Chemical Senses Flashcards
Does olfactory tract have a thalamic relay?
No, goes directly to cortices. Projects to piriform cortex, olfactory tubercle, amygdala, and entorhinal cortex.
Structure of olfactory epithelium
Sits below cribiform plate. Basal surface has small unmyelinated axons that transmit information centrally. Apical surface has a single dendritic process that expands into knob from which cilia containing odorant receptors extend into a layer of mucus.
Olfactory basal cells
Stem cells that give rise to receptor cells
Olfactory sustentacular cells
Provide mechanical support for olfactory receptor cells and secrete mucus.
Bowmans glands
Produce mucus
Patterning of olfactory epithelium
Four bilaterally symmetric zone that have specific receptor subtypes.
Olfactory nerves composed of?
Axons of olfactory receptors that coalesce. each nerve passes through cribiform plate and projects ipsilaterally to olfactory bulb.
Olfactory glomeruli
Synaptic target of primary olfactory axons, synapses with mitral cells
Mitral cells
Principal projection neurons.
Are projections of olfactory bulb ipsilateral?
Mostly, some contralateral input maybe to inhibit other side to localize an odor.
Projection to dorsomedial thalamus?
Olfactory guided memory
Projection to hippocampus
Olfactory guided memory
Projection to insular and orbital cortex
Discrimination and identification of odors (taste integration)
Projection to lateral hypothalamus
Feeding behavior
Unique attributes of the olfactory system
The somas of the primary afferent neurons occupy the surface epithelium, the axons of primary afferents enter cortex directly, continuous turnover of neurons, pathway is mostly ipsilateral
Anosmia
Loss of smell
Hyposmia
Decreased sensitivity to odorants
Hyperosmia
Increased olfactory acuity
Olfactory agnosia
Aware of smell, can’t recall name
Parosmia/Dysosmia
Distortion in a smell experience
Cacosmia
Formation of repugnant olfactory hallucinations
Why does rhinitis/sinusitis affect smell?
Block access to olfactory epithelium, can also cause edema.
Raccoon/Panda Eyes
Drainage of venous blood to periorbital sinuses. Sign of skull fracture.
Why does aging cause olfactory dysfunction?
Decrease in turnover of new receptor neurons.
Epilepsy and olfactory system
Cacosmia before uncal seizures
Basic Pathway for Processing Taste Info
CN VII, IX, X project to NST in brainstem, which projects to the VPM of the thalamus, which projects to the insula and frontal cortex (specific interpretation of what we’re eating) then projects to amygdala (emotional response).
Where are taste buds distributed?
Along the lateral surfaces of taste papillae throughout the tongue.
How are taste buds structured?
Arranged around a taste pore, synapse immediately onto afferent axons.
Channels for 5 tastes?
Ion: Salt + sour
GPCR: Sweet bitter and umami
Projection of second order neurons from NST to thalamus?
Central tegmental tract
Primary gustatory cortex
Insula
How do neurons get from VPM to insula?
Through the posterior limb of the internal capsule. This is exclusively ipsilateral.
