4. Strength and sensation

Skeletal musculature is controlled by the peripheral motor neuron in the anterior horn of the spinal cord. This motor neuron acts within a reflex arc steered by sensory information from the peripheral parts of the body. The spinal reflex is modulated by higher parts of the central nervous system in order to damp the motor reaction. In the case of failing central regulation, reflexes become exaggerated and spasticity occurs. Sensory information can be divided into protopathic and epicritic sensibility. These two modalities are processed in different parts of the nervous system. There is a somatotopy for both sensory and motor functions in the central nervous system. As different systems follow different paths, it is possible to make a topical diagnosis by combining the patient’s signs and symptoms. History-taking and technically correct physical examination are therefore crucial; time needs to be devoted to these to enable a targeted investigation to be carried out. The first part of this chapter explains the physiology of sensation and reflexes and discusses the central control of strength (sect. 4.1). We then describe the examination of motor and sensory functions, with various do’s and don’ts (sect. 4.2). Central hemiplegia is common, due to central nervous system dysfunction, especially after a stroke: this is therefore dealt with separately (sect. 4.3). Not every dysfunction displayed will be indicative of actual loss of neurological function; there may be a functional neurological disorder, which needs to be recognized (sect. 4.4).