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Biological Sciences
Jason Brown

MUSCLES & MOVEMENT 3 SLIDE 2: MUSCLE CONTRACTION ITSELF PRODUCES SOUND  Motor unit- a single motor neuron and all the muscle fibers in it  In vertebrates, not true in invertebrates, every muscle cell only get innervated by only one muscle neuron  If you have one muscle and want to contract quite forcefully, you do it by stealing multiple motor units o Lifting something light, don’t need a lot of motor units but if it were something heavy, need more motor units  All come down to the idea that the total force a muscle can produce depends upon to total number of myosin heads that are going through cross-bridge cycling  One motor unit = there are fewer myosin heads acting  More motor units = more myosin heads, greater total force  Discovered in the late 1600’s, Wollaston described two methods he used to estimate the frequency of the sound. o Stick you thumbs in your ear and clench your fist and you can hear a high frequency noise which are your muscles contracting. This is due to the muscle changing shape that contracts. When a muscle contracts, the length gets shorter and the width increases.  This can be used to find problems with muscles. Listen to the sounds and you can find muscle disorders because they cause changes in the sounds the muscles make SLIDE 3: HEARING RANGE  Human hearing range is between 20-20000 Hz (cycles per second) o When you clench your fist, there is at least 20 vibrations occurring to produce that sound (contract 20 times)  In order to make sound, they have to be able to contract that particular frequency SLIDE 4: PRODCUING SOUNDS WITH “ORDINARY” MUSCLES : STIDULATION IN GRASSHOPPERS  Hindleg is moving, semi rapid contractions and then you hear a sound. What causes this sound is filalin scraper system  Grasshoppers have these little pegs along the inside of their hindlegs and its going to contract its leg up and down so the pegs drag across a very hard vein on the wing which serves as a scraper.  Every time the peg comes into contact with the vein on the wing, it creates a vibration  The frequency on the sound that is produced depends on the density of these pegs  The frequency is also dependent on the number of pegs present  In a 200ms interval, you see around 10 movements which would give a 10Hz frequency o Typical for most vertebral skeletons, contract 5-20 times per second  What if you stipulate them more frequently? o They under tetanus and don’t have enough calcium to relax and stimulate again and add new twitch to the previous one and end up all twitches to come together causing tetanus SLIDE 5: SONIC MUSCLES: RATTLESNAKE TAIL = “WARNING SIGNAL”  Pretty small rattle not making huge movements  What is dictating the frequency of the tail is the frequency of which the muscles are contracting  Rattlesnake tail is made of hollow, keratinized, interlocking plates  These plates fit into each other and contact to make this sound  What allows the tail to make this high frequency sound is the rate in which the muscles can contract  The peaks in the graph show when the muscle contracts and relaxes  A, B, C correspond to the muscle that are on one side of the tail; Muscles are all stimulated at the same time  In this period of time, 100 ms, you see 6-7 contractions. If you were you to calculate how many contractions in a second, you see a 60Hz frequency  D indicates one of the muscles on the other which you can see that it is out on sync o Has alternating contractions SLIDE 6: SONIC MUSCLES: TYMBAL OF MALE CICADA  The noise comes from the tymbal  The structure is like a little accordion which is being pulled on then relaxes to create the sound  The tymbal has a muscle attached to it called the tymbal muscle which contracts and relaxes, as this occurs, the tymbal buckles in then relaxes which creates vibrations producing this sound  Have a tymbal on each side, which one is contracting, the other is relaxing  The arrows on the graph indicate the muscle contractions and relaxations  50 ms bar, 4 distinct contractions. In a full second, it would be an 80 Hz frequency SLIDE 7: SONIC MUSCLES: TOADFISH SWIMBLADDER = BOATWHISTLE MATING CALL  What makes the sound are the muscles that are surrounding the swim bladder are going to contract and relax, deforming the shape of the swim bladder producing vibrations making boat whistle sound o Think of it as a balloon. When you squish a balloon, parts pop out. When you remove your hand from squishing the balloon, it takes its original form  Swim bladder muscles are known to be the fastest vertebrate muscles present on earth  Can contract and relax up to 300Hz per second SLIDE 8: SONIC MUSCLES  Sonic muscles contract 50-300 times/second BUT they do not undergo tetanus  How are they able to contract and relax very frequently without undergoing tetanus? o Calcium is cycled very, very quickly  The graph shows the amount of free calcium in the myoplasm o At time zero, muscle is stimulated and calcium levels rise and we see how long it will take for the calcium levels to reach the resting level o In red muscle, calcium levels rise quickly but take a very long time for the levels to reach a resting stage o In white muscles, calcium levels rise quickly but also drop quickly o In sonic muscles, calcium levels rise and drop in the matter of 5 ms  What allows these muscles to cycle their calcium? o They have an abundant amount of sarcoplasmic reticulum and small myofibrils  Look at the pictures of the sonic and white muscles. On the white muscle, you can see individual myofibrils and sarcoplasmic reticulum. On the sonic muscle, they are much smaller is this is due to the fact that it decreases the amount that calcium has to travel o TnC has a low affinity for calcium which allows it to unbind easily which allows to muscle to relax o They have high levels of parvalbumin which is described as a “slow” cytosolic Ca2+ binding protein  It has a much greater affinity than TnC  It also has affinity for magnesium. If magnesium is bound, that means there is no room for calcium to be bound. In order for calcium to bind to parvalbumin, it has to displace the magnesium.  The role for parvalbumin is to facilitate muscle relaxation because it binds calcium. The calcium cannot be bound to TnC so the muscle relaxes. The importance of it being a slow calcium binding protein is
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