Anatomy - Brachial Plexus
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Describe the Brachial Plexus
- The brachial plexus supplies innervation of the upper limb.
- Consists of nerves derived from the anterior rami of the lower four cervical and the first thoracic spinal nerves.
- The five roots (anterior rami) give rise to three trunks (superior, middle, and inferior) that emerge between the scalenus medius and scalenus anterior to lie on the floor of the posterior triangle of the neck.
- Each trunk divides onto an anterior and a posterior division behind the clavicle, at the apex of the axilla.
- Within the axilla, the processes combine to produce the three cords, which are named the lateral, medial, and posterior, according to their relationships to the axillary artery.
- Each cord ends near the lower border of pectoralis minor by dividing into two terminal branches.
What are the terminal branches of the brachial plexus?
- 5 main nerves of brachial plexus, in order laterally to medially "My Aunty Raped My Uncle" -
- Musculocutaneous N
- Axillary N
- Radial N
- Median N
- Ulnar N
Describe course and innervation of Musculocutaneous N.
- Terminal branch of the lateral cord.
- It pierces the coracobrachialis muscle and lies between biceps and brachialis, supplying both of these muscles.
- Continues distally as the lateral cutaneous nerve of the forearm, which pierces the deep fascia between biceps and brachioradialis to lie superficially over the cubital fossa.
Describe course and innervation of Median N.
- Derived from the lateral and medial cords
- Traverse the entire length of the arm, but no branches above the elbow joint.
- In the upper part of the arm, the nerve lies lateral to the brachial artery.
- At midarm level, crosses anterior to the
- vessels and lies medial to the brachial artery - continuous its path through the cubital fossa.
- The median nerve enters the forearm from the cubital fossa between the two heads of the pronator teres.
- Crosses anterior to the ulnar artery and descends between the superficial and
- deep flexors.
- At the wrist, the median nerve is superficial, lying medial to the tendon of flexor carpi radialis and just deep to the palmaris longus tendon.
Describe course and innervation of Ulnar N.
- Terminal branch of the medial cord.
- Together with the medial cutaneous nerve of the forearm, the nerve initially lies medial to the brachial artery but leaves the artery at midarm through the intermuscular septum.
- The nerve enters the posterior compartment, passes behind the medial epicondyle and enters the forearm between the two heads of flexor carpi ulnaris.
- It traverses the medial side of the anterior compartment, accompanied in the lower part of the forearm by the ulnary artery.
- The ulnar nerve emerges near the wrist lateral to the flexor carpi ulnaris tendon and crosses super-ficial to the flexor retinaculum with the ulnar artery on its lateral side.
- The nerve terminates in the hand by dividing into superficial and deep branches.
- UN supplies the elbow joint and gives branches to the flexor carpi ulnaris and the medial part of flexor digitorum profundus.
- Also provides palmar cutaneous nerve that supplies the skin on the medial aspect of the palm and dorsal cutaneous branches that innervate part of the medial part of the dorsum of the hand.
Describe course and innervation of Radial N.
- Terminal branch of the posterior cord
- Leaves the axilla by passing
- below teres major and between the humerus and the long head of the
- The nerve passes between the medial and lateral heads of triceps in the posterior compartment. It then leaves the posterior compartment by piercing the lateral intermuscular septum to reach the lateral part of the cubital fossa in front of the elbow joint.
- In the arm, the radial nerve gives muscular branches to the medial and lateral heads of triceps and branchioradialis and extensor radialis longus.
- Cutaneous branches innervate the lateral
- aspect of the arm and the posterior aspect if the forearm.
- The branch to the long head of triceps usually arises in the axilla.
Describe/Draw Innervation of Brachial Plexus
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