Arm Muscles: Names, Diagram and Functions of the Upper Limb

Have you ever wondered which arm muscles let you lift a cup, turn a key or push open a heavy door? Most of us use them hundreds of times a day without knowing their names or how they are controlled. In this guide, we walk you through arm muscle anatomy, from the shoulder to the fingertips, and explain when a change in strength or sensation deserves a medical opinion.

How the Upper Limb Is Divided: Arm, Forearm and Hand

The upper limb has four main regions: the shoulder, the arm, the forearm and the hand. The muscles in each region work as a chain, so a problem in one part often changes how the next part performs. Once you can place a human arm muscle in its region, its name, nerve and job start to make sense. We begin with the terminology, because it causes most of the confusion.

Anatomical Meaning of Arm Compared With Everyday Usage

In anatomy, the arm (brachium) means only the segment between the shoulder and the elbow. The international standard, Terminologia Anatomica, calls the segment from the elbow to the wrist the forearm (antebrachium). The hand (manus) lies beyond the wrist, and the shoulder (omos) lies above the arm.

In everyday speech, people use the word arm for the whole limb, which is why a search on this topic returns results about the biceps, the forearm and even the fingers. We follow the everyday meaning in this guide and name each region as we go. For example, the biceps sits in the arm, while the muscles that bend your fingers sit in the forearm.

Compartments, Fascia and Intermuscular Septa of the Upper Limb

Muscles of the upper limb are grouped into compartments, which are spaces wrapped in a tough sheet of connective tissue called fascia. In the arm, the brachial fascia and the medial and lateral intermuscular septa divide the muscles into an anterior (flexor) compartment and a posterior (extensor) compartment, and the forearm follows a similar plan. Muscles in one compartment usually share a nerve and a blood supply, so the three anterior arm muscles, for example, are supplied mainly by one nerve. To see what commands each compartment, we turn to the nerves next.

Nerve Supply That Organizes Every Arm Muscle

Every arm muscle contracts only when a nerve tells it to, and in the upper limb those nerves arise from one network called the brachial plexus. Knowing which nerve supplies which muscle helps clinicians trace a weakness back to its source. We outline the plexus first, then the four nerves you will hear about most often.

Brachial Plexus Branches and the Muscles They Control

The brachial plexus is formed by the spinal nerve roots C5, C6, C7, C8 and T1, which leave the neck and pass toward the armpit. Think of it as a highway interchange where lanes merge, reshuffle and then split toward different destinations. Each level carries different fibers, so the pattern of weakness helps clinicians locate a problem. The plexus has five levels from neck to arm:

1. Roots: the five spinal nerve roots, C5 to T1.
2. Trunks: upper (C5 and C6, where damage mainly affects shoulder and elbow movement), middle (C7) and lower (C8 and T1, where damage tends to affect the small hand muscles).
3. Divisions: each trunk splits into an anterior and a posterior division.
4. Cords: the lateral, posterior and medial cords form around the axillary artery.
5. Terminal branches: the musculocutaneous, axillary, radial, median and ulnar nerves.

Musculocutaneous, Radial, Median and Ulnar Territories

Four terminal nerves supply almost every muscle of the arm, forearm and hand, and each has a recognizable territory. The axillary nerve, the fifth terminal branch, mainly serves the deltoid at the shoulder. Here is what each of the four main nerves controls:

• Musculocutaneous (C5 to C7): the three anterior arm muscles, with a small radial contribution to the brachialis.
• Radial (C5 to T1): the triceps brachii and the forearm extensors.
• Median (C5 to T1): most forearm flexors, the thenar muscles and the first two lumbricals.
• Ulnar (C8 to T1): the flexor carpi ulnaris, the ulnar half of the flexor digitorum profundus and most small hand muscles.

Sensation follows a similar map. For example, tingling in the little finger and half of the ring finger often points toward the ulnar nerve, while tingling in the thumb, index and middle fingers often points toward the median nerve, although only a clinician can confirm the cause. Nerves are half of the supply line, so we look at the arteries next.

