Mechanical properties muscle

Astana 2014

Plan:

-Mechanical properties of biological objects. Hooke’s law in the deformation of tissue.

-Mechanical properties of muscles and bones.

-Mechanical properties of blood vessel walls.

-Mechanical in the lung.

-Molecular basis of the elastic properties of biological objects.

Mechanical properties of biological tissues

The mechanical properties of biological tissues and organs are shown in their response to mechanical stress. A measure of the interaction of physical bodies os power. The force acting on a unit surface of the body, called the surface force or surface load.

It is physical quantity is usually characterized in biomechanics mechanical effects on living tissues and organs.

Consider the most important mechanical properties of biological tissues, to help through a variety of mechanical phenomena - such as the functioning of the musculoskeletal system, the process of deformation of tissues and cells, wave propagation of elastic deformation, contraction and relaxation of muscles, movement of liquid and gaseous biological media. Among these properties are distinguished:

-Resilience -the ability of body to renew dimensions (shape or volume) after removal of the load;

- Rigidity - ability of a material to resist the external load; flexibility - the ability to change the size of the material under the action of external loads;

- Strength - the ability to resist the destruction of bodies under the action of external forces;

- Plasticity - the ability to store phone (fully or partially) resizing after removal of the load;

- Fragility - a material's ability to break down without the formation of significant residual strain;

- Viscosity - a dynamic property that characterizes the ability of the body to resist a change in its form under the action of tangential stresses;

- Fluidity - the dynamic properties of the medium, which characterizes

the ability of its individual layers move with a certain velocity in the space relative to the other layers of the medium.

Hooke's law - the claim that the deformation that occurs in an elastic body is proportional to the applied voltage to this body. Opened in 1660, the English scientist Robert Hooke.

It should be borne in mind that Hooke's law holds only for small deformations. If you exceed the limit of proportionality relationship between stress and strain becomes nonlinear. For many environments, Hooke's law can not be applied even for small deformations.

F = k*Delta L.

Here, F - force, which is stretched rod, Delta l - absolute elongation of the rod, and k - coefficient of elasticity.

Mechanical properties muscle

The main function of muscle is to convert chemical energy into mechanical work or power. The main biomechanical parameters describing muscle activity, are:

a) the force recorded at its end (this force is called tension or pulling force of the muscles) and b) the rate of change of length.

Upon excitation of the muscle changes its mechanical condition. These changes are called reduction. It manifests itself in changing the tension and length of the muscle, as well as its other mechanical properties.

Mechanical properties muscle complicated and depend on the mechanical properties of the elements forming the muscle (muscle fibers connecting formation, etc.) and condition of the muscles (excitation, fatigue, etc..).

Understand many of the mechanical properties of muscles helps a simplified model of its structure - a combination of elastic and contractile components. Elastic components of the mechanical properties are similar to springs: to stretch them, you need to apply a force. The work force is equal to the elastic strain energy, which can be in the next phase of the movement to go into mechanical work. Distinguished: a) the parallel elastic components - connective tissue formation, shell components of muscle fibers and their bundles, and b) the serial elastic components (POSCO) - tendon, place of transition myofibrils in the connective tissue, as well as some parts of the sarcomere, the exact location which is currently unknown.

Contractile (contractile) components correspond to those portions of the muscle sarcomere, where actin and myosin myofilaments overlap. In these areas when there is a mechanical excitation of the muscles of the interaction between actin and myosin filaments, leading to a change in muscle length and tension.

Since each myofibril consists of a large number (n) successively arranged sarcomeres, the magnitude and rate of change of the length of myofibrils n times larger than the one of the sarcomere. The force developed by each of them, the same and equal to the force recorded at the end of the myofibrils (just as equal force in each of the links in the chain, which are attached to the ends of the tensile strength). These same sarcomeres n connected in parallel (which corresponds to the greater number of myofibrils) would give fold increase in force, but the rate of change in muscle length would be the same as the speed of one of the sarcomere. Therefore, ceteris paribus increase in the diameter of the physiological muscle would lead to an increase in its strength, but would not change the rate of contraction, and vice versa, an increase in muscle length would have a positive effect on the rate of contraction, but would not affect its strength.

Resting muscle has elastic properties, if its end by an external force, the muscle is stretched (increasing the length), and after removal of the external load recovers its original length. The relationship between the magnitude of the load and elongation of the muscles of proportion (not obey Hooke's law)

First, muscle stretches easily, and then even for a small extension is necessary to apply more and more force (sometimes muscle in this respect compared with knitted things: when it is stretched, for example, knitted scarf, the first he easily changes its length, and then becomes essentially inextensible).

If the muscles are stretched repeatedly at short intervals of time, its length increases more than that for a single "assistance. This property muscles widely used in practice during exercise flexibility (springy movements, repetitive swings, etc.).

Length, which tends to take the muscle, being delivered from all the load is called the equilibrium. With such a length of the muscle its elastic force is zero. In the living body muscle length is always slightly greater than the equilibrium and therefore even relaxed muscles retain some tension.

Muscle characteristic as a property such as relaxation - decrease of the elastic deformation forces over time. While pushing off in jumps from place immediately after a quick jump squats will be higher than the case of repulsion, after a pause at the lowest point podseda: after a pause elastic forces caused by rapid squat, due to relaxation are not used.

Mechanical properties of bones

The primary tissue of bone, osseous tissue, is a relatively hard and lightweight composite material. It is mostly made up of a composite material incorporating the mineral calcium phosphate in the chemical arrangement termed calcium hydroxylapatite (this is the osseous tissue that gives bones their rigidity) and collagen, an elastic protein which improves fracture resistance. It has relatively high compressive strength of about 170 MPa (1800 kgf/cm²) but poor tensile strength of 104–121 MPa and very low shear stress strength (51.6 MPa), meaning it resists pushing forces well, but not pulling or torsional forces. While bone is essentially brittle, it does have a significant degree of elasticity, contributed chiefly by collagen. All bones consist of living cells embedded in the mineralized organic matrix that makes up the osseous tissue.

Date: 2016-01-03; view: 1174