Video: Main muscles of the upper limb
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When you think of the muscles of the upper limb, you might think, “Pfft, I know those already!” Everyone knows where their bulging biceps are. We all know how to flex those. Maybe, you're even awar... Read more
When you think of the muscles of the upper limb, you might think, “Pfft, I know those already!” Everyone knows where their bulging biceps are. We all know how to flex those. Maybe, you're even aware of your popping triceps after doing some triceps dips. What about deltoids? You might have even heard of those before. But if we look a little bit deeper, there's much more to the muscles of the upper limb than it may seem at first. So rather than building up our muscles at the gym, let's build up our knowledge on the main muscles of the upper limb.
In today's tutorial, we're going to take a look at some of the main muscles of the upper limb. There are quite a lot of them; but don't worry, we're going to break them down into regions to make it more manageable. We will first begin with muscles of the shoulder region moving down to the arm, the forearm, and finally, the hand. We will then identify the different groups of muscles within each region. As we go along, we will discover the main actions associated with each group of muscles as well as their anatomical relations to surrounding structures. So let's dive right in and begin with the main muscles of the shoulder.
We're going to focus on six of the main muscles of the shoulder today. Most of these muscles originate at the bony shoulder girdle and attach distally on the humerus. That means most of these muscles cross the shoulder joint; therefore, when they contract, movement of the arm at the shoulder joint occurs.
Muscles of the shoulder can be divided into superficial and deep layers. The main superficial muscle of the shoulder is the well-known deltoid muscle. This large muscle is a bit like an upside down triangle extending both anteriorly and posteriorly. Its wide flat base attaches at the shoulder with its apex descending to attach to the arm. The anatomists who discovered this muscle must have known their Greek alphabet very well as they named this muscle after the triangular-shaped Greek letter delta.
If we were to peel back the deltoid muscle, we would find a group of smaller but still very important muscles lying just beneath. These four deep muscles of the shoulder are known as the rotator cuff muscles. You may be wondering why these muscles are grouped together as the rotator cuff muscles. The term rotator comes from the rotational movement these muscles elicit when they contract whereas cuff originates from their positioning and insertion as they extend from the scapula and ‘cuff’ the head of the humerus.
The rotator cuff muscles are also sometimes known as SITS muscles. SITS is a handy little mnemonic that can help you remember the rotator cuff muscles where S stands for supraspinatus, I for infraspinatus, T for teres minor, and the final S for subscapularis. The rotator cuff muscles all extend to insert onto the head of the humerus, but it is their origins that reveal their differences. Let's take a quick look at these muscles individually.
Three of the rotator cuff muscles are located on the posterior aspect of the scapula. The first of these muscles is the supraspinatus muscle. This muscle sits on the posterior surface of the scapula within a hollow known as the supraspinous fossa. This attachment is where the supraspinatus gets its name. Just below the supraspinatus, we meet the infraspinatus muscle, sitting in the infraspinous fossa. Are you starting to see the pattern here? This is a triangular muscle with a wide base and a narrow apex. The last rotator cuff muscle on the posterior surface of the scapula is the teres minor muscle. The teres minor is smaller than both the supraspinatus and infraspinatus muscles and sits inferior to both at the lateral border of the scapula.
In order to see the final rotator cuff muscle, we need to flip the scapula around so that we can view its anterior surface. Here we find the subscapularis muscle sitting in the subscapular fossa, hence, its name. This muscle is the largest of the rotator cuff muscles and covers essentially the whole anterior surface of the scapula.
You may have noticed that there is another muscle on the posterior surface of the scapula that we haven't mentioned yet. Sitting just inferior to the teres minor muscle, we meet the teres major muscle. Teres major is one of the deep muscles of the shoulder. It inserts a little lower on the shaft of the humerus and, therefore, does not contribute to the tendinous rotator cuff.
Let's take a look at the movements that occur when some of the main muscles of the shoulder contract.
