The nose is the protruding structure at the center of the face that serves as the organ of smell and entrance of the respiratory system. The paranasal sinuses (maxillary, frontal, ethmoidal, sphenoid) are air-filled cavities within the bones of the skull that surround the nasal cavity. The nose and the paranasal sinuses provide resonance to the voice and humidify and warm inhaled air. The nasal cavity consists of a respiratory region, which is lined with ciliated pseudostratified columnar epithelium interspersed with goblet cells, and an olfactory region, which is lined with pseudostratified ciliated columnar epithelium interspersed with olfactory receptor neurons. Olfactory information is communicated to the brain via the olfactory nerve (CN I), which arises from the respiratory epithelium. The olfactory receptor neurons in the respiratory epithelium react with odorants via diffusion of odorant-binding proteins. The signal is carried by olfactory receptor neurons, whose axons bundle in fascicles. These fascicles then pass through the cribriform plate of the ethmoid bone and form the olfactory bulb within the forebrain. From there the signal is transmitted on to the target regions in the brain via the olfactory tract. Unlike other sensory tracts, the olfactory tract bypasses the thalamic nuclei and projects directly into the primary olfactory cortex. Diseases affecting the nose and the paranasal sinuses include nasal polyps, epistaxis, choanal atresia, and sinusitis.
The nose contains the human olfactory system, which is responsible for the sense of smell. The paranasal sinuses are a group of air-filled structures within the frontal bone and the facial skeleton. Together, they fulfill the following functions:
- The nose contains the , which is responsible for transmission of olfactory signals from the olfactory epithelium to the brain.
- Paranasal sinuses are air-filled cavities within the bones of the skull (, , ) and face ().
- The nose and paranasal sinuses aid help provide resonance to the voice.
- The nose and paranasal sinuses warm and humidify air that is inhaled.
- The nose and paranasal sinuses are part of the mucosal immune system
|Frontal sinus|| || |
|Ethmoidal sinus|| |
|Sphenoid sinus|| || |
|Maxillary sinus|| || |
- Frontal, , , nasal, palatine,
- Roof: composed of the nasal, frontal, ( ), and
- Floor: composed of the (palatine process) and the (horizontal plate).
- Medial wall (nasal septum): composed of septal cartilage, the vomer, and the perpendicular plate of the ethmoid bone
- Lateral wall: composed of the , , medial pterygoid plate of the , perpendicular plate of the , frontal process of the , nasal surface of the , and the inferior, middle, and superior meatus
|Inferior meatus|| |
|Sphenopalatine recess|| |
- Ophthalmic artery
- Maxillary artery
- Facial artery
- Via the (cranial nerve I)
- Other sensation
- Formed by the lower two thirds of the nasal cavity
- The anterior part of the vestibule in the nasal cavity is lined with keratinized, stratified, squamous epithelium.
- Posterior to the vestibule, the epithelium becomes pseudostratified, with (respiratory epithelium).
- Contains vibrissae, short and thick hair that filter large particles from inspired air.
- The lamina propria is abundantly vascularized.
- Serves to warm, humidify, and clean air that is inhaled.
- Found on the roof of the nasal cavity, in the superior nasal meatus, on both sides of the nasal septum
Lined by tall, pseudostratified, ciliated, columnar epithelium
- Olfactory cells
- Sustentacular and microvillar (supporting) cells
- Basal cells
The lamina propria contains Bowman cells, fibroblasts, blood vessels, and unmyelinated fibers from the olfactory neurons.
Olfactory glands (Bowman glands)
- Tubulo-alveolar glands in the olfactory mucosa that secrete odorant-binding proteins, , ,
- Moistens the nasal mucosa and acts as a solvent for odor molecules
- Olfactory glands (Bowman glands)
- Molecules are inspired and absorbed by the respiratory region of the nose before reaching the olfactory epithelium.
- Smell is the sensation produced when the olfactory epithelium reacts with dissolved odorant substances.
- Mucus secretion is required for odorant molecules to interact with the olfactory epithelium (aids in dissolving odorants).
- The conscious and unconscious perception of smell takes place in different areas of the brain.
- Smell plays an important role in the formation of memory and emotions.
- Smell aids in gustation (sense of taste).
Anatomy of smell
- The olfactory neurons are primarily located in the superior part of the nasal cavity.
- Odorants travel through the superior nasal meatus to reach the olfactory bulb.
- The olfactory system is characterized by direct projections that connect directly to the cortex, bypassing the thalamic nuclei (unlike other sensory systems).
- Olfactory receptor cells:
- Sustentacular cells: contain microvilli and secretory granules
- Basal cells: stem cells of the olfactory epithelium
- Mucus is produced by Bowman cells.
- Odorants react with olfactory receptor cells via diffusion or odorant-binding proteins.
- Olfactory glomerulus: neurons with identical olfactory receptors form glomeruli in the olfactory bulb.
- Second neurons
- Periglomerular cell: inhibit mitral cells and tufted cells laterally → sharper contrast between different smells
- Granule cells
|Olfactory tract|| |
|Primary olfactory cortex|| |
|Secondary olfactory cortex|
|Olfactory nuclei|| |
Development of the nose and paranasal sinuses