General Structure of the Nervous System II: Sensory Systems

Practice flashcards covering stimulus attributes, sensory transduction, tonic vs. phasic receptors, labeled lines, rate and population coding, distributed representations, and cortical topographical maps.

Four basic attributes of a stimulus

Modality (type of sensation), location (where the stimulus occurred), intensity (strength of the stimulus), and timing (when the stimulus occurred).

Stimulus transduction

The physiological process by which environmental stimulus energy is converted by a sensory receptor into an electrical signal.

Adequate (appropriate) stimulus

The specific form of stimulus energy that excites a given sensory receptor at the lowest relative intensity threshold.

Receptor potential

A graded electrical change (analogous to an EPSP) triggered by an adequate stimulus that scales with intensity, mediated either directly by ion channels or indirectly through second messengers.

Divergent synapses

A circuit pattern in which a single presynaptic neuron synapses onto two or more postsynaptic neurons (ratio $< 1$), distributing one signal to multiple target cells.

Convergent synapses

A circuit pattern in which multiple presynaptic neurons synapse onto a single postsynaptic neuron (ratio $> 1$), enabling input comparison and integration.

Tonic vs. phasic receptors

Tonic receptors adapt slowly or not at all, continuously signaling ongoing stimulus presence; phasic receptors adapt rapidly, signaling stimulus changes and often producing an off response upon removal.

Sensory receptor adaptation

The property of a receptor that governs how long it sustains action potential discharge during a maintained, unchanging stimulus.

Labeled line coding

The signaling scheme where sensory information travels along dedicated anatomical pathways to discrete CNS areas, enabling the brain to interpret modality and location.

Stimulus location coding

Spatial signaling determined by the anatomical site of the stimulated receptor, which projects along a dedicated labeled line to a corresponding CNS topographical zone.

Receptive field

The specific region on a sensory sheet (or stimulus parameter space) within which an adequate stimulus increases or decreases neuronal firing.

Rate coding of stimulus intensity

Mechanism where larger receptor potentials drive the membrane to threshold earlier in the relative refractory period, producing higher action potential firing frequencies.

Population coding of stimulus intensity

Mechanism where increasing stimulus strength engages a broader group of sensory receptors due to differences in their individual activation thresholds.

Specificity coding vs. distributed coding

Specificity coding relies on single neurons dedicated solely to individual stimuli, whereas distributed coding represents stimuli through the collective activity pattern across a population of broadly tuned neurons.

Insect distributed coding: Fly profile

A population activity pattern where Neuron 1 (Danger) has low firing, Neuron 2 (Big-sensitive) has high firing, and Neuron 3 (Small-sensitive) has low firing.

Nearest-neighbor relationship in sensory maps

The organizational rule where adjacent cortical neurons possess receptive fields that lie next to each other on the peripheral sensory receptor surface.

Cortical magnification and distortion

Topographical mapping where peripheral regions with higher receptor density and greater functional significance (such as the fovea) receive a disproportionately large area of cortex.