Download Document 8570771

DENT/OBHS 131
Neuroscience
taste & smell
2009
Learning Objectives
1. Describe the cranial nerve / brainstem sensory
innervation of the taste buds / tongue
2. Explain the general ionic mechanism of taste cell
excitation
3. Identify the cortical regions important for primary
gustation
4. Compare and contrast olfaction with other sensory
modalities, including its cranial nerve and nature of
projection to cortex
5. Discuss how sub-modalities of taste and smell are sorted
as they ascend to the cortex
6. Appreciate that taste / smell and other sensory modalities
are combined at the level of the cortex along with limbic
information to produce full sensation of flavor
Gustatory & olfactory systems
• Extract information from chemicals in the
environment
• G-protein coupled receptors
• Taste: (+ ion channels)
• Taste and olfactory receptor cells undergo
continual lifetime turnover
• Taste: modified epithelial cells
• Smell: neurons
• Stimulus information is encoded in
populations of neurons
Significance
• Emotion and memory: limbic system
Perception of flavor
• The chemical senses act
in concert
• Multiple components:
• Taste buds
• Olfactory receptors
• Free-nerve endings (CN V)
e.g. spiciness &
temperature
• Emotional and cognitive
valence
Taste
Blue tongue disease
Taste buds
• Lingual buds:
• Foliate
• Fungiform
• Circumvallate
• 2000-5000 buds
• 50-150 taste cells
Papillae, buds & cells
• circumvallate
Learning Objective #1
• Describe the cranial nerve / brainstem
sensory innervation of the taste buds /
tongue
Innervation
• Chorda tympani (VII)
• Taste map - myth?
• palate & pharynx
Rostral medulla
• Why are we here?
CNs and solitary nucleus/tract
VII
IX
X
• Principal visceral sensory relay
• Rostral portion
Learning Objective #2
• Explain the general ionic mechanism of
taste cell excitation
Taste transduction
• Specific chemical interaction
• microvillae
• G-protein receptor
• Ion channel
• Depolarization
• Passive spread is enough
• …but can produce APs
• Ca2+ entry
• Transmitter (glutamate) release
G-proteins & ion channels
•
•
•
•
•
•
Sweet
Salty
Sour
Bitter
“Umami”
TRP
channels
(see PAIN)
Tim Jacob
(Cardiff University, UK)
Anatomical path
• Primary gustatory cortex
• Insular / frontal operculum
• VPM (head - sensory)
• Cortical relay
• via central tegmental tract (ipsi)
• Rostral pons (to other regions)
• Parabrachial nucleus (non-human)
• Rostral medulla
• reflexes, e.g. DMN X
Cortical processing
• orbitofrontal cortex
• integration, e.g.,
olfactory information
• Projections
• amygdala
• hypothalamus
• striatum
Learning Objectives #3 & 4
• Identify the cortical regions important for
primary gustation
• Discuss how sub-modalities of taste and
smell are sorted as they ascend to the
cortex
Broad tuning of taste pathway
• Solitarius cell - multiple
• Orbital cortex cell - selective
Neural coding of taste
Olfaction
• My dog’s got no nose….
• How does it smell?
• Awful
Teaching Objective #5
• Compare and contrast olfaction with other
sensory modalities, including its cranial
nerve and nature of projection to cortex
Anatomical points
• Olfactory receptor cells are real neurons
• CN I & bulb is really part of the CNS
• No thalamic relay
Olfactory receptor neurons
Epithelia - surface area
Olfactory transduction
• very fine unmyelinated axons
Learning Objective #5
• Discuss how sub-modalities of taste and
smell are sorted as they ascend to the
cortex
Glomeruli - olfactory bulb
• mitral cells
• Convergence (1000’s) & sorting
CNS pathways
• Anterior olfactory nucleus
• Inhibit contralateral bulb
• Olfactory tubercule
• Primary olfactory cortex
• Piriform cortex (temporal lobe)
• Periamydaloid cortex
• (part of) parahippocampal gyrus
• Further projections
• Limbic system - amygdala
• Thalamus
Learning Objective #6
• Appreciate that taste / smell and other
sensory modalities are combined at the
level of the cortex along with limbic
information to produce full sensation of
flavor
Thalamic relay
memory &
emotion
dorsomedial nucleus
smell selectivity & integration
damage
• Anosmia
• Taste loss?
• Parkinson’s disease
• Seizures (uncinate)
• Begin with smell or taste
(unpleasant)