Human Anatomy - Upper Limb 4

Human Anatomy - Upper Limb 4 (Anterior & Posterior Compartments of Arm)

• The arm is enclosed by deep fascia.
• Two intermuscular septa, one on each side (medial & lateral), extend inward from the fascia and connect to the medial & lateral supracondylar ridges of the humerus.
• These septa divide the arm into anterior & posterior compartments.

Contents of Anterior Compartment

• Muscles: Biceps brachii, coracobrachialis, and brachialis muscles.
• Blood vessels: Brachial artery and its branches.
• Nerves: Musculocutaneous, median, and ulnar nerves.

Muscles of the Anterior Compartment

• Biceps brachii: Three flexors
• Brachialis
• Coracobrachialis
• Supplied by the musculocutaneous nerve.

1- Biceps Brachii Muscle

• Origin: Supraglenoid tubercle of scapula (long head), coracoid process of scapula (short head).
• Insertion: Bicipital tuberosity of radius & bicipital aponeurosis into the deep fascia of the medial forearm.
• Action: Strong supinator of the forearm, flexor of the elbow joint, and weak flexor of the shoulder joint.

2- Coracobrachialis Muscle

• Origin: Coracoid process of scapula.
• Insertion: Middle of the medial side of the humerus shaft.
• Action: Flexes the arm at the shoulder joint; weak adductor.

3- Brachialis Muscle

• Origin: Lower half of the anterior surface of the humerus.
• Insertion: Coronoid process of ulna (ulnar tuberosity).
• Action: Strong flexor of the elbow joint.

Arteries of the Arm

• Axillary Artery: The continuation of the subclavian artery; becomes the brachial artery.
• Brachial Artery: Supplies the entire upper arm; divides into radial & ulnar arteries.
• Branches: Profunda brachii artery(important branch), radial collateral artery, middle collateral artery.

Brachial Artery

• Origin: Lower border of the teres major.
• Relations: Superiorly, overlapped by coracobrachialis and biceps muscles. Medially related to the median nerve and bicipital aponeurosis in the middle and lower part. Posteriorly related to triceps and brachialis muscles. Laterally related to the upper part of the ulnar nerve & basilic vein.

Branches of the Brachial Artery

• Profunda brachii artery: Arise near origin of brachial artery; runs into spiral groove of humerus and supplying the triceps muscle.
• Sup. Ulnar Collateral artery: Arises at middle of the arm & supplies post compartment.
• Inf. Ulnar Collateral artery: Arises near termination of brachial artery and forms anastomosis around elbow joint.

Nerves of the Anterior Compartment of Arm

• Musculocutaneous nerve: Originates from lateral cord of brachial plexus, pierces coracobrachialis muscle and passes between biceps brachii and brachialis muscles. It then descends as the lateral cutaneous nerve of forearm on the lateral aspect of the forearm.
• Branches: Muscular branches to coracobrachialis, biceps and brachialis muscles; cutaneous branch (lateral cutaneous nerve of forearm), and articular branches to elbow joint.

Injury to the Musculocutaneous Nerve

• Usually caused by lesions of the lateral cord. Leads to greatly weakened flexion of the elbow, and supination of the forearm. This may also be accompanied by anesthesia on the lateral aspect of the forearm.

Median Nerve

• Origin: Medial and lateral cord of brachial plexus in axilla.
• Course: Lies at upper arm, laterally to brachial artery. At mid-arm, crosses front of brachial artery. At elbow joint, crosses bicipital aponeurosis; becomes medial to brachial artery.
• Branches: It gives off no branches in the arm, except for a small vasomotor nerve for brachial artery.

Ulnar Nerve

• Origin: Medial cord of brachial plexus.
• Course: Runs along the medial side of brachial artery. Crosses the medial intermuscular septum. Enters the posterior compartment in middle of arm. Accompanied by sup. ulnar collateral artery; passes behind medial humeral epicondyle.
• Branches: It gives off no branches in the anterior compartment of the arm.

Contents of Posterior Compartment of Arm

• Contains: Triceps muscle, radial and ulnar nerves, & profundus brachii & ulnar collateral vessels.

• Triceps muscle: A large muscle on the back of the arm with three heads.

• Long head: arises from infraglenoid tubercle of scapula.

• Lateral head: arises from upper half of the posterior surface of humerus, above the spiral groove.

• Medial head: arises from lower half of the posterior surface of humerus, below the spiral groove. All parts unite to insert into the upper border of the olecranon process of ulna.

Radial Nerve

• Entry: Enters posterior compartment of the arm between long & medial heads of triceps.
• Course: Runs in the spiral groove of the humerus, passes between lateral & medial heads of triceps. Then passes into posterior compartment, lateral fascial septum in front of elbow.
• Branches: Muscular branches to medial & long heads of triceps, and posterior cutaneous nerve of the arm. Supplies the posterior compartment of forearm.

Cubital Fossa

• A triangular depression anterior to the elbow.
• Boundaries: Laterally: brachioradialis; Medially: pronator teres; Imaginary line drawn between epicondyles.
• Contents: Median nerve, bifurcation of the brachial artery, biceps tendon, lateral cutaneous nerve of the forearm, radial nerve and its deep branch.