all right hello anatomy friends this is dr. Alsup  and in this video we are going to focus on the  
all right hello anatomy friends this is dr. Alsup  and in this video we are going to focus on the  

infrahyoid muscles aka the strap muscles which are  named because of their strap like or ribbon like  
infrahyoid muscles aka the strap muscles which are  named because of their strap like or ribbon like  

appearance so with infrahyoid muscles there are  two different layers there will be a superficial  
appearance so with infrahyoid muscles there are  two different layers there will be a superficial  

layer and a deep layer we'll talk about which  muscles are in which layer we also talked about  
layer and a deep layer we'll talk about which  muscles are in which layer we also talked about  

what these muscles do what are their actions and  lastly what innervates these muscles with three  
what these muscles do what are their actions and  lastly what innervates these muscles with three  

out of the four sharing a common innervation and  one outlier and we love a good outlier alright so  
out of the four sharing a common innervation and  one outlier and we love a good outlier alright so  

let's get our bearings regarding where we are in  the neck and where these muscles are located kind  
let's get our bearings regarding where we are in  the neck and where these muscles are located kind  

of the key relationship and where this group gets  its name is that all of these muscles are inferior  
of the key relationship and where this group gets  its name is that all of these muscles are inferior  

to the hyoid thus the infrahyoid so let's get  a clue of where we're at so here is your hyoid  
to the hyoid thus the infrahyoid so let's get  a clue of where we're at so here is your hyoid  

bone let's take a moment to discuss the hyoid  bone because it's a really important landmark  
bone let's take a moment to discuss the hyoid  bone because it's a really important landmark  

in the anterior neck and particularly a lot of  what we're talking about today it is going to be  
in the anterior neck and particularly a lot of  what we're talking about today it is going to be  

located around the c3 to c5 vertebral levels  and that's gonna be between the mandible and  
located around the c3 to c5 vertebral levels  and that's gonna be between the mandible and  

the thyroid cartilage so I always describe if you  palpate your own anterior neck right in the middle  
the thyroid cartilage so I always describe if you  palpate your own anterior neck right in the middle  

you will first feel your thyroid cartilage because  it's the part that projects the most anteriorly  
you will first feel your thyroid cartilage because  it's the part that projects the most anteriorly  

and more to come on the thyroid cartilage later  I promise but if you move your fingers a little  
and more to come on the thyroid cartilage later  I promise but if you move your fingers a little  

more superiorly and sometimes I have to kind of  tilt my chin down you can palpate the hyoid bone  
more superiorly and sometimes I have to kind of  tilt my chin down you can palpate the hyoid bone  

certainly more difficult to palpate than thyroid  cartilage but it's possible to palpate it this  
certainly more difficult to palpate than thyroid  cartilage but it's possible to palpate it this  

bone is unique in its isolation from the rest  of the skeleton and the fact that it does not  
bone is unique in its isolation from the rest  of the skeleton and the fact that it does not  

directly articulate with any other bone rather  is completely suspended by muscles tendons and  
directly articulate with any other bone rather  is completely suspended by muscles tendons and  

some ligaments so the hyoid's functioning as an  attachment site for many anterior neck muscles  
some ligaments so the hyoid's functioning as an  attachment site for many anterior neck muscles  

including the infrahyoid muscles that we're  talking about right now and it can also play  
including the infrahyoid muscles that we're  talking about right now and it can also play  

an important role in propping the airway open all  right so that's our quick stop to talk about the  
an important role in propping the airway open all  right so that's our quick stop to talk about the  

hyoid bone and all these muscles will be inferior  to it the infrahyoid muscles will also be superior  
hyoid bone and all these muscles will be inferior  to it the infrahyoid muscles will also be superior  

to the sternum which would be right about here  ish so not projecting into the thorax region the  
to the sternum which would be right about here  ish so not projecting into the thorax region the  

muscles will also be medial to the carotid sheath  in its contents so here would be a carotid sheath  
muscles will also be medial to the carotid sheath  in its contents so here would be a carotid sheath  

here a credit sheath would also be located over  here and lastly and importantly these muscles  
here a credit sheath would also be located over  here and lastly and importantly these muscles  

will all be superficial to the thyroid gland and  the larynx so one has to reflect these muscles to  
will all be superficial to the thyroid gland and  the larynx so one has to reflect these muscles to  

gain access or view these deeper structures now as  mentioned at the beginning there are two layers or  
gain access or view these deeper structures now as  mentioned at the beginning there are two layers or  

planes of muscles the superficial layer is going  to be composed of the sternohyoid as well as the  
planes of muscles the superficial layer is going  to be composed of the sternohyoid as well as the  

