Hip Joint & Pelvic Girdle Anatomy: Muscle Actions

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[DR. JACOB GOODIN] Dr.
Goodin here.

Back with the third lecture for
the trunk and spinal column.

And in this lecture
we're gonna talk about

the specific muscles themselves.

We've given the overview,
we've looked at some of the

bony landmarks as well as the
movements of those joints.

But what muscles
move those joints?

We're gonna start off
with muscles of the head.

Hint, most of these muscles
have the word capitis in it.

So all of these originate on the
cervical vertebrae and insert on

the occipital bone of the skull.

There are three anterior
vertebral muscles,

the longus capitis,
rectus capitis anterior,

and rectus capitis lateralis.

Note that they all have
capitis in their name

because they move your head.

And then the other words
are descriptive as well.

Longus capitis is the longest.

Rectus capitis anterior is
on the anterior aspect and

rectus capitis lateralis
is lateral to that.

All of these flex the head
and the upper cervical spine.

Now rectus capitis
lateralis, because of

its position laterally,
it can laterally flex the head

if it contracts unilaterally.

It also assists rectus capitis
anterior in stabilizing the

atlantooccipital joint.

Here are some pictures of those.

We have rectus capitis lateralis
here, rectus capitis anterior.

These are very small and
I don't expect you to be

able to palpate these.

Here's rectus longus
capitis, sorry not rectus,

just longus capitis.

And then you can see
longus colli as well.

Longus colli doesn't
move the head but it

does do cervical flexion.

You can tell because it's on the
anterior aspect of the cervical

spine running down along it.

So if these muscles shorten,
it pulls that way, then it's

going to flex the neck.

Here's another picture.

Now there's a lot of muscles in
here that we don't need to know.

You do need to be able to
palpate the hyoid bone.

I have a video link in Canvas
showing how to do that.

Be very gentle when
you palpate it.

You can jiggle it
around a little bit.

But be careful of the Adam's
apple and the trachea and

all that important stuff.

Here is the longus
capitis, right in there,

hidden underneath the
sternohyoid muscle

and omohyoid muscle.

Posteriorly.

We have the rectus capitis
posterior, major and minor.

Obliquus capitis.

And obliquus you can tell
it's going to run diagonally,

because of that word obliquus.

Obliquus capitis
superior and inferior

and semispinalis capitis.

Now all of these are
extensors of the head

except for obliquus capitis.

Most likely because
of that angle.

We haven't seen it yet

But we know that
it goes diagonal.

It rotates the atlas.

Obliquus capitis superior
assists with rectus capitis

and lateral flexion of the head.

And that's going to be
because of its position.

Laterally it's not very medial.

Rectus capitis posterior
major rotates ahead to

the ipsilateral side.

Ipsilateral means
to the same side.

So to the same side that rectus
capitis posterior is on, when

it contracts unilaterally, it
rotates ahead to that same side.

Contralateral means
opposite side.

That's what semispinalis does.

It rotates to the
contralateral side.

And then we have the upper
trapezius which is going

to be the most prominent
muscle in this region.

It extends the head and rotates
it to the ipsilateral side.

So here are pictures of most
of these rectus capitis,

posterior major right here,
and then minor right here

running down this way.

Obliquus capitis,
superior and inferior.

Here's inferior running
obliquely, and here's

superior and it's deep.

Remember those rotate the
head to the ipsilateral side.

So you can imagine when
those fibers contract and

shorten, they're gonna pull,
they're gonna yank on that

nuchal line up here and
pull your head around

to rotate it that way.

Here is splenius capitis.

Underneath that,
semispinalis capitis.

So splenius capitis
and sternocleidomastoid,

these are larger muscles.

And they are more
powerful in moving the

cervical head and spine.

So let's take a look at them.

Here is sternocleidomastoid.

Not only is it a mouthful,
its name is actually

very descriptive.

It originates on the
sternum and the clavicle,

the midpoint between those
two, as well as up here

on the mastoid process.

Hence, the
name sternocleidomastoid.

But notice how it's at this
oblique angle to the cervical

spine, which is interesting.

Because when both sides
of it contract, you get

extension of the head.

So it's gonna actually pull
into the head extension

but flexion of the neck.

It's gonna pull the
neck into flexion.

Sorry that was not a good arrow.

Flexion of the neck,
and it's because of

that oblique angle.

Now if one side contracts,
so we have bilateral, sorry,

unilateral contraction,
we get rotation.

So if just the right
side contracts,

rotation to the
left and lateral

flexion to the right.

If this shortens,
it's going to pull

the head around that
way or if it's gonna

do lateral flexion,
it's gonna pull this mastoid

process down to the shoulder.

The splenius muscles,
both services and capitis.

We saw these in a
different picture as well.

When both sides contract,
so bilateral contraction,

we get extension of
the head and neck.

So unlike sternocleidomastoid,
they extend the head and

the neck at the same time.

Whereas sternocleidomastoid,
when it contracts,

you get extension of the
head but flexion of the

neck, cervical flexion.

When they contract unilaterally
we get rotation and lateral

flexion to the ipsilateral side.

