Sensory Systems 1 2.0 version

Receptor Transduction

The fundamental process by which environmental energy (physical pressure, light, sound, chemicals) is transformed by a specialized receptor into an electrical signal (receptor potential), which are graded and increase in amplitude with greater stimulus intensity.

Labeled-Line Coding (Modality)

How stimulus modality (type of sensation like touch, vision, sound) is represented;

How do action potentials from specialized receptors travel?

They travel via unique, disticnt anatomical pathways to dedicated CNS regions

Receptor Fields & Location

Location is coded by the specific site of the stimulated receptor

• a receptive field is the specific area on a sensory surface within which an adequate stimulus evokes a change in activity.

Lateral Inhibition

A neural mechanism where heavily stimulated center receptors inhibit receptors at the edge, enhancing contrast and sharpening localization/discrimination.

Rate Coding (Intensity)

A stronger stimulus elicits a larger receptor potential, allowing the membrane at the trigger zone to reach threshold earlier in the relative refractory period, resulting in a higher action-potential firing rate.

Population Coding (Intensity)

Individual receptors vary in sensory thresholds; stronger stimuli recruit and excite a larger number of receptors simultaneously.

Representing Stimulus Timing

Coded by the adaptation properties of receptors (such as tonic vs. phasic receptors), which signal the onset, maintenance, and off-response/offset of sensory inputs.

Tonic vs. Phasic Receptors

Tonic receptors adapt slowly and continue to fire during a maintained stimulus to signal intensity over time

Phasic receptors adapt rapidly and fire primarily to changes/transitions (onset/offset) in stimulus.

Cutaneous Mechanoreceptors

Specialized sensory receptors in superficial and deep layers of the skin that translate mechanical contact (touch, pressure, stretch, vibration) into electrical signals.

Merkel Cells (SA1)

Superficial skin receptors with small receptive fields and a slow adaptation rate; encode fine spatial details, shape, texture, and steady pressure.

Meissner’s Corpuscles (RA1)

Superficial skin receptors with small receptive fields and a rapid adaptation rate; specialize in detecting low-frequency vibration, slip, and skin movements.

Ruffini Endings (SA2) & Pacinian Corpuscles

Ruffini endings have large receptive fields/slow adaptation (stretch);

Pacinian corpuscles have large receptive fields/rapid adaptation (high-frequency vibration/transients).

General Somatosensory Rule

Sensations originating from one side of the body are projected to the cerebral cortex on the opposite (contralateral) side.

Spinothalamic Pathway

Carries information specifically from thermoreceptors and nociceptors (temperature and pain); crosses over (decussates) directly within the spinal cord.

Dorsal Column Pathway

Carries information from mechanoreceptors and proprioceptors (touch, pressure, body position); ascends ipsilaterally and crosses to the contralateral side higher up in the brainstem.

Somatotopy

The organization of the primary somatosensory cortex (S1) into a topographical map of the body, where adjacent body parts are processed close together (maintaining place and modality specificity).

Cortical Magnification

Disproportionate representation where body regions with higher receptor densities and finer tactile control (fingers, lips) are allocated a larger area of the somatotropic cortex to enhance spatial resolution.