WEBVTT

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Webtoon Advanced
Structural Understanding of the Arms

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GCC Academy

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Hello, I am Webtoon artist Uksoo

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Let’s talk about the arm this time

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There’s more to discuss about the arm than you might think,
so we’ll divide it into two parts

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This time, we’ll focus on
the anatomical explanation of the arm,

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and in the next part, we’ll look at

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how the contours and internal details form
when the arm actually moves

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Also, we’ll take a closer look at the hands,

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which could be considered the second face

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The arm plays an important role
in expressing various emotions in the upper body

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For example,

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when they stretch their arm high into the air,

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it gives a feeling of freedom and hope

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On the other hand, when the arms
are in pockets or crossed,

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it can express a defensive or passive psychological state

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Additionally, it can give us a sense of
who the character is just by their posture

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Take this pose, for example

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You’d know immediately what kind of character this is,
without them saying a word

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With broad pectorals, a robust deltoid, and clear biceps,

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And the biceps brachii,

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along with the clearly defined muscles of the upper arm,

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makes you think,

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I shouldn't mess with him

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The position and movement of the arms are important elements
in revealing a character’s emotions and intentions

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The Anatomical Structure of the Arms

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Now, let’s start by learning

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about the bones of the arm

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First, here is the sternum

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Now, we need to attach the arm bones to this

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How should we attach them?

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If evolution

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were human, it might have been a tough decision

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This is because, unlike quadrupeds,

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the human arm has a very wide range of motion

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and it needs to be strong

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The arm doesn’t just bend and straighten

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It also moves side to side, front to back, up and down

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Furthermore, the shoulder joint, where the arm attaches,

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also has to be able to move freely

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Nothing can be fixed in place

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It has to be firmly secured while also allowing movement

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This created a tough problem for evolution

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So, after much consideration, evolution created
the scapula and the clavicle

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Here, the scapula is attached here

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And here’s the other scapula

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The humerus attaches here,

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and then this scapula is connected to the clavicle

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It connects to the front here

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The back part is hidden and not visible

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And the clavicle connects to the sternum
as we discussed last time

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This forms a delicate mechanism

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where the arm, scapula, clavicle,

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and the entire sternum are all connected

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It’s really amazing how evolution worked this out

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The way it all fits together is remarkable

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It's so beautiful that it almost makes me believe

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there’s some higher being involved in creation

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Anyway, now we’ve started talking about the arm bones,

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let’s proceed to a detailed explanation

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The arm bones can be divided into

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the arm attachment bones and the free arm bones

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The arm attachment bones,

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which connect the arm to the upper body,

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are composed of the scapula and clavicle

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The clavicle

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and the scapula

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The scapula

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The clavicle

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On the other hand, the free arm bones are made up
of several bones for the functional movement of the arm

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First, let’s talk about the scapula,

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also known as the shoulder blade

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The scapula serves as the starting point of the arm
and plays a crucial role in supporting the arm

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The scapula has several functional areas

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Here, we have the slanting part of the scapula

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his is called the scapular spine,

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The scapular ridge in Chinese characters

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The scapular spine is the point where
many muscles of the back and arm attach

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It also serves as a prominent landmark
that reveals clear lines

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When you follow this ridge upwards,
it connects to the front part

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This is where the scapular ridge rises from the back

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Now, let’s talk about the acromion,

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which is this point right here

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The acromion, as I explained earlier,

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connects with the clavicle and fixes itself to the sternum

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It’s an important point when drawing face shots as well

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Next, we have the shallow dish, which is the area here

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This is where the arm bone
directly connects to the shoulder

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Lastly, there’s the coracoid process,
this small protrusion here

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It contributes greatly to the movement
and stabilization of the arm

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We will revisit this point
when we discuss the humerus later on

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It’s a bit complicated, right?

