Anatomy of the Upper Respiratory Tract: The Nose

Anatomy of the Upper Respiratory Tract: The Nose

Objectives

  • Understand the functions of the nose and paranasal air sinuses.
  • Identify parts of the nose.
  • Recognize parts of the nasal cavity.
  • Describe the bony skeleton of the external nose and nasal cavity.
  • Examine features of the lateral wall of the nose.
  • Learn the anatomy of each paranasal air sinus.
  • Comprehend the innervation of the external nose and nasal cavity.
  • Detail the blood supply of the external nose and nasal cavity.
  • Understand the development of the paranasal air sinuses.

Anatomy and Location

  • The nose is located centrally within the facial skeleton.
  • Connects with several regions:
    • Orbit
    • Cranial cavity
    • Oral cavity
    • Paranasal air sinuses

Functions of the Nose

  • Olfaction (Organ of Smell): Responsible for the sense of smell.
  • Respiratory Role: Essential for respiration, as "humans breathe to live".
  • Filtration: Filters dust and other particulates from inhaled air.
  • Humidification: Adds moisture to the air before it reaches the lungs.
  • Secretions Management: Assists in the reception and elimination of nasal secretions.

Parts of the Nose

  • The structural components include:
    • Cartilage of the Nasal Septum: Supports the septum, protecting nasal integrity.
    • Lateral Nasal Cartilage: Provides shape and structure to the external nose.
    • Sesamoid Cartilage: A small cartilage that supports the nasal structures.
    • Major Alar Cartilage: Forms the nostrils (nares) and contributes to the shape of the nose.
    • Minor Alar Cartilage: Supports the lower part of the nostrils.
    • Fibrofatty Tissue of Ala: Helps in shaping the nostrils.
  • Nasal Bone: Forms the bony bridge of the nose.
  • Frontonasal Process of Maxilla: Connects the frontal bone to the nasal structure.
  • Anterior Nasal Spine: A bony projection that forms part of the nasal septum.
  • Septum: Divides the nasal cavity into two halves.
  • Turbinates: Bony structures that increase the surface area for air filtration and humidification.
    • Maxillary Sinus: An important sinus adjacent to the nasal cavity, situated within the maxillary bone.

External Nose Structure

  • The external nose consists of:
    • Dorsum: The ridge of the nose.
    • Nares/Nostrils: Openings for air entry, which can dilate due to muscle action from facial expression.
    • The external nose is lined with skin and mucous membrane, and contains hair-like structures known as vibrissae within the vestibule.

Bony Skeleton of the External Nose

  • The bony structure includes:
    • Nasal Bones: Two flat bones forming the bridge.
    • Frontal Processes of the Maxilla: Connects the maxillae to the frontal bone.
    • Nasal Part of Frontal Bone: Forms the upper part of the nose.
    • Nasal Spine: A bony protrusion involved in forming the nasal septum.
    • Vomer: Forms the bony part of the nasal septum.

Nasal Septum Structure

  • Divides the Nose into Two Nasal Cavities: Not perfectly in the median plane, which leads to common nasal septal deviation seen in over 60% of the population.
  • Components of the Nasal Septum:
    • Frontal Bone: The superior portion of the septum.
    • Crista Galli: Projects from the ethmoid bone, providing attachment for the falx cerebri.
    • Septal Cartilage: The flexible part of the septum.
    • Perpendicular Plate of the Ethmoid: A bony component of the septum.
    • Vomer: Completes the septum inferiorly.

Nasal Cavity

  • The nasal cavity extends from the nares (anteriorly) to the choana (posteriorly) and leads into the nasopharynx.
  • Lining: The cavity is lined with mucosa, except for the vestibule, which is lined with skin and hair.
    • Choana/Post-Nasal Aperture: Connects with the nasopharynx.
  • The nasal cavity is sectioned into:
    • Nasal Vestibule: The front part of the nasal cavity.
    • Respiratory Area (Inferior 2/3): Warms and moistens inspired air.
    • Olfactory Area (Superior 1/3): Contains sensory receptors for smell.

Boundaries of the Nasal Cavity

  • Roof: Composed of the frontonasal, ethmoid, and sphenoid bones.
  • Floor: Formed by the palatine process of maxilla and horizontal plates of the palatine.
  • Medial Wall: Consists of the nasal septum.
  • Lateral Wall: Contains three bony projections, or conchae, that increase the surface area.

Features of the Lateral Wall

  • The lateral wall has several elements and features, including:
    • Frontal Sinus.
    • Superior, Middle, and Inferior Turbinates: Play roles in the flow of air and moisture control.
    • Vestibule: The entrance area before entering the nasal cavity.
    • Cribriform Plate of Ethmoid Bone: Allows passage for olfactory nerves.
    • Hard and Soft Palate: Form the lower boundary of the nasal cavity.
    • Sphenoid Sinus: Opens into the spheno-ethmoidal recess.
    • Pharyngeal Tonsil and Uvula: Located near the posterior aspect of the nasal cavity.
    • Opening of Auditory (Eustachian) Tube: connects to the middle ear, situated in the lateral wall.

Paranasal Air Sinuses

  • Frontal Sinus: Located in the frontal bone, it can be unique to individuals.
  • Maxillary Sinus: Known as the Antrum of Highmore, primarily involved in sinusitis; first to develop, nestled within the body of the maxilla.
    • Typical dimensions:
    • Shape: Pyramidal.
    • Ostium: Approximately 3-4 mm in size, positioned within the hiatus semilunaris.
    • Nerve Supply: Supplied by branches of the maxillary nerve.
  • Sphenoidal Air Sinus: Located in the sphenoid bone,
    • Openings: Drains directly into the spheno-ethmoidal recess.
  • Frontal Air Sinus: Differentiated by its unique configuration.
    • Drainage: Opens into the hiatus semilunaris through the frontonasal duct.
    • Nerve Supply: Supplied by the supraorbital nerve.
  • Ethmoidal Air Sinuses: Comprising anterior, middle, and posterior air cells, situated between the orbit and nose.
    • Openings: Each sinus has specific drainage pathways:
    • Posterior opens into superior meatus.
    • Middle opens into the hiatus semilunaris via the ethmoidal infundibulum.
    • Anterior provides drainage into the anterior part of the hiatus semilunaris.

Development of the Paranasal Air Sinuses (PAS)

  • Intrauterine Development: Begins at the end of the third month. Air sinuses develop from expansions of the mucous membrane of the nasal meatuses.
    • Primary Pneumatization: Initial outpouching of mucosal tissue into the surrounding bone.
    • Secondary Pneumatization: Expansion of this outpouching into maxillary, sphenoidal, frontal, and ethmoidal sinuses.
  • Timelines:
    • Maxillary sinus develops by 10 weeks, present at birth.
    • Ethmoidal sinuses also present at birth; posterior ethmoidal air cells develop significantly later.
    • Frontal and sphenoidal sinuses undergo secondary development beginning from age 2, with frontals visible radiographically by ages 7-8.

Historical Context and Significance of Paranasal Air Sinuses

  • Various historical perspectives on the functions of these sinuses:
    • 16th Century: Seen as reservoirs for "grease" or harmful spirits.
    • Renaissance artists like Leonardo Da Vinci contributed to the discussions about these spaces.
    • Their roles have evolved, with contributions from numerous medical philosophers over centuries.
  • Recent Understanding: Emerging evidence indicates that these sinuses may play a role in immune defense mechanics, aiding in the overall health of the respiratory system.