Lec 24 Special Senses Flashcards
What is anosmia?
loss of smell
What is hyposmia?
decreased sensitivity to odorants
What is specific anosmia? possible cause?
inability to perceive odor of particular compound or class of compounds
- usually genetic/congenital
what is hyperosmia/olfactory hyperesthesia? cause?
increased olfactory acuity
- migraine, psychosis, substance abuse
What is olfactory agnosia? what does it suggest?
- aware of smel lbut can’t recall name
suggests problem with higher cortical area
what is parosmia/dysosmia?
distorting in a small experience
can happen with seizures
what is phantosmia?
- olfactory hallucination
- perceptions of smeel when no odor present
- happens in migraines/seizures
What is cacosmia? cause?
formation of disagreeable olfactory auras
- epilepsy/psychiatric disorders
What causes olfactory hallucinations/cacosmia/parosmia?
epilepsy
psychiatric disorders
Which bone is cribiform plate a part of?
ethmoid bone
what are raccoon eyes? sign of what?
sign of basilar skull fracture – tears meninges –> blood goes into sinuses
have trouble with smell
How does infection/sinus disease affect sense of smell?
- blocks access of odorants to olfactory epithelium
- can cause edema of olfactory epithelium
- treat with systemic anti-inflammatory drugs
how can viruses of URI effect smell?
can permanently damage olfactory epithelium
Where does seizures often originate from? why cause distorted smell?
originate from uncal region of temporal lobe
this is really close to olfactory bulb –> get cacosmia
How does olfaction change in aging?
- normal decline with age
- diminished peripheral sensitivity or altered central activity
- can affect palatabiliyt of foods
What is association olfactory and neurodegenerative diseases?
- involves central olfactory paths in alzheimers + parkinsons
- appears early in course of disease
What 3 CNs are responsible for taste?
CN V: anterior 2/3
VN IX: posterior 1/3
VN X: epiglottis
Where do taste nerves project?
synpase in solitary nucleus –> to VPM of thalamus –> insula and frontal cortex
travels via internal capsule
Where is primary taste cortex?
- frontal cortex
- insula
What is function of insula cortex vs frontal in taste response?
insula: specific interpretation of what you are eating
frontal: integration with other sensory stimuli
What is function of taste neurons that project to amygdala?
emotional response to what you are eating [yum vs yuck]
what are taste papillae?
consist of multiple taste buds [taste buds on lateral surface of papillae protuberances]
What are the functions of olfactory system?
- detection/identification of odorants
- intake regulation
- detection of nonmicrobial hazards
- role in human sexual behavior
What is unique about the olfactory tracts path to the cortex?
no stop over in thalamus [unlike the other senses] and goes straight to the olfactory cortex
What makes up the olfactory cortex?
piriform cortex = amygdala + incus + parahippocampal gyrus of temporal lobe
How does olfactory epithelium receive smell?
- cilia on apical epithelium capture odorants
What parts of olfactory receptors neurons on basal olfactory epithelium? what about apical?
basal: small, unmyelinated axons
apical: dendritic process that expands into knob from which cilia with odorant receptors extend
What are the basal cells of the olfactory epithelium?
stem cells that give rise to receptor cells
What is function of bowmans glands in olfactory epithelium?
produce mucus
What is contained in lamina propria?
- bundles of olfactory axons, blood vessels, fibrous tissue, bowmans glands
What is olfactory discrimination?
- usually specificity of receptors for different odorants
Ipsilateral or contralateral projections from olfactory bulb to olfactory neurons?
ipsilateral
What are the glomeruli of the olfactory bulb?
synaptic target of primary olfactory axons
– site of synapse with apical dendrites of mitral cells
what are mitral cells?
principal projection neurons of the olfactory bulb
what are tufted and periglomerular cells?
local circuit neurons that send dendritic processes to glomeruli
- can sharpen sensitivity of glomerular smell
What are granule cells?
innermost layer of olfactory bulb
- synapse on base dendrites of mitral cells
- establish local lateral inhibitory circuits with mitral cells and participate in synaptic palsticity
How do we localize smell?
process not totally clear, may be some sort of crossing over of fibers to inhibit contralateral side and help localize
What are the 4 unique attributes of olfactory system?
- somas of primary afferent neurons occcupy a surface epithelium
- axons of primary afferents enter cerebral cortex directly [no thalamic relay]
- primary afferent neurons undergo continuous turnover
- path to cortical centers in frontal lobe entirely ipsilateral
What are 3 main cell types in olfactory epithelium?
- olfactory receptor neurons
- supporting [sustentacular] cells
- basal cells
from what places does the olfactory bulb receive info?
- from neurons in nose
- also top-down info from amygdala, neocortex, hippocampus, substantia nigra, locus coeruleus
What is function of top down info that olfactory bulb receives?
- discriminating among odors, enhanced sensitivity
What does ability to detect odorous substance suggest about an olfactory lesion?
suggests the peripheral nerve and pathway are intact
what does ability to identify what a specific odor is suggest about an olfactory lesion?
indicates that cortical function is intacts
where is disorder likely to reside if pt is aware of smell but cannot recall name of scent?
likely in higher cortical levels of sensory system
What types of lesions typically present with unilateral olfactory deficiency?
due to nasal cavity disease or following tumor-associated compression injury of one olfactory bulb/tract
What types of lesions typically present with bilateral olfactory deficiency?
- head injury or common cold
- also advanced cases of olfactory groove meningioma
What types of neoplasms associated with olfactory dysfunction? unilateral or bilateral?
- olfactory neuroblastomas or meningiomas
- unilateral if compression injury of 1 olfactory tract/bulb; bilateral in advanced cases
what part of thalamus associated with taste?
VPM [ventral posterior medial]
What is the function of reciprocal projections connecting the nucleus of solitary tract to hypothalamus and amygdala?
- influence affective aspects of appetite [pleasure vs disgust] and satiety
What is the function of the secondary neocortical taste area? where is it?
- located in caudolateral orbitofrontal cortex
- neurons there respond to combo of visual, somatic sensory, olfactory, gustatory stimuli
- may be involved in conscious motivation to eat
What is contained in a single taste bud?
40-60 taste receptor cells
How long do taste cells last?
~ 2 wks, undergo continuous turnover
What are the 5 different types of taste?
- salt
- sour
- sweet
- bitter
- umami
What are the 3 afferent nerves that innervate taste buds?
- chorda tympani + greater petrosal of CN VII
- lingual branch of CN IX
- superior laryngeal branch of CN X
Where is the nucleus of solitary tract located?
medulla
What happens to 2nd order gustatory neurons from the solitary nucleus?
travel in central tegmental tract to VPM of thalamus
What happens to gustatory neruons from VPM?
travel through ipsilateral posterior limb of internal capsule to inner portion of frontal operculum and anterior insular cortex
Is the solitary nucleus –> VPM –> cortex path ipsilateral or contralateral?
exclusively ipsilateral
Where does integration of multiple sensory stimuli with taste occur?
secondary taste area in orbitofrontal cortex
What part of brain does affective associations with eating/food?
reciprocal projections from nucleus of solitary tract to hypothalamus and amygdala
What is ageusia?
complete lost of taste
what is hypogeusia?
decreased taste sensitivity
what is gustatory hallucination?
perception of taste when none present
What happens to taste in aging?
get progressive hypogeusia = decreased taste sensitivity
what happens to taste if lesion of CN 7 root OR tumor in internal auditory meatus OR oropharyngeal tumor?
ipsilateral loss of taste perception from anterior 2/3 tongue
What is effect of diabetes on taste?
progressive loss of taste sensation
