GRADATION OF STIMULI & STRENGTH DURATION CURVE.pptx

Physiotherapy

1. GRADATION OF STIMULI

2. INTRODUCTION The height of contraction is increase with increase in strength of stimuli. Grades of stimuli : 1)SUBTHRESHOLD STIMULI (SUBMINIMAL/SUBLIMINAL) 2) THRESHOLD STIMULI (MINIMAL / LIMINAL) 3)SUBMAXIMAL STIMULI 4)MAXIMAL STIMULI 5)SUPRAMAXIMAL STIMULI

3. GRADES OF STIMULI 1)SUBTHRESHOLD STIMULI :strength of stimuli less than threshold stimuli which is unable to produce response. 2)THRESHOLD STIMULI : a minimum strength of stimuli that is just sufficient to produce response. 3)SUBMAXIMAL STIMULI : strength between threshold and maximal stimuli. 4)MAXIMAL STIMULI : minimal strength of stimuli that produce maximum response. 5)SUPRAMAXIMAL STIMULI : strength of stimuli more than maximal stimuli.

4. FACTOR AFFECTING HEIGHT OF CONTRACTION Number of motor units activated by stimulus Strength of stimuli Frequency of stimuli

5. MOTOR UNIT Single motor neuron and all the muscle fibres supplied by it. Functional unit of muscle contraction. Innervation ratio or size of motor unit. Extraocular & hand muscles 3-6 muscle fibres/motor unit. Gastrocnemius & back muscles 2000 2000 muscle fibres/motor unit.

6. Size principal: force of contraction is increase by recruitment of additional motor units. Which stat that additional motor units are recruited ,more motor neurons are involved and more tension generated. When muscle is stimulated with increasing strength of stimuli more and more motor units are recruited.this results in increase in the amplitude of contraction.

7. requirements Electric connections for single induction shock Kymograph Muscle trough and lever Nerve muscle preparations

8. Method Set up the myograph and nerve muscle preparation for recording SMC. Exclude the drum from the primary circuit and engage the gear in the neutral position. Move the secondary coil of the inductorium far away from the primary coil. Keep the writing point of the lever away from the drum and release the spring key. Observe for the contraction at ‘make’ and ‘break’.

9. If there is no contration move the secondary coil 1 cm closer to the primary coil and press and release the key, and look for the contraction at ‘make’ and ‘break’. Repeat the procedure till the break shock gives a contraction and record the contraction on the drum. Measure and note the distance between primary and secondary coils.

10. Move the secondary coil 1 cm closer to the primary coil, rotate the drum manually and record the contraction at both make and break.Record each pair of make and break contractions close to each other. Repeat this procedure by moving secondary coil closer to the primary coil till there is no further increase in the amplitude of contractions by increasing the intensity of stimulus. Label the response as M for make stimulus and B for break stimulus below each pair of recordings.

11. METHOD Same as for recording SMC Use ELECROMAGNETIC TIME MARKER to mark make and break stimulus. Drum of kymograph remain in stationary position. Rotate the drum manually so that the pointer move about 1 cm on drum ,step by step move secondary coil near primary coil by 1 cm at a time. Test response of muscle to make and break stimulus seperately. Label the graph and note distance between two coil.

12. OBSREVATION Muscle does not response initially to stimuli, so this is the subthreshold strength of stimuli. (2)First response appear only at break stimulus , so it’s a threshold strength of stimuli. because during break circuit there is no self induction and no copper wire resistance.

13. OBSERVATION (3)As we further increasing the strength height of contraction is gradually increase and also break response is more than make response.it is the submaximal stimuli . The threshold of excitation of different motor neurons supplying single skeletal muscle is different. So with increase the strength , more and more quata(mass) of motor units get recruited and their response are summated together which is called QUANTAL SUMMATION , and that’s why height of contraction gradually increase.

14. OBSERVATION (4)Finally further increasing the strength that produce maximum response and height of contraction is equal in both make and break stimulus so it’s a maximal strength of stimuli. All motor units are involved in contraction which produce maximum response and height of contraction is same in both make and break response.

15. OBSERVATION (5)Further increasing the strength of stimuli , the height of contraction can not be increase and also a same response in both make and break circuit.its a supramaximal strength of stimuli. All motor units are already involved in contraction in maximal stimuli, so no other motor unit remain, that’s why height of contraction can not further increase even increasing the strength of stimuli.

16. STRENGTH DURATION CURVE

17. It is a relationship between different strengths of stimuli and time taken for those stimuli to induce response of either a nerve fiber or a muscle fiber(excitable tissues).

18. OBSERVATION The subthreshold strength of stimuli does not produce any response. With minimum strength of stimuli a long time is required to produce response to stimulate nerve fiber or muscle fiber. This current strength which applied for longer period of time to produce a first response is called as “RHEOBASE CURRENT”.

19. OBSERVATION The time required by Rheobase to stimulate a tissue is called “UTILISATION TIME”. When a nerve fiber or a muscle fiber is stimulated with a current strength double than Rheobase , it will respond and time taken for response is called “CHRONAXIE”. Chronaxie is important to measure excitability of excitable tissue. Chronaxie is minimal for nerve fiber than muscle fiber. It is minimal for thick myelinated nerve fibers.

20. FACTOR AFFECTING THE EXCITABILITY Strength of stimulus Duration of stimulus Temperature Mechanical pressure Blood supply Chemicals Ph Effect of ions.

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