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- Lab

- Rama Nada

- Aya Alomoush

- Mohammad khatatbeh

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In this sheet well discuss four main topics which are measuring the:

1- Simple muscle twitch

2- Treppe phenomena

3- Summation

4- Muscle fatigue

The frog muscle is used in this laboratory exercise in place of

mammalian muscle because of its tolerance to temperature change and

handling. The results are similar to what would be seen in more

carefully controlled mammalian experiments.

Preparation of the Frog

The first step: we dissect a frog so we get its gastrocnemius muscle and

the nerve which inervates it .

The second step: we hang gastrocnemius musclein a way to record

isotonic contraction (shortening in the muscle with no changing in the

tension ).

The third step: we stimulate the nerve that innervates gastrocnemius

muscle using a device called electrical stimulator to get the muscle

contracted.

To record the shortening of the muscle we are going to fix one head of

the muscle and insert the other head to the recording stylus of the

transducer device( remember that the transducer here coverts

mechanical energy into electrical energy ), so when the muscle gets

contracted the long arm of the stylus will move upward and with

This is the nerve

that innervates

the gastrocnemius

muscle

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relaxation it will return to its normal position ( remember that the stylus

is L shaped with long and short arms ).

Note from practical lab:

We have power lab recording system which is composed of transducer

( it is connected to the stimulator ) that converts mechanical to

electrical energy , data acquisition system, amplifier and software that

analyses the data.

Nerve bath: is where we put the nerve in order to stimulate it .

The stimulator

It is connected to the kymograph which closes an electrical circuit in

order for the stimulator to work by producing the stimulus and it can

give many stimuli per a unit of time so It controls the frequency of the

stimuli (the number of the stimuli per a unit of time).

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The kymograph

The parts of the kymograph:

1- Smoked drum: where the paper is placed and

the data appears , it rotates around the axis .

2- Drum shaft : where the rotating drum is

attached

3- Controllers :to adjusts the rotation speed of

the drum

4- Arm: when it touches the switch it closes the

circuit, this circuit is connected to the electical

stimulator so once you have this electrical

circuit closed the stimulator will give one

stimuls (one stimulus per one circuit closing)

So, what happens?

We said that one head of the muscle is inserted in the kymograph stylus,

so when the muscle gets contracted the stylus is pulled upward on the

smoked paper around the drum removing the smoking (imagen it as you

draw on the sand by your finger) and when its relaxed the stylus pulled

downward, if there is no stimulus the stylus will draw a base line only.

By controlling the speed of the drum, you can control the shape of the

graph which you get. The time of the simple muscle twitch is fixed so

upon (Remember that speed=distance/time):

increasing the speed of the drum the distance will increase and

the graph will show the latent, contraction and relaxation phases

clearly.

decreasing the speed of the drum the distance decreases and

the graph will appear as ascending line and descending line

without showing the three phases.

How to determine at which point you give the stimulus?

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At the point of the stimulation there is a small movement in the drawing

then the draw goes up (contraction) and down (relaxation).

So, to define the point of the stimulation for one stimulus in the

previous record we rotate the drum slowly backward and we notice at

which point the draw just start to move exactly here the stimulation

occur (latent period), (it will give the stimulus each round at the same

point).By the same mechanism you can figure out where the contraction

occurs and where the relaxation occurs.

The same idea in Arabic for whom who didn’t catch it:

حرك مع عقارب الساعة و بتحركها باالتجاه العكسي ببطء )يعني لو كانت تت بتمسك الدرم

حركها عكس( لما تالحظ انو المنحنى بنقطة معينة بطل خط مستقيم وبلش يتحرك هاي النقطة

ولما يرتفع بتحكي انو هون صار الكونتراكشن ولما يرجع تحديدا بكون صار فيها الستميوليشن

تخيل كانك بتركض بساحة دائرية و ضيعت اغراضك وبعد ما كملت زل بكون الريالكساشنين

اللفة رجعت بالعكس مشان تشوف وين وقعوا منك.

-I hope that the idea has become clearer-

-Now you know the point where the stimulation occurs, How to find at

which time it occurs?

Simply by knowing the speed you can calculate the time .

-The smart question is HOW TO CALCULATE THE SPEED?

Say that the circumference of the drum was 50 cm and it took 1 min to

complete a simple muscle twitch then the speed can be found by

dividing the circumference of the drum (distance) on the time of

complete simple muscle twitch (time) (speed=distance/time)

The area in the square

represents the latent

period where the

stimulation occurs, pay

attention to the small

elevation in the curve.

