PSY1BNB WEEK 1 – Sensory Systems, Introduction, Taste, & Smell

Introduction to Sensory Systems

  • Sensory systems provide vital information about our surroundings.

  • This lecture will cover:

    • The distinction between sensation and perception.

    • Common features of sensory systems.

    • Physical properties of light and sound stimuli.

Part 1: Introduction

Sensing and Perceiving

  • Importance of sensory systems in delivering information about the environment.

Distinction Between Sensation and Perception

  • Sensation:

    • Definition: The physical process by which sense organs gather information about the environment and transmit it to the brain.

  • Perception:

    • Definition: An active and continuous process by which the brain selects, organizes, interprets, and consciously experiences sensory information.

General Features of Sensory Systems

  • Sensory systems perform the following functions:

    • Detect and translate physical energy or chemicals into neural signals.

    • Sensory transduction is the conversion of energy to neural signal.

Sensory Receptor Organs

  • Specialized cells (sensory receptors) convert sensory energy into neural activity.

  • Adequate stimulus is the specific type of stimulus a sensory organ is adapted to, e.g., light for the eye.

Classification by Adequate Stimuli

  • Each sensory system is classified by its modality and type of adequate stimuli:

    • Mechanical:

    • Touch: Deformation of body surface.

    • Pain: Tissue damage.

    • Hearing: Sound vibrations in air or water.

    • Vestibular: Head movement and orientation.

    • Visual: Visible radiant energy.

    • Chemical: Smell and taste from substances.

    • Electrical: Electroreception (differences in electrical currents).

    • Magnetic: Magnetoreception (orientation to Earth's magnetic field).

Restricted Range of Responsiveness

  • Each type of sensory receptor has a narrow range of energy to which it responds, e.g., hearing varies with species regarding frequency range.

Sensory Processing Begins in Receptor Cells

  • Receptor cells detect stimuli leading to action potentials, which are electrical signals.

  • Action potential generation:

    • A graded potential must reach a threshold to trigger an action potential.

    • Action potentials travel along sensory neurons to the CNS for perception.

Action Potentials

  • Neurons communicate using action potentials.

  • Resting potential: Inside neuron is negatively charged.

  • Action potential mechanism involves voltage-gated ion channels:

    • Na$^+$ and K$^+$ ions movement changes membrane potential:

    • Rapid movement of ions leads to a briefly reversed membrane polarity.

  • Action potentials:

    • Are all-or-nothing events.

    • Changes in stimulus intensity affect the frequency of fired action potentials (referred to as 'firing rate').

How Sensory Stimuli Produce Action Potentials

  • Example: Tactile stimulation through hair displacement.

  • Dendrites of sensory neurons detect displacement, causing Na$^+$ ion influx, leading to depolarization and potential action potential generation.

Brain Recognition of Sensations

  • Separate nerve tracts convey unique sensory modalities via labeled lines.

Cranial and Peripheral Nerves

  • Cranial Nerves: 12 pairs, with some sensory, some motor, some mixed.

  • Spinal Nerves: 31 pairs, contain dorsal (sensory) and ventral (motor) roots.

Learning Outcomes for Part 1

  • Distinguish between sensation and perception.

  • Identify features of sensory systems:

    • Sensory transduction and restricted responsiveness.

  • Describe function of sensory receptor cells and action potential generation.

  • Recognize how the brain uses nerve tracts to convey sensory information.

Part 2: Sensory Processing

Sensory Processing Characteristics

  • Sensory pathways transmit limited information.

  • Sensory processing is selective and analytical.

Factors in Sensory Processing

  • Stimulus Intensity: Reflected in action potential patterns and frequencies.

  • Stimulus Location: Determined by activated cells' position, with sensitive areas housing more cells.

  • Adaptation: Sensory habits gradually decrease response to a constant stimulus.

  • Suppression: Accessory structures may reduce sensory input; top-down processing adjusts lower brain activity.

  • Neural Relays: The route sensory information takes from receptor to cortex.

  • Receptive Fields: The space where a stimulus causes a response in a sensory neuron.

  • Attention: Focus on certain stimuli enhances processing.

Coding in Sensory Systems

  • Coding: Patterns of action potentials encode a stimulus.

  • Intensity Coding: More intense stimuli lead to higher frequencies of action potentials.

  • Range Fractionation: Different receptors respond to varying stimulus intensities, enabling accurate intensity coding across a broad range.

Adaptation and Suppression

  • Tonic Receptors: Little adaptation.

  • Phasic Receptors: High adaptation.

Sensory Processing Learning Outcomes

  • Describe features of sensory processing and information selection/analysis:

    • Coding, adaptation, suppression, neural relays, receptive fields, and attention.

Part 3: Taste and Smell

Chemical Senses

  • Taste (gustation) and smell (olfaction) help in survival.

  • Taste Qualities:

    • Sweet, sour, salty, bitter, umami (protein), and fats.

  • Smell Functions: Identify palatability, predators, prey, mates.

Taste (Gustation)

  • Humans can detect five basic tastes with complex flavor sensations involving both taste and smell.

  • Other factors contributing to taste experience include food appearance, texture, and temperature.

Taste Receptors

  • Taste receptors located primarily on the tongue, also in mouth and throat.

  • Taste buds are found within papillae, consisting of taste receptor cells with a lifespan of about two weeks.

Inaccurate Taste Map of the Tongue

  • The tongue can perceive all five tastes despite sensitivity variations across regions; each taste cell primarily responds to a single basic taste.

Taste Transduction Mechanisms

  • Salty and Sour Taste: Ionotropic taste receptors responding to ions (Na$^+$, H$^+$).

  • Bitter, Sweet, Umami: Metabotropic taste receptors activated by food molecules, leading to neurotransmitter release.

Transmission of Taste Information

  • Taste information travels via cranial nerves (Facial, Glossopharyngeal, and Vagus) to the gustatory cortex and integrates with sensory information in the orbitofrontal cortex.

Learning Outcomes for Part 3: Taste

  • Identify how taste cells work, the mechanisms of taste transduction, the cranial nerves involved, and the significance of the orbitofrontal cortex in flavor perception.

Smell (Olfaction)

  • Olfaction involves sensing airborne chemicals and can discriminate up to 10,000 odors.

  • Theorems suggest olfaction helps in identifying safety through food familiarity and social signals like pheromones.

Olfactory Sensitivity Variation

  • Rat sensitivity compared to humans; olfactory thresholds (anosmia to supersensitivity).

Anatomy of Olfaction

  • Odorants travel through nostrils to olfactory epithelium, where receptor cells generate signals transferred to the olfactory bulb and brain.

Olfactory Transduction Process

  • Odorants create depolarization, leading to action potential generation through GPCR activation.

Recognition of Odors

  • Each olfactory receptor cell uses a unique receptor from the olfactory gene set.

  • Recognition of scents associated with various receptor patterns leads to unique olfactory experiences.

Transmission of Odor Information

  • Information is transmitted to cortical areas for perception of smell; can affect emotions and memories.

Clinical Relevance of Chemosensory Dysfunction

  • Olfactory ability declines with age; deficits can indicate neurodegenerative diseases.

Learning Outcomes for Smell

  • Describe variations in olfactory sensitivity, the anatomy of olfaction, the mechanisms underlying transduction, and the pathways for odor information transmission.

Conclusion

  • This comprehensive understanding of sensory systems lays the foundation for further exploration of complex interactions and functioning in human perception relevant for various fields including psychology and neuroscience.