Neuroanatomy of Gustation and Olfaction Flashcards
What is the role of olfactory receptor neurons?
Allows you to recognize thousands of air-borne odors even at extremely low concentrations
What is the significance of thin nasal bones?
Thin bones allows the olfactory receptor neurons to be sensitive to facial trauma
Describe the taste capabilities of the gustatory system
Very limited range
Sweet, salty, sour, bitter and umami (important for identifying amino acids)
What allows you to accept/reject foods and taste things other than the four basic tastes
Different combination of taste receptors
What is the significance of the olfactory bulb and tract?
Olfactory receptors synapse at the bulb in the cribiform plate and processes odors.
Tract transmits sensory info to the brain
*Anatomy of the cribriform plate
The bulb sits here. Located at rostral end of the olfactory sulcus and anterior cranial fossa
*Anatomy of olfactory receptor neurons
Located on the roof of nasal cavity/inferior surface of cribriform plate, along nasal septum and medial wall of superior nasal conchae
What is CN I?
Olfactory receptor Neuron. Has a single dendritic process that receives info from envt. Receptors are in the olfactory mucosa of the superior nasal cavity
What is the importance of ducts and glands?
Keep the olfactory epithelium moist
*What is the role of the supporting cells?
Surround the olfactory nerve bodies. Have receptors extending to the olfactory epithelium to catch smell molecules
Cilia on ORNs
Nonmotile and contain GPCR (ligand gated) receptors. Ligand binding = signal sent to olfactory bulb
What is the significance of the lamina propria?
How about Basal cells?
- Holds immune cells (important since the mucosa is exposed to external envt)
- act as stem cells for ORNs and supporting cells
What is the significance of Brush cells?
How about Mucus
- ciliated columnar epithelial cells
- made and secreted by glands and ducts in the Olfactory epithelium
Describe how the smell molecules reach the olfactory bulb
Smell molecule ligand binds to GPCR on ORN > contact mucus layer on olfactory epithelium and interacts with odorant binding proteins in the mucus > adenyl cyclase activation = increase cAMP > ion channels open and increase in Ca and Na influx > action potential to the olfactory bulb
*Describe the organization of the olfactory bulb
An ORN GPCR accepts a particular smell ligand. In the bulb the ORNs are grouped according to the ligand they respond to. Different ORN combination results in smelling different things
What is the significance of granule cell layer?
Deepest of the olfactory bulb. Has granule cells which are the interneurons of the olfactory bulb that help regulate other cells
*What is the significance of the mitral cell layer?
Has mitral cell bodes and axons of the tufted cells that carry sensory info received from the ORNs and transmit it to the brain
What is the importance of the External plexiform layer?
Has dendrites of the tufted, mitral and granule cells. Cross talk between these cells happen in this layer.
What molecule do granule cells use to modulate tufted and mitral cell output?
GABA (lowers mitral/tufted cell activity)
*What is the importance of the glomerular cell layer?
ORNs synapse to the olfactory bulb in this layer
*What is the importance of the olfactory nerve layer?
Has the ORN axons that penetrate the cribriform plate
**What is the role of centrifugal fibers?
Carry info from brain to bulb via the anterior commissure. Regulates feedback loops
What is the olfactory glomeruli? Describe the nature of the ORNs synapsing on the glomerulus
ORNs will synapse on tufted and mitral cells in the glomerulus.
One glomerulus has lots of ORNs sensitive to the same odor molecule synapsing but ORN only synapses on 1 glomerulus.
How do you adapt to smell?
Negative feedback of granular cells inhibit the propagation of info by mitral and tufted cells when you smell something for long enough
How is info about olfaction transmitted to the brain?
Via mitral/tufted cells to the lateral olfactory tract
Importance of olfactory projections to the hippocampus, amygdala and dorsomedial thalamic nucleus
Hippocampus - memory
Amygdala - recognize danger and fear
Dorsomedial nucleus - secondary projection from the olfactory cortex for further info processing
Draw the different projections of olfactory info from the lateral olfactory tract
Ok
What is the paleocortex and neocortex and what are their significance?
Paleocortex (primitive cortex) where the olfactory cortex is. Sends projections to other areas (neocortex areas)
Neocortex helps discriminate odors
Significance of the orbitofrontal cortex?
Where integration of smell and taste occur
Where are taste buds found?
All over the oropharyngeal cavity, not just the tongue
Describe the pathway of taste perception
Taste molecules diffuse through taste pore and bind to receptors on apical microvilli > cell depolarize or hyperpolarize > action potential relayed to afferents > fibers from the facial nerve (chorda tympani) synapse to the solitary tract > solitary nucleus > gustatory nucleus (rostral portion of the solitary nucleus)
Importance of the chorda tympani and soft palate
- Innervates the fungiform papillae and anterior foliate papillae (anterior 2/3)
- taste buds here are innervated by the greater superficial petrosal nerve (also from CN VII)
Importance of the pontomedullary junction and geniculate ganglia
Afferents from facial nerve carry info and enter the brainstem here
Where sensory cell bodies of CN VII are. Carry taste to the rostral solitary nucleus (gustatory nucleus)
Tongue innervation
Anterior 2/3 = lingual n. (from CN V) for sensation and chorda tympani for taste
Posterior 1/3 = CN IX
Which papillae does VII innervate?
Which papillae does IX innervate?
Which does X innervate?
Filiform, fungiform and anterior foliate
Posterior foliate, vallate
Median glosso-epiglottic fold
*Describe the gustation pathway
Taste molecule binds receptors on papillae > depolarize the taste bud receptors > AP > travels to solitary tract > solitary nucleus > ipsilateral central tegmental tract > parvicellular ventral posteromedial nucleus > ipsilateral posterior limb of internal capsule > frontal operculum and anterior insular cortex > Brodmann area 3b > Lateral posterior orbitofrontal cortex with all other action potentials
What is anosmia?
Hyposomia?
- loss of smell
- decreased sensitivity to odorants
What is ageusia?
Hypoguesia?
Parageusia/dysgeusia
Complete loss of taste. Rare since many CNs ( VII , IX and X) carry taste info
Decreased taste sensitivity
Altered taste perception (due to drug use)
Lesions of CN VII
Can be caused by vestibular schwannoma in the Internal Auditory meatus by compressing the chorda tympani. Results in loss of taste in anterior 2/3 of tongue on ipsilateral side, ipsilateral facial paralysis, hearing loss (due to stapedius), impaired gland secretion
Lesion of distal geniculate ganglion?
Facial nerve fibers synapse here first. Facial paralysis possibly with or without taste loss