So to the same side.

Muscles of the vertebral column.

What we just looked at were
muscles that move the head and

also maybe the cervical region.

But now we're just gonna
look at muscles that are

only in the vertebral column.

So first we have the
longus colli muscles

on the anterior aspect.

These flex the cervical and
upper thoracic vertebrae.

You can see how they're
running down here, along the

bodies of the vertebrae from
vertebrae to vertebrae.

Posteriorly, you have all
of these intrinsic muscles.

You have the multifidus muscles,
which are running from the

spinous process down to the
transverse process of the

vertebrae, a couple lower.

You have these
intertransversarii, which

are going from transverse
to transverse process.

Rotatores is in here,
you don't have to

know all of these,
you just have to

know multifidus.

And all of these small
intrinsic muscles stabilize

each of the individual
intervertebral joints.

Now some of the
larger musculature,

posteriorly we have
the serratus posterior,

and it has both a superior
and an inferior region.

So here's the superior,
and down here is the inferior.

And you can see how this runs
off of the spinous process

and then onto the ribs.

Here and here.

And it's called serratus
because it has a sort of

serrated appearance.

If someone's very lean and
you can see their serratus

posterior or serratus anterior.

It looks like the edge
of a serrated knife.

We also have
semispinalis thoracis.

So semispinalis is also coming
off of the spinous processes

of the vertebrae and attaching
on the ribs but more medially.

So we also have
the interspinal-intertransverse

group.

And these muscles flex for the
vertebral column laterally.

And they connect to transverse
processes of adjacent vertebrae.

So here is intertransversarii
group running down between

the spinous processes of
this lumbar vertebrae.

Now the muscles of the thorax.

These muscles are
involved in breathing.

The first is the diaphragm.

It's responsible for
breathing during quiet rest.

So most of you listening right
now, unless you're listening

to this while you exercise,
on the StairMaster or something.

Most of you are at
quiet rest currently.

So your diaphragm is
the only muscle that is

active in your respiration.

As it contracts and flattens,
it expands the thoracic volume

to suck air into your lungs.

But when larger amounts
of air are needed, like

when you're exercising,
other thoracic muscles have

a more significant role.

So some of those muscles,
we have the scalenes.

These elevate the
first two ribs.

You can see them here.

Sternocleidomastoid is
here above.

We have the external
intercostals, which

also expand the chest.

Those are gonna be here.

Levator costarum and
serratus posterior superior.

So these first ones,
I just mentioned,

are all for inspiration.

And then the
internal intercostals,

transversus thoracis,
serratus posterior inferior,

and subcostals, these all
aid in forced expiration.

This is when you're blowing
air out really hard.

And if you want,
go ahead right now and

take a deep fast breath
in, and then hold it,

and then blow out as
hard as you can.

And you've just activated
all of those muscles.

Now your erector spinae muscles.

This is one of the larger,
so it's easier to palpate, but

also more complex muscle groups.

And you can see in this
picture that it's not

exactly one muscle,
it's really a group of muscles.

We have layers and
levels of this.

So we have the spinalis layer,
which is the most medial.

Here is the spinalis layer.

And it's these

running along the spinous
processes of these vertebrae.

It's the most medial,
spinalis, spinous process.

We have the longissimus layer.

This is the middle layer.

And these are running
just lateral to spinalis.

And then we have the
iliocostalis layer,

which goes from the
iliac crest to the ribs.

Iliocostalis.

And then I mentioned
that they have regions.

So we have the thoracis
region, cervical region,

there's also the capitis
region, lumbar region.

So depending on which layer
and which region you're

talking about, you might say,
the longissimus thoracis.

Because it's the longissimus
layer in the thoracis region.

Or you might say the
iliocostalis thoracis.

This would be
longissimus thoracis.

Or you could have spine,
the lumbar spinalis.

And the actions that
these muscles do,

extension of the spine.

So if they contract bilaterally,
you can imagine if we have all

of these muscles contracting,
even though they don't

directly cross these joints.

But if they
contract bilaterally,

they're gonna pull the
spine into extension.

But if one side contracts,
then it's lateral flexion

to the ipsilateral side,
to that same side, as well

as ipsilateral rotation.

Now I mentioned before
that this pelvic girdle,

let's draw both sides.

It moves as a unit when
you have movement at the

lumbar spine and at the hip.

So this musculature,
especially iliocostalis,

because it's coming up
off of the iliac crest.

But also spinalis as
well because it's coming

up off the sacrum too.

They can assist in
anterior pelvic rotation.

Now the quadratus lumborum.

This is an interesting muscle
because it's arising off of

the iliac crest, going up to
the transverse processes of

your lumbar vertebrae and
then also onto the 12th rib.

So it has a lot of roles.

It stabilizes the
pelvis and lumbar spine.

So if you've ever sat crookedly
for a long time or laid on your

side with your legs curled up,
especially if you're doing that

for a long period of time,
you may have allowed one of

your quadratus lumborum to
become tight and shortened

after sitting there for a
prolonged period of time.

And what that does is that
could lead you to having some

sort of a hip hike where,
maybe this side is a little

higher than the other because
of these shortened fibers.

