Search research articles

ABOUT JoVE

Overview Leadership Blog JoVE Help Center

AUTHORS

Publishing Process Editorial Board Scope & Policies Peer Review FAQ Submit

LIBRARIANS

Testimonials Subscriptions Access Resources Library Advisory Board FAQ

RESEARCH

JoVE Journal Methods Collections JoVE Encyclopedia of Experiments Archive

EDUCATION

JoVE Core JoVE Business JoVE Science Education JoVE Lab Manual Faculty Resource Center Faculty Site

Terms & Conditions of Use

Related Concept Videos

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 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 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...

The Muscular System

The Muscular System

The muscular system is essential to the body's overall structure and function, playing a crucial role in movement, stability, and internal processes. It consists of three distinct types of muscle tissue: the skeletal, the smooth, and the cardiac muscles.

Fascicle Arrangement in Skeletal Muscles

Fascicle Arrangement in Skeletal Muscles

Fascicles are bundles of muscle fibers in a skeletal muscle. Muscle fascicle arrangement is directly associated with the power and range of motion of various muscles. The configuration of these fascicles can vary, leading to different functional outcomes.
The four primary types of muscle based on fascicle arrangement are:

Specialized Characteristics of Cardiac Muscles

Specialized Characteristics of Cardiac Muscles

The primary role of cardiac muscles is to propel blood throughout the cardiovascular system. The cardiac muscle cells, or cardiomyocytes, exhibit specialized characteristics that allow them to perform this function.
Cardiac muscle cells are smaller than skeletal muscles, averaging 10–20 mm in diameter and 50–100 mm in length. However, they have large energy demands for continuous contraction and relaxation. This energy is almost exclusively derived from aerobic metabolism of energy reserves in...

You might also read

Related Articles

Articles linked to this work by shared authors, journal, and citation graph.

Sort by

Same author

It Is Hard to Be Soft: Length-Force Relationships in Muscles of Hydrostatically Supported Animals.

Integrative and comparative biology·2025

Same author

Predicting the effects of spatiotemporal modifications of muscle activation on the tentacle extension in squid.

Frontiers in bioengineering and biotechnology·2023

Same author

One size does not fit all: diversity of length-force properties of obliquely striated muscles.

The Journal of experimental biology·2023

Same author

Evidence that eye-facing photophores serve as a reference for counterillumination in an order of deep-sea fishes.

Proceedings. Biological sciences·2020

Same author

Muscle force is modulated by internal pressure.

Proceedings of the National Academy of Sciences of the United States of America·2020

Same author

Specialization for rapid excitation in fast squid tentacle muscle involves action potentials absent in slow arm muscle.

The Journal of experimental biology·2020

Search research articles

Related Experiment Video

Updated: Jul 8, 2026

Extracellularly Identifying Motor Neurons for a Muscle Motor Pool in Aplysia californica

Extracellularly Identifying Motor Neurons for a Muscle Motor Pool in Aplysia californica

Published on: March 25, 2013

Muscle specialization in the squid motor system.

William M Kier¹, Frederick H Schachat

¹University of North Carolina, Chapel Hill, NC 27599, USA. billkier@bio.unc.edu

The Journal of Experimental Biology

|January 1, 2008

Summary

Cephalopod muscle performance is modulated by changes in myofilament dimensions and arrangement, not myosin differences. This contrasts with vertebrate muscle specialization, offering new insights into invertebrate muscle evolution.

Area of Science:

Muscle physiology
Evolutionary biology
Invertebrate zoology

Background:

Vertebrate muscle specialization is well-studied, but invertebrate mechanisms remain less understood.
Cephalopod muscle diversity, particularly in squid, suggests unique evolutionary pathways.
Existing research indicates differences in myofilament dimensions and arrangement in cephalopods compared to vertebrates.

Purpose of the Study:

To investigate the molecular basis for functional differences in squid muscle.
To compare myosin heavy chain messenger RNA (mRNA) expression in different squid muscle types.
To determine if myofilament arrangement or biochemical differences drive contractile property variations.

Main Methods:

Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis.

More Related Videos

Historical View and Physiology Demonstration at the NMJ of the Crayfish Opener Muscle

Historical View and Physiology Demonstration at the NMJ of the Crayfish Opener Muscle

Published on: November 9, 2009

Establishing an Octopus Ecosystem for Biomedical and Bioengineering Research

Establishing an Octopus Ecosystem for Biomedical and Bioengineering Research

Published on: September 22, 2021

Related Experiment Videos

Last Updated: Jul 8, 2026

Extracellularly Identifying Motor Neurons for a Muscle Motor Pool in Aplysia californica

Extracellularly Identifying Motor Neurons for a Muscle Motor Pool in Aplysia californica

Published on: March 25, 2013

Historical View and Physiology Demonstration at the NMJ of the Crayfish Opener Muscle

Historical View and Physiology Demonstration at the NMJ of the Crayfish Opener Muscle

Published on: November 9, 2009

Establishing an Octopus Ecosystem for Biomedical and Bioengineering Research

Establishing an Octopus Ecosystem for Biomedical and Bioengineering Research

Published on: September 22, 2021

Analysis of myosin heavy chain mRNAs from cross-striated tentacle and obliquely striated arm muscle fibers.

Comparison of protein profiles and peptide mapping of myofilament preparations.

Main Results:

Few biochemical differences were found in myofilament lattice proteins between fast and slow muscle fibers.
Differential expression of myosin heavy chain isoforms does not explain contractile property variations.
A previously identified alternatively spliced myosin isoform was present in low abundance in both muscle types.

Conclusions:

Squid muscle specialization primarily relies on modulation of myofilament arrangement and dimensions.
This contrasts with vertebrate muscle specialization, highlighting distinct evolutionary strategies.
Further research into myofilament structural variations is warranted for understanding cephalopod muscle function.