omohyoid which is a personal favorite of these  infrahyoid because it's so unique with the deep  
omohyoid which is a personal favorite of these  infrahyoid because it's so unique with the deep  

layer made up of the sternothyroid and the  thyrohyoid and there's that hyoid bone right  
layer made up of the sternothyroid and the  thyrohyoid and there's that hyoid bone right  

there if you have a thyro or thyroid in the name  you know you're talking about the deep layer so  
there if you have a thyro or thyroid in the name  you know you're talking about the deep layer so  

let's talk about each one we will start with one  of the larger ones and this is the sternohyoid  
let's talk about each one we will start with one  of the larger ones and this is the sternohyoid  

which you can see outlined here in blue I bolded  the attachment points that match up to the muscles  
which you can see outlined here in blue I bolded  the attachment points that match up to the muscles  

names and you will see that as a common theme for  these infrahyoid muscles and many other muscles in  
names and you will see that as a common theme for  these infrahyoid muscles and many other muscles in  

the body this muscle will extend inferiorly from  the sternum and medial clavicle all the way up  
the body this muscle will extend inferiorly from  the sternum and medial clavicle all the way up  

to the hyoid so here's your highlight here your  sternum is right here and your clavicle is right  
to the hyoid so here's your highlight here your  sternum is right here and your clavicle is right  

here it as you can see here completely blocks the  view of the deep strap muscles so this has to be  
here it as you can see here completely blocks the  view of the deep strap muscles so this has to be  

reflected in order to see any of those this muscle  like most strap muscles will play an important  
reflected in order to see any of those this muscle  like most strap muscles will play an important  

role in stabilization of the hyoid so kind of  keeping it in place while other things happen  
role in stabilization of the hyoid so kind of  keeping it in place while other things happen  

also just looking at the location of this muscle  if you think about this muscle concentrically  
also just looking at the location of this muscle  if you think about this muscle concentrically  

contracting so shortening it makes sense that  it will take the hyoid with it inferiorly thus  
contracting so shortening it makes sense that  it will take the hyoid with it inferiorly thus  

depressing the hyoid okay this next muscle is a  fun one the Omohyoid muscle this muscle is unique  
depressing the hyoid okay this next muscle is a  fun one the Omohyoid muscle this muscle is unique  

amongst the infrahyoid muscles because it has two  bellies it has a superior belly and an inferior  
amongst the infrahyoid muscles because it has two  bellies it has a superior belly and an inferior  

belly these bellies are going to be connected by  an intermediate tendon which is tethered to the  
belly these bellies are going to be connected by  an intermediate tendon which is tethered to the  

clavicle by this fascial sling which you can see  here outlined in this lighter blue doesn't need  
clavicle by this fascial sling which you can see  here outlined in this lighter blue doesn't need  

to one know what the prefix Omo what does Omo mean  because that gives you an indication of where it  
to one know what the prefix Omo what does Omo mean  because that gives you an indication of where it  

attaches it means shoulder so the name Omohyoid  indicates that that inferior belly will have an  
attaches it means shoulder so the name Omohyoid  indicates that that inferior belly will have an  

attachment to the scapula or the shoulder but  more specifically the scapula with the superior  
attachment to the scapula or the shoulder but  more specifically the scapula with the superior  

belly attaching to the hyoid bone similar to its  superficial partner the sternohyoid the omohyoid  
belly attaching to the hyoid bone similar to its  superficial partner the sternohyoid the omohyoid  

play a role in stabilization and depression  of the hyoid bone all right moving on to the  
play a role in stabilization and depression  of the hyoid bone all right moving on to the  

deeper infrahyoid muscles let's start with the  sternothyroid note that the sternohyoid had to  
deeper infrahyoid muscles let's start with the  sternothyroid note that the sternohyoid had to  

be removed in this image in order to see these  muscles this muscle will extend in fear early  
be removed in this image in order to see these  muscles this muscle will extend in fear early  

from the sternal manubrium you can see it even  is heading a little bit towards the clavicle as  
from the sternal manubrium you can see it even  is heading a little bit towards the clavicle as  

well so there's manubrium here all the way up  to the oblique line of the thyroid cartilage  
well so there's manubrium here all the way up  to the oblique line of the thyroid cartilage  

note something important here this muscle does  not make its way all the way up to the hyoid  
note something important here this muscle does  not make its way all the way up to the hyoid  

bone so it does not attach to the hyoid so not  playing any direct role in hyoid bone movement  
bone so it does not attach to the hyoid so not  playing any direct role in hyoid bone movement  

based on its location and attachments when it  contracts it can play a role in depressing the  
based on its location and attachments when it  contracts it can play a role in depressing the  

