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Nervous System: Unit III > Chemosensation > Flashcards

Flashcards in Chemosensation Deck (17)
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1

"Loss of taste" =

"Loss of smell" = 

"ageusia"

"anosmia"

2

Chemosensory systems that make up "taste" sensation

  • olfaction = smell;  olfactory neuroreceptors @ roof of nasal cavity
  • gustation = taste buds @ oral cavity/pharynx to detect sweet, sour, bitter, salty, umami
  • chemesthesis = detection of irritant/noxious chemicals by sensory processes of tigeminal extending into nose/mouth

3

Smell: receptor cell, CN, primary sensory nucleus @ CNS, morphology of sensory epithelium

  • ciliated, bipolar neuron
  • CN I
  • nucleus = olfactory bulb

4

Gustation: receptor cell, CN, primary sensory nucleus @ CNS, morphology of sensory epithelium

  • modified epithelial cell ==> synapses onto nerve fiber from cranial ganglion cell
  • CN VII, IX, X
  • Nucleus of the solitary tract

5

Chemesthesis:  receptor cell, CN, primary sensory nucleus @ CNS, morphology of sensory epithelium

  • free nerve ending of cranial ganglion cell
  • CN V
  • Spinal trigeminal nucles

6

Types of papillae

  • Taste papillae = contain taste buds
    • fungiform = @ anterior end of tongue
    • foliate papillae = @ sides of the tongue
    • cirumvallate papillae = @ posterior part of tongue
  • filiform papillae = non-taste = tactile organs

7

Innervation of the tongue

  • chorda tympani (facial nerve) ==> fungiform taste papillae @ anterior 2/3
  • glossopharyngeal ==> circumvallate papillae
  • superior petrosal (facial nerve) ==> palate
  • vagus ==> extreme posterior tongue, oropharynx, epiglottis

8

Types of taste receptor cells stimuli-response

  • salty/sour (protons) detected via ion-gated channels
  • sweet, bitter, umami rely on G-protein coupled receptors

9

Central taste pathways (conscious)

  • afferents from tongue (via CN VII, CN IX, CN X) ==> ipsilateral nucleus of the solitary tract
    • organized "orotopically"
  • ==> bilateral medial portion of ventrobasal thalamus (VPMpc) ==> insular cortex = primary gustatory area = conscious appreciation of taste
  • integration/perception of flavor = @ secondary gustatory cortex (receives projections from primary gustatory and olfactory areas of insula

10

Central taste pathways (sub-conscious)

  • NST ==> hypothalamus and amygdala for regulation of food intake and visceral reactions to ingested foods
  • NST ==> reflex connections to brainstem nuclei involved in gagging, swallowing and salivation

11

Variations in taste sensitivities and impacts on health

  • bitter = evoluntionarily important in avoidance of noxious/harmful chemicals and foods
  • bitterness of drugs ==> decreased compliance; use-limiting factor
  • sensitivity to bitterness ==>
    • eating less vegetables
    • nutritionnally-related pathology (e.g. colonic neoplasms)

12

Peripheral anatomy of olfactory system

  • olfactory neuroepithelium is covered w/a thin layer of mucus
  • olfactory neurons extend cilia into mucus layer
    • cilia ==> expand SA of olfactory membrane exposed to mucus
  • olfactory neurons = bipolar = dendrite @ one end & single, thin unmyelinated axon from other end ==> olfactory bulb ==> CN I

13

Characteristics of odorant interaction with olfactory neurons

  • odorants dissolve in mucus ==> interact w/olfactory receptor proteins
    • clia contain most of biochem machinery necessary to tranduce chemical to electrical signal

14

15

Peripheral mechanisms of olfactory transduction

  • recognition of odors via one or more olfactory receptor proteins on ciliary membrane
    • 7TM g-coupled receptor proetins
    • subfamilies probably bind distinct odorants
    • each receptor predominantly expresses one type of receptor
  • Golf ==> activates adenylate cyclase ==> increase cAMP ==> opening of ion channels ==> amplified depolarization ==> AP @ cell body

16

Olfactory sensation @ the olfactory bulb

  • overall: olfactory neurons ==> olfactory bulb ==> central olfactory system
  • olfactory neurons ==> excitatory synapses w/apical dendrites of  mitral (tufted) cells
    • olfactory neurons w/similar ORproteins proect to same glomerulus ==>
    • odor-related map of glomeruli @ olfactory bulb
  • identification of odors entails recognitions of the pattern of activity across all glomeruli

17

Central olfactory pathways

  • olfactory bulb projects directly to cortex
  • olfactory bulb axons ==> lateral olfacotry tract ==>
    • olfactory cortex = lateral olfactory gyrus + part of uncus
      • olfactory cortex divided into:
      • piriform cortex ==> orbitofrontal (secondary gustatory) cortex directly + via MD thalamus
      • entorhinal cortex ==> hippocampus
    • olfactory tubercle ==> hypothalamus
    • amygdala ==> hypothalamus