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-Do all the muscles have the same speed of contraction and the same

period?

The answer is NO, we have fast muscles (contract in shorter time) such

as ocular muscle and slow muscles (contract in longer time) such as

soleus muscle. But for all of them all most we have the same latent

period.

Treppe phenomena

Here we are stimulating many

times note that the amplitude of

contraction for the first stimulus

is low and it increases in the

second stimulus and more in the

third this is called Treppe

phenomena( it isn’t summation )

After many stimuli the amplitude of contraction is fixed and stay at the

same value even if we give more stimuli(look to the line in green in the

next graph).

No increase in the

amplitude of

contraction

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**Note: in this curve the speed of the drum is sited on low speed, so the

curves appear as ascending and descending lines without showing the

three phases.

Note that the graph shows complete contraction and relaxation in each

curve, this achieved by sitting the stimulator at low frequency, this

allows the muscle to have complete relaxation (the curve refer to the

base line) before the second stimulus (there is no summation).

Wave (frequency ) summation:

Match the numbers on the figure with the corresponding paragraphs

If you increase the frequency of the stimulator the number of stimuli per

unit of time will increase, that means the time between two stimuli will

be less than the duration of a simple muscle twitch, thus the muscle will

contract as a respond for the second stimulus before being completely

relaxed, this is called wave summation( remember if the period between

two stimuli was equal or more than the period of simple muscle twich

there will be no summation ).

As you increase the frequency of stimuli more but still there is a small

relaxation, the summation will become incomplete tetanisation.

If you increase the frequency more and more so there is no relaxation at

all (just contraction), the incomplete tetanisation will become complete

tetanisation ( a straight line ).

1

2

1 2 3

3

The frequency of stimulation increases with the arrow direction

Simple muscle

twitch Wave

summation

Incomplete

tetanisation

Complete

tetanisation

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-What happens to the muscle with time after stimulating it with high

frequency?

The curve will return to the base line, that’s mean no more contraction

even if you keep stimulating, this phenomenon is called Muscle

Fatigue,here you are stimulating the nerve but without getting any

contraction, but by a direct stimulation to the muscle you get

contraction, why?

-In the neuromuscular junction we have neurotransmitters to transmit

the action potential from the nerve terminal to the muscle. By giving

many stimuli per a unit of time the vesicles that carry the

neurotransmitters in the nerve terminals will be depleted (consumed by

the previous stimuli), once these vesicles become depleted no more

transmission of action potential will take place, so the fatigue happens in

the neuromuscular junction and direct stimulation to the muscle results

in its contraction, this type of fatigue couldn’t take place in our body

only in the lab, because the neurotransmitter won’t be depleted

(as we reach the fatigue before the neurotransmitter become depleted)

What happens in our body is the accumulation of lactic acid in the

muscles upon long and hard exercises and this accumulation will cause

changing in the PH inside the muscles and changing their properties

resulting in pain and decrease in the muscle activity, some people

consider this phenomenon muscle fatigue.

**Muscle fatigue can be also results from nerve cutting or blocking the

receptors of neurotransmitters at the neuromuscular junction, these

events prevent the transmission of action potential thus can be

considered as muscle fatigue.

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The effect of temperature on simple muscle twitchThe

previous experiments carried out at the room temperature what

happens if we change the temperature?

If we increase the temperature of the preparation up to 45 the time

needed for simple muscle twitch become lesser (shorter contraction

)but the amplitude of contraction will be greater, so by increasing the

temperature of the preparation we change the performance of the

muscle to shorten more and faster;

**this occurs due to decrease the viscosity inside the muscle (the

cytoplasm of the muscle cells). Decreasing the viscosity inside the

muscle facilitate the sliding between thick and thin filaments because

they face less resistance, also higher temperature means higher kinetic

energy so the calcium ions diffusion from the endoplasmic reticulum will

be more, more calcium ions diffusion leads to more contraction in the

muscle.

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The opposite will happen with decreasing the temperature; the

amplitude of contraction will decrease, and the time needed for simple

muscle twitch will be more, so the muscle shortening will become less

and slower.

WHAT HAPPENS TO THE LATENT PERIOD?

It will be shorter (less time needed to start contraction )at high

temperature and longer at low temperature why ?

It may be because the diffusion of action potential through the

sarcolemma will increases by increasing the temperature .

Seize your moment

Best of luck