2. To record simple muscle curve (twitch)- SMT.
To study the effect of Increasing strength of stimulus.
To study the effect of Temperature.
To study the effect of Two successive stimuli on SMT.
To study the genesis of Tetanus.
To study the genesis of Fatigue.
Determination of Conduction Velocity of the Sciatic Nerve.
DR.PRIYANKA VERMA 2
4. A simple muscle twitch , PS – point of stimulus ,LP , CP, and RP – Latent ,
Contraction & Relaxation Periods respectively.
DR.PRIYANKA VERMA 4
5. PRINCIPLE
• When a single adequate stimulus is applied to a skeletal muscle through its
motor nerve it responds by a brisk contraction followed by a quick
relaxation. This response is called simple muscle twitch (SMT).
• Muscles and nerve are excitable tissues.
• Therefore, they respond to different stimuli.
• Any change in the environment to which the tissue responds is called a
stimulus.
DR.PRIYANKA VERMA 5
6. • The reactivity of the nerve and muscle to different stimuli depends on the
type, strength and duration of stimulation.
Different types of stimuli are:-
Electrical - Galvanic or direct current, faradic or induced current
Mechanical - Tapping, pinching, cutting.
Chemical - Acid / alkali or other chemicals
Thermal - Cooling / warming.
DR.PRIYANKA VERMA 6
7. An electrical stimulus is preferred because –
• Its site, intensity, frequency, duration & timing can be exactly
known & can be easily controlled.
• It causes least damage to the tissue.
• Tissue recovers immediately after stimulation.
• Phenomenon of excitation & conduction of impulse in the
excitable tissue is 'electrical' in nature.
DR.PRIYANKA VERMA 7
8. TYPE OF STIMULUS-
• Threshold: Minimum strength of stimulus to obtain a response.
• Sub-threshold (sub-minimal): Stimulus weaken than a threshold stimulus
unable to produce a response.
• Maximal stimulus: Adequate stimulus to produce a maximal response.
• Sub-maximal: Has strength more than threshold but less then maximal, sub-
maximal stimulus of varying intensity produce graded response.
• Super-maximal: Greater strength than maximal stimulus but response obtain
is not greater than maximal because all motor unit are stimulated.
DR.PRIYANKA VERMA 8
9. PHASES OF SIMPLE TWITCH
• The duration of simple muscle twitch is about 100 Msec.
• It is divided in to
LATENT PERIOD (LP)
CONTRACTION PERIOD (CP)
RELAXATION PERIOD (RP)
DR.PRIYANKA VERMA 9
10. LATENT PERIOD (LP) - Time interval from point of stimulation to
the beginning of Contraction- it is about 10 ms.
Intrinsic Cause
• Time taken for depolarization of the nerve.
• Time taken for the passage of nerve impulse throughout the
length of the nerve.
• Time taken for impulse to cross the neuromuscular junction.
• Time taken for the excitation-contraction coupling.
• To overcome the viscous resistance of the muscle.
DR.PRIYANKA VERMA 10
11. EXTRINSIC CAUSE
• Inertia of the instruments.
• Friction between the writing point of the lever and smoked
paper.
• Time taken by the induced shock to reach the nerve.
DR.PRIYANKA VERMA 11
12. FACTORS MODIFYING THE LATENT PERIOD
1. Increasing
• Inertia of the instruments.
• Increasing the load.
• Cold temperature.
• Using fatigued muscle.
2. Decreasing
• Warm temperature.
• Decreasing inertia by making the lever as light as possible.
• Minimum load.
• Decreasing strength of stimulus.
• Direct stimulation muscle
DR.PRIYANKA VERMA 12
13. CONTRACTION PERIOD (CP)
• Time interval from beginning of contraction to the peak of contraction. It is
about 40 ms.
FACTORS INFLUENCING THE HEIGHT OF CONTRACTION OF A TWITCH
• Type, Character and condition of muscle.
• Strength of stimulus.
• Temperature.
• Load.
• Inertia of recording instrument.
• Repetition of stimuli at certain interval.
DR.PRIYANKA VERMA 13
14. CHANGES IN MUSCLE PROPERTIES DURING CONTRACTION PERIOD
• Muscle becomes hard.
• Muscle develops tension and resists stretching.
• Muscle can shorten.
• Muscle lifts a weight.
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15. RELAXATION PERIOD (RP)
• Time interval from beginning of relaxation to end of relaxation it is about 50
ms.
REACTIONS IN THE RELAXATION PERIOD
• Heat production.