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I remember when I first heard
a lecture on the shoulder blade,

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I had no idea what they were talking about

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So, let me simplify it for you

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If we simplify the shape of the scapula,
it’s basically triangular

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It could look like this

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And there’s a protruding ridge coming out like this

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This is the basic shape of the scapula

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But this is too simple, so let’s go a bit further

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Looking at this material,

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you can see how the scapula emerges from the body

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You can see where the scapular spine is located

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As mentioned earlier, the shoulder blade
moves just like the arm does

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In order to raise our arms outward,
not only do the arm bones move,

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but the shoulder blades must also shift like this

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Like this

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At first, the shoulder blades

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are simply positioned in place

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But as we lift our arms,
the shoulder blades also move accordingly

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However, due to their connection with the clavicle

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the shoulder blades rotate in a circular motion
around the clavicle’s connection point

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This movement affects the silhouette

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of the latissimus dorsi, or the broad back muscle

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In individuals who are lean or have less muscle mass,

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the shoulder blade silhouette is more visible

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Next, let’s discuss the clavicle

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The clavicle, also known as the collarbone,

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was previously covered when discussing the torso,
so we will go over it briefly

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As you can see, the clavicle connects
with both the pectoralis major and the deltoid muscles

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The structure formed by
the humerus, scapula, clavicle, and sternum

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functions similarly to the latch of a door

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The clavicle connects firmly to the sternum at this point

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The clavicle enhances the stability of the shoulder

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while allowing for a wide range of motion

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by responding flexibly to various shoulder movements

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However, it can be difficult to grasp the exact shape

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of the shoulder girdle when viewed from the front

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It often appears as just a straight or flat structure

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This is how it actually looks

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The clavicle and scapula connect here,

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here,

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here,

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and here, like so

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In the past, criminals were made to wear
a cangue around their neck

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The way the scapula and clavicle connect
forms a structure similar to that

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When a person raises their arms,

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the movement of the scapula

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follows a circular trajectory,

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all because of these connecting points

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Understanding the structure of the shoulder girdle

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will give you a much clearer grasp

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of many upper-body close-up shots

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Now, let’s move on to the free arm bones

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The free arm bones primarily consist of the humerus,

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ulna, and radius

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Those are the prats

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First, let’s talk about the humerus,

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or the upper arm bone

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It makes up about half of the total arm length,
including the hand

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The key point of interest here

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is the shape of the humeral head,
which fits into the glenoid cavity

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It's right here

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This is an enlarged view of that area

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Rather than fitting straight into the cavity,

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the humeral head extends outward at an angle

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Like so

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Just like an AirPod

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The bean sprout look, right?

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In a similar way, the humeral head is inserted
at an angle into the glenoid cavity

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This anatomical structure creates a limitation
in the arm’s range of motion

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Try raising your arm to the side
as if you’re reaching upward

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How was it?

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You’ll notice that beyond a certain point,
the arm no longer moves freely

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But if you raise your arm forward
and continue lifting it above your head,

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then it moves smoothly

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This happens because the AirPod-like humeral head
gets obstructed by the acromion

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when the arm is raised sideways

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If you continue forcing the movement,

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the shoulder blade will have to move along with it

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This is where the mechanics of
the shoulder girdle come into play again

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In contrast, lifting the arm forward
and above the head does not cause this obstruction

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The humeral head moves freely
without getting caught under the acromion

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This interplay between the humerus
and the shoulder girdle mechanics

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is always quite fascinating

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The major muscles that attach to the humerus

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include the pectoralis major
and the latissimus dorsi from the torso

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The deltoid muscle, which occupies the upper arm,

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and the biceps brachii and triceps brachii,

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and the brachioradialis,  connected to the lower arm,

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the wrist extensor muscles, and the wrist flexor muscles

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As you can see from the pictures,

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the muscles attached to the humerus

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are essentially a hub for the upper body muscles,

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including the chest, back, and arms

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Almost all major muscles pass through this humerus

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You know that pose where people flex their arms

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to show off their biceps?

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There’s a reason for that

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Next, let’s look at the ulna

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The ulna connects from the elbow to the wrist

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In Chinese characters,

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the term refers to

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a unit of measurement

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Measurement

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Historically, the length of the ulna
has remained relatively consistent,

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making it a useful reference for measurement units

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The ulna is a primary bone
forming the joints for flexion and extension

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The concave-shaped head of the elbow

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interlocks with the trochlea of the humerus,

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allowing unidirectional movement

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The ulna also creates key anatomical landmarks,

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such as the protrusion at the elbow

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and the visible bump at the wrist

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Now, let’s move on to the radius

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Let's take a look

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The radius is the counterpart to the ulna, 
forming the other half of the forearm bones

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If the ulna is responsible for the bending
and extending movements of the arm,

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what’s the purpose of the radius?

