Safety margin at single neuromuscular junctions

Abstract

Jitter measurement with axonal microstimulation was used to study synaptic function at 115 neuromuscular junctions (NMJs) of normal subjects at various stimulation rates. Jitter was lowest at 0.5 Hz; it increased slightly at 1, 2, and 5 Hz and remained at that level at 10 Hz (a light work load) and 20 Hz (a heavy work load); and it increased further at 50 Hz (an extreme load). This pattern was seen for the majority of the NMJs, suggesting a high safety factor of neuromuscular transmission maintained rather uniformly over a wide range of discharge rates. A proportion of the normal NMJs had relatively large jitter; these tended to show prominent facilitation as the rate was raised from 5 or 10 to 20 Hz. Similar but more dramatic facilitation improving the safety factor was seen at most NMJs in myasthenia, which was studied for comparison. Such facilitation was not found at normal NMJs with low jitter.

Monitorización intraoperatoria del bloqueo neuromuscular y la presión arterial con un solo dispositivo (TOF-Cuff): estudio comparativo con la mecanomiografía y la presión arterial invasiva

“…Al producirse el acoplamiento, los dominios M2 de las cinco subunidades de las que se compone el receptor sufren una rotación de 15º, lo que produce la apertura del canal del receptor nicotínico y la entrada de sodio al interior de la fibra muscular. Esto supone la formación de un micropotencial de placa terminal, que se suman a los miles de micropotenciales de todos los receptores nicotínicos que se ponen a disposición en cada estímulo contráctil y dan lugar a un potencial responsable de la apertura de los canales de sodio y la despolarización de la fibra muscular 12 . La trasmisión del voltaje de despolarización a través de la membrana es debido a la apertura de los canales de sodio que se van abriendo a medida que el estimulo pasa.…”

Myasthenia gravis in dogs with an emphasis on treatment and critical care management

“…Diseases that affect the neuromuscular junction, such as MG, reduce end‐plate potential amplitude decreasing the safety factor. If the end‐plate potential drops below the level required for the firing threshold, neuromuscular transmission is blocked 18–20 . In MG, the amplitude of the muscle action potential with repetitive stimulation shows a progressive decline and a decreased safety factor 21…”

“…16,17 There is a safety margin for neuromuscular transmission defined as the ratio between the number of acetylcholine quanta released and the number of acetylcholine quanta required for depolarization of a muscle fiber. [18][19][20] The safety margin is the amount of interference with the end-plate and transmission that can exist without failure of neuromuscular transmission. [18][19][20] Normally there is an excess number of AChR, which produce an end-plate potential magnitude that is significantly larger than what is required for the muscle action potential threshold.…”

“…[18][19][20] The safety margin is the amount of interference with the end-plate and transmission that can exist without failure of neuromuscular transmission. [18][19][20] Normally there is an excess number of AChR, which produce an end-plate potential magnitude that is significantly larger than what is required for the muscle action potential threshold. Diseases that affect the neuromuscular junction, such as MG, reduce end-plate potential amplitude decreasing the safety factor.…”

Análise do jitter com agulha concêntrica em pacientes com miastenia gravis autoimune adquirida

“…Em uma JNM normal, o fator de segurança é grande o suficiente para garantir que cada impulso nervoso resulte em contração muscular (Trontelj et al, 2002 Praticamente todo o jitter obtido em músculos normais, com frequências de ativação regulares, provém da JNM (Stålberg et al, 2010 (Trontelj et al, 2002).…”