The brachial plexus

Plexus

A plexus is a part of nervous system. Plexus has a slightly different definition in vertebrates and in invertebrates.- In vertebrates :In vertebrates, a plexus is an area where nerves branch and rejoin. The electrical signals do not mix; rather, the fibres travel together with their electrical...

is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots

Spinal nerve

The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body...

 (C5

Cervical spinal nerve 5

The cervical spinal nerve 5 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 5 ....

-T1

Thoracic spinal nerve 1

The thoracic spinal nerve 1 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 1 ....

). It proceeds through the neck, the axilla (armpit region), and into the arm.
The brachial plexus is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle innervated by the spinal accessory nerve (CN XI) and an area of skin near the axilla innervated by the intercostobrachial nerve

Intercostobrachial nerve

-Second intercostal nerve:The lateral cutaneous branch of the second intercostal nerve does not divide, like the others, into an anterior and a posterior branch; it is named the intercostobrachial nerve. It pierces the Intercostalis externus and the Serratus anterior, crosses the axilla to the...

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Lesions can lead to severe functional impairment.