Anatomy of Bones, Muscle groups, Nerves, and Extra, Diagram, Issues

The arms are the higher limbs of the physique. They’re among the most complicated and incessantly used physique elements.

Every arm consists of 4 fundamental elements:

Learn on to be taught extra concerning the bones, muscle tissue, nerves, and vessels of the higher arm and forearm, in addition to widespread arm issues it’s possible you’ll encounter.

Higher arm

The higher arm consists of the shoulder in addition to the world between the shoulder and elbow joint. The bones of the higher arm embody the:

  • Scapula. The scapula can also be known as the shoulder blade. It’s a triangle-shaped flat bone that’s related to the physique by largely muscle. It attaches the arm to the torso.
  • Clavicle. The clavicle can also be known as the collarbone. Just like the scapula, it attaches the arm to the torso. It additionally helps to distribute pressure from the higher a part of the arm to the remainder of the skeleton.
  • Humerus. The humerus is a protracted bone within the higher arm. It’s positioned between the scapula and the elbow joint. Many muscle tissue and ligaments within the arm are connected to the humerus.

The higher arm additionally accommodates a number of joints, together with the:

  • Acromioclavicular joint. The scapula and the clavicle meet at this joint.
  • Glenohumeral joint. That is the joint the place the scapula and humerus meet.
  • Sternoclavicular joint. The clavicle connects to the sternum (breastbone) at this joint.


The forearm is the world between the elbow joint and the wrist. Its two main bones are the radius and the ulna:

  • Radius. The radius is positioned on the aspect of the forearm closest to the thumb. It twists across the ulna and may change its place relying on how the hand is moved. There are a lot of muscle tissue connected to the radius that support in motion of the elbow, wrist, and finger joints.
  • Ulna. The ulna runs parallel to the radius. It’s on the aspect of the forearm that’s closest to the pinky finger. Not like the radius, the ulna is stationary and doesn’t twist.

Elbow joint

The elbow joint is the place the humerus bone of the higher arm connects with the radius and ulna bones within the forearm.

The elbow joint is definitely composed of three separate joints:

  • Ulnohumeral joint. That is the place the humerus connects to the ulna.
  • Radiocapitellar joint. At this joint, the radius connects to an space of the humerus known as the capitellum.
  • Proximal radioulnar joint. This joint connects the radius and ulna, permitting for rotation of the arms.

The higher arm accommodates two compartments, generally known as the anterior compartment and the posterior compartment.

Muscle motion

Earlier than studying concerning the completely different muscle tissue, it’s essential to know the 4 main sorts of motion they’re concerned in:

  • Flexion. This motion brings two physique elements nearer collectively, such because the forearm and higher arm.
  • Extension. This motion will increase the area between two physique elements. An instance of that is straightening the elbow.
  • Abduction. This refers to transferring a physique half away from the middle of the physique, akin to lifting the arm out and away from the physique.
  • Adduction. This refers to transferring a physique half towards the middle of the physique, akin to bringing the arm again in so it rests alongside the torso.

Anterior compartment

The anterior compartment is positioned in entrance of the humerus, the principle bone of the higher arms.

The muscle tissue of the anterior compartment embody:

  • Biceps brachii. Also known as the biceps, this muscle accommodates two heads that begin at the back and front of the shoulder earlier than becoming a member of collectively on the elbow. The top close to the elbow flexes the forearm, bringing it towards the higher arm. The 2 heads close to the shoulder assist with flexion and adduction of the higher arm.
  • Brachialis. This muscle lies beneath the biceps. It acts as a bridge between the humerus and ulna, one of many fundamental bones of the forearm. It’s concerned with the flexing of the forearm.
  • Coracobrachialis. This muscle is positioned close to the shoulder. It permits adduction of the higher arm and flexion of the shoulder. It additionally helps to stabilize the humerus inside the shoulder joint.

