The sensory system

• Sensory System


  • Part of peripheral nervous system (afferent division)
  • Perceives environmental stimuli
• Sensory receptors


  • Convert physical stimuli to receptor potentials (type of graded potential)
  • Transducer
• Types of sensory receptors


  • Visual
  • Auditory
  • Olfactory
  • Gustatory
  • Somatic
• Sensory receptor types


  • Mechanoreceptors
  • Thermoreceptors
  • Photoreceptors
  • Chemoreceptors
  • Nociceptors
• Sensory receptors


  Dendrites of sensory neurons or separate cells
• Sensory receptor locations


  • Exteroceptors
  • Interoceptors
  • Proprioceptors
• General vs. Special Senses


  General senses: somatic

  Special senses: visual, auditory, olfactory, gustatory
• Receptive field


  Stimulated physical area, specific chemicals, or specific set of sound frequencies that cause a sensory response
• Receptive fields of different senses


  • Somatic
  • Auditory
  • Olfactory
  • Gustatory
  • Visual
• Sensory coding

  Use of organizational and functional features of the nervous system to indicate specific details about a stimulus
• Labeled lines


  Sensory coding to indicate specific details about a stimulus
• Quality discrimination


  Ability to distinguish among different submodalities
• Feature abstraction


  Detection of several features of a stimulus by several sensory neurons
• Acuity


  Differences in arrival time for somatic and visual senses

  Size of receptive field & lateral inhibition for olfactory and auditory senses
• Two-point discrimination threshold


  Stimulus location for somatic and visual senses is encoded by location of activated receptive field
• Frequency


  Use of action potential frequency to determine stimulus intensity
• Intensity


  Number of active sensory receptors

  Duration of stimulus
• Adaptation


  Response with prolonged stimulus

  Slowly adapting (tonic) vs. rapidly adapting (phasic)
• Somatic senses


  Stimulation of sensory receptors in skin, subcutaneous layer, skeletal muscles, tendons, and joints
• Somatic sense modalities


  • Light touch
  • Heavy touch
  • Vibration
  • Thermal
  • Pain
• Light touch


  Rapidly adapting receptors like Meissner corpuscles and root hair receptors
• Heavy touch


  Slowly adapting receptors like Merkel discs and Ruffini endings
• Vibration


  Rapidly adapting receptors like Meissner corpuscles and Pacinian corpuscles
• Thermal


  Thermoreceptors detect changes in temperature

  Involve transient receptor potential (TRP) channels
• Chemicals that activate thermoreceptors


  • Menthol
  • Camphor
  • Mint
  • Eucalyptol
  • Garlic
  • Mustard
  • Wasabi
  • Cinnamon
  • Sweet
  • Bitter
  • Umami
  • Capsaicin
  • Garlic
  • THC
  • CBD
  • Thyme
  • Basil
  • Clove
  • Nutmeg
• Pain


  Very important for survival, protective against continuous tissue damage

  3 types of nociceptors: mechanical, thermal, and polymodal
• Pain pathways


  • Spinal reflex pathway
  • Ascending pathway
• Pain threshold


  We all have the same pain threshold
• Pain responses


  • Conscious awareness
  • Arousal
  • Emotional response
  • Autonomic response
• Types of pain


  • Somatic pain
  • Visceral pain
  • Referred pain
• Olfaction


  Odorants dissolve into mucus membrane, bind to receptors, and signals sent to brain
• Olfactory receptor cells have over 1 trillion scent combinations
• Olfactory receptor cells


  Olfactory receptor cells, supporting cells, and basal cells
• Olfaction involves olfactory receptor cells, supporting cells, and basal cells
• Olfaction has very low threshold and rapidly adapts
• Interesting smell studies


  • Rikowski & Grammer 1999
  • Herz & Inzlicht 2002
  • Kuukasjärvi et al. 2004
  • Miller et al. 2007
• Taste


  Taste buds with gustatory receptor cells, supporting cells, and basal cells

  Also somatic receptors on tongue for touch, heat/cold
• Tastants


  Dissolve in saliva, enter taste pores, and bind to receptors
• Primary tastes


  • Sweet
  • Salty
  • Sour
  • Bitter
  • Umami
• Taste thresholds


  Sweet: 0.01 M

  Salty: 0.01 M

  Sour: 0.0007 M

  Bitter: 0.000008 M

  Umami: 0.0009 M