CRYDER’S: Muscle Models Breakdown

CRYDER’S: Muscle Models Breakdown


Okay, this is a sarcomere the sarcomere is the smallest contractile unit of a muscle. It is part of the structure of a myofibril which is made up of actin, myosin, troponin and tropomyosin proteins. Right and so the actin filaments (these small filaments) are going to be In a 6 to 1 ratio and will either be 6 actin filaments, surrounding every one of the thick myosin filaments. The myosin filaments are going to be the larger of the two and the myosin heads (these) are, when the binding site opens on the troponin complex, able to bind? Thick filaments will bind to thin and will (in a ratchet-type manner) perform the power stroke and shorten this overall sarcomere’s length (Like so) One powerstroke to the next starts contracting the muscle either completely or partially. This would bring together the z disc (right here). It would be the z disc or z line to the next that is seen here. A sarcomere consists of the proteins from z line to z line. That structure would be what we have (here) attached to the Z line or Z disk (the protein disc) attached to a group of actin filaments. The coiled actin is coiled with the yellow tropomyosin protein (here) It’s going to actually be wrapped around two actin filaments. Troponin proteins are found on each of those in the binding site where the myosin head is going to grab on. Here you have what’s referred to as the troponin complex. It’s the release of calcium from the terminal cisternae within the sarcoplasmic reticulum and the binding of that calcium to the troponin complex is what causes a conformational change and embedding of this troponin complex into the actin filaments (COUPLING). Opening up the binding sites so that these two things can interact in the sliding filament mechanism can ensure the shortening of the sarcomere overall. It would be seen in this structure. When the actin filaments (these structures here) are pulled inward into the H zone, which is this zone here) during contractions. So this would be a relaxed muscle and this relaxed muscle would only be said to be contracted if the actin filaments would be pulled into that H zone towards this M line at the center here. The sarcomere is made up of an A band which would be made of both actin and myosin here in the center of this structure And the I band which would be on the lateral edges (here) where just actin is bound The z-discs are located at the ends (as I’ve already said) and are moved in to the H zone? Here, in the middle of that H zone is the M line where the actin filaments are pulled toward the middle. all right, so each of those structures… ARE ALSO SEEN IN THIS MUSCLE FIBER Each of the structures that I just discussed are found in this model (here), So this model is a muscle fiber Right, a muscle fiber is going to be made up of MYOFIBRILS. (Each of these circular units) and if I were to bundle many of these FIBRILS together, I would have a FASCICLE and we’ll talk about that in a moment. These myofibrils (the bundles seen here) are made up of actin and myosin proteins in a six to one ratio. It is the arrangement of those proteins that give you this striated appearance that you see right here on the model. The striations that are visible now from the surface of this muscle (as you can see here). Here you have openings that go into the muscle through the sarcolemma. This is the phospholipid bilayer of the muscle around this particular opening (right here). Each of these openings lead into these structures called T tubules. They are how sodium gets deep into the muscle to allow for a complete muscle fiber contraction Okay, so On this muscle is its neuromuscular Junction (here) The neuron (right there) is connecting at the neuromuscular Junction to the sarcolemma of this muscle. That is where you would have excitation coupling of these two things together. As we said, you would have sodium influx into this muscle fiber and that sodium influx is how it all reaches threshold as we discussed in class. This will result in AN ALL-OR-NONE-action potential to be generated and shortening to occur ultimately.. It is from this site, all of the way through sliding filament mechanism within this muscle. But on this particular model; what I would hope that you guys know would be 1) the neuromuscular Junction. That’s these two things together? This is neuron axon and it terminates in an axon terminal (here) (or terminal Bouton’s). That is the motor end plate or synaptic cleft found on the sarcolemma of this particular muscle. So, the sarcolemma or the cell surface is where we have an interaction between a neuron and this particular muscle fiber. Each of these small organelles will be mitochondria producing oxygen— Whoops! MITOCHONDRIA MAKE ATP USING OXYGEN. SORRY!! So that this muscle could continue to function over and over again for prolonged periods of time Notice that on the surface of this muscle you have nuclei. This is a multi nucleated skeletal muscle and therefore this skeletal muscle would need the ability to produce its various proteins in abundance over and over as the contraction shortens the muscle. This allows you to build muscle mass with each time it is used. (And Here) deep in the muscle you have these openings. These openings are the T tubules. These T tubules lead into these blue channels This is the T tubule itself and notice it goes all throughout the muscle fiber (even in areas where it looks like there is nothing. Also surrounding myofibrils would be (of course) the sarcoplasm of the muscle fiber. Now, the T tubules again are these blue channels. They are surrounded on either side by the sarcoplasmic reticulum and its extensions Its extensions are called terminal cisternae. This triad (seen right here) would contain calcium ions. Which flow on either side of it. And in the center the T tubules (which are open to the outside), you’d have sodium influx. The neuron’s ability to fully contract this particular muscle fiber will require anywhere from four to hundreds of neuron axon terminals to innervate and excite one muscle fiber. BUNDLES OF MUSCLE FIBERS=A MUSCLE FASCICLE If I bundle many of these fibers together into a unit (like we would see in the body) each look like this model. Each individual unit seen here then is what we previously looked at in the muscle fiber model. So I know that from structures within this model (here) that I saw on previous models; I see another neuromuscular junction, I see multiple nuclei which are all indicators helping us to know that this particular unit (right here) would be a muscle fiber like we just looked at on the larger model a moment ago. So these muscle fibers, when bundled together with other muscle fibers, forms a fascicle. So this entire model is a Fascicle. When I combine many fascicles together, I form a muscle tendon. Tendons will be studied on the models of the arm and leg and torsos that we will be studying more. Compartmentalization of these components or compartments within the muscle are surrounded by connective tissue C.t. that’s either dense regular, or dense irregular connective tissue (mostly dense irregular unless It’s the tendon itself). So, it’s being reinforced in all direction like this layer for example right here) on the individual muscle fibers. Also on the muscle fiber model that we just looked at that had this layer. That’s the white tissue right here that we referred to earlier as the endomysium? Perimysium surrounds that muscle unit and so if this is multiple fibers together each individual fiber would be surrounded by endomysium On the individual fiber model. This is endomysium And then if I bundle all of those individual units together in a fascicle Perimysium surrounds that whole fascicle You can also see what we showed first- The sarcomere structure (seen here). Here’s the z-disc and there’s another z-disc. This is the H zone in the middle This is the A band here, and then on either side these lighter areas would be the I bands As I pull the I band inward and as we bring the actin filaments into the H zone toward the M line I would be contracting these contractile units called sarcomeres

One Reply to “CRYDER’S: Muscle Models Breakdown”

  1. Cryder is the best Damn Anatomy instructor on Earth!. Had him both A & P courses. I am Nursing Now because of his influence! !! #Beastmode Cryder

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