Posterior compartment

The posterior compartment is positioned behind the humerus and consists of two muscle tissue:

  • Triceps brachii. This muscle, normally known as the triceps, runs alongside the humerus and permits for the flexion and extension of the forearm. It additionally helps to stabilize the shoulder joint.
  • Anconeus. It is a small, triangular muscle that helps to increase the elbow and rotate the forearm. It’s typically thought-about to be an extension of the triceps.

The forearm accommodates extra muscle tissue than the higher arm does. It accommodates each an anterior and posterior compartment, and every is additional divided into layers.

Anterior compartment

The anterior compartment runs alongside the within of the forearm. The muscle tissue on this space are largely concerned with flexion of the wrist and fingers, in addition to rotation of the forearm.

Superficial layer

  • Flexor carpi ulnaris. This muscle flexes and adducts the wrist.
  • Palmaris longus. This muscle helps with flexion of the wrist, although not everybody has it.
  • Flexor carpi radialis. This muscle permits for flexion of the wrist along with abduction of the hand and wrist.
  • Pronator teres. This muscle rotates the forearm, permitting the palm to face the physique.

Intermediate layer

  • Flexor digitorum superficialis. This muscle flexes the second, third, fourth, and fifth fingers.

Deep compartment

  • Flexor digitorum profundus. This muscle additionally helps with flexion of the fingers. As well as, it’s concerned with transferring the wrist towards the physique.
  • Flexor pollicis longus. This muscle flexes the thumb.
  • Pronator quadratura. Just like the pronator teres, this muscle helps the forearm rotate.

Posterior compartment

The posterior compartment runs alongside the highest of the forearm. The muscle tissue inside this compartment enable for extension of the wrist and fingers.

Not like the anterior compartment, it doesn’t have an intermediate layer.

Superficial layer

  • Brachioradialis. This muscle flexes the forearm on the elbow.
  • Extensor carpi radialis longus. This muscle helps abduct and lengthen the hand on the wrist joint.
  • Extensor carpi radialis brevis. This muscle is the shorter, wider counterpart to the extensor carpi radialis longus.
  • Extensor digitorum. This muscle permits for the extension of the second, third, fourth, and fifth fingers.
  • Extensor carpi ulnari. This muscle adducts the wrist.

Deep layer

  • Supinator. This muscle permits the forearm to rotate outward so the palm faces up.
  • Abductor pollicis longus. This muscle abducts the thumb, transferring it away from the physique.
  • Extensor pollicis brevis. This muscle extends the thumb.
  • Extensor pollicis longus. That is the longer counterpart to the extensor pollicis brevis.
  • Extensor indices. This muscle extends the index finger.

Discover the interactive 3-D diagram under to be taught extra concerning the arm.

Brachial plexus

The brachial plexus refers to a gaggle of nerves that serve the pores and skin and muscle tissue of the arm. It begins within the backbone and runs down the arm.

The brachial plexus is split into 5 completely different divisions:

  • Roots. That is the start of the brachial plexus. The 5 roots are shaped from the spinal nerves C5, C6, C7, C8, and T1.
  • Trunks. Three trunks kind the brachial plexus roots. These embody the superior, center, and inferior trunks. The superior trunk is a mixture of the C5 and C6 roots, the center trunk is a continuation of the C7 root, and the inferior trunk is a mixture of the C8 and T1 roots.
  • Divisions. Every of the three trunks accommodates an anterior and posterior division, that means there are six divisions in complete.
  • Cords. The anterior and posterior divisions of the brachial plexus mix to kind three cords, generally known as the lateral, posterior, and medial cords.
  • Branches. The branches of the brachial plexus go on to kind the peripheral nerves that provide the arm.

Peripheral nerves

The peripheral nerves of the arm present motor and sensory features to the arm.