larynx if it was previously elevated so you can  see if this is your thyroid cartilage right here  
larynx if it was previously elevated so you can  see if this is your thyroid cartilage right here  

think about what that contracts it will pull the  larynx and down alright moving on to the last of  
think about what that contracts it will pull the  larynx and down alright moving on to the last of  

the infrahyoid muscles and also the smallest is  the thyrohyoid inferiorly from the oblique line  
the infrahyoid muscles and also the smallest is  the thyrohyoid inferiorly from the oblique line  

of the thyroid cartilage up to the hyoid bone  so there's a hyoid bone again I'm going to keep  
of the thyroid cartilage up to the hyoid bone  so there's a hyoid bone again I'm going to keep  

labeling it because it is such an important area  here so when it concentrically contracts it can  
labeling it because it is such an important area  here so when it concentrically contracts it can  

depress the hyoid bone but also based on its  other attachment to the the thyroid cartilage  
depress the hyoid bone but also based on its  other attachment to the the thyroid cartilage  

it can elevate or bring up the larynx as well  so kind of an opposite of what we had with the  
it can elevate or bring up the larynx as well  so kind of an opposite of what we had with the  

sternothyroid and so it's all about the location  of these muscles thyrohyoid is the muscle that  
sternothyroid and so it's all about the location  of these muscles thyrohyoid is the muscle that  

is the oddball in terms of innervation love  a unique innervation I would always suggest  
is the oddball in terms of innervation love  a unique innervation I would always suggest  

putting stars or hearts or whatever works for you  next to anytime that you have something unique in  
putting stars or hearts or whatever works for you  next to anytime that you have something unique in  

terms of innervation or something unique in terms  of actions this is something that almost always  
terms of innervation or something unique in terms  of actions this is something that almost always  

finds its way into some form of assessment it is  innervated by fibers from the c1 spinal nerve that  
finds its way into some form of assessment it is  innervated by fibers from the c1 spinal nerve that  

are not associated with ansa cervicalis which  is going to be the innervation for the other 3  
are not associated with ansa cervicalis which  is going to be the innervation for the other 3  

infrahyoid muscles these fibers of c1 will travel  with or what we often refer to as hitchhike with  
infrahyoid muscles these fibers of c1 will travel  with or what we often refer to as hitchhike with  

the hypoglossal nerve and we'll talk a bit more  about what we mean by hitchhiking in a moment  
the hypoglossal nerve and we'll talk a bit more  about what we mean by hitchhiking in a moment  

all right the rest of the infrahyoid muscles  are innervated by the beautifully named ansa  
all right the rest of the infrahyoid muscles  are innervated by the beautifully named ansa  

cervicalis one of my all-time favorite anatomical  names which is a branch of the cervical plexus  
cervicalis one of my all-time favorite anatomical  names which is a branch of the cervical plexus  

similar to those efferent nerves from the nerve  point of the neck or herbs point fibers of c1  
similar to those efferent nerves from the nerve  point of the neck or herbs point fibers of c1  

will hitchhike similar to what happened with  the thyrohyoid so fibers of c1 will hitchhike  
will hitchhike similar to what happened with  the thyrohyoid so fibers of c1 will hitchhike  

along the hypoglossal nerve or cranial nerve  12 so some of those fibers will shoot off to go  
along the hypoglossal nerve or cranial nerve  12 so some of those fibers will shoot off to go  

innervate thyrohyoid and other c1 fibers will  leave that close proximity to the hypoglossal  
innervate thyrohyoid and other c1 fibers will  leave that close proximity to the hypoglossal  

nerve to join the superior limb or to form excuse  me the superior ansa cervicalis sometimes you'll  
nerve to join the superior limb or to form excuse  me the superior ansa cervicalis sometimes you'll  

have fibers of c2 also forming the superior line'  the inferior limb of ansa cervicalis is formed by  
have fibers of c2 also forming the superior line'  the inferior limb of ansa cervicalis is formed by  

fibers of c2 and c3 so the ansa cervicalis will  send small muscular branches to all the infrahyoid  
fibers of c2 and c3 so the ansa cervicalis will  send small muscular branches to all the infrahyoid  

muscles accepting the thyrohyoid so let's return  to this concept of nerve fibers hitchhiking with  
muscles accepting the thyrohyoid so let's return  to this concept of nerve fibers hitchhiking with  

other nerves because this is something that will  come up quite commonly throughout our discussion  
other nerves because this is something that will  come up quite commonly throughout our discussion  

of nerves in this course particularly when we  get to the parasympathetics-- so keep in mind  
of nerves in this course particularly when we  get to the parasympathetics-- so keep in mind  

that nerves are just collections of axons wrapped  up together by connective tissue in the peripheral  
that nerves are just collections of axons wrapped  up together by connective tissue in the peripheral  

