Physiotherapy

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
1) Number of motor units activated by stimulus
2) Strength of stimuli
3) 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.

12. OBSREVATION
(1) 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.

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).

19. 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”.

20. 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.

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