Blood Supply and Why It Matters for Arm Muscle Function

The muscles of the arm depend on a steady flow of oxygen-rich blood, delivered mainly by one artery that changes its name along the way. The subclavian artery becomes the axillary artery as it enters the armpit, then the brachial artery in the arm, and finally the radial and ulnar arteries in the forearm. A muscle that receives too little blood tires quickly and may ache during use.

Brachial Artery Course and Deep Arterial Branches

The brachial artery begins at the lower border of the teres major muscle and runs down the inner side of the arm to the elbow. There, in the cubital fossa, it divides into the radial and ulnar arteries, and this is where the brachial pulse is usually felt when blood pressure is measured. Its first and largest branch, the profunda brachii, travels with the radial nerve around the humerus to supply the triceps. Next, we move from supply lines to the muscles themselves, beginning with the front of the arm.

Anterior Arm Muscles at a Glance

The anterior arm muscles sit in front of the humerus and mainly bend the elbow and shoulder. There are three of them: the biceps brachii, the brachialis and the coracobrachialis. All three receive their nerve supply from the musculocutaneous nerve, and together they handle lifting, pulling and carrying.

Flexor Group Overview From Shoulder to Wrist

The flexor group is a relay that begins at the shoulder and ends at the fingertips, with each layer bending the next joint down the limb. In the upper arm, the biceps also turns the palm upward, and the brachialis is often called the workhorse of elbow flexion. The list below summarizes each level:

• Upper arm: biceps brachii, brachialis and coracobrachialis (musculocutaneous nerve).
• Forearm, superficial and intermediate layers: pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris and flexor digitorum superficialis (mostly median nerve).
• Forearm, deep layer: flexor digitorum profundus, flexor pollicis longus and pronator quadratus (median nerve, plus the ulnar nerve for the ulnar half of the profundus).

We keep this overview brief on purpose. Our dedicated upper arm muscles guide covers attachments and exercises in detail, and our forearm muscles guide explains the forearm layers one by one. Both are good next steps if you want to go deeper. Now we turn to the back of the limb.

Posterior Arm Muscles at a Glance

The posterior arm muscles sit behind the humerus and mainly straighten the elbow. In the upper arm, this job belongs to the triceps brachii, helped by the small anconeus at the back of the elbow. Some sources count the anconeus with the arm and others with the forearm. Both muscles are supplied by the radial nerve.

Extensor Group Overview and the Elbow Extension Chain

Elbow extension works as a chain: the triceps does most of the straightening, the anconeus assists, and the forearm extensors keep the wrist firm. The triceps has three heads (long, lateral and medial) that join one tendon at the olecranon, the bony tip of the elbow. When you push a heavy door open, for example, the triceps straightens your elbow while the muscles behind the forearm hold your wrist steady. The forearm extensors, supplied by the radial nerve, form two layers:

• Superficial layer: brachioradialis (which sits here but helps bend the elbow), extensor carpi radialis longus and brevis, extensor digitorum, extensor digiti minimi and extensor carpi ulnaris.
• Deep layer: supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus and extensor indicis.

Together, the front and back groups explain how the elbow, forearm and wrist move. The last set of muscles in the limb is much smaller, yet just as important for daily life, and it sits entirely within the hand. We look at these small muscles next.

Small Muscles of the Hand That Complete the Limb

The hand contains about 20 small intrinsic muscles that begin and end within the hand itself. Long tendons from the forearm supply raw power, while these small muscles fine-tune the position of the thumb and fingers. Without them, everyday tasks such as buttoning a shirt or holding a pen would become difficult.

