Dominic Stone
The brachialis muscle is located in the upper arm, beneath the biceps brachii, and is responsible for flexing the elbow. The brachialis is the prime mover of elbow flexion, generating about 50% more power than the biceps. The musculocutaneous nerve, a major peripheral nerve of the upper limb, is the primary source of innervation for the brachialis muscle. However, in a significant portion of individuals, the brachialis exhibits dual innervation, receiving additional input from the radial nerve.
| Characteristics | Values |
|---|---|
| Muscle | Brachialis |
| Location | Anterior compartment of the upper arm |
| Function | Elbow flexion |
| Innervation | Musculocutaneous nerve, with contributions from the radial nerve |
| Nerve Roots | C5, C6, C7 |
| Blood Supply | Muscular branches of the brachial artery and the recurrent radial artery |
| Dual Innervation | 70-80% of people have dual innervation with the radial nerve |
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What You'll Learn
- The brachialis muscle is primarily innervated by the musculocutaneous nerve
- The nerve runs on the superficial surface of the brachialis muscle
- The musculocutaneous nerve is derived from the lateral cord of the brachial plexus
- In 70-80% of people, the brachialis muscle has dual innervation with the radial nerve
- The musculocutaneous nerve gives rise to the lateral cutaneous nerve of the forearm
The brachialis muscle is primarily innervated by the musculocutaneous nerve
The musculocutaneous nerve is a major peripheral nerve of the upper limb. It is derived from the lateral cord of the brachial plexus, a web of intersecting nerves that arises from the cervical region of the spinal cord. The musculocutaneous nerve typically receives fibres from the fifth, sixth, and seventh cervical nerve roots (C5, C6, and C7).
The musculocutaneous nerve gives articular branches to the humerus and the elbow. It then continues into the forearm as the lateral cutaneous nerve, providing sensory innervation to the lateral aspect of the forearm. This nerve is well-protected within the axilla, and injury is relatively uncommon. However, certain mechanisms of injury, such as penetrating trauma to the axilla or iatrogenic injury during shoulder surgery, can affect the musculocutaneous nerve.
In addition to the musculocutaneous nerve, the brachialis muscle also commonly receives innervation from the radial nerve. This dual innervation is observed in approximately 70-80% of people. The radial nerve branch penetrates the inferolateral part of the brachialis muscle in most cases. The presence of dual innervation suggests the fusion of two different embryonic muscular primordia: the ventral (flexor) and the dorsal (extensor) muscle masses.
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The nerve runs on the superficial surface of the brachialis muscle
The brachialis muscle is located deep within the upper arm, beneath the biceps brachii. It is responsible for flexing the arm at the elbow joint. The musculocutaneous nerve is the primary nerve that innervates the brachialis muscle. This nerve is a major peripheral nerve of the upper limb and is derived from the lateral cord of the brachial plexus. It typically receives fibres from the fifth, sixth, and seventh cervical nerve roots (C5, C6, and C7).
The musculocutaneous nerve runs on the superficial surface of the brachialis muscle, between it and the biceps brachii. It pierces the coracobrachialis muscle near its point of insertion on the humerus and then passes down the flexor compartment of the upper arm. The nerve innervates both the biceps brachii and the brachialis muscles and provides articular branches to the humerus and the elbow.
In addition to the musculocutaneous nerve, the brachialis muscle also receives innervation from the radial nerve in 70-80% of people, resulting in dual innervation. The radial nerve branch penetrates the inferolateral part of the brachialis muscle in most cases. This dual innervation may be attributed to the fusion of two different embryonic muscular primordia: the ventral (flexor) and the dorsal (extensor) muscle masses.
The brachialis muscle is supplied by muscular branches of the brachial artery and by the recurrent radial artery. It is occasionally doubled, with additional muscle slips found rarely. The brachialis muscle is the prime mover of elbow flexion, generating about 50% more power than the biceps muscle.
