As we look at this example here, it says to fill in the table below indicating which muscles you would expect to contract or relax during inspiration and expiration for both eupnea, that quiet breathing, and forced breathing. In each cell, write a "c" if you expect that muscle to be contracting, and write an "r" if you expect that muscle to be relaxed. Alright. As we look here, we have sort of 2 large columns, 1 for eupnea or quiet breathing and one for forced breathing. And in each of these large columns, we have 2 smaller columns, 1 for inspiration and one for expiration.
We look on the left here. We have this big list of muscles that we've been over, so let's see if we can figure out what's going on. Alright. So for eupnea, we'll start there, that quiet breathing, inspiration. Which muscles do you expect to be contracting during inspiration? Alright. We said that that was the role for the primary respiratory muscles, and that was the diaphragm and the external intercostals. The diaphragm pulls down, sort of expanding the space inside the rib cage, and those external intercostals pull kind of up on all of the ribs sort of making you pulling those ribs sort of hinging them up and outwards making the size of that rib cage bigger. So these 2, I expect to be contracting. Now all the rest of these muscles here, these are our accessory respiratory muscles, and we said that they don't do anything during eupnea. So I expect all of these to be relaxed. I'll put an "r" next to all of them, at least in terms of breathing.
Now, what about during expiration? Well, expiration during eupnea, we said that that is just the relaxation of muscles. So, I don't expect anything to be contracting here. So here, I'm just going to put an "r" and I'm just going to put a down arrow indicating that I expect all of these muscles to be relaxed during expiration, during eupnea. Alright. What about forced breathing? Alright. Forced breathing, we said that's when we're going to pull in these accessory muscles.
Let's go through it. We're going to start with inspiration. Which muscles do you expect to be contracting during inspiration? Well, I still expect that diaphragm and those external intercostals to be contracting. Those are always going to be working during breathing. But now we're going to bring in some of those accessory respiratory muscles. Remember, we want to sort of lift the rib cage up, lift it up and back, and those muscles are just sort of trying to bring that rib cage up as much as you can. So when that diaphragm pulls down, you just get as much space in there as you can. So I sort of had a little memory tool for that. I said we scale up the size of the rib cage. And so I remember the scalenes and those other "s" muscles and the up reminds me that one of them starts with a "p."
As I go down here, well, that means that the sternocleidomastoid and the scalenes, those are both sort of lifting up on that rib cage basically from your neck. And then the pectoralis minor and the serratus anterior, those, remember, those are attached to your scapula, and so they're sort of pulling upwards and back on that rib cage, lifting your rib cage up as much as you can. Alright. That means that these other muscles here, transversus thoracis, internal intercostals, and rectus abdominis, well, those aren't going to be doing anything yet. These are going to be relaxed.
Now, what about expiration? Well, for expiration, I still expect that diaphragm and external intercostals to be relaxed. Those muscles are activated during inspiration, so they need to be relaxed during expiration. Now these muscles that were used during forced breathing during inspiration, well, now these are going to have to relax so that we're not pulling up on that rib cage anymore. And now we're going to use these muscles that sort of pull down and in on the rib cage. So, we have the transversus thoracis. Remember, that's that muscle sort of underneath the sternum there that sort of collapses your chest. So that is going to be contracting.
We have the internal intercostals, those muscles between the ribs underneath the external intercostals and running in the opposite direction. So instead of sort of lifting up and hinging those ribs outwards, they pull down and hinge them inwards. Those are going to be contracting. And then finally, the rectus abdominis, that major abdominal muscle is going to be squeezing in, pushing all your organs inwards and sort of pushing up on that diaphragm even more. So that will be contracting as well. Alright. Those are your muscles. That's how we ventilate. More problems after this. I'll see you there.