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The discharge behaviour of single vasoconstrictor motoneurones in human muscle nerves.
Author(s) -
Macefield V G,
Wallin B G,
Vallbo A B
Publication year - 1994
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1994.sp020482
Subject(s) - microneurography , cardiac cycle , supine position , heart rate , latency (audio) , baroreflex , peripheral , cardiology , chemistry , blood pressure , anesthesia , medicine , anatomy , electrical engineering , engineering
1. The discharge behaviour of fourteen single sympathetic vasoconstrictor efferents was studied using a tungsten microelectrode inserted percutaneously into a motor fascicle of the radial or peroneal nerve in eight awake supine subjects. Units were classified as vasoconstrictor because their firing properties correlated appropriately to changes in cardiac interval and arterial pressure. 2. On average, individual vasoconstrictor units discharged in only 21% of heart beats, with an overall mean frequency of 0.47 Hz. Usually only one spike was generated per cardiac cycle. Calculated from cardiac cycles in which a unit fired from two to seven spikes, the mean within‐burst firing rate was 18.8 +/‐ 2.5 Hz (mean +/‐ S.E.M.); but instantaneous frequencies above 50 Hz were occasionally observed. 3. Measured from a defined R‐wave of the ECG, the spike onset latency varied over 358 +/‐ 33 ms, suggesting considerable variation of synaptic delays in the baroreflex arc. This latency had a relatively uniform temporal relationship with the burst onset or peak latency, compatible with a fixed recruitment order of individual sympathetic neurones. 4. In view of the low average firing rate of individual units we suggest that the variable instantaneous firing rates may optimize the contractile responses of vascular smooth muscle.