Smell
Terms
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- Four groups of Olfactory Disturbances
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1. Quantitative abnormalities
2. Qualitative abnormalities
3. Olfactory Hallucinations/delusions
4. Higher-Order loss of discrimination - 1. Quantitative Olfactory Abnormalities
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a. Anosmia (or hyposmia)
b. hyperosmia - 2. Qualitative Olfactory Abnormalities
- a. dysosmia (or parosmia)
- 3. Olfactory Halllucinations/delusions
- a. uncinate fits
- 4. Higher order loss of Olfactory discrimination
- a. Olfactory agnosia
- Anosmia (or hyposmia)
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Loss or reduction of sense of smell
- can be at the nasal, neuroepithelial, or central level
- if bilateral, pt usually complains of ageusia (loss of taste) - Hyperosmia
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Increased olfactory acuity
- very rare - Dysosmia (or parosmia)
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Distortions or illusions of smell
- may be assoc with depressive illness - Uncinate fits
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Olfactory hallucinations associated with temporal lobe seizures
- always of central origin - Olfactory Agnosia
- Perceptual aspects intact, but can't recognize the smell
- What is the Olfactory Epithelium?
- receptor surface for olfaction and is located in the nasal cavity (peripheral beginning of olfactory system)
- What is the Olfactory tract?
- Formed by the axons of the olfactory receptor cells
- Where do the axons of the olfactory receptor cells synapse?
- The Olfactory Bulb
- After the olfactory bulb, what is the next connection of the olfactory system?
- The Pyriform cortex
- From the pyriform cortex, the primary projection goes to:
- Dorsal medial thalamic nucleus
- The Dorsal medial thalamic nucleus projects where?
- The Orbital frontal cortex
- The second projection from the pyriform cortex goes to:
- Lateral hypothalamus
- The lateral hypothalamus projects where?
- The Orbital frontal cortex
- What is the primary olfactory neocortex?
- The orbital frontal cortex
- What are the two parallel routes for olfactory input to the cortex?
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1. Dorsal medial thalamus
2. Lateral hypothalamus - What are the majory connections of the olfactory system?
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1. Olfactory Bulb
2. Pyriform cortex
3/4. Dorsal medial thalamus/Lateral hypothalamus (parallel routes)
5. Orbital frontal cortex - Olfactory receptor neurons
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1. Are true neurons
2. A single dendrite and a single axon
3. Axon is unmyelinated, resulting in slow conduction - What is the Olfactory filia?
- Collection of olfactory receptor neurons which make up the first cranial nerve
- What is unique about the sense of smell?
- It does not involve a direct relay from the thalamus (although the thalamus is part of subsequent olfactory circuitry)
- Are olfactory receptor neurons represented in the contralateral or ipsilatera cerebral hemisphere?
- Ipsilateral
- What are the two general kinds of processes that can disrupt the sense of smell?
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1. Conductive olfactory deficit
2. Sensorineural olfactory deficit - What happens in a conductive olfactory deficit?
- A process prevents odorants from reaching the olfactory epithelium
- What happens in a sensorineural olfactory deficit?
- A process damages olfactory receptor neurons or parts of the olfactory CNS
- What can cause conductive olfactory deficits?
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Nasal polyps
Septal deviations
Inflammations - What can cause sensorineural olfactory deficits?
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Head Injuries
Neurodegenerative disorders (Parkinson's and Alzheimer's)