Thenar, Hypothenar and Interosseous Muscle Groups

The intrinsic hand muscles fall into five practical groups: thenar, adductor pollicis, hypothenar, lumbricals and interossei. Most are supplied by the ulnar nerve, while the median nerve covers the thenar muscles and the first two lumbricals. Here is what each group does:

• Thenar muscles (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis): form the pad at the base of the thumb and let it move across the palm to meet the fingers.
• Adductor pollicis: draws the thumb toward the palm for a firm pinch.
• Hypothenar muscles (abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi): form the pad on the little finger side and control that finger.
• Lumbricals (four): bend the knuckle joints while straightening the fingertips.
• Interossei: the dorsal ones spread the fingers, and the palmar ones close them.

Wasting of the thenar pad can be an important clue to a median nerve problem at the wrist, so doctors often check it during a hand examination. Next, we show you how to read all of these muscles on a diagram, which is easier once you know the layers.

Labeled Upper Limb Muscle Diagram Explained

A labeled diagram shows the muscles in layers, from the surface inward, so you need a reading order to make sense of it. Most charts show a front view and a back view side by side, with deeper muscles shaded lighter or cut away. Use these five steps with any arm muscles chart, textbook figure or 3D model:

1. Check the view: front (anterior) or back (posterior).
2. Find the regions: shoulder, arm, forearm and hand, using the elbow and wrist creases as dividers.
3. Name the surface muscles: the deltoid, biceps brachii, triceps brachii and brachioradialis are the easiest to spot.
4. Follow the tendons: the joint a muscle crosses tells you the movement it produces, so the biceps, which crosses the shoulder and the elbow, acts on both.
5. Look for the deep layers: the brachialis lies beneath the biceps, and the supinator lies deep in the forearm.

Surface Anatomy Landmarks Used in European Anatomy Teaching

Surface anatomy uses landmarks you can see or feel through the skin to locate the structures beneath. Anatomy courses teach these landmarks with the Latin names of Terminologia Anatomica, so the vocabulary carries across languages and countries. You can try the checklist below on your own arm, gently and without pressing hard:

• Acromion: the bony tip of the shoulder, above the contour of the deltoid.
• Biceps belly: the front bulge that appears when you bend the elbow against resistance.
• Cubital fossa: the hollow at the front of the elbow, where the biceps tendon and the brachial pulse can be felt.
• Medial epicondyle: the inner elbow bump, with the ulnar nerve just behind it, which is why a bump there tingles in the little finger.
• Olecranon: the tip of the elbow, where the triceps tendon attaches.
• Brachioradialis: the muscle bulge on the thumb side of the upper forearm.

These landmarks help clinicians place a stethoscope, an injection or a nerve test in the right spot. They also help you describe symptoms precisely, such as pain over the outer elbow. With the landmarks in mind, we can look at what these muscles achieve in everyday life.

Movements the Arm Muscles Produce in Daily Life

The muscles of the arm produce four families of movement: bending (flexion), straightening (extension), turning the forearm (pronation and supination) and gripping. Most daily tasks blend several of them at once. Brushing your teeth, for example, combines elbow flexion, forearm rotation and a controlled grip on the brush.

Pushing, Pulling, Carrying and Fine Motor Control

Pushing relies mainly on the triceps, pulling on the biceps and brachialis, and carrying on teamwork between the arm, forearm and hand. Both pushing and pulling also recruit shoulder and back muscles. When you carry shopping bags home from the market, your elbow flexors hold the weight while your forearm and hand muscles maintain the grip. Fine motor tasks, such as threading a needle, depend on the small hand muscles and on precise signals from the median and ulnar nerves.

Action Table: Muscle Group, Joint and Movement Produced

The table below links each muscle group to the joint it moves, the movement it produces and the nerve that supplies it. Use it as a quick reference when a diagram or a symptom description names a muscle you do not recognize. The groups are simplified, so individual muscles may differ slightly.

Two points help when reading the table. First, one muscle can act on several joints, as the biceps does at the shoulder, elbow and forearm. Second, muscles work in opposing pairs, such as the elbow flexors and the triceps, which allows smooth movement and a steady hold. Next, we look at what happens when this system does not work as expected.

