Hey this is Jack at AnatomyZone and in this tutorial we're going to go through the anatomy of the biceps brachii muscle
The biceps or biceps brachii is the most superficial muscle of the anterior compartment of our arm it extends from the scapula superiorly to the proximal forearm inferiorly. It sits above the two other muscles within the anterior compartment of the arm the coracobrachialis and the brachialis muscles. Our biceps has two heads, it has a long head and a short head and it's known as a bi-articular muscle because it extends across two joints the shoulder joint and the elbow joint
Let's begin with its origin; the short head of biceps originates at the coracoid process and that is this anterior projection that comes off of the scapula. The long head originates at the supraglenoid tubercle. Here is the tubercle just with the biceps removed. The supraglenoid tubercle is found as a bump at the most superior aspect of the glenoid fossa and the glenoid fossa is on the scapula and that houses the humeral head to form the shoulder joint. So the long head of biceps then passes underneath the transverse humeral ligament. The transverse humeral ligament essentially braces the long head tendon within this which is the bicipital groove . The long head of biceps runs through the bicipital groove which is held in place by the transverse humeral ligament and that bicipital groove is found between the Greater and Lesser tubercles of the humerus.
Just as a quick aside, the biceps brachii as I said has these two heads but it's one of the most variable muscles and the most common variant is that of a third head which is typically found next to the short set of biceps and that's found in about 10% of us and actually there are even rarer cases of four or five or more heads of the biceps being noted in people
From their origin those two heads then join to form a common muscle belly and then they attach through a common tendon into the radial tuberosity so the radial tuberosity is on the proximal and medial aspect of the radius bone and again it's been noted that in up to 40 percent of people that distal biceps tendon remains persistently divided so that in actual fact there are two separate tendons attaching into the radial tuberosity. As a final note some would also argue the biceps brachii inserts to the bicipital aponeurosis. This is a flat tendon sheet that comes off of the distal biceps tendon to provide reinforcement to an anatomical area on the front of the elbow that's called the cubital fossa.
What the bicipital aponeurosis is doing is predominantly providing protection to the structures underlying it. The big ones are the brachial artery and the median nerve as they run underneath the bicipital aponeurosis.
In terms of its action the biceps brachii performs flexion of our elbow and it's also a very powerful supinator of the forearm
Because it crosses the elbow and the shoulder and it's bi-articular it should therefore exert some effect on the shoulder and in most textbooks that's written as flexion of the shoulder but what we found this that actually what the biceps is doing is more of a dynamic stability role so rather than actually producing flexion of the shoulder it's providing support to the front of the shoulder as you start to flex your arm. That is stated to be sort of within the first 30 degrees or so.
Considering the nerve supply to the biceps muscle its innervated by the musculocutaneous nerve. The musculocutaneous nerve originates from the lateral cord of the brachial plexus and that lateral cord is made up of the anterior ramus of the cervical nerve roots c5 c6 and c7. Now if we just look at the musculocutaneous nerve in isolation you can actually see that it runs underneath the biceps brachii muscle and above the brachialis and coracobrachialis muscles to innervate the bicepss.
The biceps receives its blood supply from the brachial artery. This is the major blood vessel of the upper arm and it lies underneath the biceps muscle and it begins essentially as a continuation of the axillary artery. As the axillary artery reaches the lower margin of the teres major muscle, it then continues on as the brachial artery; that then runs to supply the biceps muscle.
As a quick clinical point a clinically relevant condition to the biceps will be that of a tendon rupture; this can occur either proximally at the bicipital groove where the long head of biceps originates or at the radial tuberosity where the distal tendon of the biceps inserts. So if you rupture the long head of biceps then you may not get that much reduction in power because you've still got the presence of the short head. But of course if you rupture the distal biceps tendon at the radial tuberosity then you will lose power in flexion and significantly in supination and so those ruptures of the distal biceps tendon do need surgery. The long head of biceps can be managed non-operatively and these patients present with the clinical finding of asymmetry between their two heads which is known as Popeye's sign.