Task 4. Muscles contractions dependence on single irritations force.

The observations are performed on nerve-muscular preparation (gastrocnemius muscle and femur bone residue). The preparation are fixed in myograph and the electrods are brought up to the muscle. Find the threshold level. To perform this muscular contraction registration on kymograph. The investigator must write voltmeter numerals under the myogram. To continue the voltage increasing and myogram registration on kymograph. Then one must find the irritation level at which further altidude rising up is absent, i.e. the muscular contraction becomes maximal. These are so-called optimum irritation conditions.

After that one should increase quickly current force and determine the contraction force diminishing. The phenomenon observed is called force pessimum. The curves received must be glued into students’ copy-books.

The students must make the conclusion about dependence between irritation level and muscular contraction force. Explain the phenomena of force pessimum and optimum.


Task 5. Draw and analize the curve “force-time”.

To mark “rheobase”, “useful time”, “chronaxy” on your graphic. Make the conclusions.


5. Literature recommended:

1. Lecture course.

2. Mistchenko V.P., Tkachenko E.V. Methodical instructions for dental students (short lecture course).-Poltava, 2005.-P.3-6.

3. Mistchenko V.P., Tkachenko E.V. Methodical instructions for medical students (short lecture course).-Poltava, 2005.-P. 3-6.

4. Ganong W.F. Review of Medical Physiology.-21st ed.-2003.-Section II.

5. Bullock J., Boyle III J., Wang M.B. Physiology.-1991. P. 18-35.

6. Materials for self-control:

Control questions:

1.Irritability and irritation as they are.

2. Stimuli, definition and classification.

3. Excitability.

4. Call excitable tissues.

5. Law “everything or nothing”.

6. Muscular contraction force dependence on irritation force.

7. Stimulus threshold force dependence on its duration.

8. Excitability measures.

9. Lability as one of the excitable tissues features.

10. Excitability changes in course of excitement.



Nervous and muscular fibers resting potential and action potential.

The topic studied actuality.

One can use potentials leads from body surface in clinical practice. The records received are called correspondingly to the potentials origin: electrocardiogram (ECG), electroencephalogram (EEG), electromyogram (MG) and so on.

Tooth solid tissues electrical features determining is performed in dental practice for acute and chronic pulpitis diagnostics. This methodics is rather complicated. It requires measurements taking into account individual peculiarities of teeth morphological shape and geometric sizes as well as obligatory following the mot possible stimulus parameters.

Nowadays one uses also possibility of oral mucosa biopotentials measurement for its functional state assessment. There was detected summary biopotentials age dynamics as well as their level change at parodontosis, oral mucosa diseases which is of important diagnostic value.

Dentist can touch with potentials occurrence between similar metals (for instance, amalgame) of different content or between crowns made from the same metal if there is metal filling under them. Appearing microcurrents can be the reason of such a phenomenon named as galvanism. Sometimes pathological process is developed in years after denturing. It depends on the patient individual reactivity. Galvanism clinical symptoms are rather different. They can be divided into two big groups: subjective complaints which occur directly right after metallic fillings and crowns fixation in oral cavity. “Metallic taste” and some others belong to them. They are usually stopped in several days. Complaints which are appeared in prolonged time (sometimes in several years) belong to other group: metallic taste, pain. Oral mucosa inflammation can be developed: reddish color, tongue papillas swelling, erosions and ulcers appearance.

2. Study aims:

To know: resting and action potentials physical and physiological characteristics, registrative methods, ionic mechanisms.

To be able to: draw action and resting potentials developmental schemes during time; resting potential changings during membrane de-, re- and hyperpolarization as well as scheme of excitability changings during action potential development.

3.  Pre-auditory self-work materials.

3.1.Basic knowledge, skills, experiences, necessary for study the topic:

Subject To know To be able to
Medical biophysics Resting and action potentials nature and developmental mechanisms Investigate electrical phenomena nature on experimental models
Medical biology Biological membranes structure and functions  
Histology Passive and active transport mechanisms through biological membranes Draw biological membranes structure and characterize their functions
Neurology Biopotentials nature, occurrence and distribution mechanism in muscular and nervous tissues, physiological importance, excitability changings during action potential development.  

3.2.Topic content.

The muscle contracts when it is stimulated. Contraction of the muscle is a physical or mechanical event. In addition, various other changes occur in the muscle. The changes, which take place during muscular contraction are:

1.Electrical changes

2.Physical changes

3.Histological (molecular) changes

4.Chemical changes

5.Thermal changes

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