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The ulna is responsible for the bending and extending,

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while the radius is mainly responsible for wrist rotation

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As you can see,

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the ends of both the ulna and radius are significantly
larger at their respective functional joints

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For example,

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the radius here

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plays a major role in wrist rotation,

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and you can see that the bone near the thumb side
of the wrist is much broader

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Meanwhile, the ulna

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interlocks with the humerus at the elbow,

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making its upper portion much larger

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The radius is wider at the lower end
where it connects with the wrist bones,

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enabling pronation and supination movements of the hand

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Before continuing, let’s briefly explain wrist rotation

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The default position of the hand is with
the palm facing forward,

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known as supination

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known as supination

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When you rotate the hand so that
the back of the hand faces forward,

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that movement is called pronation

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The opposite is called supination

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Let's go back

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An interesting fact is

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that the head of the radius

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always moves in sync with the direction of the thumb
during both pronation and supination

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These bones not only facilitate pronation

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and supination but also play a role in absorbing impact

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When the arm experiences a fall or shock,

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the ulna and radius help distribute the force,
preventing injuries to the wrist and elbow

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At the same time, they generate counterforce,

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aiding in movement propulsion

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That covers the bones of the arm

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Now, let’s discuss an interesting feature of the forearm,

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the carrying angle

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If you observe the arm in a supinated position,

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you’ll notice that

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the forearm angles slightly outward

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This angle is called the carrying angle,

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also referred to as the valgus angle

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Usually we say the carrying angle

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It is an evolutionary adaptation that developed
from quadrupedal to bipedal locomotion

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When the arms are relaxed in a supinated position,

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they are naturally affected by the protruding pelvis

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00:14:30.608 --> 00:14:33.504
As a result, the arms angle outward

253
00:14:34.182 --> 00:14:38.020
Since pelvic structure varies significantly

254
00:14:38.842 --> 00:14:39.656
between genders,

255
00:14:39.756 --> 00:14:43.719
this also affects the carrying angle,

256
00:14:43.719 --> 00:14:45.510
which is very interesting

257
00:14:45.769 --> 00:14:47.719
As you can see, women generally have wider pelvises

258
00:14:47.719 --> 00:14:50.299
than men, resulting in a greater carrying angle

259
00:14:50.917 --> 00:14:53.090
Typically, men have a carrying angle of 0 to 15 degrees,

260
00:14:53.090 --> 00:14:55.960
while women have fom at least 10 to 20 degrees

261
00:14:56.887 --> 00:15:00.434
This angle also contributes to differences
in upper body strength between men and women

262
00:15:00.882 --> 00:15:05.724
Because flexion and extension movements

263
00:15:05.727 --> 00:15:07.789
follow a more linear path in men,

264
00:15:08.136 --> 00:15:10.972
their muscle force is more efficiently transmitted

265
00:15:11.333 --> 00:15:15.101
Therefore, men’s arms tend to stay closer to their bodies,

266
00:15:15.554 --> 00:15:18.719
and when they exert force,

267
00:15:18.719 --> 00:15:20.315
they can extend their arms

268
00:15:20.316 --> 00:15:22.732
straight more effectively

269
00:15:22.954 --> 00:15:25.515
On the other hand, due to
the larger carrying angle in women,

270
00:15:25.515 --> 00:15:28.936
their elbows tend to angle outward,

271
00:15:28.936 --> 00:15:31.838
resulting in a more rounded and flexible motion

272
00:15:32.247 --> 00:15:35.713
This difference is often reflected in posing styles

273
00:15:36.129 --> 00:15:40.108
Men frequently take poses where their arms extend

274
00:15:40.108 --> 00:15:43.008
outward in a Superman-like fashion

275
00:15:43.606 --> 00:15:48.428
Meanwhile, women’s poses often emphasize
outward hand gestures,

276
00:15:48.428 --> 00:15:49.927
naturally showcasing

277
00:15:50.679 --> 00:15:54.925
their carrying angle in a more fluid and soft manner

278
00:15:55.097 --> 00:15:58.988
Overview of Arm and Shoulder Muscles

279
00:15:59.400 --> 00:16:03.886
I mentioned that arm muscles can be broadly classified
into flexor and extensor muscles

280
00:16:03.887 --> 00:16:05.888
Flexors, also known as flexor muscles,

281
00:16:06.476 --> 00:16:08.249
engage when bending the arm

282
00:16:08.249 --> 00:16:11.859
A key example is the biceps,

283
00:16:11.859 --> 00:16:13.500
or biceps brachii,

284
00:16:14.309 --> 00:16:17.638
along with the brachialis

285
00:16:17.904 --> 00:16:21.922
These muscles generate force at the elbow
to facilitate arm flexion