The large deltoid muscle is the major abductor of the arm at the shoulder joint. It moves the arm away from the midline of the body. The deep muscles of the shoulder – the rotator cuff muscle and the teres major – are responsible for its rotational movements. They work together to internally and externally rotate the arm at the shoulder joint.
Let's now travel down and take a look at the main muscles of the arm.
Muscles of the arm and forearm can be divided into an anterior and a posterior group. Muscles of the anterior compartment of the arm include the biceps brachii, the coracobrachialis, and the brachialis muscles. The main muscle of the posterior compartment of the arm is the triceps brachii. Another small muscle that can be considered both the muscle of the arm and the forearm is the anconeus muscle; however, we'll not discuss it further in this tutorial as this muscle is often morphologically and functionally classed as a continuation of the triceps. If you want to find out more about the anconeus muscle and the other muscles of the arm, feel free to check out our more in-depth videos on the muscles of the arm.
Okay, let's now take a look at the muscles of the anterior arm in a little more detail.
The biceps brachii muscle is one of the major muscles of the arm. Its name comes from the Latin bi- meaning two and caput- meaning head. It has a long head and a short head. The biceps brachii muscle extends over two joints – the shoulder joint and the elbow joint – meaning that it contributes to movement at both of them.
The coracobrachialis muscle is a small muscle that lies beneath the biceps brachii. Its name is derived from its origin and location. Coraco- indicates this muscle's origin at the coracoid process of the scapula while brachialis indicates that it is located within the brachial or arm region. This muscle only acts on the shoulder joint.
A final muscle in the anterior compartment of the arm is the brachialis muscle. This muscle sits tucked behind the lower portion of the biceps brachii muscle and can be quite hard to find. The brachialis muscle is a large and powerful muscle that acts only on the elbow joint. It is the main and most powerful flexor of the forearm at the elbow.
Now that we are familiar with the muscles of the anterior compartment of the arm, let's take a quick look at the posterior compartment.
The triceps brachii muscle is the main muscle of the posterior compartment. As we saw with the biceps brachii which is a two-headed muscle, the triceps brachii is given its name because it has three heads. Here we can see the long head and the lateral head, and peeking through, we can just about make the medial head. The triceps brachii muscle is a powerful muscle that acts at both the shoulder and elbow joints.
Now that we've had a look at the anterior and posterior muscles of the arm, let's see how they act on the shoulder and elbow joint as they contract.
Muscles of the anterior compartment of the arm are predominantly flexors. Depending on their origin, these three muscles will either flex the arm at the shoulder or flex the forearm at the elbow. Some muscles will also contribute to other movements such as adduction of the arm and supination of the forearm. The movement that occurs in the posterior arm is quite simple. The triceps brachii muscle extends the arm and forearm posteriorly at the shoulder and elbow joints.
So now that we've had a look at the muscles of the arm, let's move distally to take a look at the muscles of the forearm – the region between the elbow and the wrist.
Muscles of the forearm are a little bit more complex. Just like the arm, the muscles of the forearm are divided into anterior and posterior compartments as well as superficial and deep regions within each compartment. Let's begin by taking a look at some of the superficial muscles of the anterior region of the forearm first, starting off with the pronator teres.
The pronator teres muscle is one of the most superficial muscles of the forearm. It has two heads – a humeral and ulnar head. We can only see the humeral head here as the ulnar head is hidden under the muscle belly. Unlike most muscles of the forearm, it does not travel down to reach the hand, but instead, inserts onto the radius of the forearm.
Lying just medial and slightly posterior to the pronator teres muscle is the flexor carpi radialis muscle. The names of this muscle give us an idea of where it's headed. Carpi in Latin refers to the bones of the hand while radialis indicates the radial or lateral aspect of the hand, therefore, by this muscle's name, we can presume that flexor carpi radialis is heading down to the lateral metacarpal bones.