• Resynthesis of glycogen from lactic acid.
• Resynthesis of creatine Phosphate and ATP.
FACTORS CAUSING PROLONGATION OF RELAXATION PERIOD
• Muscle dehydration.
• Cold temperature.
• Fatigue of muscle.
DR.PRIYANKA VERMA 15
18. • The temperature of frog's saline affects the contraction of the gastrocnemius
muscle.
• WHEN A SIMPLE MUSCLE CURVE IS RECORDED WITH WARM SALINE
a. Latent period is decreased due to
• Fast conduction of impulse along the nerve.
• Less time taken to cross the neuromuscular junction.
b. Contraction period is decreased due to
• Increased enzymatic activity.
• Decreased viscosity of muscle.
• The temperature of frog's saline affects the contraction of the gastrocnemius
muscle.
• WHEN A SIMPLE MUSCLE CURVE IS RECORDED WITH WARM SALINE
a. Latent period is decreased due to
• Fast conduction of impulse along the nerve.
• Less time taken to cross the neuromuscular junction.
b. Contraction period is decreased due to
• Increased enzymatic activity.
• Decreased viscosity of muscle.
DR.PRIYANKA VERMA 18
19. C. Increased amplitude of contraction due to
• Increased enzymatic activity.
• Increased chemical activity.
• Decreased viscosity of muscle.
D. Relaxation period is decreased due to-
• Increased enzymatic activity.
• Decreased viscosity of muscle.
DR.PRIYANKA VERMA 19
20. If a muscle is heated gradually up to about 40°C (it begins to contract
slowly about 34°C the contraction reaches its maximum at 40 °C).
Hence this temperature is called optimum temperature.
Between 42°C-45°C, the functional activity become depressed muscle gets
stiff, opaque and shorten its length because at this temperature the
muscle are denatured.
The muscle remain in a state of sustained contraction. This phenomenon
is known as HEAT RIGOR
DR.PRIYANKA VERMA 20
21. 2. WHEN A SIMPLE MUSCLE CURVE IS RECORDED WITH COLD SALINE
a) Latent period is increased due to -
• Slow conduction of impulse along the nerve.
• More time taken to cross the neuromuscular junction.
b) Contraction period is increased due to –
• Decreased enzymatic activity.
• Increased viscosity of muscle.
DR.PRIYANKA VERMA 21
22. c) Decreased amplitude of contraction due to-
• Decreased enzymatic activity.
• Decreased chemical activity.
• Increased viscosity of muscle.
d) Relaxation period is increased due to-
• Decreased enzymatic activity.
• Increased viscosity of muscle.
DR.PRIYANKA VERMA 22
23. The effect of cold is reversible and all the processes of contraction are slowed
down due to depression of chemical processes involved for shortening.
Slight cooling causes lowering the threshold of excitability of muscle.
Prolonged exposure to severe cold cause loss of irritability irreversibly.
The muscle remains in sustained contraction which does not relax as long as
temperature is at the lowest. This called cold rigor and is due to leakage of
calcium ions from the cisternae.
The calcium pump is inactivated so calcium ions cannot be pumped back into the
cisternae.
DR.PRIYANKA VERMA 23
24. TEMPERATURE LP CP RP AMPLITUDE EXCITABILITY CONDUCTIVITY
NORMAL [25° C] N N N N N N
WARM RINGER [40° C] ↓ ↓ ↓ ↑ ↑ ↑
COLD RINGER [10° C] ↑ ↑ ↑ ↓ ↓ ↓
COLD RINGER [0° C] Sustained contraction [cold rigor ] reversible
WARM RINGER [> 45 ° C] Sustained contraction [Heat rigor ] irreversible
DR.PRIYANKA VERMA 24
26. Effect Of Increasing Strength Of Current
• When a muscle is stimulated with increasing strength of
stimuli more and more motor units are recruited.
• This results in an increase in the amplitude of contraction.
• A motor unit is defined as a single motor neuron (together
with its branches) and the muscle fibers that it supplies.
DR.PRIYANKA VERMA 26
27. Factors that affect the magnitude of contraction
1) Number of motor units activated by the stimulus
2) The strength of the stimulus
3) The frequency of the stimulus
DR.PRIYANKA VERMA 27
28. Motor unit
• Motor unit is the functional unit of muscle contraction in the intact
body.
• It consists of the single motor neuron cell body, its axon fibers , and
the muscle fibers innervated by it .
