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Motor Unit Stimulation

Motor Unit Stimulation

When the neuron of a motor unit fires an action potential, it triggers a series of events, leading to a twitch contraction in the muscle fibers. The process of excitation-contraction coupling is crucial in relaying the action potential to the muscle fibers.
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...

Generation of Action Potential in Skeletal Muscles

Generation of Action Potential in Skeletal Muscles

Every cell in the body maintains a membrane potential due to an uneven distribution of positive and negative charges across its plasma membrane. The membrane potential is measured in millivolts and quantifies the difference in charge across the membrane.
Like neurons, muscle cells are also regarded as excitable due to their capacity to change in response to stimuli, primarily due to voltage-gated ion channels embedded in their plasma membranes, which get activated by alterations in the...

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Related Experiment Video

Updated: Jan 10, 2026

Measuring Neuromuscular Junction Functionality

Measuring Neuromuscular Junction Functionality

Published on: August 6, 2017

Intrinsic Motoneuron Excitability Differentiates Sarcopenic, Nonsarcopenic and Athletic Ageing Phenotypes.

Lucas B R Orssatto^1,2, David Scott^2,3, Brian C Clark^4,5

¹Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, The University of Queensland, Brisbane, Queensland, Australia.

Journal of Cachexia, Sarcopenia and Muscle

|November 26, 2025

Summary

Reduced intrinsic motoneuron excitability contributes to sarcopenia and physical decline in older adults. Exercise may preserve this excitability, offering a target for interventions to restore neuromotor function.

Keywords:

HD‐EMG dynapenia functional capacity motor unit muscle persistent inward currents sex ageing

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Last Updated: Jan 10, 2026

Measuring Neuromuscular Junction Functionality

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Published on: August 6, 2017

The Preparation of Oblique Spinal Cord Slices for Ventral Root Stimulation

The Preparation of Oblique Spinal Cord Slices for Ventral Root Stimulation

Published on: October 13, 2016

Application of Chronic Stimulation to Study Contractile Activity-induced Rat Skeletal Muscle Phenotypic Adaptations

Application of Chronic Stimulation to Study Contractile Activity-induced Rat Skeletal Muscle Phenotypic Adaptations

Published on: January 25, 2018

Area of Science:

Neuromuscular physiology
Gerontology
Exercise science

Background:

Sarcopenia's physical decline mechanisms are unclear, with neural factors like motoneuron excitability gaining attention.
Reduced intrinsic motoneuron excitability may drive age-related weakness and mobility loss.

Purpose of the Study:

To investigate differences in intrinsic motoneuron excitability among sarcopenic older adults, controls, and master athletes.
To determine the relationship between these excitability differences and physical function.

Main Methods:

Recruited 56 older adults (sarcopenic, controls, master athletes).
Recorded high-density electromyography (HD-EMG) during isometric contractions.
Analyzed motor unit discharge properties using paired motor unit analysis to calculate delta frequency (ΔF) as a measure of intrinsic motoneuron excitability.

Main Results:

Sarcopenic adults showed significantly lower strength and physical function compared to controls.
Intrinsic motoneuron excitability (ΔF) was substantially reduced in sarcopenic individuals across all intensities.
Master athletes exhibited preserved or enhanced excitability at higher intensities compared to controls, correlating with better physical function.

Conclusions:

Reduced intrinsic motoneuron excitability is a key feature of sarcopenia in older adults, impacting functional capacity.
Long-term exercise practice preserves motoneuron excitability, especially during demanding tasks.
Intrinsic motoneuron excitability is a potential therapeutic target for sarcopenia interventions.