Functions of the Nose
- Nose supplies and conditions the air. It warms and moistens the air.
- The nasal hair traps any particulate matter and helps in passing only air to the lungs.
- The nose also plays a role in speech.
The nose is one of the five sense organs of our body. It has olfactory functions. The nose is an essential part of our body because it gets detrimental if we lose the sense of smell. Just imagine, something is burning in your house, and you can’t smell! The thought itself is scary. Today we will learn about the structure and the function of the nose. Let us begin.
Structure and Function of the Nose: Structure
Nose works both as a respiratory organ and an organ of smell. The receptors for smell are placed in the upper 1/3rd part of the nasal cavity.
This upper 1/3rd part is covered by olfactory mucosa. The rest of the nasal cavity is lined by respiratory mucosa.
The respiratory mucosa is vascular and warms the inhaled air. The secretions of serous glands warm and moistens the air. In contrast, the mucous glands’ secretions trap any dust or foreign particles.
The olfactory mucosa lines the upper 1/3rd part of the nasal cavity and even the roof formed by medial and lateral walls till superior concha and cribriform plate (a bone which separates nasal cavity and brain).
The nose is divided into the external nose and nasal cavity.
The external nose has a skeletal framework, which is partly cartilaginous and partly bony.
The bony part is the nasal bones, which form the bridge of the nose and frontal processes of the maxillae (upper jaw).
The cartilages are superior cartilage, inferior cartilage, septal cartilage, and other small cartilages.
The skin of the nose is innervated with external nasal, infratrochlear and infraorbital nerves.
The nasal cavity is seen to extend from nostrils or external nares to posterior nasal apertures.
It is divided into right and left halves by the nasal septum.
Each half has a roof, floor, medial and lateral walls. Each half measures nearly 5 to 7 centimeters in length, 5 centimeters in height, 1.5 centimeters in width near the floor. In contrast, the width near the roof is 1 to 2 millimeters.
The roof of the nose is 7 centimeters long and 2 millimeters wide. The middle part of the roof is made of the cribriform plate of the ethmoid bone.
The anterior slope of the roof is made up of nasal bones, nasal cartilages, nasal part of the frontal bone. The posterior slope is formed by the sphenoid bone.
The floor is about 1.5 centimeters wide and 5 centimeters long. It is formed by the palatine process of the maxilla and horizontal plate of the palatine bone.
The nasal septum divides the nasal cavity into two halves. It is made from bone and cartilage. The nasal septum is lined by mucous membrane.
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Cells of the Nose
The olfactory mucous membrane consists of two types of cells – sustentacular cells and progenitor cells for the receptors of olfaction.
Spread between these two cells are receptor cells or olfactory cells.
Each olfactory receptor is a neuron with short dendrite having an expanded end called olfactory rod or olfactory knob.
From each rod, 6 to 12 olfactory hair-like projections called cilia to arise and reach the surface of the mucous layer.
Cilia are unmyelinated processes of about 2mu meters long and 0.1 mu meters in diameter.
The mucous membrane also has glands of Bowman, which secrete mucous on the membrane.
Axons of the olfactory cells breach the cribriform plate of the ethmoid bone and enter the olfactory bulbs.
Axons of the olfactory cells form a synapse with the primary dendrites of mitral cells in the olfactory bulbs and form olfactory glomeruli.
Tufted cells and periglomerular cells participate in the formation of olfactory glomeruli.
Tufted cells and mitral cells are called projection neurons and are helpful in sending signals from olfactory glomeruli to the brain.
The axons of mitral cells pass posteriorly to the olfactory cortex (part of the cerebral cortex, which deals with olfactory sensation).
There the axons terminate on the top dendrites of the pyramidal cells in the olfactory cortex.
The olfactory cortex is in the piriform or pyriform cortex (a region of the rhinencephalon of the cerebrum) and is bilaterally stimulated by olfactory stimuli.
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Structure and Function of the Nose: Function
The nose helps in respiration and olfaction. It is the first organ of the respiratory system.
The nasal mucosa gets irritated by the unwanted particles, and the nose and the mouth expel those unwanted particles by a protective reflex action called sneezing.
It also helps in the sense of smell. The olfactory receptor neurons help in the sense of smell.
It helps in speech modulations, amplification, and modifications. It helps in pronouncing click consonants and nasal vowels.
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Book: Animal Physiology and Biochemistry by H. R. Singh and Neeraj Kumar Pg. No. 427.