This muscle travels down to insert onto the ligamentous structures of the palm of the hand. The palmaris longus muscle is extremely variable, and in fact, not everybody has it. You might be able to find this muscle's tendon if you flex your hand at the wrist joint. If you have this muscle, you should be able to spot three tendons on the anterior surface of the wrist. If it's absent, you'll only see two tendons – the flexor carpi radialis and ulnaris tendons.
The flexor carpi ulnaris muscle lies just medial to the palmaris longus muscle. Much like the flexor carpi radialis muscle, this muscle also inserts at the metacarpal bones of the hand but at the ulnar or medial aspect.
The last muscle of the superficial layer that we're going to look at today is the flexor digitorum superficialis muscle. This muscle is the deepest of all the superficial muscles of the anterior compartment and lies just behind the flexor carpi ulnaris and radialis muscles. It is a large muscle with two heads.
Let's now move on to the deep compartment of the anterior arm.
Here we meet the flexor pollicis longus and the flexor digitorum profundus muscles. These muscles are quite small and their actions weak, so they are not considered main flexors by many sources. However, we do cover them in detail in our other videos.
The final muscle that we will look at in the anterior deep layer is the pronator quadratus muscle. It is the deepest muscle of the anterior forearm and sits next to the wrist. It stretches between the distal end of the radius and ulna hidden underneath layers of deep and superficial muscles. Quadratus in Latin means square which is reflected in the shape of the muscle.
Before we move on to the posterior muscles, let's take a quick look at some of the movements of the muscles of the anterior forearm.
The muscles of the anterior forearm are predominantly all flexors as their names suggest. Most of the superficial muscles flex the forearm at the elbow joint, hand at the wrist, and digits at the metacarpophalangeal and interphalangeal joints.
Deep muscles will also aid in flexing the hand and digits, but do not act on the elbow joint. Muscles positioned medially or laterally such as flexor carpi ulnaris and flexor carpi radialis will also contribute to abduction and adduction of the hand at the wrist. The pronator teres and pronator quadratus muscles work together to produce a twisting motion known as pronation.
So now we're finished with the anterior group of the forearm, let's flip that arm around and take a look at some of the main muscles of the posterior forearm.
Just like the anterior forearm, the muscles of the posterior forearm are also divided into superficial and deep regions. Muscles within this compartment are known as the extensor muscles as this is the main action they perform. Let's begin by taking a look at the six muscles of the superficial layer first.
The most superficial muscle of the posterior forearm is the brachioradialis muscle. This muscle can sometimes be confused for a muscle of the anterior compartment due to its positioning. It sits on the lateral aspect of the forearm and is best identified from the anterior view. It even behaves like a muscle of the anterior compartment as it flexes the forearm at the elbow. It is, however, considered to be a muscle of the posterior compartment as it is innervated by the radial nerve, just like its fellow posterior muscles.
Slightly inferior to the brachioradialis muscle, we meet the extensor carpi radialis longus muscle. Phew! That was quite a mouthful. As this muscle's name suggests, it is located to the radial or lateral aspect of the posterior forearm. The longus in the name might also give you a clue that this muscle has a shorter counterpart, and that is the extensor carpi radialis brevis, which is almost completely hidden by the more superficial longus.
You might notice that the three muscles we just mentioned all contain radial in their names signifying their location along the radius. These three muscles are the most lateral muscles of the forearm and are collectively known as radial muscles.
At the mid-portion of the posterior forearm just medial to the extensor carpi radialis longus, we find the extensor digitorum muscle. This muscle is similar to the flexor digitorum muscles of the anterior forearm. It lies centrally, but instead of inserting onto the palmar surface of the hand, it travels on the back or dorsal surface to insert onto the digits.
Just medial to the extensor digitorum muscle is the extensor digiti minimi muscle. This muscle travels right down to the little finger.
The last muscle of the superficial compartment is the extensor carpi ulnaris muscle. Much like the extensor carpi radialis longus muscle, the name of this muscle also gives us a vague idea of where it is headed – carpi meaning the carpal bones of the hand and ulnaris indicates the ulnar side or the medial aspect of the forearm along which it travels. This muscle sits just medial to the extensor digitorum muscle along the length of the forearm.
