2024 NE 101 Lecture 13-14 Full

Sensory Transduction

Overview

  • Sensory transduction is the process by which sensory stimuli are transformed into neural signals.

  • Specialized receptor cells are crucial to detect specific environmental stimuli.

Sensory Modality

  • Different modalities include:

    • Somatosensation: Interactions between the body and its environment.

      • Mechanoreception: Sensation of touch.

      • Nociception: Sensation of pain.

      • Thermoception: Sensation of temperature.

      • Vision: Detection of light.

      • Audition: Perception of sound (pressure waves).

      • Chemoreception: Detection of chemicals.

        • Olfaction: Smell (volatile chemicals).

        • Gustation: Taste (dissolved chemicals).

Sensory Perception

Limitations of Perception

  • Animals do not perceive the physical world directly, but rather their filtered perceptions.

  • Sensory receptors are tuned to specific stimulus parameters, leading to selective filtering of stimuli.

Specialized Receptor Cells

Functionality

  • Each sensory modality has specific receptor cells that respond to adequate stimuli.

  • Information from sensory receptors is transmitted to the Central Nervous System (CNS) through labeled lines.

Classification of Sensory Systems

  • Overview of sensory systems based on modality and adequate stimuli:

    • Mechanical:

      • Touch: Contact or deformation of body surface.

      • Hearing: Sound vibrations in air/water.

    • Visual:

      • Seeing: Visible radiant energy.

    • Thermal:

      • Cold: Decrease in skin temperature.

      • Warmth: Increase in skin temperature.

    • Chemical:

      • Smell: Odorous substances in air/water.

      • Taste: Substances on tongue.

    • Electrical:

      • Electroreception: Differences in electrical currents.

    • Magnetoreception: Orientation with Earth’s magnetic field.

Somatosensory System

Importance

  • Key for sensing temperature, pain, pressure, and object texture discrimination.

  • Somatosensory pathways extend signals from peripheral receptors to the brain.

Types of Exteroception

  1. Touch (mechanical stimuli)

  2. Temperature (modified by warmth and cold receptors)

  3. Pain (nociceptive stimuli)

Other Sensory Modalities

  • Proprioception: Mediated by mechanoreceptors in muscles/tendons (body orientation).

  • Interoception: Internal body state communication with the brain.

Nociception

Mechanisms

  • Nociceptors express receptor proteins that detect various noxious stimuli like temperature, chemical, and mechanical signals.

  • Specialized ion channels on nociceptors (e.g., TRPs) are crucial for responding to noxious stimuli.

Pain Transduction

  • Damage leads to the release of "inflammatory soup" (histamine, neurotransmitters, cytokines) which signal pain.

  • Primary nociceptors synapse in the dorsal horn of the spinal cord, releasing glutamate and substance P to activate secondary neurons.

Pain Pathways

Central Pain Pathways

  • The spinothalamic (anterolateral) pathway carries pain and temperature signals to the ventral posterior nucleus of the thalamus.

  • Dorsal column-medial lemniscus pathway transmits touch and proprioceptive information.

Referred Pain

  • Pain from visceral organs may be misidentified as originating from the skin, due to the proximity of sensory pathways.

CNS Pain Modulation

Effects on Pain Processing

  • The CNS can modulate pain responses through descending pathways releasing endorphins, reducing pain perception.

  • The perception of pain can vary based on psychological factors, highlighting the complexity of pain experiences (placebo vs. nocebo effects).

Highlights from Research

  • Notable discoveries, such as the role of specific NaV1.7 channels in nociception and the adaptation of sensory receptors to ongoing stimuli, further emphasize the intricate biology behind sensory pathways.

  • Recent research includes studies on particular animals that exhibit unique adaptations to nociception, shedding light on potential therapeutic targets for pain management.