What is Neurology?
Neurology is a medical speciality which deals with physical disorders affecting the brain, spinal cord, peripheral nerves and muscles. Since the brain and nervous system control so many functions in the body, Neurology deals with a wide range of diseases including headaches, epilepsy, strokes, multiple sclerosis, dementia, pain, spinal issues, Parkinson’s disease, etc.
What is Neurophysiology?
Neurophysiology is a sub-specialty of Neurology. It is the study of how nerve cells (neurones) receive and transmit information, both electronically and chemically. Electrical events propagate a signal within a neurone and chemical processes transmit a signal from one neurone to another (or to a muscle cell).
A neurone is a long cell with a thick, central body containing the nucleus. It has one long process (axon) and one or more short, bushy processes (dendrites). Dendrites receive impulses from most other neurones. These impulses are propagated electrically along the cell membrane to the end of the axon. At the end of the axon, the signal is chemically transmitted to an adjacent neurone or muscle cell.
Neurones are normally negatively charged (polarised) at rest. However, when a stimulus is applied, potassium ions flow into the cell, reducing this negative charge (depolarisation). The properties of the membrane then change and the cell becomes permeable to sodium, which also enters the cell and causes a positive charge inside the neurone (action potential). Once this ‘potential’ is reached in the neurone, it travels down the axon. The potassium, and then sodium ions, are then pumped out of the cell, restoring the negative charge (repolarisation). This whole process takes less than one-thousandth of a second and, after a brief period, is repeated.
When the above electrical signal reaches the end of an axon, it stimulates small vesicles in the cell. These vesicles contain chemicals (neuro-transmitters), which are released in between the neurones. These neuro-transmitters attach to receptors on the adjacent neurones, causing the adjacent cell to depolarise and propagate an action potential of its own.
The above processes result in electrical signals being generated. Although the voltages are very small, it is possible to study the brain, peripheral-nerves and muscles by recording and analysing these electrical signals. This is done through neurophysiology testing.
What is Neurophysiology Testing?
Neurophysiology testing uses computer, electrical, magnetic and electronic means to investigate the function of the brain, spinal cord, spinal roots, peripheral nerves and muscles to diagnose disorders of the peripheral nervous system (e.g. carpal tunnel syndrome).
The main types of neurophysiology testing include:
Nerve Conduction Study (NCS)
NCS studies can give an overall impression of nerve function and is used for diagnosing localised nerve-entrapments. NCS are typically performed by using an externally-generated electrical pulse to cause a nearby nerve to discharge, resulting in propagation of a signal proximally or distally along the nerve. These signals are then recorded by skin or muscle electrodes, which are placed along the nerve being tested. NCS are typically performed for symptoms such as tingling, numbness, weakness and muscle wasting; often in conjunction with EMG.
EMG studies test the nerve supply to a muscle or group of muscles. Fine needles are inserted into the muscle and the patient is asked to contract and relax that muscle. EMG is used in the diagnosis of nerve-root compressions, myopathies and acute or chronic denervation following injury or disease. Typical symptoms requiring EMG include muscle-weakness/wasting, abnormal muscle twitches and abnormal movements.
Quantitative EMG (qEMG)
When appropriate, computerised qEMG is performed in conjunction with EMG to distinguish between isolated peripheral mononeuropathies and proximal nerve-root pathologies.