Unit 3: Locomotion Flashcards
What are the building blocks of skeletal muscles?
Each muscle cell _________ __________ the _________ ___________ of the __________.
What are the bundles called that fill muscles fibres?
What units fuse to form these muscles cells during growth?
Skeletal muscles are made up of bundles of muscle fibres (which are muscle cells). Each muscle fibre (cell) is made up of myofibrils — which do the contracting that causes movement — and then tendons connect muscles fibres to other fibres and to bones.
Each muscle cell runs along the entire length of the muscle (bundle of muscles cells), and has multiple nuclei to supply this long size.
The bundles that fill muscle fibres are called myofibrils.
During growth hundreds of myoblasts fuse to form a long, multi-nucleate cell.
What are myofibrils made up of? What are sarcomeres?
Myofibrils consist of stacks of thick and thin filaments, which slide along each other to produce contractions. A sarcomere is a unit of this muscle cell — a functional unit. So a section of thin and thick filaments separated by something called a “z-line” where more filaments are attached on the other side is a sarcomere.
What is the sliding filament model and how does it work? How do short and long muscles compare in terms of generating force?
The sliding filament model describes how muscles contract and do work. Essentially, the thick and thin filaments slide along each other to produce these contractions. The X-line is the part where thin filaments are attached, and the M-line is where thick filaments are attached. The thick filaments stay stationary, while the thin ones slide towards each other and the M-line, and away from the z-line. However the z-line comes with the sliding thin filaments, and so the z-lines move towards the m-line as they contract. The sarcomere is then becoming shorter in length, as this is the unit between two z-lines.
Essentially, the myosin heads in the thick filaments grab onto the thin filaments and using force in the “power stroke” pull those filaments towards the M-line. Then the heads release and go back to their original position (recovery stroke) and then grab onto another point on the actin (thin) filament. So these heads stay stationary in the same position, but on their own they do move.
The contractions are called cross bridges between the fibres, and the longer the fibres are, the more cross bridges there are total. Therfore, longer muscles are able to generate more force overall!
The cross bridge cycle: Describe the contraction process in more detail and how ATP is used…
Myosin head on the thick filaments start in the bent, low energy configuration. Then ATP comes and is hydrolysis, producing ADP and Pi, which are uptaken by the myosin heads. This produces a cocked position where the head is active. Myosin then locks on and bonds to the actin filament because it now has the proper molecular bonding due to the phosphorus to allow it to do this. This ATP gives the potential energy it requires to do work. This is called a cross bridge, and more are formed on a longer muscles cell so more potential energy is accumulated and hence more force can be generated.
Then, once this bond occurs, the myosin head can release ADP and Pi, and this bends it back to its original position, and it brings the actin filament with it as it does this — this is the power stroke where it causes the contraction. So this occurs as the ADP and Pi are released. Then a new ATP comes to the myosin head in its low energy configuration, which takes away its connection to actin and releases it from that position in the recovery stroke. And it goes back to its original low energy position.
What 4 factors increase the force being produced when muscles contract?
- When the number of cross bridges between actin and myosin in each sarcomere increases, this allows for more power strokes and therefore faster muscles contraction and hence more force overall.
- When the number of muscles cells in the tissue increases, there will be more myofibrils total, and therefore more actin and myosin within each muscle total. This then allows for more cross bridges total, and hence more force total.
- When the length of the muscle increases, the length of each muscle fibre (and hence muscle cell cus these are the same thing) increases, allowing once again for more total cross bridges and therefore more total force. Obviously this is needed in larger bodies because you have to generate more force total move that larger mass.
- When the muscle contracts more slowly, more force will be able to be generated because all of the ATP can be used and strokes can be done to their completion. Rapid contraction will be very inefficient and generate a lot of waste heat — like with shivering, as this heat is desired to warm the body up. This is inefficient because it decreases the number of cross bridges that can form and the number of power strokes that can be effectively completed, and so less force total can be accumulated. So most of this energy coming from ATP is turned into heat.
Why is there a difference between maximum and sustained metabolic rates? Why is there a maximum? What are the physiological limitations that lead to this?
This is because there are two different types of muscle fibres, and each one can generate a maximum amount of force before something runs out. For sprinting, fast twitch muscle fibres are used, because this produces a ton of force over a short amount of time, without the use of any oxygen. However it cannot last for long because the energy stores reserved in those muscles will quickly run out.
Then for slow twitch muscles fibres for endurance, it also depends on the rate at which energy can get to the muscles fibres, and this will determine the maximum rate of contraction and hence movement. Once these energy stores run out completely though, power output will greatly decrease because ATP is needed for these muscle contractions!
