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The Sarcomere

The Sarcomere

A sarcomere is a microscopic segment repeating in a myofibril. The sarcomere fundamentally consists of two main myofilaments: thick filaments called myosin and thin filaments called actin. These filaments interact by sliding past each other in response to stimulus. In addition to myosin and actin, several other proteins, such as tropomyosin, troponin, titin, nebulin, myomesin, α-actinin, and dystrophin, play crucial roles in regulating, structuring, and functioning of the sarcomere.
Each myosin...

Excitation-Contraction Coupling in Skeletal Muscles

Excitation-Contraction Coupling in Skeletal Muscles

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 potential...

Actin and Myosin in Muscle Contraction

Actin and Myosin in Muscle Contraction

Actin and myosin are contractile proteins that form the sarcomere found in skeletal muscle tissues for regulating muscle contraction. Actin, a globular contractile protein, interacts with myosin for muscle contraction. The skeletal tissue appears striped or striated under a microscope due to the repeated arrangement of contractile proteins actin and myosin along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes...

Relaxation of Skeletal Muscles

Relaxation of Skeletal Muscles

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.

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 cell's...

Actin Polymerization

Actin Polymerization

Actin polymerization occurs through the head-to-tail association of binding sites on monomeric actin or G-actin to form filamentous or F-actin. The polymerization can be divided into three phases ̶ nucleation, elongation, and steady-state phase.
The nucleation phase involves forming a stable nucleus consisting of three actin monomers to form a new actin filament. Actin-binding proteins such as formins and Arp2/3 complex help filament growth post-nucleation. The Formins form straight actin...

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Related Experiment Video

Updated: Jun 5, 2026

Sarcomere Shortening of Pluripotent Stem Cell-Derived Cardiomyocytes using Fluorescent-Tagged Sarcomere Proteins.

Sarcomere Shortening of Pluripotent Stem Cell-Derived Cardiomyocytes using Fluorescent-Tagged Sarcomere Proteins.

Published on: March 3, 2021

Spontaneous sarcomere dynamics.

Stefan Günther¹, Karsten Kruse

¹Theoretical Physics, Saarland University, 66041 Saarbrücken, Germany. stefan.guenther@physik.uni-saarland.de

Chaos (Woodbury, N.Y.)

|January 5, 2011

Summary

This summary is machine-generated.

Isolated sarcomeres can spontaneously oscillate due to myosin detachment dynamics. This study analyzes these dynamics, revealing complex bifurcations that may explain experimental observations in muscle contraction.

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Area of Science:

Muscle physiology
Biophysics
Nonlinear dynamics

Background:

Sarcomeres are the fundamental force-generating units in striated muscles, composed of actin and myosin filaments.
Muscle contraction is typically initiated by neural signals, but isolated sarcomeres exhibit spontaneous oscillations between contracted and relaxed states.

Purpose of the Study:

To analyze a mathematical model of sarcomere dynamics.
To investigate the role of a force-dependent myosin detachment rate in spontaneous oscillations.
To identify and characterize the types of bifurcations underlying these dynamics.

Main Methods:

Numerical bifurcation analysis of a mathematical model for sarcomere dynamics.
Focus on a model incorporating a force-dependent detachment rate of myosin from actin.

Main Results:

The analysis revealed complex nonlinear phenomena, including Hopf bifurcations, canard explosions, and gluing bifurcations.
These bifurcations characterize the transitions between different dynamic states of the isolated sarcomere.

Conclusions:

The identified bifurcations provide a theoretical framework for understanding spontaneous sarcomere oscillations.
The findings suggest potential explanations for experimental observations in muscle physiology and offer directions for future research.