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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...

Smooth Muscle Contraction

Smooth Muscle Contraction

Smooth muscle contraction is a complex process vital for various bodily functions, from maintaining blood vessel tension to facilitating the movement of food through the digestive tract. Unlike striated muscles, smooth muscle contraction begins more slowly and lasts longer.
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...

Muscle Contraction

Muscle Contraction

Muscle Contraction

Muscle Contraction

In skeletal muscles, acetylcholine is released by nerve terminals at the motor endplate—the point of synaptic communication between motor neurons and muscle fibers. The binding of acetylcholine to its receptors on the sarcolemma allows entry of sodium ions into the cell and triggers an action potential in the muscle cell. Thus, electrical signals from the brain are transmitted to the muscle. Subsequently, the enzyme acetylcholinesterase breaks down acetylcholine to prevent excessive muscle...

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...

Cross-bridge Cycle

Cross-bridge Cycle

As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.

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Related Experiment Video

Updated: Jun 19, 2026

High-Throughput Contractile Measurements of Hydrogel-Embedded Intact Mouse Muscle Fibers Using an Optics-Based System

High-Throughput Contractile Measurements of Hydrogel-Embedded Intact Mouse Muscle Fibers Using an Optics-Based System

Published on: May 5, 2023

CONTRACTION IN GLYCERINATED MYOFIBRILS OF AN INSECT (ORTHOPTERA, ACRIDIDAE).

D Gilmour¹, P M Robinson

¹Division of Entomology, Commonwealth Scientific and Industrial Research Organisation, Canberra, Australia.

The Journal of Cell Biology

|October 30, 2009

Summary

Locust muscle fibrils reveal that the A band shortens during ATP-induced contraction, forming new bands. This suggests thick filament coiling and stretching are key mechanisms in muscle contraction.

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Last Updated: Jun 19, 2026

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Isolating Myofibrils from Skeletal Muscle Biopsies and Determining Contractile Function with a Nano-Newton Resolution Force Transducer

Isolating Myofibrils from Skeletal Muscle Biopsies and Determining Contractile Function with a Nano-Newton Resolution Force Transducer

Published on: May 7, 2020

Area of Science:

Muscle physiology
Biochemistry
Insect muscle structure

Background:

Glycerol-treated myofibrils from locust femoral muscles were studied.
The A-substance exhibits properties of actomyosin.
Actomyosin is crucial for muscle contraction.

Purpose of the Study:

To investigate the structural changes in locust myofibrils during contraction.
To understand the role of A bands and I bands in the contraction process.
To elucidate the mechanism of muscle contraction at the sarcomere level.

Main Methods:

Isolation and treatment of locust myofibrils.
High ionic strength salt solution extraction.
Phase contrast microscopy for observing structural changes.
ATP-induced contraction experiments.

Main Results:

The A band of most myofibrils shortened during ATP-induced contraction.
Density changes within the A band led to the formation of C(m) and C(z) bands.
In some cases, I bands disappeared before A band shortening was observed.
The A band region between contraction bands showed decreased density.

Conclusions:

Muscle contraction involves the shortening of the A band.
Observed changes suggest coiling and stretching of thick filaments within the sarcomere.
The interplay between A and I bands is critical for understanding muscle mechanics.