• The cell bodies of the motor neurons (α motor neuron) supplying
the skeletal muscle fibers lie in the ventral horn of the spinal cord or
the motor cranial nerve nuclei.
DR.PRIYANKA VERMA 28
30. MOTOR UNIT
• It is a single motor neuron with its branches to get with the muscle
fibers that it supplies.
• There are many motor units present in a skeletal muscle.
• As the strength of stimulus increases the number of motor units
excited, also increases.
• Maximal stimulus excites all the motor units present in the skeletal
muscle, resulting into a maximum response.
DR.PRIYANKA VERMA 30
33. Effect Of Increasing Strength Of Current
• The amplitude of contraction increases with increase in strength of
stimuli. There are different types of stimuli:
• A subminimal stimulus or subthreshold stimulus is a stimulus that
does not evoke a response. (no motor units are recruited)
• A threshold stimulus is the minimum strength of stimulus that is
just sufficient to evoke a response. This is also called minimal or
liminal stimulus.(the minimum number of motor units (say 1 or 2) )
DR.PRIYANKA VERMA 33
34. • At suprathreshold stimuli, more and more motor units are
recruited producing progressively increasing response.
• A maximal stimulus produces maximum response. [all the motor
units]
• A supramaximal stimulus is stronger than a maximal stimulus
but does not change the magnitude of contraction after reaching
a peak level. [no further motor units are left]
DR.PRIYANKA VERMA 34
37. • PRINCIPLE:
• When two successive stimuli are applied, the response of the
muscle to the stimuli depends on the timing of the second
stimulus. The second stimulus may be applied in:
• Latent period
• Contraction period
• Relaxation period
AIM- To study the Effect of Two Successive Stimuli on
simple muscle twitch
DR.PRIYANKA VERMA 37
40. Latent period : divided into two halves-
• First half
• Second half
• First half of the latent period:
• This is called absolute refractory period because, second stimulus applied
during this period does not produce any response, no matter how long the
stimulus is.
• Second half of the latent period:
• This is called relative refractory period because, there occurs summation of
stimuli due to which the height of contraction is increased. A simple muscle
curve is recorded.
DR.PRIYANKA VERMA 40
41. • Contraction period: when the second stimulus is applied during contraction
period of the first stimulation, a single curve with increased magnitude of
contraction is recorded. This may result due to-
• Wave summation-
• Stimulation of same motor units and summation of contraction waves, by
both stimuli.
• Quantal summation-
• An increase in response due to the stimulation of additional fibers by stimuli
subsequent stimulus.
DR.PRIYANKA VERMA 41
42. Relaxation Period: second stimulus may be applied-
1. During relaxation period of previous stimulation
2. At the end of relaxation period of previous stimulation.
During relaxation period of previous stimulation-
• Two peaks of contractions are recorded the second peak is bigger than
the first one. The effect is called imposition of waves.
At the end of relaxation period of previous stimulation.
• The magnitude of contraction of the second stimulus is greater than the
first. This referred as summation of contraction or summation of effects.
DR.PRIYANKA VERMA 42
43. • This occurs due to beneficial effects of previous stimulation
which are-
Increased concentration of calcium ions in the sarcoplasm
Increased temperature
Increased H+ concentration
Decreased viscosity
DR.PRIYANKA VERMA 43
45. As the frequency increases, there comes a point where each new
contraction occurs before the preceding one is over.
As a result, the second contraction is added partially to the first,
and force of contraction rises progressively with increasing
frequency
When the frequency reaches a critical level, the successive
contractions become so rapid that they fuse together; state of
sustained contraction
GENESIS OF TETANUS
DR.PRIYANKA VERMA 45
46. When force of contraction reaches maximum no effect of
increasing frequency of stimulus.
B,coz enough Ca2+ ions are maintained so that full contractile
state is sustained without any relaxation.
DR.PRIYANKA VERMA 46
48. STAIRCASE PHENOMENON (TREPPE)
• When the frequency of rapid, repeated stimuli is so adjusted that the
subsequent stimuli fall immediately at the end of relaxation of
previous stimulation, there occurs a progressive increase in the
magnitude of subsequent contractions resembling a staircase.
• Treppe is believed to be due to release of more & more Ca2+ ions from
This phenomenon is known as treppe, or "staircase" phenomenon.
• This is the basis of “warm up”.
DR.PRIYANKA VERMA 48
49. INCOMPLETE TETANUS (CLONUS)
• When the frequency of rapid, repeated stimuli is so adjusted
that the subsequent stimuli fall during relaxation period of
previous stimulation, there occurs incomplete relaxation resulting
into a state of incomplete tetanus or clonus.
