Muscle Metabolism and ATP (Nursing)

00:00 So now that we've talked about how a muscle contraction happens, let's talk a little bit about what makes the muscle have the ability to contract? So pop quiz.

00:12 How do muscles derive the ATP or the energy necessary to power this contraction cycle? So there are three different ways that we're going to be able to derive enough ATP in order to power the contraction cycle.

00:35 First, we have the creation of creatine phosphate.

00:39 Second, anaerobic glycolysis.

00:43 And lastly, cellular respiration.

00:46 Let's look at these a little more closely.

00:50 So inside of our muscle fibers, we have a molecule known as creatine.

00:56 Creatine has the ability to bind to phosphate.

01:00 This allows for us to recycle or reuse the phosphates between the creatine and the ATP.

01:09 The way this happens is ATP combines to the creatine, and the creatine is going to take the phosphate from ATP, also referred to as adenosine triphosphate and it will then become adenosine diphosphate.

01:25 So it now only has two phosphates and the creatine has the other.

01:30 Then there is an enzyme known as creatine kinase, which will then re hydrolyze the creatine phosphate and remove the phosphate from the creatine back to ATP.

01:43 This cycle allows for us to have about 15 seconds of energy.

01:49 An anaerobic glycolysis we're going to get a little bit more energy as we are going to create two ATP molecules that can be used for energy expenditure.

02:00 In this process, we take glucose from either the blood or from glycogen stored in our muscles.

02:07 And we're going to go through a series of steps in order to elicit two ATPs and two Pyruvate molecules.

02:17 If we are doing this process in the absence of oxygen, this ends with the production of lactic acid.

02:23 So when you are performing a function or when you're using your muscles and you start to feel sore, this soreness is due to the buildup of lactic acid from this process.

02:37 Anaerobic glycolysis, unlike the creatine phosphate is going to give us a little bit more energy and that you can get about two minutes of energy per glucose molecule.

02:51 The final way that we get ATP is cellular respiration.

02:56 So under aerobic conditions or conditions where there is ample oxygen the pyruvic acid is going to actually enter into the mitochondria found inside of our muscle fibers.

03:08 And from there, it's going to undergo a series of oxygen requiring steps that leads to a large amount of ATP.

03:16 In this process, we're going to get glucose from either the blood or from the breakdown of fatty acids, or from pyruvic acid.

03:25 Again, the proving acid will enter into the mitochondria and undergo cellular respiration.

03:32 Out of this process, we can get anywhere from 28 to 34 ATP molecules.

03:39 This process, unlike the others, is going to provide minutes up to hour's worth of energy.

03:47 Sometimes we're using our muscles so much that we start to lose the ability for our muscles to contract.

03:53 This is referred to as muscle fatigue.

03:57 Muscle fatigue can be brought on by several different factors.

04:02 Muscle fatigue can be due to an inadequate release of calcium from the sarcoplasmic reticulum.

04:09 It can also be due to a depletion of the creatine phosphate, or oxygen and nutrients necessary to make more ATP.

04:19 Also, the buildup of lactic acid or that soreness, as well as a buildup of ATP instead of an adequate amount of ATP can lead to muscle fatigue.

04:30 And finally, an insufficient release of acetylcholine at the neuromuscular junction.

04:37 Sometimes central fatigue can occur, and in this case, the central nervous system takes over and generally results in a cessation of exercise.

04:48 So sometimes you're using your muscles so much that you may pass out.

04:54 Pop quiz: Why do you continue to breathe heavily for a period of time after stopping excercise? The answer, is to pay back your oxygen debt.

05:12 Recall that in cellular respiration, we're going to be using oxygen in order to make more ATP.

05:18 So this is kind of like you're paying oxygen in the beginning, and now you're breathing heavy in order to restore your oxygen levels.

05:29 The extra oxygen can then be use to replenish the creatine phosphate stores.

05:35 Also, to convert that lactic acid back into pyruvate.

05:41 And third, to reload oxygen onto myoglobin.

05:46 Myoglobin is the molecule that's very similar to hemoglobin, but it's specific for muscle fiber cells.