Nerves of the Brachial plexus Flashcards
Which five nerve roots form the brachial plexus?
C5,C6,C7,C8 and T1. This may vary in individuals and start one root earlier or one later (C4 or T2).
What is the first section of the brachial plexus and how many of them are there?
There are the 3 trunks. There are the superior, middle and inferior trunks.
Which nerve roots feed into these 3 trunks?
C5 and C6 fuse together to form the superior trunk. C7 alone makes up the middle trunk whilst C8 and T1 make up the inferior trunk.
How do the 3 trunks change to form the divisions?
Each of the three trunks splits into two branches, one being called the anterior division and the other being called the posterior division.
How do the 6 divisions now change to form the cords?
anterior division of superior and middle trunk= lateral cord. anterior division of inferior trunk alone= medial cord all three posterior divisions= posterior cord
How do the 3 cords now branch off to form the nerves?
Lateral cord splits = laterally (musculocutanous nerve) Medial cord splits= medially (ulnar nerve) 2nd branch of lateral cord + 2nd branch of medial cord= median nerve Posterior cord splits= axillary nerve and radial nerve
Name all the nerves of the brachial plexus and whether they innervate the anterior or posterior side of the arm.
Anterior of arm= Musculocutaneous nerve, median nerve, and ulnar nerve. Posterior of arm= Axillary nerve and radial nerve.
Draw the structure of the brachial plexus.
Refer to the diagram
Where is the brachial plexus with respect to the clavicle?
The roots and trunks are supra clavicular whilst the divisions and cords are infra clavicular.
Where is the musculocutaneous nerve and what structures does it innervate?
The musculocutaneous nerve arises from the lateral cord. It pierces coracobrachialis and sits between the it, the biceps and the brachialis muscle. It innervates all three of them.
The musculocutaneous nerve travels distally,pass the elbow and into the lower forearm. Here it changes name and becomes the lateral cutaneous nerve. It now supplies the lateral skin of the forearm.
Where is the ulnar nerve located and what structures does it innervate?
The ulnar nerve originates from the medial cord.
It has no branches in the upper arm. Instead it passes behind the medial epicondyle (this is where the funny bone phenomonon occurs).
It enters the forearm and innervates flexor carpi ulnaris and flexor digitorum profundus muscles.
In the hand, the ulnar nerve innervates the skin of the medial 1 and a half digits.
The ulnar nerve does not pass through the flexor retinaculum, instead bypassing it via the Guyon’s canal.
The ulnar nerve innervates all of the hand, except for the muscles that median nerve innervates.
Where is the median nerve found and what structures does it innervate?
The median nerve starts medially and crosses over the brachial artery. It passes the elbow joint through the cubital fossa.
It innervates all the muscles of the forearm except what the ulnar nerve innervates (carpi ulnaris and digitorum profundus). In the hand, it innervates the thenar muscles and the lateral 2 lumbricals.
The median nerve innervates the skin of the lateral 3 digits.
Considering the posterior upper limb nerves, what is the major landmark that enables us to find them?
Teres major- the nerve that comes off above it (above meaning into the quandrangular space) is the axillary nerve and the nerve that comes off below it (into the triangular space) is the radial nerve.
Where is the axillary nerve and what structures does it animate?
The Axillary nerve innervates the teres minor and deltoid muscles and the skin over the deltoid muscles in the area refered to as the ‘regimental badge’ area.
Where is the radial nerve and what structures does it innervate?
The radial nerve innervates most of the posterior upper and forearm. It is **innervated by all 5 roots of the brachial plexus. **
The radial nerve crosses over the humerus diagonally, and innervates the triceps brachii heads.
Then the radial nerve passes the elbow joint via the cubital fossa and splits into two branches.
The deep branch becomes the posterior interosseous nerve, which innervates the extensor muscles.
Then the superficial branches of the radial nerve **innervate all the skin of the posterior arm and the back of the lateral 3 digits. **
