The brachial plexus is a network of nerves that arises from the cervical and thoracic spinal nerves and provides motor and sensory innervation to the upper limbs. It is formed by the ventral rami of C5-T1 nerves and passes through the neck and axilla, dividing into trunks, divisions, cords, and branches before terminating as peripheral nerves. Injuries to different parts of the brachial plexus can cause specific deficits, like Erb's palsy which affects shoulder muscles after injury at Erb's point, or Klumpke's palsy which causes a claw hand from damage to C8-T1 nerves.