The six peripheral nerves of the arm embody the:

  • Axillary nerve. The axillary nerve travels between the scapula and humerus. It stimulates the muscle tissue within the shoulder space, together with the deltoid, the teres minor, and a part of the triceps.
  • Musculocutaneous nerve. This nerve travels in entrance of the humerus and stimulates the biceps, brachialis, and coracobrachialis muscle tissue. The musculocutaneous nerve additionally gives sensation to the skin of the forearm.
  • Ulnar nerve. The ulnar nerve is positioned on the skin of the forearm. It stimulates many muscle tissue within the hand and gives sensation to the pinky finger and a part of the ring finger.
  • Radial nerve. The radial nerve travels behind the humerus and alongside the within of the forearm. It stimulates the triceps muscle of the higher arm in addition to muscle tissue within the wrist and hand. It gives sensation to a part of the thumb.
  • Median nerve. The median nerve travels alongside the within of the arm. It stimulates many of the muscle tissue within the forearm, wrist, and hand. It additionally gives sensation for a part of the thumb, the forefinger, center finger, and a part of the ring finger.

Every arm accommodates a number of essential veins and arteries. Veins carry blood towards the guts, whereas arteries transport blood from the guts to different areas of the physique.

Under are among the fundamental veins and arteries of the arm.

Higher arm blood vessels

  • Subclavian artery. The subclavian artery provides blood to the higher arm. It begins near the guts and travels below the clavicle and to the shoulder.
  • Axillary artery. The axillary artery is a continuation of the subclavian artery. It may be discovered below the armpit and provides blood to the shoulder space.
  • Brachial artery. The brachial artery is a continuation of the axillary artery. It travels down the higher arm and splits into the radial and ulnar artery on the elbow joint.
  • Axillary vein. The axillary vein transports blood to the guts from the world of the shoulder and armpit.
  • Cephalic and basilic veins. These veins journey upward via the higher arm. They finally be a part of the axillary vein.
  • Brachial veins. The brachial veins are giant and run parallel to the brachial artery.
  • Radial artery. That is one in every of two arteries that provide blood to the forearm and hand. It travels alongside the inside aspect of the forearm.
  • Ulnar artery. The ulnar artery is the second of the 2 vessels supplying blood to the forearm and hand. It travels alongside the skin of the forearm.
  • Radial and ulnar veins. These veins are located parallel with the radial and ulnar arteries. They be a part of the brachial vein on the elbow joint.

Forearm blood vessels

As two of essentially the most closely used physique elements, the arms are weak to a wide range of well being issues. Right here’s a have a look at among the fundamental ones.

Nerve accidents

The nerves of the arm will be injured in a wide range of methods, together with stretching, pinching, or a lower. These accidents can happen slowly over time or shortly resulting from some kind of trauma.

Whereas the particular signs of a nerve harm rely upon the placement and nature of the harm, basic signs embody:

  • ache, which will be on the web site of the harm or wherever alongside the nerve
  • a sensation of numbness or tingling within the arm or hand
  • weak spot in or across the affected space

Some examples of nerve situations of the arm embody carpal tunnel syndrome and medial tunnel syndrome.


A fracture happens when bone cracks or breaks resulting from an harm or trauma. Any bone within the higher arm or forearm will be fractured.

Signs of a fractured bone within the arm embody:

  • ache or tenderness within the arm
  • swelling of the arm
  • bruising on the web site of the harm
  • a restricted vary of arm movement

Joint issues

The joints of the higher arm and forearm, such because the shoulder and elbow, will be affected by a wide range of issues. Repeated use, accidents, and irritation can all trigger joint points.

Some basic signs of an arm joint downside might embody:

  • ache within the affected joint
  • restricted vary of movement or stiffness within the affected joint
  • irritation or swelling of the affected joint

Examples of arm joint issues embody arthritis, tennis elbow, and bursitis.

Vascular issues

Vascular issues within the arms are much less widespread than they’re within the legs.

After they do happen, they are often brought on by a wide range of situations, together with plaques on the partitions of the arteries (atherosclerosis) or blocking of an artery by one thing like a blood clot.

Signs of a vascular situation affecting the arm embody:

  • ache, cramping, or discomfort within the affected arm
  • a sense of weak spot within the affected arm
  • a sensation of heaviness within the affected arm

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