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The musculocutaneous nerve is derived from the lateral cord of the brachial plexus
The musculocutaneous nerve is a major peripheral nerve of the upper limb. It is a component of the brachial plexus, which is a network of intersecting nerves that arise from the cervical region of the spinal cord, specifically from nerve roots C5 through T1. The brachial plexus gives rise to nerves in the upper limbs, including the musculocutaneous nerve.
The musculocutaneous nerve innervates the brachialis muscle, along with the biceps brachii and coracobrachialis muscles. It provides motor functions to these muscles, allowing for flexion at the shoulder and elbow. The nerve also gives articular branches to the humerus and the elbow. Additionally, it contributes to the median nerve, which innervates the pronator teres and forearm flexor muscles.
The musculocutaneous nerve has a varied anatomical course and can interact with the median nerve, exchanging fibres. It may also pass through or under the coracobrachialis and/or the biceps brachii. In about 70-80% of people, the brachialis muscle has dual innervation, receiving additional input from the radial nerve.
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In 70-80% of people, the brachialis muscle has dual innervation with the radial nerve
The brachialis muscle is a muscle in the upper arm that flexes the elbow. It is innervated by the musculocutaneous nerve, which runs on its superficial surface, between it and the biceps brachii. The musculocutaneous nerve is a major peripheral nerve of the upper limb. It gives rise to the lateral cutaneous nerve of the forearm, which innervates the lateral aspect of the forearm.
The musculocutaneous nerve passes down the flexor compartment of the upper arm, superficial to the brachialis but deep to the biceps brachii muscle. It innervates both these muscles and gives articular branches to the humerus and the elbow. The nerve then pierces the deep fascia lateral to the biceps brachii to emerge lateral to the biceps tendon and brachioradialis.
However, in 70-80% of people, the brachialis muscle has dual innervation with the radial nerve. This was observed in a study of 45 male and 31 female cadavers, with an average age of 59 years. The radial nerve branch was found to penetrate the inferolateral part of the brachialis muscle in 83% of cases and its middle third in 17% of specimens. Another study of 70 specimens found that 72.14% of the brachialis muscles were innervated by the radial nerve.
The brachialis muscle contains a great deal of mechanoreceptors, and its innervation pattern means it plays a key role in proprioception concerning the elbow.
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The musculocutaneous nerve gives rise to the lateral cutaneous nerve of the forearm
The musculocutaneous nerve is a major peripheral nerve of the upper limb. It is derived from the lateral cord of the brachial plexus, receiving fibres from the fifth, sixth, and seventh cervical nerve roots (C5, C6, and C7). The musculocutaneous nerve innervates the brachialis muscle, along with the biceps brachii and coracobrachialis muscles.
The lateral cutaneous nerve of the forearm is responsible for the sensory functions of the musculocutaneous nerve. The musculocutaneous nerve itself has motor functions in the muscles of the anterior compartment of the arm, including the coracobrachialis, biceps brachii, and brachialis muscles. It also provides articular branches to the humerus and the elbow.
The musculocutaneous nerve is well-protected within the axilla, and injuries are relatively uncommon. However, penetrating trauma to the axilla, such as stabbing, or iatrogenic injury from heavy retraction during shoulder surgery, can result in damage to the nerve. The musculocutaneous nerve exhibits a varied anatomical course and can interact with the median nerve, exchanging fibres.
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Frequently asked questions
The brachialis muscle is primarily innervated by the musculocutaneous nerve.
The musculocutaneous nerve is a major peripheral nerve of the upper limb. It is derived from the lateral cord of the brachial plexus and typically receives fibres from the fifth, sixth, and seventh cervical nerve roots (C5, C6, C7).
The musculocutaneous nerve has motor and sensory functions. It innervates the coracobrachialis, biceps brachii, and brachialis muscles, and contributes to the median nerve, innervating the forearm flexor muscles.
In addition to the musculocutaneous nerve, the brachialis muscle also commonly receives innervation from the radial nerve. In 70-80% of people, the brachialis muscle has dual innervation with the radial nerve.
The brachialis muscle is the primary flexor of the elbow joint, generating about 50% more power than the biceps.
