Human Anatomy Vol 1

Roots

Lateral pectoral nerve

Branches

Dorsal scapular nerve

Suprascapular nerve

Divisions

Radial nerve

Median nerve

Fig. 4.14: The right brachial plexus

Long thoracic nerve

Upper subscapular nerve

Nerve to latissimus dorsi

Lower subscapular nerve

Medial pectoral nerve

Medial cutaneous nerve of arm

Medial cutaneous nerve of forearm

Ulnar nerve

T1

Musculocutaneous nerve

Axillary nerve

Lateral root and medial

root of median nerve

Trunks

Roots C5 and C6 join to form the upper trunk. Root C7

forms the middle trunk. Roots CB and T1 join to form

the lower trunk.

Divisions of the Trunks

Each trunk (three in number) divides into ventral and

dorsal divisions (which ultimately supply the anterior

and posterior aspects of the limb). These divisions join

to form cords.

Cords
i. The lateral cord is formed by the union of ventral
divisions of the upper and middle trunks (two
divisions).
ii. The medial cord is formed by the ventral division
of the lower trunk (one division).
iii. The posterior cord is formed by union of the dorsal
divisions of all the three trunks (three divisions).

L Sympathetic nerves for the upper limb are derived

from spinal segments T2 to T6. Most of the vaso-

constrictor fibres supplying the arteries emerge from

segments T2 and T3.

The preganglionic fibres arise from lateral horn cells

and emerge from the spinal cord through ventral

nerve roots.

Passing throughwhite rami communicans they reach

the sympathetic chain.

They ascend within the chain and end in the middle

cervical, inferior cervical and first thoracic ganglia.

Postganglionic fibres from middle cervical ganglion

pass through grey rami communicans to reach C5,

C5 nerve roots.

Postganglionic fibres from inferior cervical ganglion

pass through grey rami communicans to reach C7,

C8 nerve roots.

Postganglionic fibres from first thoracic sympathetic

ganglion pass through grey rami communicans to

reach Th1 nerve roots.

The arteries of skeletal muscles are dilated by

sympathetic activity. For the skin, however, these

nerves are vasomotor, sudomotor and pilomotor.

Vasomotor: Constricts the arterioles of skin.

Sudomotor: Increases the sweat secretion.

Pilomotor: Contracts the arrector pilorum muscle to

cause erection of the hair.

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