DR.PRIYANKA VERMA 49
50. CLONUS
When a series of maximal stimuli are delivered to a
skeletal muscle, so that each stimulus fall during mid
relaxation phase of previous twitch.
Muscle relaxes, but not completely Such response
is known as Clonus
DR.PRIYANKA VERMA 50
51. TETANUS
• When the frequency of rapid, repeated stimuli is so adjusted
that the subsequent stimuli fall during contraction period of
previous stimulation, there occurs summation of
contractions, resulting into a state of sustained tonic
contraction or tetanus.
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52. • A minimum frequency of stimuli that is required to cause
complete tetanus is called minimum tetanizable frequency
(MTF) which can be calculated by dividing 1 second with
contraction period.
MTF = 1/CP = 1000m sec/40m sec = 25 sec
DR.PRIYANKA VERMA 52
55. GENESIS OF FATIGUE
Aim – To Study the Genesis of Fatigue
Principle – Fatigue is decrease in work performance due to
continuous and prolonged activity.
It is reversible phenomenon as there occurs no permanent
functional or structural change in the tissue and passes off after a
rest.
DR.PRIYANKA VERMA 55
56. In a muscle – nerve preparation the cause of Fatigue are :-
a) Depletion of nutrients
b) Accumulation of metabolites
c) Depletion of neurotransmitter – Acetylcholine, at the
neuromuscular junction.
DR.PRIYANKA VERMA 56
57. When stimulated repeatedly, few initial contractions have
increased magnitude due to beneficial effect.
The subsequent contractions progressively decrease in amplitude.
As fatigue sets in, the contraction becomes feeble & relaxation is
incomplete. This is called CONTRACTION REMAINDER.
It occurs due to a decrease in ATP content & accumulation of the
metabolites in the muscle.
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58. SITE OF FATIGUE :-
In an isolated nerve muscle preparation the site of fatigue is
neuromuscular junction.
Muscle is not the site of fatigue as it responds briskly to a direct
stimulation even after the onset of the fatigue.
The nerve is theoretically unfatigable, In human beings, the first
site of fatigue is the central synapses in CNS, not the
neuromuscular junction.
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59. The Recovery in the isolated preparation is due to:
1. Resynthesis and release of ACh.
2. Removal of metabolic products.
3. Resynthesis of ATP.
The recovery can be hastened by :-
Changing the ringer solution and also by providing nutrients for
energy production.
DR.PRIYANKA VERMA 59
60. Factors influencing rapid onset of fatigue:
1. Higher rate of work.
2. Greater amount of work.
3. Untrained person.
4. White or fast contracting muscles go into faster than the red
or slow contracting muscle.
5. Inadequate blood supply.
6. Myasthenia, myopathies and neuropathies.
DR.PRIYANKA VERMA 60
61. Factors resisting onset of fatigue:-
1. Exercise training
2. Increased muscle capillary density.
3. Increased number of mitochondria.
4. More myoglobin
5. Low ATPase activity
6. Adequate blood supply
7. Stimulation of sympathetic nervous system. This is referred to as
Orbeli's effect. This is due to increased oxygen supply and availability
of glucose, release of ACh and increase sensitivity of motor end plate
to ACh.
8. Suggestions and motivation
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62. CONDUCTION VELOCITY OF THE SCIATIC NERVE
PRINCIPLE
• The detection of the velocity of nerve conduction is one of the important
tests in clinical neurophysiology.
• The velocity of conduction mainly depends on the diameter and the
myelination of the nerve.
• Conduction velocity of is determined by dividing the between the two
points of stimuli (proximal and distal) with the difference in the latent
period of both the recordings.
DR.PRIYANKA VERMA 62
65. PRINCIPLE
• The detection of the velocity of nerve conduction is one of the important
tests in clinical neurophysiology.
• The velocity of conduction mainly depends on the diameter and the
myelination of the nerve.
• Conduction velocity of is determined by dividing the between the two
points of stimuli (proximal and distal) with the difference in the latent
period of both the recordings.
DR.PRIYANKA VERMA 65
67. CALCULATION
• Difference between LP of two twitches (L1-L2) = t sec.
• Length of the nerve between two points where electrodes applied = d meters.
DR.PRIYANKA VERMA 67
68. The normal conduction velocity of the frog's sciatic
nerve
Normally it is 40 meters/sec.
DR.PRIYANKA VERMA 68