Signs of Arm Muscle Dysfunction Worth Investigating

Arm muscle dysfunction usually shows up as weakness, numbness, pain or clumsiness, and the pattern often points to the cause. Many of these problems come from overuse or nerve irritation at the neck, elbow or wrist, and most are easier to treat when assessed early. Some symptoms, however, need urgent attention, so we separate the two groups below.

Weakness, Numbness and Loss of Grip Strength

Weakness, numbness and a weaker grip are the most common reasons people seek advice about their arms. They can arise from a muscle, a nerve, a joint or, less often, from the brain or another part of the body. Please arrange a routine appointment with your doctor if you notice any of the following:

• Gradual weakness when lifting, gripping or turning a key.
• Tingling or numbness in particular fingers, especially at night or with a bent elbow.
• Dropping objects more often than before.
• One arm or hand looking thinner than the other.
• Muscle pain or weakness that began after you started a new medicine.

Medicines are worth a mention because they can occasionally affect muscles and nerves. The European Medicines Agency (EMA) has warned that fluoroquinolone antibiotics can, very rarely, cause long-lasting muscle, tendon and nerve side effects, and it advises patients to stop the antibiotic and contact a doctor at the first sign. Never stop other prescribed medicines without medical advice.

Grip strength is also a simple marker of overall muscle health. In European sarcopenia guidance (EWGSOP2, 2019), a handgrip below 27 kg in men or 16 kg in women is a screening threshold for low muscle strength in older adults, and it prompts further assessment rather than a diagnosis. Some symptoms need help without delay:

• Sudden weakness or numbness in one arm, especially with a drooping face or slurred speech, which may be a stroke. Get help straight away even if the symptoms pass.
• Arm pain together with chest pressure, shortness of breath, sweating or nausea, which may be a heart attack.
• Severe pain, tense swelling or a pale, cold hand after an injury.

In the European Union, 112 is the single emergency number and is free of charge from fixed and mobile phones. In the United Kingdom you can also call 999, and in the United States, 911. If you suspect a stroke, do not drive yourself to the hospital. Next, we explain how this guide was prepared and reviewed.

Popular Questions About Arm Musculature

These are the questions we hear most often about the anatomy of the upper limb. Each answer is short so that you can scan it quickly. If your question is not listed here, our upper arm and forearm guides may cover it in more depth.

How Many Muscles Are in the Human Arm?

The arm proper contains four or five muscles, while the whole upper limb has more than 40 even before you count the shoulder muscles. The upper arm holds the biceps brachii, brachialis, coracobrachialis and triceps brachii, plus the anconeus if you include it. The upper arm and forearm together contain more than 20 muscles, and the hand adds about 20 intrinsic muscles. Counts differ between textbooks, and the palmaris longus is missing in about 15 percent of people, which is a normal variation.

Which Arm Muscle Is the Largest?

The triceps brachii is the largest muscle of the upper arm. In an MRI study of 32 upper limb muscles in 10 healthy adults, the triceps made up about 14.5 percent of total upper limb muscle volume, compared with about 5.6 percent for the biceps brachii. The deltoid, a shoulder muscle, was slightly larger at about 15.2 percent. The sample was small, so treat these figures as approximate.

What Muscles Sit Underneath the Arm?

The armpit, or axilla, is bordered by chest, back and shoulder muscles rather than by arm muscles. The pectoralis major and minor form the front wall, while the subscapularis, teres major and latissimus dorsi form the back wall, and the serratus anterior covers the inner wall. The space also holds the axillary artery, the brachial plexus and lymph nodes. If you mean the underside of the upper arm instead, that is the triceps brachii.

Understanding arm muscles means seeing them as a connected system: compartments that group muscles, nerves that command them, arteries that feed them and small hand muscles that finish the job. We covered the regions of the limb, the front and back groups, how to read a diagram, everyday movements and the warning signs that deserve attention. If anything here raises a question about your own strength or sensation, please speak with a doctor, and explore our upper arm and forearm guides for the next level of detail.