Neural Systems: Synaptic Modulation Mechanisms, Electrophysiology, and Signal Integration

Comprehensive vocabulary flashcards covering neural cable theory, spike train metrics, coding schemes, synaptic summation, nociceptive wind-up, central pattern generators, and somatosensory pathways.

Cable Equation

The partial differential equation describing passive voltage spread and decay along a cylindrical neurite: $C_m \frac{\partial V}{\partial t} = \frac{1}{r_i}\frac{\partial^2 V}{\partial x^2} - \frac{V}{r_m}$, where $C_m$ represents membrane capacitance, $r_i$ is axial resistance, and $r_m$ is membrane resistance.

Spike Train

A temporal sequence or series of action potentials generated by an individual neuron over time.

Raster Plot

A graphical representation of neural activity wherein each tick or dot denotes an individual action potential and each row corresponds to spikes recorded during a single experimental trial or from a single neuron.

Bin

An equally spaced time interval used to discretize continuous time and aggregate action potential counts when constructing a spike rate or spike time histogram.

Peri-Stimulus Time Histogram (PSTH)

A histogram depicting the time course of average neuronal firing rates across repeated trials aligned to the onset of a specific stimulus.

Trial Average Firing Rate

A metric quantifying neuronal activity by calculating the average number of spikes across trials divided by the stimulus duration: $R = \frac{\langle N_i \rangle_i}{T}$, where $N_i$ is the spike count on trial $i$ and $T$ is the trial duration.

Inter-Spike Interval (ISI)

The duration of time elapsed between consecutive action potentials emitted by a neuron, calculated as $\text{ISI}_i = t_{i+1} - t_i$.

Rate Code

A neural coding scheme in which information is represented primarily by the overall frequency of action potentials (spikes per second) rather than the precise timing of individual spikes.

Temporal Code

A neural coding strategy in which information is carried by the precise timing or pattern of individual action potentials, often relative to a stimulus or other reference event.

Latency Code

A neural coding mechanism in which the time interval between the onset of an external stimulus and the occurrence of the first action potential conveys information.

Synchrony Code

A neural coding mechanism based on the simultaneous or coordinated firing of action potentials across multiple distinct neurons in a network.

Population Code

A neural coding scheme where information is represented collectively across the distributed activity of an ensemble of multiple neurons.

Feature Vector

An ordered array of numerical metrics (such as burst duration, synchrony, latency, and inter-burst intervals) extracted from electrophysiological raster data used as input for computational classifiers and machine learning algorithms.

Picrotoxin

A $GABA_A$ receptor antagonist identified in multielectrode array screening as having the highest seizure liability at the lowest concentration ($0.1\,\mu\text{M}$).

Generalized Linear Model (GLM)

A statistical point-process neuron model describing instantaneous firing probability across small time bins via the relationship $\eta(t) = (k * s)(t) + (h * y)(t) + (w * y_{\text{other}})(t) + b$, incorporating a stimulus filter, spike history, and coupling without explicitly modeling membrane potential.

Spatial Summation

The additive integration of simultaneous postsynaptic potentials originating from physically distinct synaptic locations across the dendritic tree.

Temporal Summation

The algebraic addition of successive postsynaptic potentials occurring in rapid sequence at the same synaptic terminal before preceding potentials have fully decayed.

Length Constant ($\lambda$)

The spatial distance over which an electrotonic potential passively decays to $1/e$ ($\approx 37\%$) of its initial magnitude; spatial summation fails if synaptic inputs are physically separated by distances much greater than this value.

Membrane Time Constant ($\tau$)

A passive property defined by membrane resistance and capacitance ($\tau = r_m C_m$) that governs the rate of membrane voltage rise and decay; temporal summation fails if consecutive inputs arrive at intervals significantly exceeding this duration.

Sensory Acuity

The ability of a sensory system to distinguish between closely spaced, discrete stimuli, optimized by small receptive fields with minimal convergence onto secondary neurons.

Sensory Sensitivity

The capacity of a sensory system to detect very low-intensity stimuli, facilitated by high degrees of convergence from multiple primary sensory receptors onto a single secondary neuron.

Nociceptive Wind-Up

A progressive, frequency-dependent amplification in dorsal horn neuronal firing and perceived pain intensity evoked by repeated C-fiber stimulation of constant intensity delivered at frequencies of $\ge 0.33\,\text{Hz}$.

NMDA Receptor Magnesium ($\text{Mg}^{2+}$) Block

The voltage-dependent occlusion of the NMDA channel pore by extracellular $\text{Mg}^{2+}$ at resting potentials, which is electrostatically expelled only upon sufficient and sustained AMPA-mediated membrane depolarization, permitting subsequent $\text{Ca}^{2+}$ and $\text{Na}^+$ influx.

Fibromyalgia

A chronic disorder characterized by widespread pain and fatigue, physiologically associated with central sensitization and hyperactive nociceptive wind-up.

Cold Pressor Test

A diagnostic pain assessment procedure in which a subject's limb is submerged in iced water to measure pain tolerance, autonomic reactivity, and wind-up temporal summation.

Axosomatic Synapse

A synaptic junction located directly on the soma of a postsynaptic neuron, where inhibitory inputs are strategically positioned to exert powerful, global suppression over action potential initiation.

Axo-axonic Synapse

A synaptic contact formed on another axon terminal that serves a targeted modulatory role by mediating presynaptic inhibition to selectively decrease neurotransmitter release from that specific terminal.

Central Pattern Generator (CPG)

An autonomous neuronal network capable of producing rhythmic, coordinated motor outputs (such as walking, trotting, or breathing) without requiring rhythmic sensory feedback or rhythmic descending commands.

Antiphase Firing

An alternating, out-of-phase pattern of neural activity between antagonistic neuronal populations, essential for coordinating reciprocal motor actions such as alternating flexor and extensor contractions during locomotion.

Spinothalamic Tract

An ascending sensory pathway mediating pain and temperature, wherein primary afferents synapse in the dorsal horn with second-order neurons that decussate immediately in the spinal cord before projecting to the thalamus.