The Human Nose

The Human Nose

The Human Nose: Anatomy and Function

The human nose is a complex organ that serves as the primary gateway for the respiratory system and houses the sense of smell. It is divided internally into two passages by the nasal septum.

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Anatomy

1. External Structure: The visible part of the nose is supported by bone (the nasal bone) at the top and flexible cartilage at the bottom, which forms the nostrils (nares).

2. Nasal Cavity: This large, air-filled space behind the nose is lined with a specialized mucous membrane.

   • Turbinates (Conchae): Three pairs of scroll-shaped bones (superior, middle, and inferior) project into the nasal cavity. These structures increase the surface area and create turbulence in the inhaled air.

3. Olfactory Epithelium: Located in the roof of the nasal cavity, this small patch of tissue contains olfactory receptor cells—the neurons responsible for detecting odors.

4. Paranasal Sinuses: These are air-filled, mucous-lined cavities within the facial bones (frontal, ethmoid, sphenoid, and maxillary) that connect to the nasal cavity.

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Primary Functions

The nose performs three essential functions for the body:

1. Respiration (Filtering and Conditioning Air)

The nose acts as an air conditioner and filter for inhaled air before it reaches the sensitive lungs:

• Warming: Blood circulating near the surface of the turbinates warms the incoming air to body temperature.

• Humidifying: The mucous lining adds moisture to the air.

• Filtering: Hairs in the nostrils (vibrissae) and sticky mucus trap dust, pollen, bacteria, and other foreign particles. Tiny hair-like projections called cilia then sweep the contaminated mucus towards the throat to be swallowed or expelled.

2. Olfaction (Sense of Smell)

The sense of smell, or olfaction, is the nose's unique sensory function:

• Airborne odor molecules dissolve in the mucus of the olfactory epithelium.

• They bind to the olfactory receptor cells, which fire electrical signals up the olfactory nerve (Cranial Nerve I).

• The signals are transmitted directly to the olfactory bulb in the brain, and from there to the limbic system (explaining the strong link between smell, memory, and emotion) and the olfactory cortex for conscious interpretation.

3. Voice Resonance

The nasal cavity and the connected paranasal sinuses act as resonating chambers, affecting the unique sound quality and tone of a person's voice.

Diagram of the Human Nose
The external human nose, composed of bone and cartilage, is the most prominent feature of the face in humans. The internal human nose is a hollow structure above the roof of the mouth, divided by the septum into two nasal cavities that extend from the nostrils to the pharynx. 

The mucous membrane that lines the nasal cavities is covered with fine hairs known as cilia that help to filter dust and impurities from the air before it reaches the lungs; the air is also moistened as it passes over the sticky nasal membrane. In the human nose, there are three horizontal folds on the walls of the nasal cavities, called the conchae: other mammals may have more conchae. 

The uppermost concha is densely supplied with capillaries that warm the air passing over them to near body temperature. High in the nasal cavity is a small tract of mucous membrane containing the nerve cell endings of the olfactory nerve, which impart the sense of smell. Therefore, inflammation of the nasal mucous membranes, which commonly accompanies colds and other infections, not only obstructs breathing but also impairs the sense of smell.

Diagram of the human nose...