286
00:16:22.368 --> 00:16:27.541
In contrast, extensors are muscles
that straighten or extend the arm,

287
00:16:27.541 --> 00:16:31.045
with the triceps brachii being the primary extensor

288
00:16:31.582 --> 00:16:33.635
One key takeaway here is

289
00:16:33.791 --> 00:16:36.283
that flexors are generally

290
00:16:36.283 --> 00:16:39.622
more developed than extensors

291
00:16:39.636 --> 00:16:43.479
his is why when the arm is at rest in a natural position,

292
00:16:43.481 --> 00:16:45.347
it tends to stay slightly bent

293
00:16:45.347 --> 00:16:47.673
The flexor muscles exert more influence

294
00:16:47.973 --> 00:16:50.470
When you build muscle, what happens?

295
00:16:51.593 --> 00:16:52.518
That's right

296
00:16:52.518 --> 00:16:53.559
It  gets bigger

297
00:16:54.033 --> 00:16:58.243
This is why flexor muscles,
being the stronger force generators,

298
00:16:59.617 --> 00:17:02.901
tend to be more pronounced compared to extensors

299
00:17:03.063 --> 00:17:07.719
Likewise, this is also why the arms naturally

300
00:17:07.719 --> 00:17:11.081
turn slightly forward when relaxed

301
00:17:11.578 --> 00:17:12.992
Since the anterior muscles of the arm,

302
00:17:12.992 --> 00:17:18.560
the flexors, are stronger than the extensors,

303
00:17:18.564 --> 00:17:23.684
the arm naturally adopts a slightly
forward-facing posture when at rest

304
00:17:23.719 --> 00:17:29.110
This explains why the balance between flexors
and extensors isn’t perfectly symmetrical

305
00:17:29.719 --> 00:17:33.047
This natural flexed posture can also
be observed in the hands

306
00:17:33.500 --> 00:17:36.233
Just like the arms,

307
00:17:36.233 --> 00:17:40.259
the hands receive much more force from the flexor muscles
than from the extensor muscles

308
00:17:40.270 --> 00:17:41.843
In contrast, for the legs,

309
00:17:41.843 --> 00:17:45.719
the extensor muscles of the thighs are
more developed than the flexors,

310
00:17:45.719 --> 00:17:49.993
resulting in a more pronounced extensor muscle shape

311
00:17:50.968 --> 00:17:52.719
Now, let’s take a look at the arm muscles

312
00:17:53.334 --> 00:17:55.462
Starting with the shoulder,
the origin of the arm bones,

313
00:17:55.955 --> 00:17:57.980
the muscles of the shoulder girdle

314
00:17:58.542 --> 00:18:01.788
These muscles are layered in complex formations,

315
00:18:01.788 --> 00:18:03.880
so instead of analyzing them one by one,
we will group them for easier understanding

316
00:18:05.545 --> 00:18:08.085
Even knowing all of them in detail
may not be particularly useful,

317
00:18:08.786 --> 00:18:11.719
as much of them are actually covered
by the trapezius muscle

318
00:18:12.165 --> 00:18:13.824
However, understanding this part

319
00:18:14.068 --> 00:18:16.719
allows for a deeper mastery of back muscle details

320
00:18:17.343 --> 00:18:18.719
So let’s approach this without feeling overwhelmed

321
00:18:19.242 --> 00:18:23.330
Here, you can see the shoulder blade

322
00:18:23.719 --> 00:18:27.880
First, let’s look at the teres major,

323
00:18:29.631 --> 00:18:30.719
which is located at the lowest layer

324
00:18:31.136 --> 00:18:35.080
Above it, the teres minor is attached slightly forward,

325
00:18:35.559 --> 00:18:36.652
connecting to the head of the humerus

326
00:18:37.719 --> 00:18:39.276
Additionally, there is the infraspinatus muscle,

327
00:18:39.276 --> 00:18:41.862
which extends above and below the spine of the scapula,

328
00:18:41.864 --> 00:18:44.485
attaching to the humeral head

329
00:18:45.719 --> 00:18:51.534
The infraspinatus is technically divided
into the supraspinatus and infraspinatus,

330
00:18:51.536 --> 00:18:54.065
but distinguishing them in this context
doesn’t add much value

331
00:18:54.065 --> 00:18:55.878
So let’s treat them as a single unit for now

332
00:18:57.224 --> 00:19:00.509
These muscles primarily function to rotate the arm

