Nose

• The nose is a sensory organ primarily responsible for the sense of smell (olfaction) and plays a significant role in respiration.

• It is composed of several structures that work together to detect and process odours and filter, warm, and humidify the air we breathe.

Structure of the Nose

Nose is divided into external and internal parts:

1. External Nose

1. Nostrils (Nares): The external openings of the nose that allow air to enter.
2. Nasal Bridge: The bony and cartilaginous structure that supports the nose and provides its shape.
3. Alae: The sides of the nostrils, composed of cartilage and soft tissue, helping shape the nose.

2. Internal Nose

1. Nasal Cavity: A hollow space behind the nostrils, divided into two chambers by the nasal septum, which is made of cartilage and bone.
2. Nasal Septum: Divides the nasal cavity into two nostrils and supports airflow.
3. Turbinates (Conchae): Curved bony structures inside the nasal cavity that increase surface area to warm, humidify, and filter air.
4. Olfactory Epithelium: A specialized region located in the upper part of the nasal cavity containing olfactory receptor neurons responsible for detecting smells.
5. Sinuses: Air-filled spaces in the bones around the nose (frontal, maxillary, ethmoid, and sphenoid sinuses). These sinuses lighten the skull and produce mucus that drains into the nasal cavity.
6. Cilia: Tiny hair-like structures that line the nasal cavity and sinuses. They move mucus and trapped particles toward the throat for removal.

Mechanism of Smelling (Olfaction)

• The mechanism of smelling involves detecting odor molecules in the air and converting them into electrical signals that the brain can interpret as olfactory information.

Here’s a summary of the main steps involved in the mechanism of smelling:

1. Air Entry: When air enters the nostrils, it passes through the nasal cavity.
2. Odor Detection: As air flows over the olfactory epithelium, odor molecules bind to olfactory receptor cells.
3. Signal Transmission: The receptor cells convert the chemical signals from odor molecules into electrical signals.
4. Olfactory Nerve: These electrical signals are sent through the olfactory nerve (Cranial Nerve I) to the olfactory bulb in the brain.
5. Brain Processing: The brain processes these signals, interpreting them as specific smells.

Mechanism of Breathing

1. Air Filtration: As air enters the nasal cavity, it is filtered by the nasal hairs and mucus, trapping dust, pollen, and other particles.
2. Air Humidification and Warming: The turbinate in the nasal cavity help humidify and warm the incoming air to body temperature, making it suitable for the lungs.
3. Passage to Lungs: The filtered, humidified, and warmed air passes through the pharynx (throat), down the trachea, and into the lungs for gas exchange.

Diseases of the Nose

1. Rhinitis:

• Inflammation of the nasal mucous membrane, often caused by allergies (allergic rhinitis) or infections (viral rhinitis or common cold). Symptoms include a runny nose, sneezing, and congestion.

2. Sinusitis:

• Inflammation or infection of the sinuses, often causing sinus pressure, headaches, nasal congestion, and facial pain.

3. Nasal Polyps:

• Soft, noncancerous growths inside the nasal cavity or sinuses that can cause congestion, reduced sense of smell, and difficulty breathing.

4. Deviated Septum:

• A condition where the nasal septum is displaced to one side, which may cause breathing difficulties, snoring, or recurrent sinus infections.

5. Epistaxis (Nosebleeds):

• Bleeding from the nose, often due to dry air, injury, or hypertension.

6. Anosmia:

• The loss of the sense of smell, which can result from viral infections, head injuries, or neurodegenerative diseases such as Alzheimer’s.

7. Nasal Fractures:

• Trauma to the nose, which can damage cartilage, bone, and the nasal septum, leading to deformity and breathing issues.

Functions of the Nose

1. Respiration:

• The nose is the primary entry point for air during breathing.
• It filters, warms, and humidifies air before it enters the lungs.

2. Olfaction (Sense of Smell):

• The nose houses the olfactory epithelium, which is responsible for detecting odors.
• This is important for enjoying food, detecting dangers (like smoke or spoiled food), and enhancing taste through smell.

3. Filtration of Air:

• The hairs and mucus in the nasal cavity trap dust, bacteria, and other particles, preventing them from entering the respiratory system.

4. Humidification and Temperature Regulation:

• The nasal cavity warms and humidifies air to protect the delicate tissues of the respiratory system and ensure efficient gas exchange in the lungs.

5. Defense Mechanism:

• Mucus and cilia in the nasal passages help remove foreign particles and pathogens, reducing the risk of infection.

6. Resonance for Speech:

• The nasal cavity helps with vocal resonance, affecting the quality of the voice.

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