So in general: There is a limited rate of ATP production and a limited rate of O2 delivery to muscles, and both these factors determine what one’s maximum and sustained metabolic rates can be.
What are slow twitch muscles fibres? What are the 7 characteristics that apply to them? What are their main fuel sources? What metabolic rates (sustained or maximum) do these rates of contraction determine? What are they used for (endurance or sprinting?)
Slow twitch muscles fibres use oxygen and more fats then simple carbs for fuel. Therefore, they do aerobic oxidative respiration, (cellular respiration) and hence they need oxygen to occur, and they need myoglobin to move. Myoglobin is a protein that stores and transports oxygen to muscle cells, and so muscles doing oxidative phosphorylation will be very red because of this myoglobin protein.
7 characteristics of slow twitch fibres:
1. They do aerobic oxidative respiration
2. They are high in mitochondria (because they do cellular respiration)
3. High in myoglobin (which is red and stores the oxygen used for this aerobic respiration)
4. They have high vascularization because they need a lot of oxygen and fuel to be delivered to them.
5. Low glycogen levels, because they don’t use stored carbohydrates as their source of energy, instead it comes from fats and other complex molecules in surrounding tissues that are broken down.
6.They provide low power but high endurance, so can be sustained over a long period of time.
7. This is usually seen in dark meet, which is dark due to its red nature and the larger amount of fats and blood supply present.
The maximum rates of contraction of slow twitch are dependent upon the amount of oxygen and fuel present to do cellular respiration and produce ATP, as this is what makes those cross bridges work. However because ATP is produced in mitochondria who are breaking down stored carbohydrates and using oxygen that is transported from other parts of the body, the maximum rates will not be as large as for fast twitch, because nothing is just readily available, it is all needing to be transferred or broke n down first. So this results in the sustained maximum metabolic rate — how fast can someone run over a given period of time based on the rate of cellular respiration that can occur in mitochondria at those muscle sites.
Therefore, these muscle fibres are used for endurance.
What are fast twitch muscle fibres used for, and how do they work? What are their 7 characteristics?
Fast twitch muscle fibres are used for high power, short bursts of movement that require a lot of force quickly but are not sustained. So they take ATP stores (and then phosphocreatine stores as well) that are right in the muscle already, as well as they use simple carbs to do anaerobic glycolysis (fermentation) which can occur much more quickly. This allows for instantaneous muscle movement and a faster rate immediately, because nothing needs to be converted or transferred, instead this rapid fermentation can occur. However, the ATP and PCR stores in the muscles will quickly run out, and result in a steep drop of power output after his occurs — because respiration will have to turn to aerobic which is slower.
7 characteristics:
1. They do anaerobic respiration
2. Low mitochondria in these muscles because little aerobic respiration occurs.
3. Low myoglobin (don’t need oxygen)
4. Low vascularization (getting all the carb sources from stores already in the muscles, and so they don’t rely on anything being transferred from other parts of the body).
5. High in glycogen because this is the main source of carbs that they use for quick respiration. So because it is already stored at the muscles site, they don’t need vascularization to get any nutrients.
6. This results in high power due to rapid and large amounts of ATP production. This is used in bursts and not over time.
7. White meat is an example of this, because it has low vascularization but will have a lot of glycogen allowing for quick metabolism when taking off (quick burst of power in wings).
What is MRmax and MRsus? If a question talks about MR max in general, what is it referring to in our course? What does a graph of power output V.S. duration look like (for MRmax and MRsus?
MRmax is the maximum metabolic rate that can occur when doing anaerobic respiration (so quick and large ATP generation, resulting in a very large rate that can only be sustained for a short time). MRsus is the metabolic rate that can be sustained over a long period of time, and this is the maximum rate it can be sustained at. This is based on the rate of delivery of O2 to the muscle cells, and also based on the rate of ATP synthesis due to the rate of delivery of carb sources to mitochondria.
The graph of power output over duration for a certain movement starts off with very large power output when a lot of energy is available as glycogen. But as those muscle stores are depleted, this rate quickly decreases until none is left, and this is when the graph levels off to the sustained metabolic rate, which occurs at the maximum rate of aerobic respiration. So once those stores are depleted, the MRsus is the maximum possible speed we can sustain over a long period of time.
In a question, we will be talking about MRmax as either one or the other, depending on the type of movement that is occurring. So MRmax can refer to sus or max depending.
What are the physiological limitations for MRmax and MRsus? What does a graph of energy demand vs time look like for a given movement (in other words where does energy come from as a movement progresses over time)?