333
00:19:00.815 --> 00:19:03.632
Having examined these multiple layers,

334
00:19:03.954 --> 00:19:08.548
you’ll notice that they are again covered
by the trapezius and deltoid muscle

335
00:19:09.249 --> 00:19:10.992
As a result, when drawing the back,

336
00:19:11.712 --> 00:19:14.303
only a small portion of the shoulder muscles is visible

337
00:19:14.839 --> 00:19:17.116
It’s somewhat amusing

338
00:19:17.719 --> 00:19:21.405
yet also feels like we’re studying
something we barely get to see

339
00:19:21.943 --> 00:19:26.054
Now, let’s move on to the actual shoulder muscles

340
00:19:26.376 --> 00:19:27.501
A broad, powerful shoulder

341
00:19:27.805 --> 00:19:32.225
What man wouldn’t want to have one,
whether thin or muscular?

342
00:19:32.719 --> 00:19:34.572
For many men, it is the most desirable muscle group

343
00:19:35.154 --> 00:19:37.432
and a top priority in bodybuilding

344
00:19:37.719 --> 00:19:42.074
The key muscles here include
the coracobrachialis and the deltoid

345
00:19:42.794 --> 00:19:47.122
The coracobrachialis connects to the shoulder
and functions to bring the arm forward

346
00:19:47.122 --> 00:19:51.152
It also affects the armpit area when the arm is raised

347
00:19:51.472 --> 00:19:55.843
Since it is a relatively small muscle,
it doesn’t stand out much

348
00:19:56.228 --> 00:19:58.338
Next, we have the shoulder muscle itself

349
00:19:59.121 --> 00:20:00.158
The deltoid,

350
00:20:00.159 --> 00:20:01.245
yes, the famous deltoid muscle

351
00:20:01.500 --> 00:20:05.665
The deltoid is the main muscle used
to lift the arm laterally

352
00:20:06.025 --> 00:20:08.525
That’s why lateral raises with dumbbells

353
00:20:10.136 --> 00:20:12.386
are a common exercise for shoulder development

354
00:20:13.593 --> 00:20:20.195
The deltoid extends from the spine of the scapula

355
00:20:20.541 --> 00:20:26.885
and the acromion, continuing to the middle of the clavicle

356
00:20:27.796 --> 00:20:30.452
On the other end, it extends down

357
00:20:32.077 --> 00:20:35.687
to about the midpoint of the humerus

358
00:20:37.351 --> 00:20:40.423
In a flat diagram, it may be difficult
to grasp the overall shape,

359
00:20:41.188 --> 00:20:43.908
but structurally, it is attached to the bone like this

360
00:20:44.244 --> 00:20:48.394
It forms a C shape,

361
00:20:48.396 --> 00:20:51.566
extending from the scapular spine to the clavicle

362
00:20:51.566 --> 00:20:52.971
Does that make sense?

363
00:20:53.642 --> 00:20:56.492
At the lower end, the deltoid connects to the humerus

364
00:20:58.500 --> 00:21:03.599
Rather than being a simple triangular shape,
its structure resembles the canopy of a fighter jet

365
00:21:04.145 --> 00:21:06.719
This silhouette is quite common in plastic model kits

366
00:21:07.598 --> 00:21:11.442
Now, moving from the deltoid,
let’s look at the muscles that define the presence of the upper arm

367
00:21:11.907 --> 00:21:15.356
Back in the day, we used to associate
bodybuilders with their biceps

368
00:21:15.719 --> 00:21:17.545
That’s exactly where this muscle is located

369
00:21:18.596 --> 00:21:22.207
The main muscles in this area are the brachialis,

370
00:21:22.207 --> 00:21:26.799
the biceps brachii, and the brachioradialis

371
00:21:27.620 --> 00:21:32.279
The brachialis and biceps brachii
are primarily involved in elbow flexion

372
00:21:33.041 --> 00:21:36.492
These muscles are heavily used when lifting objects,

373
00:21:36.493 --> 00:21:38.393
so they are built

374
00:21:38.393 --> 00:21:40.132
with two distinct layers

375
00:21:41.282 --> 00:21:42.870
The lower brachialis originates

376
00:21:42.870 --> 00:21:46.823
from the midpoint of the humerus and attaches to the ulna

377
00:21:47.183 --> 00:21:50.913
It is positioned closer to the joints
than to the center of the humerus,

