All movements of a body are possible to pour thanks to muscles. Without them we could not chew at all I write, and blood would not make the run in an organism.
In an organism distinguish three basic types of muscles. The first is poperechnopolosatye muscles which the brain operates. Together with bones and sinews they are responsible for all our movements - from a smile before jog on a ladder. The second are the smooth muscles which have received this name because so they look under a microscope. They are responsible for involuntary movements of an internal, say, an intestines and a bladder. And the third is a cardiac muscle of which heart almost entirely consists.
the Arrangement of muscles
Cross-section-striped muscles are widely distributed on all our body, even at the newborn baby making a considerable part of weight - to 25%. They operate movements of the most different parts of a skeleton - from tiny stremjannoj a muscle moving stremechko in an ear, to big buttock which forms a buttock and orders a coxofemoral joint.
Muscles fasten to a skeleton sinews. Near to the center of a body the sinew end name a place of an attachment of a muscle, and it is shorter than a sinew on other end. Usually one sinew the muscle fastens by the near end of a joint, and another - to distant thanks to what, being reduced, it sets it in motion.
the Structure of muscles
It is possible to present the Cross-section-striped muscle as a number of the bunches of muscular fibres collected together. Least of them - and the main working element of a muscle - are aktinovye and miozinovye threads. They so are thin what to see them it is possible only under an electronic microscope, and consist of fiber which sometimes name sokratitelnym. When all miozinovye threads slide lengthways aktinovyh, the length of a muscle is reduced.
All these threads are collected in bunches, or miofibrilly. Between them stocks of muscular fuel are stored in a kind glikogena and cellular generators of energy, or mitohondrii in which burns down oxygen and the fuel which has arrived with food are located, developing energy.
Miofibrilly are collected in larger bunches or muscular fibres. These are already present muscular cages with a kernel located on external edge.
Muscular fibres too are collected in bunches in a cover from the connecting fabric similar to isolation copper provodkov in a thick cable. The small muscle can consist only of several bunches, whereas large - from many hundreds. In the same fibrous cover it is similar to an insulating cover of a multicore cable all muscle is concluded also. In smooth muscles we will not see the so geometrically ordered structure of threads and fibres, but also they are reduced thanks to sliding of threads. At the same time, the cardiac muscle looks under a microscope the same as cross-section-striped, with that difference that separate bunches of fibres are connected in it by crosspieces.
From motor (operating movements) sites of a cerebral cortex nerves pass on a spinal cord and branch on set of the terminations supervising muscle. Without signals submitted a nerve the muscle loses ability to be reduced and will gradually atrophy. Nerves "яюфъы¦ёхэ№" to muscular fibres in certain sites of their surface. Electric force of a nervous impulse arriving in a muscle is insignificant in comparison with electric changes occurring in it, the amplifier therefore is necessary. Giving sokratitelnogo an impulse occurs in the motor termination where the impellent nerve is joined to a muscular fibre. The electric impulse passing on a nerve liberates substance atsetilholin which forces a muscle to be reduced.
Power supply of muscles
Sliding miozinovyh threads on aktinovym is a difficult process in which course between them a number of chemical compounds continuously is formed and breaks up. Energy which is developed at combustion in mitohondrii oxygen and the fuel which has arrived with food is for this purpose necessary. Energy is put by and transferred in the form of substance ATF (adenozintrifosfata), rich with phosphates. Muscle reduction begins with inflow of calcium to muscular cages on set mikrokanaltsev, proceeding between miofibrillami.
Besides, in a muscle there are two more groups of fibres. One registers force of reduction, and another, being in sinews, operates its stretching. This key for management of muscular activity the information is transferred back in a brain.