MRmax is limited by ATP stores in muscles and PCr stores in muscles, which are sources of energy that are right at the active site and hence allow for rapid contraction and large force generation. However, after the first 10-15 seconds, both these stores run out. Then glycolysis will be used instead, as this is a faster way to generate ATP then with oxidative phosphorylation, and O-P takes a bit of time to kick in due to its long cycle. But after an amount of time O-P will be able to take over as it is a more sustained way to get energy, and produces a lot more then glycolysis (even though it is slower). Glycolysis is still producing energy, but not enough that it is noticeable over O-P.
So overview:
1. ATP stores in muscles cells provide instant energy and a lot of force, but it is used up fast.
2. PCr is a backup pool of ATP, as it combined with ADP in those muscles cells to produce ATP and Cr very rapidly and prolong the stores of ATP. But eventually PCr will run out as well.
PCr + ADP —> Cr + ATP
3. Once PCr and ATP stores are used up, we transition to glycolysis (still anaerobic) to make ATP quickly for the activity, producing lactic acid as a byproduct.
4. Then there will eventually be enough oxygen built up that oxidative phosphorylation takes over, and it will produce way more energy then glycolysis, so even though glycolysis is still occurring, O-D overtakes it due to the large amount of energy it is producing.
Maximum running speed VS the log of the duration graph… and compare this to the different energy sources being used.
Maximum running speed will be at a maximum when the maximum force is being generated most rapidly. So this is occurring when anaerobic respiration occurs from ATP and PCr stores. This is a flat line at first because the rate is constant so running speed should be constant at this point.
Then once these run out, glycolysis takes over and is still anaerobic, so still produces ATP relatively quickly. As this occurs, pyruvate is converted to lactic acid, resulting in a steep decline in running speed, until enough oxygen is present at the muscle cells that O-D can occur, and then the running speed decreases even more but levels out a bit, as this reaches MRsus and lactic acid begins to clear out. Then once simple carbohydrate and glycogen stores run out, triglycerides are used as an energy store, decreasing running speed even more — which is why you want to ensure you are fuelling with simple carbs throughout a long race, to prevent this drop in running speed.
What happens to metabolic rate before, during and after exercise, and how does this create O2 debt?
When exercise begins, metabolic rate quickly increases and hence so does oxygen intake. But because there is not enough oxygen present to allow for this intake, ATP and PCr stores are used, and then lactic acid fermentation is also used, until enough O2 is accumulated due to increased breathing rates that O-P can occur in a sustained manner. This then results in a leveled out graph, because metabolic rate is constant at this MRsus. Then once the activity stops, breathing rate decreases, but not immediately. There is a delay because oxygen is in debt from the anaerobic respiration that occurred at the beginning, and so oxygen must be redelivered to those muscles through “recovery metabolism” which replenishes cellular pools of ATP and PCr. This also removed lactic acid from muscles.
As mass increases, how does active MRmax change? How does mass specific MRmax change with mass?
As mass increases, MRmax increases at a slowing rate, resulting in a concave down curve. This is because larger animals need less energy per unit area because less is lost to the surroundings through SA exposure. This affects how quickly they lose heat and energy, so RMR must be larger resulting in a larger total metabolic rate as well.
So then mass specific metabolic rate is concave up and decreasing, meaning that larger animals take in much less energy per gram of body weight since they lose much less energy per gram of body weight due to a smaller SA:V ratio.
How does the log of metabolic rate (including MRmax/sus and RMR) for both endotherms and ectotherms change based on the log of the mass? What is scope and what does it look like for the endotherms and ectotherms?
Metabolic rate is going to always be higher for endotherms because they use metabolism to regulate their body temperature and hence must put much more energy into producing that heat. So both RMR and MRmax/sus will be larger for endotherms then ectotherms. And as log of mass increases, log of metabolic rate increases, because larger animals need a larger metabolic rate total.
HOWEVER:
The scope will be the same for both! Scope is just the difference between RMR and MRmax, which is similar for all organisms. So the POTENTIAL TO INCREASE MR FROM RMR FOR LOCOMOTION IS SIMILAR BETWEEN THEM ALL.
What are the two different things (from an energy perspective) that we use to measure locomotion?
Mass-specific metabolic rate gives us the energy required to move 1 unit mass of an organism over 1 unit of time, and this determines the amount of locomotion that can occur based on the size of this metabolic rate. It will be larger for smaller animals!
KJ/(kg times hr)
Then also cost of transport is used, which is the energy required to move 1 unit mass of an organism 1 unit distance, and this also determines how much locomotion can occur. The more aerodynamic the organism is, the less energy required to do this, and therefore the more locomotion that can occur in a given amount of time.
(KJ/(kg times km))
