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Neurophysiology and Synaptic Signaling

Manual: General · Subject: Neurology

Examine membrane excitability, synaptic transmission, oscillations, and the electrophysiologic basis of neurologic disease.

Excitability, Transmission, and Timing

Membrane Biophysics

Neurons encode information through membrane potentials generated by ionic gradients and selective permeability. The resting potential, action potential threshold, refractory periods, and channel kinetics shape how signals are initiated and propagated.

Essential Physiologic Variables

Resting membrane potential
Voltage difference maintained mainly by ion gradients and leak conductances
Threshold
The voltage at which regenerative sodium channel activation triggers an action potential
Synaptic delay
The time required for neurotransmitter release and receptor activation
Temporal summation
Integration of inputs over short time windows

Electrophysiology in Practice

Electroencephalography, evoked potentials, electromyography, and nerve conduction studies transform physiologic principles into clinical data. These tools detect dysfunction that may be invisible to structural imaging, especially in epilepsy, neuropathy, neuromuscular transmission disorders, and coma.

Electrophysiologic Modalities

EEG

  • Measures summed cortical activity
  • Critical for seizure diagnosis and encephalopathy
  • High temporal resolution

NCS/EMG

  • Evaluates peripheral nerve, muscle, and neuromuscular transmission
  • Helps distinguish axonal from demyelinating disease
  • Useful in motor neuron and myopathic disorders

Which property most directly explains the absolute refractory period?

Why can EEG detect seizures that MRI may miss?

Interpreting a Physiologic Signal

  1. 1

    Step 1: Identify whether the signal is cortical, spinal, peripheral nerve, muscle, or junctional.

  2. 2

    Step 2: Determine whether the abnormality is demyelinating, axonal, excitatory, inhibitory, or synaptic.

  3. 3

    Step 3: Relate waveform features to underlying biophysics.

  4. 4

    Step 4: Integrate with the clinical syndrome and temporal course.

A decremental response on repetitive nerve stimulation most strongly suggests which disorder class?