Chemosensation Flashcards
“Loss of taste” =
“Loss of smell” =
“ageusia”
“anosmia”
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
Smell: receptor cell, CN, primary sensory nucleus @ CNS, morphology of sensory epithelium
- ciliated, bipolar neuron
- CN I
- nucleus = olfactory bulb
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
Chemesthesis: receptor cell, CN, primary sensory nucleus @ CNS, morphology of sensory epithelium
- free nerve ending of cranial ganglion cell
- CN V
- Spinal trigeminal nucles
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
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
Types of taste receptor cells stimuli-response
- salty/sour (protons) detected via ion-gated channels
- sweet, bitter, umami rely on G-protein coupled receptors
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
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
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)
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
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
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