Nerve supply to the upper limb

Question 1

What is the function of the brachial plexus and what does it consist of?

Answer 1

Nerve supply to upper limb
Carries motor, sensory, sympathetic axons
Produces mixed nerves (contains axons from multiple spinal nerves) -> Important to supply large muscle groups

Question 2

How is the brachial plexus divided?

Answer 2

Roots, trunks, divisions, cords, terminal branches -> mixed nerves

Question 3

What are the roots and give examples and their supply?

Answer 3

Ventral primary rami of C5 – T1
5th cervical root -> dorsal scapular nerve -> rhomboids + levator scapulae.
5-7th cervical root -> long thoracic nerve -> serratus anterior.

Question 4

Which motor axons within each root innervate the different functional group of muscles (myotomes)?

Answer 4

C5: Arm abductor (Deltoid)
C6: Forearm flexors (Biceps)
C7: Forearm extensors (Triceps), wrist flexors/extensors
C8: Digit flexors/extensors
T1: Intrinsic hand muscles

Question 5

What are the trunks, what are they formed by and what do they pass through?

Answer 5

Roots form trunks
Pass through scalene triangle
Roots C5, C6 -> superior trunk 
Root C7 -> middle trunk
Roots C8, T1 -> inferior trunk

Question 6

How are the trunks divided?

Answer 6

Anterior + posterior divisions:
Ant. -> axons to flexor compartments -> forms lateral + medial cords.
Post. -> axons to extensor compartments -> forms posterior cord.

Question 7

What is the location of the cords and they are named in relation to which structure?

Answer 7

Under pectoralis minor

Axillary artery

Question 8

Where does the lateral cord terminate/give rise?

Answer 8

Musculocutaneous nerve

Lateral part of median nerve

Question 9

Which structures does the musculocutaneous nerve pass through and what does it innervate?

Answer 9

Coracobrachialis
Motor -> anterior arm -> coracobrachialis, biceps brachii, brachialis.
Becomes lateral cutaneous nerve -> cutaneous innervation of lateral forearm.

Question 10

Where does the medial cord terminate/give rise?

Answer 10

Medial part of median nerve

Ulnar nerve

Question 11

Which structure does the median nerve pass through and what does it innervate?

Answer 11

Carpal tunnel
Motor –> anterior forearm flexors, lateral hand
Sensory –> lateral palm hand, d1,2,3 + half d4

Question 12

Which structure does the ulnar nerve pass through and what does it innervate?

Answer 12

Cubital tunnel + under flexor carpi ulnaris muscle.
Motor –> medial side of anterior forearm + hand (flexor carpi ulnaris, flexor digitorum profundus).
Sensory –> Medial hand, half d4, d5

Question 13

Where does the posterior cord terminate/give rise?

Answer 13

Radial nerve, axillary nerve

Question 14

Which structure does the radial nerve pass through, how does it divide and what does it innervate?

Answer 14

Spiral groove of humerus. deep branch -> motor, superficial branch -> sensory.
Motor –> posterior arm, posterior forearm (extensor triceps muscle).
Sensory –> posterior arm, posterior forearm + lateral dorsum hand

Question 15

Which structure does the axillary nerve pass through and what does it innervate?

Answer 15

Quadrangular space
Motor –> deltoid, teres minor
Sensory –> badge area of arm

Question 16

What are upper limb dermatomes and its properties?

Answer 16

An individual area of skin innervated by a single spinal nerve.
Established during development
Lots of overlap/variation

Question 17

What is the clinical significance of upper limb dermatomes?

Answer 17

Altered sensation in region of dermatome indicates damage to specific spinal nerve of spinal cord segment (i.e. proximal nerve injury)

Question 18

Why does a map showing the cutaneous innervation by terminal branches look different to a dermatome map and what is the clinical significance?

Answer 18

Terminal branches contain axons from multiple spinal nerve.

Altered sensation in an area indicates damage to a more distal nerve segment (i.e. distal nerve injury).