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Motor Units

Motor Units

A motor unit consists of two main components: a single efferent motor neuron (i.e., a neuron that carries impulses away from the central nervous system) and all of the muscle fibers it innervates. The motor neuron may innervate multiple muscle fibers, which are single cells, but only one motor neuron innervates a single muscle fiber.

Motor Units

Motor Units

The motor unit is a fundamental component of the neuromuscular system and plays a crucial role in coordinating muscle contractions. It consists of a somatic motor neuron, which connects and controls multiple skeletal muscle fibers, forming a single functional segment. The axon of the motor neuron branches out and establishes synaptic connections known as neuromuscular junctions with individual muscle fibers within the motor unit.
Motor units come in different sizes, with smaller units...

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...

Hierarchy of Motor Control

Hierarchy of Motor Control

The hierarchy of motor control refers to the different levels of organization and processing involved in controlling movement in the body. These levels range from higher cortical areas involved in planning and decision-making to lower spinal cord reflexes that respond automatically to external stimuli.

Direct Motor Pathways

Direct Motor Pathways

The direct motor pathways, also known as the pyramidal tracts, are a group of neural pathways that originate in the brain and descend through the spinal cord. They control the voluntary movement of the body. There are two major direct motor pathways: the corticospinal and the corticobulbar tracts.
The corticospinal tract is responsible for the voluntary movement of the limbs and trunk. It originates in the cerebral cortex of the brain and descends through the cerebrum's internal capsule and...

Microtubule Associated Motor Proteins

Microtubule Associated Motor Proteins

Eukaryotic cells have different motor proteins for transporting various cargo within the cell. These motor proteins differ based on the filament they associate with, the direction they move within the cell, and the type of cargo they transport. Motor proteins that associate with microtubules are known as microtubule-associated motor proteins. There are two families of microtubule-associated motor proteins —Kinesins and Dyneins. Both these proteins assist in the transport of cellular...

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Related Experiment Video

Updated: Feb 6, 2026

Multifocal Electroretinograms

Multifocal Electroretinograms

Published on: December 4, 2011

Multifocal motor neuropathy.

Katie Beadon¹, Raquel Guimarães-Costa, Jean-Marc Léger

¹National Referral Center for Neuromuscular Diseases, Institut Hospitalo-Universitaire (IHU) de Neurosciences, University Hospital Pitié Salpêtrière, Paris, France.

Current Opinion in Neurology

|August 14, 2018

Summary

Multifocal motor neuropathy (MMN) diagnosis can be challenging. Recent advances include improved antibody detection, subcutaneous immunoglobulin therapy, and potential complement inhibitors, alongside revised diagnostic guidelines and advanced imaging techniques.

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Area of Science:

Neurology
Immunology
Neurophysiology

Background:

Multifocal motor neuropathy (MMN) presents with specific, yet sometimes atypical, clinical and electrophysiologic features.
Intravenous immunoglobulin (IVIg) is the established primary treatment for MMN.
Accurate diagnosis and effective management are crucial for patient outcomes.

Purpose of the Study:

To review recent advancements in the diagnosis, monitoring, and treatment of MMN.
To highlight challenges in diagnosing atypical MMN cases.
To discuss emerging therapeutic strategies and diagnostic tools.

Main Methods:

Review of current literature on MMN diagnosis and treatment.
Discussion of immunopathologic mechanisms, including antibody detection and complement activation.
Evaluation of diagnostic aids like nerve ultrasound and MRI.
Assessment of monitoring scales and potential novel therapies.

Main Results:

Antiganglioside antibodies (e.g., GM1/galactocerebroside complexes) are found in over 50% of MMN patients, with improved detection sensitivity.
Complement activation is a key factor in MMN pathophysiology.
Subcutaneous immunoglobulins offer an effective alternative to IVIg for maintenance therapy.
Complement inhibitor eculizumab shows potential as a future treatment.

Conclusions:

Current diagnostic guidelines for MMN may require revision.
Nerve ultrasound and MRI can aid in complex diagnostic scenarios.
Disease-specific scales like the MMN-Rasch-built overall disability scale can improve monitoring.
Further research into MMN pathophysiology is essential for developing targeted treatments.