378
00:21:50.913 --> 00:21:53.098
and it has a slightly diagonal orientation

379
00:21:53.806 --> 00:21:58.719
The biceps brachii has two heads that originate
from the upper part of the scapula and extend downward,

380
00:21:58.719 --> 00:22:02.278
attaching to both the radius and ulna

381
00:22:02.564 --> 00:22:06.291
Thus, in the front of the arm,
the biceps brachii takes center stage,

382
00:22:06.849 --> 00:22:09.047
while the brachialis defines the contour from behind

383
00:22:09.719 --> 00:22:13.583
The brachioradialis originates
from the anterior portion of the humerus

384
00:22:13.814 --> 00:22:19.058
Specifically, it starts from the lower half
of the humerus at the anterior side

385
00:22:19.678 --> 00:22:22.596
It then extends downward to attach near the elbow joint

386
00:22:23.584 --> 00:22:28.387
As you can see, the brachioradialis plays
a crucial role in flexion movements

387
00:22:29.419 --> 00:22:31.674
Even though it belongs to the upper arm muscles,

388
00:22:31.678 --> 00:22:33.826
it primarily shapes the forearm’s contour

389
00:22:34.719 --> 00:22:37.874
When the hand is in a supinated position,
this muscle forms a noticeable protrusion on the forearm

390
00:22:38.947 --> 00:22:42.646
It is one of the key muscles responsible for changes
in forearm shape depending on pronation and supination

391
00:22:43.090 --> 00:22:45.353
On the posterior side of the upper arm,
we have the triceps brachii,

392
00:22:45.739 --> 00:22:46.991
commonly referred to as the triceps

393
00:22:47.946 --> 00:22:49.264
That's the muscle

394
00:22:49.907 --> 00:22:51.583
This muscle functions as an extensor,

395
00:22:51.583 --> 00:22:53.794
primarily used for extending the arm

396
00:22:54.719 --> 00:22:57.719
It is activated when extending the elbow
or lowering the arm backward

397
00:22:57.719 --> 00:23:03.226
The triceps brachii originates
from three different points on the scapula

398
00:23:03.228 --> 00:23:04.719
and humerus before converging at the elbow

399
00:23:05.402 --> 00:23:08.380
This muscle has three distinct heads,

400
00:23:08.380 --> 00:23:11.533
which merge at the olecranon process,
where it forms a broad tendon

401
00:23:11.870 --> 00:23:13.307
That's why it looks like this

402
00:23:13.550 --> 00:23:17.483
Overview of the Forearm Muscles

403
00:23:17.744 --> 00:23:20.593
Now, things are about to get even more complicated

404
00:23:20.837 --> 00:23:23.076
You might be thinking,
It was already complicated, what do you mean?

405
00:23:23.620 --> 00:23:24.372
No,

406
00:23:24.696 --> 00:23:26.206
up until now, it was relatively simple

407
00:23:26.719 --> 00:23:27.358
The forearm,

408
00:23:27.358 --> 00:23:31.502
especially the muscles responsible for wrist and hand movements,

409
00:23:31.502 --> 00:23:34.073
is where things truly get intricate

410
00:23:34.719 --> 00:23:36.597
Let’s start with the muscles related to flexing the hand

411
00:23:36.893 --> 00:23:38.302
These are located on the anterior side of the forearm

412
00:23:38.302 --> 00:23:40.127
The flexor digitorum profundus,

413
00:23:40.127 --> 00:23:42.256
flexor pollicis longus,

414
00:23:42.256 --> 00:23:44.465
and flexor digitorum superficialis

415
00:23:44.465 --> 00:23:46.215
control finger movements

416
00:23:46.567 --> 00:23:48.159
Meanwhile, the flexor carpi ulnaris,

417
00:23:48.166 --> 00:23:49.417
palmaris longus,

418
00:23:49.417 --> 00:23:50.997
and flexor carpi radialis

419
00:23:50.997 --> 00:23:52.340
contribute to wrist flexion

420
00:23:52.719 --> 00:23:53.906
Pretty amazing, right? Next!

