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Related Concept Videos

Motor Unit Stimulation01:20

Motor Unit Stimulation

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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...
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Muscle Stimulation Frequency01:22

Muscle Stimulation Frequency

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The contraction strength of muscles is regulated by motor neurons, which modulate the frequency of action potentials dispatched to the motor units based on the body's requirements. This process of varying the muscle stimulation frequency allows muscles to contract with a force that is precisely tailored to the needs of the moment, whether lifting a feather or a heavy box.
Wave summation
At low firing rates, motor neurons induce individual twitch contractions in muscle fibers. These twitches...
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Excitatory and Inhibitory Effects of Neurotransmitters01:29

Excitatory and Inhibitory Effects of Neurotransmitters

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When an action potential reaches the presynaptic axon terminal, it releases neurotransmitters from the neuron into the synaptic cleft at a chemical synapse. The released neurotransmitter can be excitatory or inhibitory. The critical criteria commonly used to determine whether a molecule is a neurotransmitter at a chemical synapse are the molecule's presence in the presynaptic neuron. Second, its release is in response to strong presynaptic depolarization. And lastly, the presence of...
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Somatic Spinal Reflexes01:22

Somatic Spinal Reflexes

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Somatic spinal reflexes are rapid, involuntary muscular responses to external stimuli that involve the somatic musculature and the spinal cord.
One of the most well-known somatic spinal reflexes is the stretch reflex, which is activated by the sudden stretching of a muscle. This reflex involves the activation of specialized sensory receptors called muscle spindles, which are located in the muscle tissue and detect changes in the length and speed of muscle contractions. When a muscle is suddenly...
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Relaxation of Skeletal Muscles01:29

Relaxation of Skeletal Muscles

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The period of muscle contraction primarily influences the duration of stimulation at the neuromuscular junction (NMJ), the presence of free calcium ions in the sarcoplasm, and the availability of energy or ATP to support contractions.
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open....
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Excitation-Contraction Coupling in Skeletal Muscles01:20

Excitation-Contraction Coupling in Skeletal Muscles

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Excitation-contraction coupling is a series of events that occur between generating an action potential and initiating a muscle contraction. It occurs at the triad, a structure found in skeletal muscle fibers that comprise a T-tubule and terminal cisternae of the sarcoplasmic reticulum on each side. These triads are visible in longitudinally sectioned muscle fibers. They are typically located at the A-I junction — the junction between the A and I bands of the sarcomere.
When an action...
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Related Experiment Video

Updated: Oct 28, 2025

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation
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Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

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Mechanisms modulating spinal excitability after nerve stimulation inducing extra torque.

Florian Vitry1, Maria Papaiordanidou1, Alain Martin1

  • 1INSERM UMR1093-CAPS, Université Bourgogne Franche-Comté, UFR des Sciences du Sport, F-21000, Dijon, France.

Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 15, 2021
PubMed
Summary

Spinal excitability decreases after 20-Hz stimulation due to homosynaptic postactivation depression (HPAD) of Ia afferents. Conversely, 100-Hz stimulation increases spinal excitability via altered motoneuron intrinsic properties.

Keywords:
D1 presynaptic inhibitionH-reflexextra torquehomosynaptic postactivation depressionmotoneuron excitability

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Author Spotlight: Advancing Spinal Cord Stimulation - Exploring the Cellular Responses of Motor Neurons Through Patch-Clamp Electrophysiology
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Author Spotlight: Advancing Spinal Cord Stimulation - Exploring the Cellular Responses of Motor Neurons Through Patch-Clamp Electrophysiology

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Methods to Quantify Pharmacologically Induced Alterations in Motor Function in Human Incomplete SCI
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Methods to Quantify Pharmacologically Induced Alterations in Motor Function in Human Incomplete SCI

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Related Experiment Videos

Last Updated: Oct 28, 2025

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation
07:53

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Published on: September 13, 2015

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Author Spotlight: Advancing Spinal Cord Stimulation - Exploring the Cellular Responses of Motor Neurons Through Patch-Clamp Electrophysiology
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Author Spotlight: Advancing Spinal Cord Stimulation - Exploring the Cellular Responses of Motor Neurons Through Patch-Clamp Electrophysiology

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Methods to Quantify Pharmacologically Induced Alterations in Motor Function in Human Incomplete SCI
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Methods to Quantify Pharmacologically Induced Alterations in Motor Function in Human Incomplete SCI

Published on: April 18, 2011

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Area of Science:

  • Neuroscience
  • Motor Control
  • Electrophysiology

Background:

  • Spinal excitability is crucial for motor control.
  • Understanding modulation mechanisms is key for neurological rehabilitation.
  • Previous research has explored various factors influencing spinal excitability.

Purpose of the Study:

  • To investigate the mechanisms underlying spinal excitability changes following different stimulation frequencies.
  • To differentiate the roles of presynaptic inhibition, postactivation depression, and motoneuron properties.

Main Methods:

  • Three experiments assessed spinal excitability via H-reflex, D1 inhibition, heteronymous Ia facilitation (HF), homosynaptic postactivation depression (HPAD), and thoracic motor-evoked potentials (TMEP).
  • Stimulation trains at 20 Hz and 100 Hz were used to induce extra torque (ET).
  • Electrophysiological techniques were employed to measure changes in neural pathways.

Main Results:

  • Spinal excitability decreased after 20-Hz stimulation and increased after 100-Hz stimulation.
  • HPAD significantly decreased after 20-Hz stimulation, while TMEP significantly increased after 100-Hz stimulation.
  • D1 inhibition and HF were not significantly altered by either stimulation frequency.

Conclusions:

  • Decreased spinal excitability post-20-Hz stimulation is attributed to increased HPAD of Ia afferent terminals.
  • Increased spinal excitability post-100-Hz stimulation is linked to changes in motoneuron intrinsic properties.
  • A novel methodology was developed for assessing soleus D1 presynaptic inhibition and HF.