The central and peripheral nervous system are key to our survival. The internal regulatory functions, the conscious control of movement, our sensory awareness and our ability to navigate and interact with the world are all down to a healthy, functioning set of complex neuronal circuitry. The human brain is the most complex object in the known universe, it contains 100 billion neurons and the spinal cord 13.5 million. Multiple types of disease processes can disrupt the flow of nerve signals around the body and the majority of neurological pathologies are manifested by deficiencies or interferences of normal signalling; paralysis, sensory deficits, abnormal movements. Key to understanding the underlying aetiology of such disorders is recognising the pattern of interference, is this an upper or lower motor neurone lesion, what dermatome or spinal level is the disruption at, is there cerebellar involvement and so on. The good diagnostician is able to trace where the break in the circuitry might be and appreciate the origin based on careful history taking.