421
00:23:54.566 --> 00:23:57.429
We also need to look at the extensor muscles

422
00:23:57.820 --> 00:23:59.014
The extensor digitorum,

423
00:23:59.018 --> 00:24:00.415
extensor pollicis longus,

424
00:24:00.415 --> 00:24:01.487
extensor pollicis brevis,

425
00:24:01.490 --> 00:24:05.163
and abductor pollicis longus support
the movement of the fingers

426
00:24:05.615 --> 00:24:09.830
Additionally, the extensor carpi radialis longus,
extensor carpi radialis brevis,

427
00:24:09.830 --> 00:24:13.810
and extensor carpi ulnaris regulate wrist extension

428
00:24:13.815 --> 00:24:14.513
Next!

429
00:24:15.903 --> 00:24:16.809
Well, that's it

430
00:24:16.809 --> 00:24:17.545
That's the end of the list

431
00:24:18.372 --> 00:24:22.218
I figured that if we went through all of these one by one,
you’d probably just turn this off

432
00:24:22.529 --> 00:24:24.052
Honestly, I was a bit nervous about it myself

433
00:24:24.719 --> 00:24:28.923
The forearm is packed with muscles responsible
for wrist and hand movements

434
00:24:29.226 --> 00:24:32.719
If the fingers had thick, bulky muscles
attached directly to them,

435
00:24:32.719 --> 00:24:35.842
they wouldn’t be able to move delicately,
or do even basic movements

436
00:24:36.719 --> 00:24:40.297
That’s why the power-generating muscles

437
00:24:40.298 --> 00:24:45.077
are located in the forearm,
and they control the fingers via tendons

438
00:24:45.307 --> 00:24:48.284
However, finger movements are inherently complex

439
00:24:48.820 --> 00:24:51.114
Fingers have to flex from the palm,

440
00:24:51.115 --> 00:24:54.589
and each finger has two or three individual joints
that must move independently

441
00:24:55.242 --> 00:24:56.579
On top of that, the wrist must also move

442
00:24:56.896 --> 00:24:58.719
And let’s not forget, the arm needs
to pronate and supinate as well

443
00:24:59.213 --> 00:25:04.537
Unlike broad muscles simply layered
over the chest or back,

444
00:25:04.537 --> 00:25:09.521
the forearm is filled with multiple fine muscle strands

445
00:25:09.719 --> 00:25:13.459
The layering of these muscles
creates the forearm’s silhouette

446
00:25:13.719 --> 00:25:16.398
Given its complexity,
understanding the order of these muscle layers

447
00:25:16.398 --> 00:25:18.990
is just as important as knowing what they are

448
00:25:19.714 --> 00:25:21.774
At the deepest layer,

449
00:25:21.774 --> 00:25:24.812
you have small muscles like
the coracobrachialis and brachialis,

450
00:25:24.812 --> 00:25:28.882
which are attached to the scapula and humerus

451
00:25:29.493 --> 00:25:33.726
Above that, the various flexor muscles of
the wrist and hand run parallel to each other

452
00:25:34.719 --> 00:25:37.719
On the posterior side, we have
the shoulder blade muscles, the triceps brachii,

453
00:25:37.719 --> 00:25:41.259
and several extensor muscles for the wrist and hand

454
00:25:42.468 --> 00:25:43.874
Now, let’s examine the outermost layer

455
00:25:44.082 --> 00:25:47.993
On the anterior side, the brachioradialis runs
from the wrist up toward the humerus

456
00:25:47.993 --> 00:25:50.875
It is positioned toward the back of the forearm

457
00:25:51.408 --> 00:25:55.739
Meanwhile, the biceps brachii overlays the brachialis,

458
00:25:56.210 --> 00:25:57.311
covering it snugly

459
00:25:57.719 --> 00:26:02.723
From here, the trapezius and pectoralis major attach

460
00:26:02.723 --> 00:26:04.129
to the scapula and clavicle

461
00:26:04.533 --> 00:26:08.891
Lastly, the pectoralis major spans across the scapula
and clavicle,

462
00:26:08.893 --> 00:26:11.473
forming a cohesive structure

463
00:26:12.165 --> 00:26:13.924
And with that, the anterior view is complete

464
00:26:14.212 --> 00:26:17.068
On the posterior side, the trapezius and pectoralis major

465
00:26:17.068 --> 00:26:19.341
follow the spine and integrate into the structure

466
00:26:19.719 --> 00:26:22.040
Lower down, the brachioradialis originate

467
00:26:22.041 --> 00:26:25.573
 from the upper humerus and wraps around to the front

468
00:26:26.047 --> 00:26:27.857
And just like that, the arm muscles are complete

