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The amazing structure of the olfactory epithelium: which cells make our sense of smell so sharp?
The olfactory epithelium is a specialized epithelial tissue located in the nasal cavity that is responsible for sensing odors. In the human body, this tissue covers an area of about 5 square centimeters and is located at the top of the nasal cavity, about 7 centimeters from the nostrils. The olfactory epithelium is directly responsible for the detection of odors, so how does it work together to make our sense of smell so sensitive?
Structure
The olfactory epithelium is composed of four different cell types:
- Olfaction receptor neurons
- Supporting cells
- Basal cells
- Brush cells
Olfaction receptor neurons
Olfactory receptor neurons are sensory neurons in the olfactory epithelium. They are bipolar neurons, with their apical extremes expressing odorant receptors located at the ends of non-motile cilia that stretch into the air to interact with odorant molecules. When odor molecules bind to receptors, these compounds are dissolved in the fluid secreted by the olfactory glands and delivered to the neurons.
The axons of olfactory receptor neurons gather to form the olfactory nerve (CN I), which transmits olfactory information to the brain.
Supporting cells
Stalto cells are similar to glial cells and are non-neuronal cells located on the top layer of the olfactory epithelium. These cells provide metabolic and physical support so that the olfactory system can function properly. Supporting cells can also be divided into two categories: persister cells and microvilli cells. Persistent cells provide metabolic and structural support, while microvilli cells are distinguished from other supporting cells by different morphological and biochemical characteristics.
Basal cells
Basal cells are located in the basal layer of the olfactory epithelium and are stem cells that can divide and differentiate into supporting or olfactory cells. Basal cells play a crucial role in the renewal process of the olfactory epithelium, which occurs every 6 to 8 weeks.
Basal cells can be divided into two types based on their cellular and histological characteristics: horizontal basal cells and globular basal cells.
Brush cells
Brush cells are columnar cells with microvilli. Their basal surface is in contact with the sensory nerve terminals of the trigeminal nerve and is specifically responsible for the transduction of general sensations.
Olfactory glands (parmenian glands)
The olfactory glands are glands located beneath the olfactory epithelium that secrete proteins to capture and dissolve odorants. The flow of these secretions helps wash out stale odors from the nasal passages, constantly keeping our sense of smell clear.
Development
The origin of the olfactory epithelium can be traced to two structures during embryonic development: the nasal plate and neural crest cells. The structure of the olfactory epithelium in embryos is simpler than that in adults. The first cells it relies on during development are epithelial cells, and then the generation of stem cells causes various types of cells to gradually appear.
By the end of embryonic development, the olfactory epithelium develops into a pseudo-multilayered columnar epithelium and begins to undergo secondary neurogenesis.
Clinical significance of smell
The olfactory epithelium can be damaged by factors such as inhalation of toxic smoke and physical damage to the interior of the nose. Although it has regenerative capabilities, in extreme cases, damage can result in permanent loss of smell (loss of smell).
Whether it’s the scent of flowers that appears frequently or the smell of delicious food passing by by chance, the sense of smell plays an indispensable role in life. In future research, how can scientists further explore the mysteries of the olfactory epithelium and solve more mysteries related to our senses?
