the masseter surface 
      electromyogram. 3. The majority (65%) of tonically active masseter motor units 
      were excited in both short- and long-latency phases of the reflex. The timing of 
      the stimulus determined whether the unit discharged in the short- or long-latency 
      phase. If a non-tonically active motor unit was recruited by the stimulus, it 
      invariably discharged in the long-latency phase. 4. Although short-latency 
      responses were strongly time-locked to the stimulus, there was very little 
      shortening of interspike intervals (ISIs) in this phase of the reflex. The 
      shortening of ISIs was more prominent and prolonged during the long-latency 
      phase, which explains why this phase produces most of the reflex force changes 
      following the stretch. 5. Within pairs of concurrently active motor units there 
      was a tenfold range in the size of the short-latency response to the same 
      stretch. 6. A substantial proportion (35%) of the twenty-two masseter motor units 
      tested had no statistically significant short-latency reflex response. 7. In 
      contrast to other human muscles, there was no functional connection between a 
      population of Ia afferents and some masseter motoneurons. There are two possible 
      explanations for this result. The short-latency, presumably monosynaptic, Ia 
      afferent inputs may not be uniformly distributed to human masseter motoneurons. 
      Alternatively, these inputs may be subject to tonic presynaptic inhibition that 
      is not uniformly distributed throughout the masseter motoneuron pool.
FAU - Miles, T S
AU  - Miles TS
AD  - Department of Physiology, University of Adelaide, Australia.
FAU - Poliakov, A V
AU  - Poliakov AV
FAU - Nordstrom, M A
AU  - Nordstrom MA
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - England
TA  - J Physiol
JT  - The Journal of physiology
JID - 0266262
SB  - IM
MH  - Adult
MH  - Electromyography
MH  - Female
MH  - Humans
MH  - Jaw/*physiology
MH  - Male
MH  - Masseter Muscle/innervation/*physiology
MH  - Mastication/physiology
MH  - Membrane Potentials/physiology
MH  - Middle Aged
MH  - Motor Neurons/physiology
MH  - Reflex, Stretch/*physiology
PMC - PMC1157886
EDAT- 1995/02/15 00:00
MHDA- 1995/02/15 00:01
PMCR- 1995/02/15
CRDT- 1995/02/15 00:00
PHST- 1995/02/15 00:00 [pubmed]
PHST- 1995/02/15 00:01 [medline]
PHST- 1995/02/15 00:00 [entrez]
PHST- 1995/02/15 00:00 [pmc-release]
AID - 10.1113/jphysiol.1995.sp020582 [doi]
PST - ppublish
SO  - J Physiol. 1995 Feb 15;483 ( Pt 1)(Pt 1):251-64. doi: 
      10.1113/jphysiol.1995.sp020582.