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Related Concept Videos

Narcolepsy01:07

Narcolepsy

Narcolepsy is a chronic sleep disorder characterized by pervasive, uncontrolled sleepiness and other sleep disturbances. One of its hallmark symptoms is an abrupt transition to REM sleep upon falling asleep, which causes symptoms typically associated with this phase to occur unexpectedly during wakefulness. These include the following symptoms, which typically last from a minute or two to half an hour.
Sleep-Wake Cycles01:24

Sleep-Wake Cycles

Sleep is an essential physiological process vital to maintaining overall well-being. The reticular activating system (RAS), a network of neurons in the brainstem, regulates wakefulness and sleep. While it may seem passive, sleep consists of distinct cycles, each with its unique characteristics and functions. Two key sleep phases are non-rapid eye movement (NREM) and  rapid eye movement (REM).
NREM Sleep
NREM sleep comprises four progressive stages that seamlessly merge:
Olfactory Receptors: Location and Structure01:03

Olfactory Receptors: Location and Structure

The process of olfaction, also known as the sense of smell, is a sophisticated chemical response system. The specialized sensory neurons that facilitate this process, known as olfactory receptor neurons, are situated in an upper segment of the nasal cavity, known as the olfactory epithelium. Olfactory sensory neurons are bipolar, with their dendrites extending from the epithelium's apex into the mucus that lines the nasal cavity. Airborne molecules, when inhaled, traverse the olfactory...
Olfaction01:25

Olfaction

The sense of smell is achieved through the activities of the olfactory system. It starts when an airborne odorant enters the nasal cavity and reaches olfactory epithelium (OE). The OE is protected by a thin layer of mucus, which also serves the purpose of dissolving more complex compounds into simpler chemical odorants. The size of the OE and the density of sensory neurons varies among species; in humans, the OE is only about 9-10 cm2.
The olfactory receptors are embedded in the cilia of the...
Physiology of Smell and Olfactory Pathway01:20

Physiology of Smell and Olfactory Pathway

Humans detect odors with the help of specialized cells located in the upper part of the nasal cavity, called olfactory receptor neurons (ORNs). ORNs possess hair-like structures called cilia, which are receptive to sensations from the inhaled air. When an odorant molecule binds to a specific receptor on the cell of the cilia, it leads to a series of events that ultimately cause the ORN to send electrical signals to the olfactory bulb in the brain through the olfactory nerves.
The olfactory...
Sleep Apnea01:21

Sleep Apnea

Sleep apnea is a condition where breathing stops intermittently during sleep, often leading to significant health issues. Each episode can last from 10 to 20 seconds or more and is frequently accompanied by a brief arousal from sleep. This disturbance, largely unnoticed by the individual, can lead to severe daytime fatigue. Commonly, individuals seek help after being informed by their partners about loud snoring and noticeable breathing pauses during sleep.
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Related Experiment Video

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Olfactory Assays for Mouse Models of Neurodegenerative Disease
07:27

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Published on: August 25, 2014

Olfactory dysfunction in narcolepsy with and without cataplexy.

Jitka Buskova1, Jan Klaschka, Karel Sonka

  • 1Department of Neurology, 1st Faculty of Medicine, Charles University, Prague, Czech Republic. vankjit@seznam.cz

Sleep Medicine
|June 2, 2010
PubMed
Summary

Olfactory dysfunction is present in both narcolepsy with cataplexy and narcolepsy without cataplexy. This suggests that even partial loss of hypocretin neurons can impact smell perception.

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Area of Science:

  • Neurology
  • Sleep Medicine
  • Sensory Neuroscience

Background:

  • Olfactory dysfunction is observed in narcolepsy patients, including those with REM sleep behavior disorder (RBD).
  • Previous research has focused on narcolepsy with cataplexy (N-C), but the olfactory function in narcolepsy without cataplexy (NwC) remains less understood.

Purpose of the Study:

  • To investigate whether olfactory dysfunction is specific to narcolepsy with cataplexy (N-C).
  • To determine if narcolepsy without cataplexy (NwC) is also associated with impaired olfactory function.

Main Methods:

  • Olfactory function was assessed in two patient groups: N-C (n=66) and NwC (n=17).
  • Standardized smell tests were used to measure olfactory threshold and odor identification.
  • Published normative data served as the control group.

Main Results:

  • Patients with both N-C and NwC exhibited significantly higher olfactory thresholds (p<0.0001 for both groups).
  • Impaired odor identification was also observed in both N-C (p<0.0001) and NwC (p<0.0001) groups.
  • This study is the first to demonstrate olfactory dysfunction in NwC, where hypocretin levels are often normal.

Conclusions:

  • Narcolepsy without cataplexy is associated with olfactory dysfunction, similar to narcolepsy with cataplexy.
  • These findings suggest that even subtle reductions in hypothalamic hypocretin neurons can affect olfactory pathways.
  • Partial loss of hypocretin neurons, even without significantly decreased CSF levels, may contribute to smell impairment in narcolepsy.