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Related Concept Videos

Actin and Myosin in Muscle Contraction01:16

Actin and Myosin in Muscle Contraction

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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...
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Excitation-Contraction Coupling in Skeletal Muscles01:20

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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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The Sarcomere01:08

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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.
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Smooth Muscle Contraction01:25

Smooth Muscle Contraction

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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.
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Cross-bridge Cycle01:26

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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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Muscle Contraction01:10

Muscle Contraction

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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...
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Related Experiment Video

Updated: Dec 9, 2025

Probing Myosin Ensemble Mechanics in Actin Filament Bundles Using Optical Tweezers
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Mechanical contribution to muscle thin filament activation.

Henry G Zot1, P Bryant Chase2, Javier E Hasbun3

  • 1Department of Biology, University of West Georgia, Carrollton, Georgia, USA; Department of Biomedical Sciences, Florida State University, Tallahassee, Florida, USA.

The Journal of Biological Chemistry
|September 9, 2020
PubMed
Summary

Skeletal muscle thin filament activation by calcium (Ca2+) is not purely thermodynamic. Myosin

Keywords:
actinactivationcalciumfibrilmechanotransductionmuscle physiologymyosinskeletal musclestatisticsstriatedthermodynamicsthin filamenttropomyosintroponin

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Area of Science:

  • Muscle physiology
  • Biophysics
  • Molecular motors

Background:

  • Vertebrate striated muscle activation is traditionally attributed to calcium (Ca2+) binding.
  • Thermodynamic models predict constant rates for transitions between muscle filament runs and pauses.

Purpose of the Study:

  • To investigate the thermodynamic activation mechanism of skeletal muscle thin filaments.
  • To determine the role of calcium and regulatory proteins in thin filament activation dynamics.

Main Methods:

  • Utilized single skeletal muscle thin filament gliding assays.
  • Measured time intervals for gliding runs and pauses under varying Ca2+ concentrations.
  • Analyzed run time distributions using Poisson and gamma distributions.

Main Results:

  • Observed run time distributions deviate from exponential at higher Ca2+ levels.
  • Ca2+ titration and addition of tropomyosin/troponin shifted distributions towards a gamma distribution.
  • Deviations suggest myosin cycling events influence thin filament activation duration.

Conclusions:

  • Muscle thin filament activation is influenced by the mechanical force of cycling myosin, not solely thermodynamic.
  • Regulatory proteins require myosin's mechanical force for activation.
  • Insufficient activation energy from myosin cycling can delay deactivation.