THE ARM

ARM
This is the part of the upper limb that lies between the shoulder and elbow joints. The bone of the arm is the humerus. The muscles of the arm are arranged in two compartments: The anterior and posterior compartments. The muscles present in the anterior compartment include:
· Bicep brachii
· Coracobrachialis
· Brachialis
In the posterior compartment is present one muscle known as the Tricep brachii.

BICEP BRACHII
ORIGIN: The bicep brachii arises by means of two heads as follows:
· Long head arises from supraglenoid tubercle forming its own belly
· Short head arises from the tip of coracoid process forming also its own belly
Both bellies will unite towards the lower aspect of the arm to become one and forms a tendon which passes through the cubital fossa to be inserted into the radial tubercle of the radius. It forms a though fascia known as bicipital aponeurosis which blends with the deep fascia of the upper medial aspect of the forearm.
Action: powerful supinator muscle of the forearm and flexor of the elbow joint.
Nerve supply: musculocutaneous nerve.

CORACOBRACHIALIS
Origin: Arises from the coracoid process.
Insertion: Medial part of the middle aspect of the humerus.
Nerve supply: Musculocutaneous nerve.
Action: Weak flexor of the shoulder joint, abductor muscle of the arm.


BRACHIALIS:
ORIGIN: Arises from the anterior surface of the lower half of the humerus.
Insertion: it is inserted into the ulnar tuberosity.
Nerve supply: Musculoctaneous nerve and radial nerve.
Action: It is the main flexor of the elbow joint. It is mainly used in smooth motions of the elbow joint like picking up a glass of wine or sipping a cup of hot tea.

TRICEP MUSCLE
It is the posterior compactment muscle which arises by means of three heads the long head, medial head and lateral head.
Origin:
Long head arises from infraglenoid tubercle; lateral head arises from the shaft above the upper lip of the radial groove while the medial head arises from the shaft of the humerus below the radial groove. In between the two origins along the spiral groove runs the radial nerve and profounda brachii artery.
The three muscle heads will later fuse to form one muscle belly at the lower 1/3rd of the humerus. Their common tendon is inserted into the tip of the olecranon process of the ulnar bone.
Nerve Supply: Radial nerve.
Action: Extension at the elbow joint and at the shoulder joint.