Myocyte

The myocytes , or muscular cells are cells capable of contraction.

One distinguishes mainly the myocytes striated with the smooth myocytes . The contractile properties of the muscular cells hold of the presence of elements of the Cytosquelette able to contract following an increase in the concentration in intracellular Calcium.

These elementary contractile elements consist of microfilaments of Actine coupled to intermediate filaments of Myosine. The myosine carries out a cycle of detachment/réattachement accompanied by a transverse movement along the actine when the intracellular calcium concentration increases. This cycle leads to a shortening of the fiber, which is at the base of the general contraction of the cell. This cycle is accompanied by hydrolysis of ATP which provides the energy necessary to the developed mechanical force and is controlled by calcium.

Contractile cycle

Cellular types

Smooth muscular cells

Striated muscular cells

Skeletal striated muscular cells

Cardiac striated muscular cells

General information: The cardiac myocyte is a particular type of striated muscle, it is mononuclée and behaves like a syncytium thanks to an electric coupling between cells by communicating junctions (GAP junctions). Contrary to the myocyte of the skeletal striated muscle its diameter and its length are limited.

the sarcomère: The contractile unit of the myocyte is the sarcomère. If this one schematically is considered defines as space between two lines Z, it is composed of filaments of actine and of myosine tangled up one in another. The filaments of actine are directly related to lines Z whereas the myosine is maintained in the center of the sarcomère by a protein: the titine itself related to line Z.

Contraction: At the time of a contraction, calcium penetrates in the cytoplasm of the myocyte through a calcic channel (standard slow). This local increase will stimulate the calcium salting out by the Réticulum sarcoplasmic and will lead to a significant growth of free calcium in the cytoplasm of the myocyte. This calcium will finish binding to a particular protein, the troponine-C (which in time normal inhibits the interaction between filaments of actine and myosine) and inducing a change of conformation of the latter to allow the heads myosine to bind to the filaments of actine. Once the possible interaction between the actine and the myosine and in presence of course of the nutrients necessary (e.g. ATP) the shortened sarcomère and the muscle contracts.

See too

Cell excitable

Random links: