Brachialis

The Naming: -

The Naming: -
/BRAY-key-AL-is/
brachialis: meaning the arm (brachium [the arm]).

General: -

A muscle of the anterior compartment; it is posterior and deep to the Biceps Brachii; located in the half distal part of the arm and it belongs to the Muscles of the Elbow and Radioulnar Joints as while, the brachialis creates the floor of the cubital fossa.

Surface of the Brachialis: -

It is possible to view the muscle from the later border of the muscle.

surface anatomy

Supply: -

The blood supply comes from Brachial artery, radial recurrent artery, (occasionally) branches from the superior and inferior ulnar collateral arteries, The accessory arteries are small and highly variable. They can arise as branches from the brachial artery directly, the profunda brachii, or the superior and inferior ulnar collateral arteries. Venous drainage of the brachialis is by venae comitantes (Latin for accompanying vein), mirroring the arterial supply and ultimately drain back into the brachial veins.

The brachialis gets the nerve supply from the Musculocutaneous n. in addition, a small lateral portion of the muscle is innervated by the radial n.

Origin & Insertion: -

-It originates from Distal ½ of the Anterior Shaft of the humerus, just distal to the insertion of the deltoid muscle aside to that, the muscle attach to the intermuscular septa of the arm with more secure attachment to the medial septa.

-Inserted into Ulnar Tuberosity and the coronoid process of the ulna, passing between two slips of the flexor digitorum profundus muscle. It sometimes has an accessory attachment to the radius or the bicipital aponeurosis.

Motion & Action: (Flexion):

The Brachialis is the main flexor of the forearm and that’s the whole function of the Brachialis, there is no other actions for it; the Brachialis flex the forearm at all positions, not effected by the supination or pronation of the forearm or whether there is resistance or not, the brachialis always contracts when the elbow is flexed and is primarily responsible for sustaining the flexed position that’s why it is considered to be the workhorse of the elbow flexors, it does not act as a supinator nor a pronator due to its lack of attachment to the radius.
During controlled extension of the elbow joint, the brachialis steadies the movement by relaxing at an even pace. This is an eccentric contraction of the muscle. This motion is used for precision movements such as lowering a teacup onto a flat surface carefully. The brachialis is also responsible for holding the elbow in the flexed position, thus, when the elbow joint is flexed, the brachialis is always contracting.

The Flexing of the Brachialis (the yellow color is where the action at)

On Your Feet Notes/ In The Field Notes: -

To test the brachialis: -
The forearm is semi-pronated and flexed against resistance. If acting normally, the contracted muscle can be seen and palpated.

Clinical Note: -

-The brachialis is the main muscle acting in common upper body exercises such as pull ups and elbow curls and overuse of it during exercises such as these can cause inflammation in the tendon of the muscle. This is called brachialis tendonitis. Climbers elbow is a form of brachialis tendonitis that is extremely common in climbers. It is caused by forceful contractions of the brachialis muscle, especially when the elbow is hyperextended. A common cause of this injury in climbers is reaching (hyperextending the elbow) and then pulling their body weight upwards by flexing the elbow joint, such as in rock climbing.
-Brachialis Tendon Tear: Due to sudden movement of over use the tendon of the muscle may get weaken and rupture.

A Ruptured Brachialis tendon

Relations: -

Although most of the brachialis is deep to the biceps brachii, the lateral margin of the brachialis is superficial between the biceps brachii and the triceps brachii. More distally, the brachialis is superficial on both sides of the biceps brachii’s distal tendon. Deep to the brachialis is the shaft of the humerus.
The proximal attachment of the brachialis forms a V shape and surrounds the distal attachment of
the deltoid.
On the medial side, the triceps brachii is posterior to the brachialis.
On the lateral side, the triceps brachii is posterior to the brachialis proximally; the brachioradialis is
posterior to the brachialis distally.
The brachialis is located within the deep front arm line myofascial meridian.

Notes: -

1. The brachialis is a strong and fairly large muscle, which accounts for much of the contour of the biceps brachii being so visible. (“Behind every great biceps brachii is a great brachialis”.)
2. The biceps brachii attaches to the radial tuberosity whereas the brachialis attaches to the ulnar tuberosity.

Sources: -

- Moore - Clinically Oriented Anatomy 7th Edition.
- The Muscular System Manual: The Skeletal Muscles of the Human Body
Book by Joseph E Muscolino.
- Netter's Human Atlas anatomy 7th Edition.
-Brachialis Muscle -Ken Hub
- CASE REPORT: Traumatic rupture of the brachialis muscle in a 52-year-old man