Neurophysiology is the study of how the nervous system functions. The nervous system is a group of cells that collectively coordinate motor and sensory function in most multi-cellular animals. In vertebrates and some invertebrates, the coordination is via specialist cells called neurons that are capable of transmitting electrochemical signals between various cell types (e.g. muscle, endocrine, neurons). Neurophysiology encompasses branches of neurology, neurobiology, neuroanatomy, psychology, bioinformatics and cognitive science. It relates the biological mechanisms of the nervous system with neuro-motor function and animal behavior.
The basis of neurophysiology is the physiology of the neuron. Neurons are cells capable of receiving and transmitting electrochemical information through the use of small molecules called neurotransmitters. As a result, the study of the nervous system processes requires special technology capable of detecting and recording an electrophysiological response of minute size. Electric potentials (maintained by ion pumps) across the nerve cell membrane are studied through the use of microelectrodes, electrophysiological electrodes small enough to penetrate the cell membrane without disrupting its function. The electrode generally consists of an outer insulative material (e.g. glass) and an inner electrical conductor (i.e. an electrolyte solution or metal wire). In addition, there is often a need for a sterotaxic instrument, or a rigid framework required to hold a living specimen and the microelectrode in position, microelectrode manipulators that are used when precise control is required to move the electrode, as well as stimulators for eliciting neural responses in a controlled environment.
Often the low level of electrical signal from the specimen is not powerful or consistent enough to be monitored without distortion. In these cases a high input impedance preamplifier processes the relatively small electrical signal for amplification without damage to the cell or without altering cell function. In addition to the preamplifier, another level of amplification via a power amplifier is required to provide enough power for measuring equipment and displays. The main type of display used in neurophysiological research is the oscilloscope, which can graph rapid voltage functions via a cathode ray tube. Modern oscilloscopes are equipped with computational equipment that can analyze results and yield statistical displays: amplitude, post-stimulus time (PST) and interval histograms.
Neurophysiology also includes the study of the molecular basis of biological activity and therefore incorporates the spectrum of biochemical, genetic and molecular biological techniques as well. Several animal models have served in the study of these processes. The nematode Caenorhabditis elegans is often chosen as a model for the simplicity of its nervous system, which contains 302 neurons in a connective pattern or connectome that has been definitively mapped. Rats and mice are critical models for studying human neurophysiologic disease both for their homology to humans with regards to many neural proteins but for the fiscal feasibility of their use. Nonhuman primates are still the gold standard for pre-clinical trials.
One type of neurophysiological disease is Alzheimer's Disease (AD), a form of degenerative dementia, of unknown etiology, characterized by symptoms of confusion, mood swings, aggression, long-term memory loss and ultimate loss of bodily function. It is diagnosed post-mortem by the presence of amyloid-beta plaques and aggregations of neurofibrillary tangles mainly throughout the neurons of the cerebral cortex. Several hypotheses have been proposed as to the disease's origin. Initial therapies were based on acetycholine deficiency but have since proven unsuccessful as an effective treatment. Other evidence supports the role of abnormal amyloid-beta precursor protein (APP) oligomerization.
Another neurophysiological disease is Parkinson's Disease (PD). Parkinson's is a neurodegenerative disorder that is also of unknown etiology. It is characterized by the loss of dopamine-producing cells in the midbrain (substantia nigra). The loss of these cells can result in hypokinesia or a loss of motor control (i.e. resting tremors, rigidity, bradykinesia and postural instability), as well as non-motor symptoms including mental and behavioral changes, mood swings and somnipathy. The study of neurophysiological diseases is not only about these degenerative processes, but also of diseases such as polio and multiple sclerosis only underscores the fundamental link between molecular dysfunction with cellular pathology and the ultimate loss of systemic neurological function.