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Core
The brachial plexus is a network of five spinal nerves that originates in the neck, passes through the axilla, and supplies the skin and musculature of the upper limb. It is divided into five parts: roots, trunks, divisions, cords and branches.
The nerves that contribute to the brachial plexus are the C5 (cervical nerve 5), C6, C7, C8 and T1 (thoracic nerve 1).
The terminal branches that are the outputs of the brachial plexus are the musculocutaneous nerve, the axillary nerve, the radial nerve, the median nerve and the ulnar nerve. These are also known as the peripheral nerves of the upper limb.
Diagram - The Brachial Plexus. The spinal roots are colour coded to make it easier to see which of the roots contribute to which terminal branches. It is important to note that the median nerve is anterior to the radial and axillary nerves (this is important to note when identifying the nerves in a specimen)
SimpleMed original by Dr. Maddie Swannack
Trying to remember which spinal nerves contribute to which peripheral nerve can be challenging. The brachial plexus story and corresponding hand signs can be handy tools to help.
The story is: “3 musketeers were assassinated by 5 rats, 4 mice and 2 unicorns” (This order can also be remembered by the acronym MARMU).
The first letters of the underlined words corresponding to the order of the peripheral nerves and the numbers corresponding to the hand signs.
For the hand signs, the fingers on one hand each represent an individual spinal nerve (with the thumb being C5 and the little finger being T1), meaning the story can be attached to specific finger positions to help remember which spinal nerves go into which peripheral nerve (see diagram and explanation below).
The first position is “3 Musketeers” - counting to 3 on the hand (thumb, index and middle finger). This represents the Musculocutaneous nerve, which has the nerve roots of C5, C6 and C7.
The second position is “assassinated” - shown by the finger gun (thumb and index finger). This represents the Axillary nerve, which has the nerve roots C5 and C6.
The third position is “by 5 Rats”, which is all 5 digits. This is for the Radial nerve, which has the nerve roots C5, C6, C7, C8, and T1.
The fourth position is “4 Mice”, which is the index, middle, ring and little fingers. This is for the Median nerve (M and M), which has the nerve roots C6, C7, C8 and T1.
The fifth position is “and 2 Unicorns”, which is the ring and little fingers. This is for the Ulnar nerve, which has the nerve roots C8 and T1.
Diagram - The ‘Brachial Plexus Story’. It is a method for remembering which spinal nerves contribute to which peripheral nerves with the aid of a story and hand position
SimpleMed original by Dr. Maddie Swannack
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