Download Temporal (wave) Summation

SUMMATION
LEARNING OBJECTIVES
By the end of this experiment student should know:
 How to pith the frog.
 How to prepare nerve and muscle for further procedure.
 How to record a graph of SUMMATION.
 Types of summations.
WHAT IS A MOTOR UNIT

A motor unit is a somatic motor neuron and all
of the muscle cells it innervates.

The number of muscle fibers per motor unit
may be as high as several hundred or a few as
four.
MUSCLE TWITCH
 The response, a contraction followed by relaxation, of a muscle to
a single brief
threshold stimulus.
MUSCLE CONTRACTION
There are three phases:
 Latent period
 Period of contraction
 Period of relaxation
LATENT PERIOD
 The time period, usually a few milliseconds, after the decision to
contract a skeletal muscle as been made and the actual shorting of
the muscle has occurred.
PERIOD OF CONTRACTION
 The period of contraction is when cross bridges are active, from
the onset to the peak of tension development, and the
myogram tracing rises to a peak.
 If the tension becomes great enough to overcome the resistance
(weight being
moved), the muscle shortens.
PERIOD OF RELAXATION

The period of relaxation follows the period of contraction, and is
the result of Ca2+ Ion concentration returning to normal levels.

The muscle tension decreases to zero and the tracing returns to
the baseline. If the muscle has shortened during contraction, it now
returns to its initial length.
GRADED MUSCLE RESPONSES
Muscle contraction can be graded
in two ways:
1. By changing the speed of stimulation.
2. By changing the strength of the stimulus.
GRADED MUSCLE RESPONSES
Muscle responses to an increase in the number of stimuli:
1. Treppe
2. Temporal (wave) summation
3. Incomplete tetani
4. Complete tetani
TREPPE
 A muscle must have been at rest for a period of time.
 All phases of muscle contraction are present.
 The stimuli are equidistance apart.


The amount of tension is increasing due to warming of the muscle.
The increase in temperature causes enzymes to be more effective.
The amount of tension developed, with the same strength of
stimulus, increases and then remains the same.
SUMMATION
 Summation is of two types
 Temporal (wave) summation
 Motor unit summation
Temporal (wave) Summation




An increase in the frequency with which a muscle is stimulated
increases the strength of contraction.
With rapid stimulation (so rapid that a muscle does not completely
relax between successive stimulations), a muscle fiber is restimulated while there is still some contractile activity.
As a result, there is a 'summation' of the contractile force. In
addition, with rapid stimulation there isn't enough time between
successive stimulations to remove all the calcium from the
sarcoplasm.
So, with several stimulations in rapid succession, calcium levels in
the sarcoplasm increase. More calcium means more active crossbridges and, therefore, a stronger contraction.
Motor Unit (spatial) Summation
 The degree of contraction of a skeletal muscle is influenced by the
number of motor units being stimulated (with a motor unit being a
motor neuron plus all of the muscle fibers it innervates).
 Skeletal muscles consist of numerous motor units and, therefore,
stimulating more motor units creates a stronger contraction.
TEMPORAL SUMMATION
If two identical stimuli are delivered to a muscle in rapid
succession, the second contraction will summate with the first.
All phases of muscle contraction are present.


Relaxation phase has been shortened.



The stimuli are of the same strength, and are equidistance apart.
The second contraction occurs before the muscle has completely
relaxed. This causes the relaxation phase to be shorted and
results in more Ca2+ .
TEMPORAL SUMMATION
BENEFICIAL EFFECT:
The amount of tension is increasing due to an increase in the
amount of Ca2+,as the Ca2+ released by previous stimulation is not
mopped off and Ca2+ continues to release due to subsequent
stimuli.

 OBJECT:
stimulate the muscle with twin pulses at different pulse intervals
and
observe
the
effect
on
muscle
contractions.
OBJECT:
 The student should be able to:
 Fix the NMP in the muscle chamber.
 See the response of stimulus on nerve muscle preparation.
REQUIREMENTS:
 Nerve muscle preparation.
 Lab tutor.
 Stand.
 Ringer’s solution or normal saline.
 Pins and dissecting instruments.
 Procedure
1.Make sure the muscle is moist and is in contact with the stimulating
electrodes.
2.In the Stimulator panel, insert your value for the supramaximal
stimulus voltage that you calculated in Exercise 1.
3.Set the Stimulator Panel to deliver 2 pulses. Check that the interval
between the two pulses is set to 400 ms (a frequency of 2.5 Hz)
4.Click Start. Lab Tutor is set to record for 625 ms. It will deliver the
first supramaximal stimulus just after you click Start, and the
second after the interval that you specify. Lab Tutor will also enter
a comment showing the stimulus amplitude.
5.Repeat step 4 decreasing the stimulus interval in the following
sequence: 200 ms, 100 ms, 80 ms, 60 ms, 40 ms, 20 ms.
 Analysis
1.You will have seven records to analyze.
2.For each record, place the marker on the baseline immediately
before the first contraction. Then use the Waveform cursor to
measure the maximum heights of the two contractions
3.Click on each peak to transfer the value into the value panel.
4.Drag the value to the appropriate place in the table.
THANKYOU