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Cross-bridge theory states that actin and myosin form a protein complex (classically called actomyosin) by attachment of myosin head on the actin filament, thereby forming a sort of cross-bridge between the two filaments. The sliding filament theory is a widely accepted explanation of the mechanism that underlies muscle contraction.
Cross-bridge cycle. Cross-bridge cycling is a sequence of molecular events that underlies the sliding filament theory. A cross-bridge is a myosin projection, consisting of two myosin heads, that extends from the thick filaments. [1] Each myosin head has two binding sites: one for adenosine triphosphate (ATP) and another for actin.
Most myosin molecules are composed of a head, neck, and tail domain.. The head domain binds the filamentous actin, and uses ATP hydrolysis to generate force and to "walk" along the filament towards the barbed (+) end (with the exception of myosin VI, which moves towards the pointed (-) end).
In invertebrate smooth muscle, contraction is initiated with the binding of calcium directly to myosin and then rapidly cycling cross-bridges, generating force. Similar to the mechanism of vertebrate smooth muscle, there is a low calcium and low energy utilization catch phase.
For a muscle cell to contract, tropomyosin must be moved to uncover the binding sites on the actin. Calcium ions bind with troponin C molecules (which are dispersed throughout the tropomyosin protein) and alter the structure of the tropomyosin, forcing it to reveal the cross-bridge binding site on the actin.
The interthalamic adhesion (also known as the massa intermedia, intermediate mass or middle commissure) is a flattened band of tissue that connects both parts of the thalamus at their medial surfaces.
Goss was the esteemed editor of the 25th edition of the seminal classic Gray’s Anatomy. Internationally lauded as the authority on all things anatomical, Gray’s Anatomy had been considered essential for any would-be physician to own since it was first published in London in 1858. It was written by Dr. Henry Gray and illustrated by Henry ...
A cross-section of the pons divides it into a ventral and a dorsal area. The ventral pons is known as the basilar part, and the dorsal pons is known as the pontine tegmentum. [3] The ventral aspect of the pons faces the clivus, with the pontine cistern intervening between the two structures.