We've made it all the way to the deep layer of the posterior forearm. Generally, these muscles are not considered main muscles of the upper limb as they are smaller and their actions are weaker, so we will only quickly run through them. There are six muscles altogether – the extensor pollicis longus muscle and brevis, the abductor pollicis longus, the extensor indicis, and the supinator muscle, which is the deepest muscle of the posterior forearm. If you want to find out more about the muscles of the posterior forearm, we have a whole video dedicated to them.
Let's pause here to take a minute to look at the movements created by the muscles of the posterior forearm.
As you may have guessed by their names, muscles of the posterior forearm are predominantly extensors. Most of the superficial muscles extend the hand at the wrist joint, and the digits at the metacarpophalangeal and interphalangeal joints. The deep muscles extend the hand at the wrist joint and the digits at the metacarpophalangeal and interphalangeal joints, but do not act at the elbow joint. Muscles positioned medially or laterally, such as extensor carpi radialis longus and extensor carpi ulnaris, will also contribute to the abduction and adduction of the hand at the wrist.
There's one unique muscle, however, and that's the supinator muscle. The supinator muscle produces supination of the forearm and wrist at the radioulnar joints. This movement can be hard to visualize so why don't you try producing these movements yourself.
Okay, so we're nearly there and we've reached our last destination which is the hand.
Muscles of the hand can be divided into intrinsic and extrinsic muscles. Intrinsic muscles are the muscles that originate and insert within the hand while extrinsic muscles are the muscles that originate within the arm or the forearm and insert onto the palmar and dorsal surfaces of the hand and digits. We already discussed the extrinsic muscles of the hand when we talked about the muscles of the forearm, so now let's focus on the intrinsic muscles.
As with the arm and forearm, intrinsic muscles of the hand are also divided into groups of muscles. The intrinsic muscles of the hands are divided into five different groups – the dorsal and palmar interossei, the lumbricals, the hypothenar muscles, and the thenar muscles. Let's begin with the dorsal interossei.
Notice we are now looking at a dorsal view of the hand, otherwise, known as the back of the hand. The dorsal interossei muscles are four short muscles between the metacarpal bones. The dorsal interossei are numbered one to four starting at the thumb. The palmar interossei come next, and as you can see, we have flipped the hand around again and now we are looking at the palm of the hand. The palmar interossei are three muscles located between the metacarpal bones. These muscles can also be numbered one to three. The third digit does not have an associated palmar interosseous muscle.
Working our way to the next group of muscles, we meet the lumbricals. They are four short hand muscles located between the digits of the hand deep in the palmar fascia. The lumbricals actually arise from the tendons of one of the extrinsic muscles of the hand as we can see here.
Moving on, we come to the hypothenar muscle group. This group is made up of four small muscles, all situated on the medial aspect of the palm at the base of the little finger. The four hypothenar muscles are the abductor digiti minimi, the flexor digiti minimi, the opponens digiti minimi, and finally, the palmaris brevis muscle. If you take a look at the palm of your hand, you might actually be able to see an outline of this muscle group at the base of your little finger. This fleshy prominence is the hypothenar eminence, which marks the surface anatomy of these muscles.
We're on the home stretch here. We've arrived at the final muscle group of the hand – the thenar muscles. The thenar muscles are located on the lateral aspect of the palm towards the base of the thumb. They form a fleshy muscle pad in this area known as the thenar eminence. The thenar muscle group also comprises four muscles. The thenar muscles are the abductor pollicis brevis, the adductor pollicis, the flexor pollicis brevis, and the opponens pollicis. Do you recognize the Latin word pollicis? That's right! All these muscles act on the thumb.
The intrinsic muscles of the hand work together to create fine motor movements. The lumbricals and interossei work together to abduct, adduct, flex, and extend the fingers, while the thenar and hypothenar muscles abduct, adduct, flex, extend, and rotate the thumb and the little finger.