nervous system so your pns axons may travel  with or in close proximity with different nerves  
nervous system so your pns axons may travel  with or in close proximity with different nerves  

particularly if this is a smaller collection  of axons on their way to the target tissue  
particularly if this is a smaller collection  of axons on their way to the target tissue  

so you can see here in this nice cartoonish  rendition that I made the fibers of c1 that  
so you can see here in this nice cartoonish  rendition that I made the fibers of c1 that  

are destined for say the thyrohyoid or to become  the superior limb of ansa cervicalis are going to  
are destined for say the thyrohyoid or to become  the superior limb of ansa cervicalis are going to  

travel in close proximity to the hypoglossal  alright so they're very close to one another  
travel in close proximity to the hypoglossal  alright so they're very close to one another  

they're traveling together but they still came  from different sources so the hypoglossal nerve  
they're traveling together but they still came  from different sources so the hypoglossal nerve  

it's it originated in the medulla oblongata and of  course c1 is from spinal cord level c1 so so they  
it's it originated in the medulla oblongata and of  course c1 is from spinal cord level c1 so so they  

are coming from different sources but they can  travel together for a while and then eventually  
are coming from different sources but they can  travel together for a while and then eventually  

move towards their different targets so the c1  fibers hang around the hypoglossal nerve before  
move towards their different targets so the c1  fibers hang around the hypoglossal nerve before  

pivoting off in different directions so you can  see traveling together for a while and then it's  
pivoting off in different directions so you can  see traveling together for a while and then it's  

heading off say to either the thyrohyoid or to  become the superior and ansa cervicalis so that's  
heading off say to either the thyrohyoid or to  become the superior and ansa cervicalis so that's  

what we mean by hitchhiking like I said this is  something that we will talk about over and over  
what we mean by hitchhiking like I said this is  something that we will talk about over and over  

again throughout the course so this is an area  that's confusing return to this think it through  
again throughout the course so this is an area  that's confusing return to this think it through  

and if any remaining questions I always feel free  to reach out to us all right so we've had so much  
and if any remaining questions I always feel free  to reach out to us all right so we've had so much  

fun with this area I have two questions instead  of my usual one so hopefully this one isn't too  
fun with this area I have two questions instead  of my usual one so hopefully this one isn't too  

tough which infrahyoid muscles has an attachment  to the scapula only one of the four will have an  
tough which infrahyoid muscles has an attachment  to the scapula only one of the four will have an  

attachment to the scapula is it A. omohyoid B.  sternohyoid C. sternothyroid or D. thyrohyoid so  
attachment to the scapula is it A. omohyoid B.  sternohyoid C. sternothyroid or D. thyrohyoid so  

take a moment and hopefully you have landed on the  correct answer which is A omohyoid and this omo is  
take a moment and hopefully you have landed on the  correct answer which is A omohyoid and this omo is  

that key here I'm gonna indicate shoulder so the  scapula is part of the shoulder joint so that is  
that key here I'm gonna indicate shoulder so the  scapula is part of the shoulder joint so that is  

going to be one of the attachment sites where the  recalling you're reviewing that the infrahyoid  
going to be one of the attachment sites where the  recalling you're reviewing that the infrahyoid  

muscles are named for their attachments and this  can really help a lot and not only remembering the  
muscles are named for their attachments and this  can really help a lot and not only remembering the  

attachments we're really thinking through what  the actions of these muscles are alright one  
attachments we're really thinking through what  the actions of these muscles are alright one  

more question all right injury to ansa cervicalis  would not affect the actions of which muscle is  
more question all right injury to ansa cervicalis  would not affect the actions of which muscle is  

it A. omohyoid B. sternohyoid C. sternothyroid  or D. thyrohyoid pause the video if you need a  
it A. omohyoid B. sternohyoid C. sternothyroid  or D. thyrohyoid pause the video if you need a  

moment to think through and when you're ready  to move on let's discuss that D is the correct  
moment to think through and when you're ready  to move on let's discuss that D is the correct  

answer this nerve is innervated by separate c1  fibers not associated with ansa cervicalis so D  
answer this nerve is innervated by separate c1  fibers not associated with ansa cervicalis so D  

thyrohyoid is the correct answer the rest of these  infrahyoid muscles are going to be innervated by  
thyrohyoid is the correct answer the rest of these  infrahyoid muscles are going to be innervated by  

the answer servic Alice well that was a lot of fun  I do do love talking about muscles as always as  
the answer servic Alice well that was a lot of fun  I do do love talking about muscles as always as  

you review and have any questions please do feel  free to ask thank you for your time and attention
you review and have any questions please do feel  free to ask thank you for your time and attention