DR2. Arm and brachial plexus Flashcards
How many flexor muscles are found in the anterior compartment of the arm
Three flexor muscles are found in the anterior compartment of the arm. One of these
muscles is a flexor at the shoulder joint, one a flexor at the elbow joint, and the third is a flexor at both the shoulder and elbow joint.
Largest muscle in the anterior compartment
- Biceps brachii
Biceps brachii - origin
- The long head has an origin from the supraglenoid tubercle of the scapula, and the short head from the coracoid process of the scapula
Path of the long head of biceps brachii
- Long head emerges out of the joint capsule and continues down the intertubercular sulcus(bicipital groove)
What do the two heads of biceps brachii unite to form
- Unite to form a large muscle that inserts by a flattened tendon into the tuberosity of the radius
What is the bicipital aponeurosis and what is its path
- An expansion of the tendon of the biceps
- It crosses medially over the superficial flexors of the forearm and attaches to the posterior border of the ulna via the deep fascia
Biceps - action
- As biceps crosses both the shoulder joint and the elbow joint, it exerts its flexor action on both joints
- Biceps is also a very powerful supinator of the forearm
Coracobrachialis - origin
- Coracoid process
- Short head of biceps and the tendon of coracobrachialis have a common origin which forms a conjoint tendon
Coracobrachialis - insertion
- Medial aspect of the humerus half way down the shaft
Brachialis - origin
- Origin from the distal half of the anterior of the humerus
Brachialis - insertion
- Inserts into the ulna tuberosity
Triceps brachii - origin
- Long head has an origin from the infraglenoid tubercle of the scapula
- The lateral head from the posterior aspect of the humerus above the spiral or radial groove of the humerus
- The medial head again from the posterior surface of the humerus but below the spiral groove
Triceps brachii - insertion -
- The three heads unite to insert into the olecranon process of the ulna
Brachial plexus - nerve roots
- C5, C6, C7, C8 and T1
Brachial plexus - trunks
- Superior (or upper), middle and inferior (or lower)
Brachial plexus - cords
- Lateral, medial and posterior (due to their relationship with axillary artery)
What does the lateral cord give rise to
- Lateral pectoral nerve
- Terminal branches of the lateral cord are the lateral head of the median nerve and the musculocutaneous nerve
Where does the musculocutaneous nerve pierce coracobrachialis
- Approx 5cm distal to the conjoint tendon
Terminal branch of musculocutaneous nerve and what does it innervate
- Lateral cutaneous nerve of the forearm, which supplies the skin of the lateral forearm on both the dorsal and ventral aspects
What does the medial cord give rise to
- Medial pectoral nerve
- Cutaneous nerves of the arm and forearm
- The terminal branches of the medial cord are the medial head of the median nerve and the ulnar nerve
What does the ulnar nerve innervate
- Gives a limited supply to the flexor muscles of the forearm and is the main supply to the small muscles of the hand
Location of ulnar nerve
- Lies medial to the brachial artery in the arm and passes behind the medial epicondyle of the humerus at the elbow joint (the cubital tunnel) to gain access to the forearm
- It can easily be damaged at the region of the medial epicondyle. At this point, if it is hit, it may cause shooting sensation that radiates down the forearm to the little and ring fingers
What does the median nerve receive contributions from
- Receives contributions from both lateral and medial cords
What does the median nerve innervate
- Supplies almost all of the muscles of the anterior compartment of the forearm
