52) Basic provisions of model of sliding strings.

Thus, actin-miosin a complex is the chemical converter of energy АТP. The considered structure and sequence of processes is called model of sliding strands. For the first time sliding of strings in sarcomere was revealed English scientist H.Haksli. It has formulated model of sliding strings.

Basic provisions of model of sliding strings:

1. Lengths of strands of actin and miosin during reduction do not change.

2. Change of length of sarcomere at reduction - result of relative longitudinal displacement of strands of actin and miosin.

3. The cross-section ponticulus departing from miosin, can connect to complementary centers actin.

4. Ponticuluses are attached to actin not simultaneously.

5. The closed bridges develop effort, then they open.

6. Reduction and a relaxation of a muscle consist in increase and the subsequent reduction of number of the bridges making a cycle closing - opening.

53) Biomechanics of a muscle.

Biomechanics is the study of the structure and function of biological systems such as humans, animals, plants, organs, fungi, and cells by means of the methods of mechanics. Biomechanics is closely related to engineering, because it often uses traditional engineering sciences to analyze biological systems.

In mammals, when a muscle contracts, a series of reactions occur. Muscle contraction is stimulated by the motor neuron sending a message to the muscles from the somatic nervous system. Depolarization of the motor neuron results in neurotransmitters being released from the nerve terminal. The space between the nerve terminal and the muscle cell is called the neuromuscular junction. These neurotransmitters diffuse across the synapse and bind to specific receptor sites on the cell membrane of the muscle fiber. When enough receptors are stimulated, an action potential is generated and the permeability of the sarcolemma is altered. This process is known as initiation.

54) Electromechanical interface in muscles.

Electromechanical interface is the cycle of consecutive processes beginning occurrence of potential of action on sarcolemma (a cellular membrane) and coming to an end retractive answer of a muscle.

Infringement of sequence of processes of interface can lead to pathologies and even by a lethal outcome.

In cardiac hystiocyte electromechanical interface goes in two steps: in the beginning the small entering stream of calcium activates membranes of sarcoplasmic reticulum, promoting the big emission of calcium from endocellular depot, and then as a result of this emission there is a reduction of sarcomere. The described two-level process of interface is proved experimentally. Experiences have shown, that: absence of a stream of calcium from the outside cells stops reduction of sarcomere, in conditions of a constancy of quantity of the calcium liberated from sarcoplasmic reticulum, change of amplitude of a stream of calcium leads to well correlating change of force of reduction. The stream of ions inside of a cell carries out thus two functions: forms long (200 msec) a plateau of potential of action of cardiac hystiocyte and participates during electromechanical interface.

In skeletal muscles potential of action short (2-3 msec) and the slow stream of ions of calcium in them is absent. In these cells the system of the cross-section tubules suitable directly to sarcomeres is strongly developed Т-, is close to z - to disks. Changes of potential of a membrane during depolarization through Т - system it is transferred in such cells directly to membrane of sarcoplasmic reticulum, causing fast liberation of ions and the furt her activation of reduction.