text: Two types of Spinal Anesthesaia are sub dural and epidural though he former is more or less considered synonymous with spinal. It Spreads along the subdural or epidural space depending on where it is adminsitered. and the nerve fibres exiting from the spinal cord are bathed in the fluids containing the anaethetic agent, which Blocks off the Soidum channels o n the surface membrane of th nerve fibres. which in turn prevent the transmission of nerve impulses by depolarisation via these nerve fibres. And your legs feel numb and heavy. The larger nerve fibres take longer to be affected than the smaler one. Hence you lose Sensations first then  movement as motor nerve fibres are usually larger than pain/sensory fibres.