When an axon is severed, the segment of the axon distal to the cut degenerates and is absorbed by Schwann cells. The proximal segment fuses, retracts, and swells, forming a "retraction bulb". The synaptic terminal function is lost, as axoplasmic transport ceases and no neurotransmitters are created. The nucleus of the damaged axon undergoes chromatolysis in preparation for axon regeneration. Schwann cells in the distal stump of the nerve and basal lamina components secreted by Schwann cells guide and help stimulate regeneration. The regenerating axon must connect to the appropriate receptors to make an effective regeneration. If proper connections to the appropriate receptors are not established, aberrant reinnervation may occur. If the regenerating axon is halted by damaged tissue, neurofibrils may create a mass known as a neuroma.