Features of red and white muscles



Red (slow) muscle Pale (fast) muscle
1. Myoglobin content is more. Myoglobin content is less
2. Sarcoplasmic reticulum is less extensive Sarcoplasmic reticulum is more extensive
3. Blood vessels are more extensive Blood vessels are less extensive
4. Mitochondria are more in number Mitochondria are less in number
5. Response is slow with long latent period   period Response is rapid with short latent period
6. Contraction is less powerful Contraction is more powerful
7. This muscle is involved in prolonged and continued activity This muscle is not involved in prolonged and continued activity
8. Fatigue occurs slowly Fatigue occurs quickly
9. Depends on cellular respiration for ATP production Depends on glycolysis for ATP production

 

TETANIC OR SUMMARIZED CONTRACTION

In reply to a rhythmic irritation (namely the such one our muscles are received) the muscle is reduced lengthly (for a long time). Such a contraction has received the name tetanic or summarized. If each subsequent stimulus approaches to a muscle in the period, when it began to be relaxed, there is an infused, dentate or incomplete tetanus. Impulsations rate is 30 in 1 min. It can be expressed under experimental conditions. Fits also are dentate tetanus example. So, it is not physiological. It requires much energy.

If the interval between irritations decreases so, that each subsequent stimulus comes to a muscle at that moment when it is in a contraction phase, there is a smooth or complete tetanus. Impulsations frequency is 60 in 1 min. Smooth tetanus is more physiologic. It requires less energy for its performance. Neck movements to the both sides can be example of such tetanus.

MUSCLE TONE DEFINITION

Muscle fibers always maintain a state of slight contraction with certain degree of vigor and tension. This property of muscle is called tone or tonus.

All skeletal muscles show little tonus. But antigravity muscles like extensors of lower limb, trunk muscles and neck muscles show tonus to a greater extent.

MAINTENANCE OF MUSCLE TONE

In Skeletal Muscle

Maintenance of tone in skeletal muscle is neurogenic. It is due to continuous discharge of impulses from gamma motor neurons in anterior grey horn of spinal cord. Gamma motor neurons in spinal cord are controlled by higher centers in brain.

ABNORMALITIES OF MUSCLE TONE

The abnormalities of muscle tone are:

1. Hypertonic State

When tone is increased, the muscle becomes spastic (rigid or stiff). This condition of the muscle is called spasticity. Upper motor neuron lesion causes spastic paralysis of muscles, because during upper motor neuron lesion, inhibition of lower motor neuron is lost. So, there is exaggeration of activity of lower motor neuron causing increased muscle tone.

2. Hypotonic State

If muscle tone is decreased or lost, the muscle becomes flaccid and the condition is called flaccidity. Lower motor neuron lesion causes flaccid paralysis of muscles. The muscles undergo wasting.

3. Myotonia

This is an inherited disease characterized by continuous contraction of muscle even after the cessation of voluntary act. The power of relaxation is decreased. Myotonia is due to some abnormal gene that affects the ionic channels in sarcolemma.

Tongue, lips muscles and masticatory muscles contractive types and regimes at conversation.

During mastication mandible displacement takes place due to masticatory muscles contractions occurring in tetanic regimen (mainly incomplete). Contraction type – auxotonic (accompanied by muscle length and tension changings). Lips participate in sounds formation; one can see isometric, isotonic and auxotonic (or auxometric) contractions. Regimen – tetanus.

Contractive types and regimens at mastication.

Masticatory muscles contractive type is auxotonic, regimen is tetanic. Tongue: types – isotonic and auxotonic, regimen – tetanic.

Masticatory muscles physiological properties. Masticatory musculature force and work.

As it is well-known, maxillary-facial region muscles are divided into 2 main groups: masticatory and mimic. They belong to skeletal muscles and possess the same features. Masticatory muscles contract mainly in auxotonic regimen i.e. with parallel tension and length changing. Masticatory muscles contracture can be developed due to masticatory muscles fatigue. Contracture means muscles retarded relaxation.

Masticatory musculature belongs to force muscles. It means that they develop mainly force comparatively to other skeletal muscles which develop velocity. In course of masticatory musculature contraction force is developed. Such force is necessary for mechanical action to the food piece, its crush, wearing down and grinding. Skeletal muscle with square in 1 cm2 can develop muscular force in 10 kg. Transversal section sum for masticatory muscles ascending mandible on 1 side of face is equal to 19,5 cm2, from the both sides – 39,0 cm2. Thus, masticatory muscles absolute force is equal to 390 kg. At the same time, separate teeth parodont durability is weak. That is why, pain occurs in parodont during jaws enforced closure and pressure further increasing reflectory stoppage is observed though muscular force has not exhausted yet.

Dental row masticatory center is dental-mandibular system region where food mechanical processing is performed maximally. In healthy people such center are small and large molars of another side from the one on which mastication takes place. During mastication left and right masticatory centers act in turns. At both masticatory centers functions loosing crushing function is transferred to the first teeth which are adapted badly for this function performance under physiological conditions. That is why food crushing becomes bad and its processing by saliva becomes non-complete.

Masticatory pressure – is a force which is developed by masticatory muscles on mechanical food processing side. This pressure is caused by masticatory muscles contraction and tension in parodontal tissues: the more it is the closer to the attaching place of masticatory muscles and mandible the tooth is.

Masticatory musculature work takes place when muscles are contracted; thus, it is dynamic one.

Muscular work effectiveness – or coefficient of useful action – is up to 30 per cent for masticatory musculature. The work which is in fact is performed during mastication is known as mastication effectiveness. It depends on:

– mastication intensivity;

– masticatory pressure force;

– saliva qualities;

– bite character;

– tongue movement during food piece formation.

Dentists should remember about such physiological methods widely used in practice. Gnatodynamometry is used for determining the tooth supporting tissues resistance to pressure. It is performed by means of gnatodynamometers. They have special plates for teeth. Teeth transmit definite pressure to the spring during mouth closure. This pressure is recorded on the scale. It is established that frontal teeth durability is equal to 60 kg while the one for masticatory one is 180 kg. Parodont durability depends on masticatory musculature and parodont individual development, their age- and sex-dependent functional state.

Masticatory muscles injury due to their inflammation or trigeminal nerve disease can be mandible contracture reason. Reason is delt with changes occurring in temporal-mandibular joint. That is why myoartrography is of clinical importance. This method allows to registrate simultaneously masticatory muscles contractions and articulatory heads movements.

 


Дата добавления: 2018-02-15; просмотров: 196; ЗАКАЗАТЬ РАБОТУ