Neurophysiology is the branch of biology and medicine that studies how the nervous system functions—how neurons generate electrical signals, how synapses transmit information, and how neural circuits produce coordinated behavior. It spans molecular mechanisms (ion channels, neurotransmitter release), cellular processes (excitability, plasticity), systems analysis (sensory, motor, autonomic pathways), and translational clinical contexts (diagnostics in neurology and monitoring in neurocritical care). As a foundational scientific discipline, neurophysiology underpins understanding of epilepsy, movement disorders, neuropathies, cognitive function, and many psychiatric and neurological diseases.
At the cellular level, neurophysiology explains how neurons convert chemical and electrical inputs into an action potential. The resting membrane potential arises from unequal ion distributions across the neuronal membrane, maintained primarily by ATP-dependent ion pumps such as the Na+/K+-ATPase. When synaptic inputs depolarize the membrane to threshold, voltage-gated sodium channels open rapidly, producing the action potential’s upstroke. Potassium efflux via voltage-gated potassium channels repolarizes the membrane, while inactivation of sodium channels and delayed potassium conductances generate the refractory period that shapes firing patterns. The conduction velocity along axons depends on axon diameter and myelination; myelin increases speed through saltatory conduction at nodes of Ranvier.
Synaptic transmission is another core concept. Most neurons communicate through chemical synapses, where presynaptic action potentials trigger calcium influx through voltage-gated calcium channels. Calcium initiates vesicle fusion and neurotransmitter release into the synaptic cleft. Postsynaptic receptors then convert the neurotransmitter signal into graded potentials: excitatory receptors (commonly glutamatergic) promote depolarization, while inhibitory receptors (commonly GABAergic and glycinergic) increase chloride or potassium conductance to hyperpolarize or shunt the membrane. The net effect is determined by temporal summation and spatial integration of excitatory and inhibitory postsynaptic potentials, determining whether the neuron fires and with what frequency.
Neurophysiology also addresses synaptic plasticity, the basis of learning and memory. Long-term potentiation (LTP) and long-term depression (LTD) reflect activity-dependent strengthening or weakening of synaptic efficacy. NMDA receptor activation, calcium-dependent signaling cascades, and AMPA receptor trafficking are central to LTP-like mechanisms in many brain regions. Homeostatic plasticity ensures stable network function by compensating for prolonged changes in activity, reducing runaway excitation or chronic suppression.
At the systems level, neurophysiology describes how networks coordinate. Sensory systems encode external stimuli via receptor transduction, ascending pathways, and cortical processing. Motor control relies on corticospinal and extrapyramidal circuits, including the basal ganglia and cerebellum, to refine movement timing, force scaling, and motor learning. Autonomic neurophysiology governs heart rate, vascular tone, and gastrointestinal motility through sympathetic and parasympathetic pathways. Dysregulation can manifest clinically as tachyarrhythmias, orthostatic intolerance, or gastrointestinal dysmotility.
Clinically, neurophysiological assessment includes electroencephalography (EEG), electromyography (EMG), and nerve conduction studies. EEG measures electrical activity from scalp electrodes and is critical in evaluating seizures, encephalopathies, and sleep disorders. EMG and nerve conduction testing evaluate peripheral nerve and muscle function by measuring compound muscle action potentials, conduction velocities, and denervation patterns. In neurocritical care, continuous EEG monitoring can detect nonconvulsive seizures and guide management of coma and delirium. These tools connect basic principles of neuronal firing and conduction to bedside diagnosis.
Neurophysiology is also relevant to mental health, because many psychiatric symptoms reflect network-level dysfunction and altered excitation/inhibition balance. For example, abnormalities in cortical oscillations and synaptic plasticity mechanisms have been linked to schizophrenia and mood disorders. Neurotransmitter systems—dopaminergic, serotonergic, GABAergic, and glutamatergic—modulate circuit dynamics that influence attention, emotion regulation, and reward processing. While psychiatric diagnoses are not determined by a single neurophysiological measure, neurophysiology informs biomarkers, circuit models, and therapeutic targets.
When considering disorders, a unifying theme is that pathology often alters one or more of: membrane excitability, synaptic transmission, plasticity, or network synchronization. Epilepsy exemplifies this with hyperexcitable circuits and aberrant synchronization leading to spontaneous recurrent seizures. Neuropathies reflect impaired conduction due to axonal injury or demyelination, producing weakness, numbness, and altered reflexes. Movement disorders can emerge from abnormal firing rates and oscillatory rhythms within basal ganglia-thalamocortical loops.
Modern neurophysiology uses electrophysiological recordings, imaging, computational models, and optogenetic or pharmacological perturbations (primarily in research settings) to dissect mechanisms with high temporal and sometimes cellular resolution. Translationally, these approaches support precision diagnostics and guide development of therapies such as anti-seizure drugs, neuromodulation techniques, and rehabilitation strategies targeting plasticity.
Source: @StewartMills (Jun 9, 2026)
Stewart Mills: Yeshayahu Leibowitz (1903-1994) was an Israeli Orthodox Jewish public intellectual and polymath. He was a professor of biochem,organic chem, & neurophysiology at the Hebrew University of Jerusalem, as well as a writer on Jewish thought & western philosophy. #breaking
— @StewartMills May 1, 2026
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