Extensor Carpi Radialis Longus

The extensor carpi radialis longus is a spindle-shaped muscle. It has a narrow tendon, which is much longer than its belly. The upper portion of this muscle is covered by the brachioradialis, while its distal part is crossed over by the abductor pollicis longus and the extensor pollicis brevis muscle.

The extensor carpi radialis longus muscle arises from the lateral epicondyle of humerus and the lateral intermuscular septum of upper arm. Then it extends downwards all along the lateral border of forearm, lying between the brachioradialis and the extensor carpi radialis brevis muscle. In the third distal portion of forearm, it becomes a narrow tendon, which runs under the extensor retinaculum. It is inserted into the base of the dorsal surface of the second metacarpal bone (of index finger side).

Action/Function

Despite its name "extensor", it is a weak flexor of the elbow-joint, assisting the brachialis muscle. It also extends the hand at the wrist joint, aiding in its abduction.

Innervation

It is innervated by the radial nerve (C5-C6-C7), which springs from the brachial plexus.

Blood Supply

The extensor carpi radialis longus muscle receives oxygenated blood from branches originating from the radial collateral and recurrent artery.

Below, two schematic pictures showing the radialis muscles of right forearm.

 

 

Extensor Digitorum

The extensor digitorum is a long bipennate muscle which is located near the medial border of posterior side of forearm. Having a spindle-shaped belly, it arises from the lateral epicondyle of humerus, the capsule of the elbow-joint, and the antebrachial fascia. Then the extensor digitorum runs downwards, along the full length of forearm. Being part of the superficial layer of muscles, it lies directly under the skin, stretching over the supinator, the abductor pollicis longus, and extensor pollicis longus muscle.

Before it reaches the distal third portion of forearm, the belly of extensor digitorum divides into four tendons which travel under the extensor retinaculum. Then these tendons are enclosed, together with the extensor indicis tendon, in a common synovial sheath. Finally, having reached the metacarpal bone, each one of the tendons ends in a tendinous expansion which fuses with the capsule of the metacarpophalangeal joint. Each one of the tendinous expansion in turn separates into three slips, with the lateral two being inserted into the base of the distal phalanx and the middle one into the base of the middle phalanx.

Action

This bipennate muscle of forearm extend the four fingers and assists the extension of hand at the wrist.

Innervation

The extensor digitorum muscle is innervated by the posterior interosseous branch of the radial nerve (C6-C7-C8).

Blood Supply

This muscle is supplied by branches of the posterior interosseous artery, which is arises from the common interosseous and this, from the ulnar.

Below, the superficial muscles of right forearm, showing the extensor muscles

Deep Muscles of Forearm

Most of the deep muscles of forearm are longitudinal, with exception of the pronator quadratus. Thus, most of them extend along the full length of the ulna and radius, from which they originate.

In this deep muscles layer, you can distinguish those lying on the anterior aspect of forearm right in front of the radius and ulna, hugging them, and those located posteriorly (behind these bones).

Anterior aspect: pronator quadratus, pronator teres, flexor pollicis longus, and flexor digitorum profundus. The first two ones, the pronators, pronates the forearm, that is to say, they rotate the forearm and hand; while the third and fourth ones flex the thumb and fingers respectively when you want to grasp something.

Posterior aspect: the abductor pollicis longus, which extends (abducts) the thumb at the wrist; extensor pollicis brevis; extensor pollicis longus, which extends the thumb; supinator, which supinates the forearm, and extensor indicis, which extends (stretches out) the index finger.

Diagram of transverse section cut across the middle of right forearm. Those that make up the deep layer are labeled with their names. The pronator quadratus is not shown here, because it lies in the distal (lower) end of forearm.

 

Anconeus

The anconeus is a triangular muscle of the proximal end of forearm. Lying behind and right below the elbow joint, it arises from the lateral epicondyle of the humerus. Then it extends obliquely downwards to be inserted into the upper fourth portion of the posterior surface of the shaft of the ulna, with its muscle fibers traveling slantingly and medially towards the ulna.

Action/Function

Abduction of the distal end of the ulna during pronation; hinge-like flexion and extension of the elbow joint.

Blood supply

The anconeus is supplied by small branches coming off the posterior interosseous recurrent and the ulnar recurrent artery.

Innervation

It is innervated by radial nerve.

Below, drawing of anconeus muscle, partially hidden by the flexor carpi ulnaris and other muscles.

 

Abductor Pollicis Longus

The abductor pollicis longus is a long skeletal muscle located in the posterior compartment of forearm. Flat and bipennate, it originates from the posterior surface of radius and ulna bone, underneath the supinator muscle. Then it travels obliquely and downwards, with its long tendon going around the distal end of radius and under the extensor retinaculum to be inserted into the base of the first metacarpal bone.

Action

The abductor pollicis longus abducts the thumb, drawing it anteriorly (backwards) away from the palm, reinforcing the extensor pollicis brevis muscle to extend the thumb.

Nerve and blood supply

It is innervated by fibers of the posterior interosseous nerve, which is a branch of the radial. It is supplied by the posterior interosseous artery, which is a branch of the common interosseous (and this latter springs from the ulnar artery).

