- Lab. - Rama Nada. - Aya Alomoush. - Mohammad khatatbeh. 1 P a g e

Transcription

1 - Lab - Rama Nada - Aya Alomoush - Mohammad khatatbeh 1 P a g e

2 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. This is the nerve that innervates the gastrocnemius muscle 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 2 P a g e

3 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). 3 P a g e

4 The parts of the kymograph: 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? 4 P a g e

5 At the point of the stimulation there is a small movement in the drawing then the draw goes up (contraction) and down (relaxation). The area in the square represents the latent period where the stimulation occurs, pay attention to the small elevation in the curve. 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: بتمسك الدرم و بتحركها باالتجاه العكسي ببطء )يعني لو كانت تتحرك مع عقارب الساعة حركها عكس( لما تالحظ انو المنحنى بنقطة معينة بطل خط مستقيم وبلش يتحرك هاي النقطة تحديدا بكون صار فيها الستميوليشن ولما يرتفع بتحكي انو هون صار الكونتراكشن ولما يرجع ينزل بكون الريالكساشن تخيل كانك بتركض بساحة دائرية و ضيعت اغراضك وبعد ما كملت 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) 5 P a g e

6 -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 6 P a g e

7 **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 ). The frequency of stimulation increases with the arrow direction Simple muscle twitch Wave summation Incomplete tetanisation Complete tetanisation 7 P a g e

8 -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. 8 P a g e

9 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. 9 P a g e

10 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 10 P a g e