Brachial plexus anatomy - Course and divisions

Roots, divisions and cords

Which nerve roots compose the upper trunk of the brachial plexus?

C5-C6

Which nerve roots compose the middle trunk of the brachial plexus?

C7

Which nerve roots compose the lower trunk of the brachial plexus?

C8-T1

Which nerve fibres compose the brachial plexus?

all fibres of C5-T1 roots from anterior rami that remain after supplying prevertebral + scalene muscles

How do the roots of the brachial plexus enter the neck?

The roots enter the neck by passing between the scalenus medius and scalenus anterior - into and along the floor of the floor of the posterior triangle of the neck

Where do the roots of the brachial plexus combine to form trunks?

In the anterior triangle of the neck

What are the borders that define the anterior triangle of the neck?

Ant - posterior border of SCM

post - ant border of trap

inf - middle 1/3 of clavicle

floor - scalenes, levator scapulae, splenius capitis

Where do the divisions lie?

behind the clavicle - each trunk divides into two divisions - 3 ant and 3 post. Ant/post status is determined by relation to second part of axillary artery - approach and embrace - ant passes ant, post passes post

How does the brachial plexus enter the axilla?

Cords enter axilla above the first part of the axillary artery

Where to the cords lie?

in the axilla

What is the spatial relationship between brachial plexus and axillary artery

cords enter axilla above axillary artery, approach and embrace second part - divisions are labelled according to ant + post relation to 2nd part of axillary artery

What is the associate motor action of and ant post divisions?

Ant provide motor to flexors, post provides motor to extensors

How does brachial plexus combine into cords?

In axilla

upper two divisions - lateral cord

all 3 posterior divisions - posterior cord

lower division - medial cord