Regional Exam I Flashcards
(95 cards)
What nerves compose the Brachial Plexus?
Mostly C5-C8 and T1
- some contributions from C4 and T2
Where do C5 and C6 rami unite?
medial border of the middle scalene
- forms the superior trunk of the plexus
What makes up the roots of the brachial plexus?
ventral rami
What nerve becomes the middle trunk of the brachial plexus?
C7
Which nerves make up the inferior trunk of the brachial plexus?
C8 and T1
What facilitates the US identification of the C7 nerve root?
C7 transverse process lacks an anterior tubercle
Where do the roots and trunks of the Brachial Plexus pass through?
interscalene groove
When do the 3 trunks of the brachial plexus undergo the first anatomic separation?
lateral border of the first rib
- anterior (flexor)
- posterior (extensor)
What parts form the lateral cord of the Brachial Plexus?
anterior divisions of the superior and middle trunks
What parts form the posterior cord of the Brachial Plexus?
posterior divisions of all 3 trunks
What parts form the medial cord of the Brachial Plexus?
anterior division of the inferior trunk
How many branches do the cords separate into?
2 major terminal branches and a variable number of minor intermediary branches
Innervation of lateral cord of the Brachial Plexus
musculocutaneous nerve and lateral component of median nerve
Innervation of posterior cord of the Brachial Plexus
dorsal aspect of the upper extremitiy
- via radial and axillary nerves
Innervation of medial cord of the Brachial Plexus
ulnar nerve and the medial component of the median nerve
Important intermediary branches of the medial cord of the Brachial Plexus
medial antebrachial cutaneous nerve and the medial cutaneous nerve
- these join the intercostobrachial nerve (T2) to innervate the skin over the medial aspect of the arm
Endoneurium
connective tissue around the myelin sheath of each myelinated nerve fiber
Perineurium
covers fascicles
Epineurium
covers groups of fascicles
- as the nerve travels away from the spinal cord, the density diminishes, but its total volume increases
- Amount of neural tissue remains constant
- 1:1 in proximal plexus to 2:1 in distal plexus
Why are peripheral nerves more difficult to block than distal nerves?
greater proportion of connective tissue compared to nerve/fascicle
Where is local anesthetic first absorbed by the nerve?
mantle fibers on the nerve’s periphery
- blockade manifests proximal to distal
- block resolution goes from distal to proximal
What may explain the relatively longer block onset times with distal compared to proximal?
increased ratio of nonneural to neural tissue as one moves away from the spinal cord
Response of superior trunk stimulation
deltoid motor response
Response of musculocutaneous nerve stimulation
arm to flex at elbow












