Notes on Non-Visual Sensory Systems from Lecture 4

Introduction to Non-Visual Sensory Systems

  • Course: NEUR2020 Neuroscience for Psychologists
  • Focus on auditory, vestibular, somatosensory, and chemical senses

Sensory Systems Overview

  • Sensory systems input and interpret information for accurate action
  • Categorized into three functional categories:
  • Exteroception: external environment information (What’s out there?)
    • Includes vision, audition, somatosensation, olfaction, gustation
    • Involves mostly conscious perception
  • Body Sense: awareness of body position (Where is my body?)
    • Includes vestibular sense and proprioception
    • Mostly unconscious processing
  • Interoception: internal states and homeostasis (How is my body?)
    • Involves bodily needs (e.g., hunger, temperature regulation)
    • Both conscious and unconscious elements

Exteroception

  • Determines external factors influencing behavior:
  • Approaching food, avoiding danger, navigating paths, engaging with potential mates

Body Sense

  • Regulates balance and movement through:
  • Vestibular sense: insights on head movements and gravity
  • Proprioception: awareness of body position and movement

Interoception

  • Sensory perception of internal states for optimal functioning
  • Homeostasis and allostasis connections with motivations and emotions

Auditory System

Overview

  • Processes sound: transmission, transduction, and interpretation

Ear Anatomy

  • Outer Ear: Auricle/pinna, auditory canal, tympanic membrane
  • Middle Ear: Ossicles (malleus, incus, stapes), oval/round windows
  • Inner Ear: Cochlea, semicircular canals

Sound Transmission

  • Outer Ear: Collects sound waves, funnels them to the tympanic membrane
  • Middle Ear: Impedance matching using ossicles to amplify vibrations
  • Up to a 22-fold increase in sound strength
  • Inner Ear: Converts pressure changes from sound waves into neural signals

Pitch Perception

  • Tonotopic Organization: Different frequencies processed in distinct regions
  • High frequencies at the base of the basilar membrane, low frequencies at the apex

Auditory Pathways

  • Complex network beginning from cochlear nuclei to the medial geniculate nucleus (MGN) of the thalamus, ultimately to primary auditory cortex (A1)

Sound Localization

  • Uses interaural time differences and interaural intensity differences for accurate localization
  • Time Difference: Sound arrives at each ear at different times based on source location
  • Intensity Difference: Head shadows sound from one ear to the other, helping to locate sound sources

Auditory Dysfunction

  1. Conduction Deafness: Issues in the outer or middle ear → hearing aids or implants
  2. Sensorineural Deafness: Problems with inner ear or auditory nerve → cochlear implants may help
  3. Central Deafness: Brain lesions affecting auditory areas → complex auditory processing issues

Vestibular System

Overview

  • Essential for maintaining body balance, head position, and coordination
  • Composed of three semicircular canals and two otolith organs

Semicircular Canals

  • Detect rotational movements along three axes
  • Fluid inertia contributes to hair cell activation during head rotations

Otolith Organs

  • Detect linear accelerations and gravitational forces
  • Hair cells respond to tilting and movement

Vestibular-Ocular Reflex

  • Coordinates eye movements to maintain visual stability during head movement
  • Loss of VOR may cause oscillopsia (perceived motion of the visual field)

Somatosensory System

Overview

  • Integrates multiple sensory modalities related to touch and body awareness

Types of Receptors

  • Exteroceptive: Mechanoreceptors (touch, pressure), nociceptors (pain), thermoreceptors (temperature)
  • Proprioceptors: Provide information about body positioning and motion
  • Interoceptors: Signal internal bodily conditions

Somatosensory Pathways

  • Dorsal Column-Medial Lemniscus Pathway: Touch and proprioception (fast)
  • Anterolateral System: Pain and temperature (slow)

Cortical Representation

  • Primary Somatosensory Cortex (S1) and Secondary Somatosensory Cortex (S2) are organized somatotopically (sensory homunculus)

Chemical Senses

Olfaction

  • Detects volatile chemicals via olfactory receptor neurons (ORN)
  • Olfactory pathways connect directly to the limbic system, influencing emotions and memories

Gustation

  • Five primary tastes: sweet, sour, salty, bitter, umami
  • Taste perception involves cortical processing of combined sensory inputs
  • Distinction between sweet and bitter based on sensitivity

Gustatory Dysfunction

  • Ageusia: inability to taste
  • Parosmia: distorted smell
  • Phantosmia: perceiving odors that aren’t present

Key Learnings

  • Importance of auditory amplification, vestibular functions, somatosensory pathways, and chemical senses for survival and interaction with the environment
  • Complexity of both processing and potential dysfunction highlights the need for integrated understanding in neuroscience studies.