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Sensation Of Smell |Olfactory Pathway - Physiology
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- Опубліковано 5 сер 2020
- limbic system at the olfactory bulbs.
Central
Details of olfaction system
The main olfactory bulb transmits pulses to both mitral and tufted cells, which help determine odor concentration based on the time certain neuron clusters fire (called 'timing code'). These cells also note differences between highly similar odors and use that data to aid in later recognition. The cells are different with mitral having low firing-rates and being easily inhibited by neighboring cells, while tufted have high rates of firing and are more difficult to inhibit.
Stria terminalis, specifically bed nuclei (BNST), act as the information pathway between the amygdala and hypothalamus, as well as the hypothalamus and pituitary gland. BNST abnormalities often lead to sexual confusion and immaturity. BNST also connects to the septal area, rewarding sexual behavior.
Mitral pulses to the hypothalamus promote/discourage feeding, whereas accessory olfactory bulb pulses regulate reproductive and odor-related-reflex processes.
The hippocampus (although minimally connected to the main olfactory bulb) receives almost all of its olfactory information via the amygdala (either directly or via the BNST). The hippocampus forms new and reinforces existing memories.
Similarly, the parahippocampus encodes, recognizes and contextualizes scenes. The parahippocampal gyrus houses the topographical map for olfaction.
The orbitofrontal cortex (OFC) is heavily correlated with the cingulate gyrus and septal area to act out positive/negative reinforcement. The OFC is the expectation of reward/punishment in response to stimuli. The OFC represents the emotion and reward in decision making.
The anterior olfactory nucleus distributes reciprocal signals between the olfactory bulb and piriform cortex.The anterior olfactory nucleus is the memory hub for smell.
1: Olfactory bulb
2: Mitral cells
3: Bone
4: Nasal epithelium
5: Glomerulus
6: Olfactory receptor cells
Clinical significance
Loss of smell is known as anosmia. Anosmia can occur on both sides or a single side.
Olfactory problems can be divided into different types based on their malfunction. The olfactory dysfunction can be total (anosmia), incomplete (partial anosmia, hyposmia, or microsmia), distorted (dysosmia), or can be characterized by spontaneous sensations like phantosmia. An inability to recognize odors despite a normally functioning olfactory system is termed olfactory agnosia. Hyperosmia is a rare condition typified by an abnormally heightened sense of smell. Like vision and hearing, the olfactory problems can be bilateral or unilateral meaning if a person has anosmia on the right side of the nose but not the left, it is a unilateral right anosmia. On the other hand, if it is on both sides of the nose it is called bilateral anosmia or total anosmia.
Destruction to olfactory bulb, tract, and primary cortex (brodmann area 34) results in anosmia on the same side as the destruction. Also, irritative lesion of the uncus results in olfactory hallucinations.
Damage to the olfactory system can occur by traumatic brain injury, cancer, infection, inhalation of toxic fumes, or neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. These conditions can cause anosmia. In contrast, recent finding suggested the molecular aspects of olfactory dysfunction can be recognized as a hallmark of amyloidogenesis-related diseases and there may even be a causal link through the disruption of multivalent metal ion transport and storage.Doctors can detect damage to the olfactory system by presenting the patient with odors via a scratch and sniff card or by having the patient close their eyes and try to identify commonly available odors like coffee or peppermint candy. Doctors must exclude other diseases that inhibit or eliminate 'the sense of smell' such as chronic colds or sinusitus before making the diagnosis that there is permanent damage to the olfactory system.
Prevalence of olfactory dysfunction in the general US population was assessed by questionnaire and examination in a national health survey in 2012-2014.[26] Among over a thousand persons aged 40 years and older, 12.0% reported a problem with smell in the past 12 months and 12.4% had olfactory dysfunction on examination. Prevalence rose from 4.2% at age 40-49 to 39.4% at 80 years and older and was higher in men than women, in blacks and Mexican Americans than in whites and in less than more educated. Of concern for safety, 20% of persons aged 70 and older were unable to identify smoke and 31%, natural gas.
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@@Dr.KareemaTabassum thank you,and I killed my exam. All thanks to you
Super explanation with time management
Thank you 😊
Thank you so much dear Ma'am 😭❤I used to find that much much tough!
Sooooo helpful thank you so much❤
Thank you so much ....it is very helpful plz do make more such vedios🙏🙏
You're welcome, sure😊
Great one
Your are saying it in a nice way put more videos
Nice explanation
Thank you for this Video!
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Read Psalm 139, 1 to 16
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ma'am this vedio was totally helpful
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Tysm ma'am!
Fabulous.
Thank you
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Very helpful
Thank you 😊
Okay but it could have been great if u discussed a bit about olfactory stria❤
Please shair the picture and video last. Its very useful
Gazab video
Thank you 😊
Excellent
Thank you😊
Thank u so much mam
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nice
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Thank you❤️
Thanks mam
Mam
In ak jain and sembulimvam both have different diagram of this pathway
.which to refer
Hello, for sensation of smell, I think the diagram given in sembulimgam suits best for the theory exam !
@@Dr.KareemaTabassum ohk .... thanks soo much 🙏🙏
You're welcome 😊
Tq so much mam
You're welcome,keep watching ❤️
nice
very halpfull
Thank you, glad it was helpful ❤️
Which book you refer mam??
I refer, A.K.Jain and Sembulimgam.
👍👍
Nice video 👍👌👏
Thank you ☺️
Well
Do you have a telegram channel???
Malayalam parayumo
Sensation of hearing 👂 and vision plz video
Can u explain in hindi or urdu?
Adenylyl cyclase*
Person with total anosmia here. Seems I was born like that. Statistically 1 in 8.000 persons has that condition.
Could be a mutation maybe morphologic structures like olfactory bulbs were not built.
Ye page mil nh sakta
OMG, thank you, that means alot!❤️
Mine is on steroids. Other people actually make me sick. I can smell everything on them.