Below, the image of forearm showing the abductor pollicis longus

 

Muscles Involved in Forearm Supination

The muscles involved in forearm supination and rotation are five in number. They cause the dextrous rotation of forearm and wrist and a twisting fashion. Human beings have been exerting fine and controlled rotatory movements of their forearm and wrist for hundreds of thousands of years, from twisting a spear shaft to sharpen its point, or an animal bone, in order to break off the tendons to dislodge it out of its carcass, to wield a rapier in parrying and thrusting or to turn a screwdriver or a socket wrench.

These five muscles that make possible this voluntary and nimble rotation of the human forearm and hand are the supinator, pronator quadratus, the pronator teres, the anconeus, and the biceps brachii muscle. They are located deep in the forearm and, superficially, in the arm. The use of these muscles, along with other muscles of the hand, have been closely related to the evolution of the cerebral cortex.

The supinator is a broad short muscle, with two heads, which arise from the humerus lateral epicondyle and the posterior surface of the ulna proximal end. Then it wraps around the head and neck and posterior surface of the radius to attach on the lateral surface of this bone. Function: it supinates (turns over) the forearm and hand, with the palm looking upwards. The supinator is supplied by the posterior interosseous nerve, which is deep branch of the radial nerve.

The pronator quadratus is a flat, short, and square muscle which stretches across the distal (lower) end of the radius and ulna bone. With strong aponeurosis (fibrous connective tissue), it originates from the oblique, linear ridge located on the anterior (front) surface of the ulna shaft, and crosses over the interosseous space to attach on the distal anterior surface of the radius bone. The pronator quadratus function is the pronation (rotation) of the hand. It is innervated by the anterior interosseous branch of the median nerve, and is supplied by small, side branches coming off the ulnar, radial, and anterior interosseous arteries.

The pronator teres is a flat and long muscle of the forearm, arising from the medial epicondyle (rounded bone projection) and supraepicondyle ridge of the humerus bone. Then it runs downwards and obliquely, crossing over the ulna, to attach on a rough area in the middle lateral surface of the radius. Function: it turns the radius over the ulna during pronation. It is innervated by the median nerve. It is supplied by branches from the radial, common interosseous, and ulnar artery.

The anconeus is flat and triangular in shape, arising from the lateral epicondyle of the humerus. It inserts in the posterolateral surface of the ulna. Function: it slightly abducts (separates) the ulna from the radius during pronation. The anconeus muscle is innervated by a branch of the radial nerve, and is supplied by branches from the recurrent radial and inferior ulnar collateral artery.

The biceps brachii is the largest and most powerful of the five upper limb muscles that rotate (pronate and supinate) the forearm and hand. The biceps is a supinator of the forearm. It is innervated by the musculocutaneous nerve (C5, C6), which originated from the brachial plexus.

Below, the main muscles involved in supination and pronation of the forearm and hand: supinator, pronator teres, and pronator quadratus.

 

Veganism and Health

Veganism and health is intimately related, but for the worst. The skin, eyes and facial appearance betrays the health condition of a human being. If you take a look at the faces of someone who has been a vegan for more than two or three years, you will see that you can get severely malnourished and your immune system in jeopardy. Yes, veganism is the diet that will put your health in danger of collapsing. It affects your brain and how you perceive yourself, not realizing that you really look like a ghastly wraith.

Not only do we have skeletal muscle mass to maintain but you must also feed a lot of calories and essential vitamins and minerals to your huge brain and complex immune system. All the tissues and organs in your body cannot be maintained on lettuce, carrot, strawberries and poems! To be in good health, Homo sapiens' body needs several essential elements which a vegan's diet lacks: vitamin B12, B6, A retinol, zinc, and, above all, essential amino acids, which our body cannot produce.

Vitamin B12 (extrinsic factor) is only found in meat, beef or chicken liver, egg yolk, cheese, and milk. It is key to the development of a nerve cell dendrite, axon and the myelin sheath that covers it. Vitamin B6 works together with B12; although it is also present in nuts, it is in meat where you can find it in enough quantity to supply you nervous system needs. Retinol is fat-soluble vitamin A, and the only type that can be fully and naturally absorbed into our body; it is found in great quantities in beef/chicken/fish liver, butter, codfish liver oil, and egg yolk as it is essential for your retina, immune system, and skin. Beta carotene vitamin A from carrot and pumpkin is not easily absorbed by our digestive system as you would need about 30 kg of carrot a day to supply half your daily needs for vitamin A. Retinol, on the other hand, is our natural way to consume vitamin A.

Aside from zinc, which is found in great quantities in red meat and mollusk, and vitamin A/B12, our immune system needs lysine, leucine, methionine, tryptophan, and valine, which are some of the essential amino acids that are obtained from animal proteins. For the production of ATP by the cell mitochondria, ketone bodies from animal fat are the best fuel. Contrary to carbohydrates, which produce a lot of harmful free radicals as byproducts, ketone bodies make the mitochondria run more efficiently and produce more ATP. Besides, animal fat does not raise your blood sugar at all, as carbs do; so, it is good for people who suffer from diabetes.