How can I easily understand neurophysiology?

Understanding Neurophysiology: A Practical Framework

Neurophysiology is best understood by focusing on three core concepts: how neurons generate and transmit electrical signals, how these signals are measured clinically, and how networks of neurons produce integrated functions. 1, 2

Cellular Foundation

The fundamental computing unit is the neuron, which transmits information as pulsed electrical code along specialized processes called axons. 2

• Neurons communicate at connection sites called synapses, where chemical neurotransmitters convert electrical signals to chemical signals and back to electrical signals in the receiving neuron 2
• Supporting cells (glia, astrocytes, oligodendrocytes, microglia) facilitate neuronal function through physical support, homeostasis maintenance, myelin formation, and immune surveillance 3
• Synapses are modifiable based on prior activity history, giving them critical roles in learning, memory, and adaptation to injury 2

Clinical Measurement Techniques

Two primary techniques measure neuronal electrical activity in clinical practice: electroencephalography (EEG) and evoked potentials (EPs). 4, 5

EEG Recording

• EEG reflects cortical neuronal activity modulated by diencephalic and brainstem influences, as well as metabolic and toxic factors 4
• The technique measures electrical brain activity non-invasively by placing electrodes on the scalp, revealing predominantly oscillatory, wave-like patterns 4
• EEG provides functional assessment complementary to neuroimaging, offering more quantitative assessment than clinical examination alone 4

Evoked Potentials

• EPs are generated through passive reception of sensory stimuli (visual, auditory, somatosensory) or cognitive processing of stimuli 4
• Visual evoked potentials (VEP), somatosensory evoked potentials (SSEP), and brainstem auditory evoked potentials (BSAEP) are most useful for diagnosing multiple sclerosis, plexus lesions, and cranial nerve tumors respectively 5
• Cognitive evoked potentials (P300 paradigm) and long-latency EPs (>100ms) reliably reflect cortical function 4

Nerve Conduction Studies and EMG

• Nerve conduction studies measure velocity of nerve impulses, providing information about myelinated nerve lesions 5
• Electromyography (EMG) assesses integrity of innervation, neuromuscular junction condition, and muscle fiber status 5

Network Integration and Function

Networks of neurons perform specific tasks through complex interconnections between cortical areas, subcortical structures (basal ganglia, cerebellum), and spinal cord. 2

Functional Organization

• The central nervous system comprises the brain and spinal cord, protected by the blood-brain barrier that regulates substance movement between bloodstream and neural tissue 1
• Specialized brain regions include cerebral cortex, brainstem, cerebellum, and subcortical structures that coordinate different neurological functions 1
• The peripheral nervous system divides into somatic and autonomic (sympathetic and parasympathetic) components 1

Information Processing

• In visual cortex, spike-field coherence is strong in the gamma band (~30-80 Hz), with phase relationships systematically dependent on stimulus orientation 4, 1
• The hippocampus demonstrates strong spike-field coherence in the theta range (4-8 Hz), with phase encoding spatial position information 4, 1
• Information processing involves both regional activity and functional connectivity between intrinsic brain networks 1

Clinical Applications

Neurophysiological investigations provide functional assessment of the nervous system, offering quantitative measurements for diagnosis and follow-up. 4

Key Clinical Uses

• Provide evidence of encephalopathy in patients with normal consciousness 4
• Rule out disturbances of consciousness from other causes (drug-induced, non-convulsive status epilepticus) 4
• Demonstrate worsening or improvement during follow-up periods 4
• Remain interpretable in patients under muscle blockade where clinical examination is not feasible 4

Important Caveats

• Short-latency EPs (<25ms) are insensitive to metabolic encephalopathies but can disclose brainstem conduction deficits from edema 4
• Many abnormal EEG patterns are non-specific and may reflect diverse pathophysiological events from transient metabolic dysfunction to irreversible cortical problems 4
• Neuronal dynamics and synaptic strengths continuously vary on multiple time scales as a function of temporal activity patterns and modulatory environment 6