Nose and sinuses

Summary

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.

Gross anatomy

Overview

  • The nose contains the human olfactory system, which is responsible for the sense of smell.
  • Paranasal sinuses
    • Air-filled cavities within the bones of the skull (frontal, ethmoid, sphenoid) and face (maxilla)
    • They reduce the weight of the skull, especially of the frontal and facial bones, to facilitate maintenance of the upright head position.
  • The nose and paranasal sinuses fulfill the following functions:
    • Aid help provide resonance to the voice
    • Warm and humidify air that is inhaled
    • Are part of the mucosal immune system

Paranasal sinuses

Characteristics of paranasal sinuses
Sinuses Location Structures
Frontal sinus
  • Connects with the middle nasal meatus via the frontonasal duct, which drains into the semilunar hiatus
Ethmoidal sinus
  • Ethmoidal labyrinth
  • Between the orbits and the nasal cavity
Sphenoid sinus
Maxillary sinus
  • Only the paranasal sinus is present at birth.
  • Drains into the middle nasal meatus

The nose

Bones

Boundaries

Meatus

Nasal meatuses and recesses
Meatus Drainage
Superior meatus
Middle meatus
Inferior meatus
Sphenoethmoidal recess
Sphenopalatine recess

Vasculature

Kiesselbach plexus is formed by the anterior ethmoidal artery, sphenopalatine artery, greater palatine artery, and the septal branch of the superior labial artery.

Innervation

Microscopic anatomy

Respiratory epithelium

Olfactory epithelium

Olfaction (smell)

Overview

  • 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 epithelium

Olfactory bulb

Smell pathways

Several areas of the brain are associated with the sense of smell, including: the anterior olfactory nucleus, amygdala, piriform cortex, entorhinal cortex, and olfactory tubercle.

Overview of smell pathaways
Structure Characteristics
Olfactory tract
Primary olfactory cortex
Secondary olfactory cortex
Olfactory nuclei

Embryology

Clinical significance

last updated 11/28/2020
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