469
00:26:28.338 --> 00:26:30.806
Now, let’s go over the layering once more

470
00:26:31.101 --> 00:26:33.921
From the front view, we group

471
00:26:34.409 --> 00:26:37.263
the humerus and biceps brachii together

472
00:26:37.263 --> 00:26:41.340
Below that, the brachialis and overlapping

473
00:26:41.340 --> 00:26:43.053
wrist flexors form another group

474
00:26:43.259 --> 00:26:47.045
To the side, the brachioradialis is grouped separately

475
00:26:47.470 --> 00:26:52.568
Above, the pectoralis major overlaps the upper part

476
00:26:52.570 --> 00:26:58.866
of the biceps brachii, while the deltoid caps it all off

477
00:26:59.131 --> 00:27:00.053
There, that’s done

478
00:27:00.053 --> 00:27:01.995
What about the posterior view?

479
00:27:02.293 --> 00:27:03.074
It follows a similar pattern

480
00:27:03.486 --> 00:27:04.829
Same thing

481
00:27:05.176 --> 00:27:07.710
The triceps brachii is grouped as a whole

482
00:27:07.710 --> 00:27:11.871
Below that, the wrist and hand extensors
extend downward

483
00:27:12.373 --> 00:27:14.493
The brachioradialis,

484
00:27:14.753 --> 00:27:17.705
wrapping around toward the front,
forms another distinct group

485
00:27:18.053 --> 00:27:21.587
Above, the deltoid overlaps the triceps brachii

486
00:27:21.587 --> 00:27:24.362
and shoulder blade muscles, forming the final layer

487
00:27:24.769 --> 00:27:28.111
When we outline the silhouette from the skin’s surface,
this is how it comes together

488
00:27:28.719 --> 00:27:30.222
That feels pretty satisfying

489
00:27:30.719 --> 00:27:32.866
That concludes today’s lecture

490
00:27:33.061 --> 00:27:36.259
We only covered the anatomical aspects of the arm,
and yet, it was a massive amount of information

491
00:27:36.719 --> 00:27:37.698
It’s a bit overwhelming

492
00:27:37.939 --> 00:27:38.903
And honestly, I’m getting hungry

493
00:27:39.541 --> 00:27:40.822
But we’re not done yet

494
00:27:41.309 --> 00:27:44.345
So far, we’ve only talked about the arm in a neutral,
resting position

495
00:27:45.155 --> 00:27:46.893
In other words, we’ve only covered the default state

496
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We haven’t even begun to explore how muscles change

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when the arm bends, twists, or rotates

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And most importantly, we still have the hand to discuss

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Even if you could get away with
drawing arms in a simple way,

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hands are a whole different challenge

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The journey through arm anatomy is far from over

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It's tough

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But I hope you’ve enjoyed it

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Great job everyone for going through this with me

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Thank you

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Arm Anatomy
Pectoral Girdle: Connects the arm to the torso, has the scapula and the clavicle
Free Arm Bones: Functional movement of the arm

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Scapular Spine: For back and arm muscles, a landmark
Acromion: Cavicle meets the shoulder blade

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Glenoid Cavity: The humerus to the shoulder
Coracoid Process: Arm movement
Clavicle: Dynamic houlder movements

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Humerus: The longest, around half of the arm
Ulna: The inner forearm bone
Radius: The outer forearm bone

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Arm and Shoulder Muscles
Arm Muscles
Flexor Muscles: For bending the arm
Biceps Brachii and brachialis

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Extensor Muscles: To straighten the arm
Triceps Brachii

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Muscle Mass Difference: Flexor muscles are more developed than extensors,
which is why the arm naturally curves forward when at rest

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Shoulder Muscles
Rotator Cuff Muscles: Attaching to the humerus, rotating the arms
Coracobrachialis: Smaller, not really visible

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Deltoid Muscle: The dominant shoulder muscle,
from the scapular spine and acromion to the clavicle

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Muscles for Forearm Rotation
Pronator Teres & Pronator Quadratus: Control forearm pronation
Supinator: Responsible for forearm supination

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Muscles for Hand Flexion
Deep, Long, Short Finger Flexor for fingers
Flexor Carpi Ulnaris, Palmaris Longus, and Flexor Carpi Radialis for wrist

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Muscles for Hand Extension
Extensor Digitorum and more for fingers
Extensor Carpi Radiali and more for writst

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Muscles are located in the forearm
Te hand is connected via tendons,
allowing the fingers to flex or extend