These fibers are
shortened on this side,

which is going to cause your
femur on this side to be higher.

I'm not gonna draw
a very good femur.

Maybe this femur is a little bit
higher, maybe just by an inch,

but that's going to
throw up your gait.

Oftentimes, low back pain can
stem from quadratus lumborum

that's overactive and over
tight or under active and tight.

But not only does it stabilize
the pelvis and lumbar spine,

it also laterally flexes
to the ipsilateral side.

Bilaterally, it extends
the lumbar spine and does

anterior pelvic rotation.

And then it can also do
lateral pelvic rotation

to the contralateral side.

So what I mean by that is if,
let's say that these fibers

on this left side, because
this is an anterior view,

let's say that they contract.

And what that's going to do is
hike this hip up even higher.

The line of the hips is
gonna go from here to here.

And that's lateral pelvic
rotation to this side.

If we imagine the pelvis like a
cup or a bucket full of water,

the direction it rotates is the
direction that water spills.

So if you rotate it this way,
the water is going to spill out

of it to the opposite side of
the muscles that contracted.

So that's lateral
pelvic rotation to

the contralateral side.

Now the muscles of
the abdominal wall.

I mentioned that the rectus
abdominis right here.

This is the muscle that most
people care about when they

talk about core training.

You get the six pack or if
you're lean enough to get

the eight pack, with these
lower abdominals in here.

But there are other
important muscles as well.

We have the external and
the internal obliques.

Now the external obliques, the
fibers, are running downwards.

They're oblique fibers.

So if you want to put
your hands in your,

let's say you had a
sweatshirt, a hoodie

sweatshirt with a
pocket in the front.

You go to put your
hands in that pocket,

the angle of your fingers as
you put your hands downward

and forward into that front
pouch pocket on either side.

That's going to be the
same angle as the fibers

of your external oblique.

And then your internal
oblique runs the opposite way.

It runs this way.

And then your transverse
abdominis is underneath

those, it's deep to those,
and it's running transverse.

We're gonna take a look
at all four of these.

Here you can see this
cutaway, external oblique,

internal oblique, transverse
abdominis, and rectus abdominis.

So rectus abdominis,
this is obviously going

to do lumbar flexion,
because this is what we do.

There used to be this
thing some of my friends

did in middle school.

I don't know why, but they did
1,000 sit-ups a day because they

thought they were going to get
totally ripped six packs.

Unfortunately, it doesn't
quite work that way.

The external abdominal oblique.

Now when both sides contract,
we get lumbar flexion along

with the rectus abdominis and
posterior pelvic rotation.

So lumbar flexion
coming that way,

moving into flexions.

But when we have just
one side contracting,

so unilateral contraction.

Let's say that we're talking
about the right side.

If the right side contracts,
we have to imagine

these fibers that are
running anteroinferiorly,

they're shortening.

So they're moving these
two points closer together.

What that will lead to,
if the right side contracts,

we will get lumbar lateral
flexion to the right.

So like a side bend
to the right side,

you're dropping your
right shoulder down.

But we don't rotate
to that side.

We would rotate to the left
because it's pulling a more

posterior point towards the
anterior point of the muscle.

And so this point is going
to move around in rotation.

So if the right side contracts,
we get lateral flexion to the

right and rotation to the left.

So the external obliques,
when they contract bilaterally,

you get lumbar flexion and
posterior pelvic rotation.

When they contract unilaterally,
you get ipsilateral

lateral flexion and
contralateral rotation.

The internal obliques are
a little bit different.

Now they still do lumbar flexion
and posterior pelvic rotation.

But when they contract
unilaterally, you still

get ipsilateral flexion.

But then you also get
ipsilateral rotation.

So let's imagine that these
fibers are contracting,

and that's going to bring
you into lateral flexion,

to that same side.

So your shoulder is going to
be dropped from there to there

And you're gonna do a side bend.

I can't really draw it in 3D.

You're side bending to
the right, ipsilateral

lateral rotation.

But let's now imagine
these fibers contracting,

and they're going to bring
these points further this way.

And so that's going
to rotate you around,

and so now your shoulders
were here, are going to

rotate around this axis.

Really the rotation is occurring
down here at your lumbar spine.

But it's a lateral
flexion and rotation

to the ipsilateral side.

Transverse abdominis.

This actually doesn't
move your spine at all.

What it does is it helps
you enforce expiration.

So when these flatten and
contract, it pushes that air

back out of your lungs fast.

So we have successfully made it
through all of the musculature

in the trunk and spinal column.

What I would recommend is
as you study these muscles,

palpate them on yourself,
go through the movements.

So do the movements using
your own body and feel

those muscles contracting.

You wanna feel it first
on your own body and then

go find a study partner or
someone that you're living with.

You know well,
ask their permission,

and then practice finding
these muscles on them as well.

That's going to help you beyond
just reading the textbook and

looking at these pictures.

It's gonna help you immensely
as you study to really ingrain

these muscles and get them
into your learned sort

of kinesthetic memory.

Thanks so much for watching
and see you guys next time.

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