Let me introduce you to this amazing structure. It scares many people who learned it as medical or paramedical student, but to me it’s wonderful clever & beautiful. A triumph of developmental neurology and essential in all we do- let me introduce the brachial plexus via a thread 
The brachial plexus is a mixing and crossing of nerves (that’s what plexus means) which controls the whole arm (which is what brachial means). This beautiful picture was drawn by @artibiotics and is the map for our story.
You can feel yours in your neck- find your collar bone (it’s proper name is a clavicle) run your fingers along the top edge of it at the base of your neck. At about halfway along you will feel a cable running diagonally.
Tilt you head away to the other side and you will feel it get tight. That called Erbs point on the upper trunk. It is a starting point for another story but today we have this story:
The nerves of your brachial plexus grew out from your neck when you were only a few weeks old as an embryo. At that point your arm had already formed with bones and muscles but the nerves set out on their journey. This is one such:
Imagine the quest of a single nerve cell leaving its home in the spine and knowing she was heading for a muscle she knew was called Abductor pollicis brevis. In a land far far away - the hand. At the base of thumb mountain!
This nerve runs from her home at the T1 spine and joins with the exodus of many others over the fast flowing artery to form the lower trunk. This band of thousands half C8ers and half her T1 clan all running through new territory.
Starting to loose some T1 friends who settle staking claims to the land of the skin of the inner arm. Most though stay with her looking for muscles. She parts with some of her band at the next break in the road.
Choosing the path to get chosen land she breaks for the medial contribution to the Median. Joining with with wild clans of C6 and C7ers that she saw from over the river running their side of the bank.
They settle in nicely together till the elbow bend - a change, under the archway of Pronator she had heard tell of as a baby neurone. Again loosing some of their number to farm muscle in the upper arm.
Then some of her old C8er friends turned left and set off to go deeper drawn by the stories of the interosseous membrane. She kept on this long long journey.
Now much much longer than she ever thought she would be. She took a breather and looked back at her course. Her long course millions of times longer than she was wide. She still had such a strong connection with her home land at T1. She could feel it. But she must push on ...
Now the last part of her quest she grows further and into a deep tunnel. Bones under her and now and most of her T1ers have left her she bands with the C6 and C7ers heading for skin. She knows she is different.
She knows she is hugely important. Destined for great things. Set to change hand function from a primate grip and to give function to an opposable thumb. All of humanity will thank her. She will change the world...
She emerges from the track through the tunnel and knows the last turn is her. She rounds the corner and sees the promised land. Muscle fibres she has dreamt of. Much better than any she ever seen. She will make them hers and rule here for ever!
The end..
The end..
