02-Touch(2)

Somatosensation - Touch

  • Course: Neuroscience II PSCH/PHIL/BIOS 485

Common Themes in Sensory Systems

Sensory Modality

  • Types: Light, sound, pressure, temperature, chemical, gravity.

Physical Stimulus and Sensory Organ

  • Types of stimuli: Eye (retina - rods & cones), Nose/Tongue (olfactory and taste epithelia), Ear (cochlea - hair cells), Skin (mechanoreceptors, proprioceptors, nociceptors).

  • Sense organs house receptors that interact with physical stimuli

Neural Signal and Transduction

  • Interaction of physical stimulus with a receptor induces neural signal (change in activity of a neuron).

  • Information processed in the central nervous system through transduction, leading to detection and discrimination.

Sensory Processing

Key Questions

  • What is it? When is it? Where is it?

Selectivity

  • Determines: adequate stimulus (modality), tuning curves (specificity), receptive fields (acuity).

Time-course

  • Factors: conduction velocity, adaptation, fidelity, onset, and offset.

Organization

  • Pathway: receptor to sensory neuron to next relay and then to cortex.

  • Information transformation and specialization; serial vs parallel processing.

Plasticity

  • Top-down influences and rewiring based on experience.

Somatosensation Submodalities

  • Mechanoreception: Sense of touch, stimuli identification (neutral, pleasant, unpleasant).

  • Proprioception: Awareness of body position in space.

  • Nociception: Awareness of pain and tissue damage.

Mechanoreception Details

Attributes

  • Adequate stimulus (modality)

  • Selectivity: tuning curves, receptive fields for acuity.

  • Temporal aspects: conduction velocity, adaptation types, elaboration of receptive fields, organizational maps.

Processing Pathways

  • Information flow from skin to sensory neuron to cortex; emphasizes serial processing.

Psychophysics in Somatosensation

  • Two-point discrimination varies across the body.

  • Proximity of sensory receptors affects discriminative sensitivity.

Receptive Fields and Properties

  • Density and depth influence receptive field properties.

  • Types of Receptors in Glabrous Skin:

    • Free nerve endings: No specialized function.

    • Meissner's corpuscle: Motion detection/well-adapted for grip. Small receptive field.

    • Merkel cells: Shape and texture perception as small receptive field.

    • Pacinian corpuscle: Vibration perception with large receptive fields.

    • Ruffini corpuscle: Skin stretch detection.

Touch and Information Flow

Conduction Velocity

  • Identified based on velocity differences of touch fibers (35-75 m/s).

Information Conveyance Rates

  • Determines how fast touch information reaches CNS based on distance and conduction velocity.

Sensory Information and Receptive Fields

  • Receptive field size and density explain the distribution of sensory information.

  • Body maps do not divide equally into pixels of information; close proximity affects sensory area representation.

Somatotopic Mapping

  • Mapping begins as spinal nerves enter spinal cord.

  • Dermatomes and impacts of conditions like shingles.

  • Mapping structures maintain organization from body parts to brain regions.

Trigeminal Nerve Pathway for Facial Sensation

  • Organization from receptors through brainstem processing to cortical representation.

Primary Somatosensory Cortex (SI)

  • Comprised of areas (1, 2, 3a, and 3b).

  • The somatotopic map indicates disproportionate representation of body areas.

Proprioception

Sensing Body Position

  • Proprioceptors detect stretch and tension in muscles.

  • Proprioception follows a specific pathway to the cerebellum.

Properties and Adaptability

  • Somatotopic organization and adaptability to sensory experience.

  • Impact of sensory deprivation leading to cortical reorganization.

Treatment for Tactile Sensitivity

  • Techniques include brushing skin, allowing exposure to varying textures, and specialized clothing to manage sensitivities.

Phantom Limb Syndrome and Reorganization

  • Sensations from missing limbs due to remapping in the brain after amputation.

Case Study Insight

  • Demonstration of sensory mapping and phantom sensations through direct touch to a participant's face revealing perceptions of missing limbs.

Conclusion: Mechanoreception Overview

  • Characteristics of mechanoreceptors in touch sensing and pathways for processing sensory information indicating organizational structure and inherent plasticity.