Now that we've had a look at all the main muscles of the upper limb and their associated movements, let's take a look at some of the muscles we saw today from a clinical perspective.
We learned earlier about the rotator cuff muscle group and how these four muscles were important in rotating and stabilizing the shoulder. If you are a gym buff or frequently play sports, you're probably familiar with the term rotator cuff injury. There are three main types of rotator cuff injuries – tendinitis, bursitis, and strains. Today, we're going to be focusing on strains.
A rotator cuff strain occurs when the tendons of the rotator cuff muscles become overstretched or torn. Symptoms of the rotator cuff strain include pain on lifting or rotating the arm, swelling around the shoulder, and shoulder joint stiffness. Strains are usually caused by overuse of the rotator cuff or may occur from acute trauma to the shoulder joint.
Treatment of a rotator cuff sprain includes rest, ice, and nonsteroidal anti-inflammatory drugs to reduce inflammation. Strengthening exercises may also be used to restore active function and strength to the tendon. On complete rupture of the tendon, surgical intervention may be necessary. Daily shoulder stretches can aid in increasing flexibility and strength of the shoulder joint. When stretching, it is important to strengthen the muscles around the shoulder blade and posterior shoulder specifically to optimize the muscle balance of the rotator cuff.
We did it! We made it to the end. Before we finish up though, I'm going to quickly summarize what we learnt today.
We started today's tutorial by looking at the main muscles of the shoulder. We learnt about the large deltoid muscle and the rotator cuff muscles which include the supraspinatus and infraspinatus, the teres minor, and the subscapularis muscles. Finally, we identified the teres major muscle. We explored how these muscles assist in creating movements of abduction, adduction, and internal and external rotation of the arm at the shoulder.
We then moved distally to the arm. The main muscles of the arm were grouped into anterior and posterior groups. Muscles of the anterior group consisted of the biceps brachii, the coracobrachialis, and brachialis muscles. We identified the anterior group to be predominantly flexors of the arm and forearm. The main muscle of the posterior region was the triceps brachii muscle and we learned that its main function was extension.
The forearm came next. The main superficial muscles of the anterior forearm that we had a look at today included the pronator teres, the flexor carpi radialis, the palmaris longus, the flexor carpi ulnaris, and the flexor digitorum superficialis muscles. The main muscles of the deep anterior forearm included the flexor pollicis longus, the flexor digitorum profundus, and the pronator quadratus muscles. Muscles of the superficial and deep compartment of the anterior forearm were seen to be predominantly flexors of the forearm, hand, and fingers.
Then we met the superficial and deep posterior forearm muscles. Some of the main superficial muscles of the posterior forearm included the brachioradialis muscle, the extensor carpi radialis longus muscle, the extensor digitorum, and the extensor carpi ulnaris. The main muscles of the deep posterior forearm include the extensor pollicis longus muscle, the extensor indicis, and the supinator muscle. We learnt that the main action of the posterior muscles of the forearm was to extend the forearm, hand, and fingers.
Finally, we came to the hand. We grouped all those little muscles into five separate groups and explored how each group created fine motor movements of the hand. We divided the muscles of the hand into the dorsal interossei, the palmar interossei, the lumbricals, the hypothenar muscle group, and the thenar muscle group. We learned that the muscles of the hypothenar group included the abductor digiti minimi, the flexor digiti minimi, the opponens digiti minimi, and the palmaris brevis muscles. The thenar muscle group included the abductor pollicis brevis, the adductor pollicis, the flexor pollicis brevis, and the opponens pollicis muscles.
Once we looked at all the main muscles of the upper limb and their associated actions, we then had a quick look at some clinical notes on rotator cuff injury. We learned about a strain injury to the rotator cuff tendon and identified the symptoms, causes, and treatment regime for this injury depending on the severity of the injury.
That brings us to the end of this tutorial. We hope you enjoyed this tutorial on the main muscles of the upper limb. See you next time and happy studying!