3. Nervous system and muscles: technical investigations in neurology

The nervous system can be divided into two parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is a hierarchical structure, with higher centres modulating lower ones. The PNS originates in the motor anterior horn of the spinal cord and terminates in the dorsal ganglion, near the spinal cord. At rest, nerves and muscles are in electrical equilibrium. When they are stimulated, action potentials develop: these follow particular paths and produce an effect remotely through nerve-to-nerve and nerve-to-muscle communication, a process that is mediated chemically by transmitters. In pathological situations nerves or muscles fail to respond when stimulated. Electromyography provides a lot of information by measuring nerve conduction velocity or abnormal muscle action. It is carried out on patients with PNS disorders. An electroencephalogram (EEG) measures brain activity. The indications for EEG are mainly epilepsy, sleep disorders and coma. To enable readers to understand the opportunities afforded by supplementary tests in the case of neurological disorders this chapter gives a brief recapitulation of neuroanatomy and neurophysiology. A broad outline of anatomy is given in sect. 3.1, and 3.2 gives information on imaging. sect. 3.3, 3.4 and 3.5 recapitulate the physiology of nerves, muscles and motor units respectively, which is required for the explanation of electromyography in sect. 3.6. The measurement of signals in and from the central nervous system is explained in sect. 3.7, and 3.8 discusses other laboratory techniques.