SENSE ORGAN - NOSE (STRUCTURE AND FUCTION)

 SENSE ORGAN - NOSE (STRUCTURE AND FUCTION)

Here we will discuss about structure and function of sense organ (nose)

NOSE

• Human nose is the first part of the respiratory organ of passing air.
• It is the organ of sense in the body, sense of smell is called as - olfaction. 
• It is also called as organ of olfaction.
• Olfaction is carried out by millions of receptors present in olfactory epithelium.

Structure

• Nose is made up of several tiny bones and cartilage and also made up of soft tissues like skin, epithelia, mucous membrane, muscles, nerves, and blood vessels.
• The structure of the nose by bone is provided by maxilla, frontal bone and number of small bones.
• Nose is consisting of bone, cartilage, nasal cavity, septum, mucus membrane, turbinate, sinuses.
• Olfaction is carried out by olfactory epithelium which forms superior part of nasal cavity and covers inferior surface of cribriform plate (portion of ethmoid bone located at the base of the skull).

Olfactory epithelium:

    It is made up of three types of cells.

        1. Olfactory receptor

        2. Supporting cells

        3. Basal cells

Olfactory receptor 

• It is the neurons of the first order of the olfactory pathway.
• Dendrites protects the cilia are the parts of the olfactory receptors which are respond to inhaled chemicals are called as olfactory hairs.
• Conversion of stimulus energy into a graded potential in a sensory receptor are called as transduction.
• A chemical substance that stimulates olfactory hairs and make potential are called as odorants.  

Supporting cells 

• These are the columnar epithelial cells of the mucous membrane make lining the nose.  
• It also provides physical support, nourishment, and electrical insulation for the olfactory receptors.
• They help detoxify chemicals that come in contact with the olfactory epithelium.  

Basal cells

• Stem cells located between the bases of the supporting cells.
• They continually undergo cell division to produce new olfactory receptors (life span nearly one month).

Olfactory (Bowman’s) glands: 

• It is present within the connective tissue and supports olfactory epithelium.
• It produces mucus which is carried to surface of epithelium by ducts.
• Both supporting cells and these glands are innervated by facial nerve (VII) which in turn innervates lacrimal glands. 
• The result is tears and a runny nose after inhaling substances such as pepper. 

Olfactory transduction: 

• Binding of an odorant molecule to an olfactory receptor protein activates a G protein
• Function on adenylate cyclase.
• Results in the production of cAMP.
• Cyclic AMP opens sodium ion (Na+) channels.
• Na+ ions enter the olfactory receptor.
• The resulting depolarization may generate an action potential.
• Generated action potential propagates along the axon of the olfactory receptor.

Physiology of Olfaction:  

1. On each side of the nose, heaps of the slim, unmyelinated axons of olfactory receptors broaden through around 20 olfactory foramina in the cribriform plate of the ethmoid bone.
2. These 40 or so heaps of axons on the whole structure the right and left olfactory (I) nerves.
3. The olfactory nerves end in the mind in matched masses of dim matter called the olfactory bulbs.
4. Inside the olfactory bulbs, the axon terminals of olfactory receptors structure neural connections with the dendrites furthermore, cell groups of olfactory bulb neurons.
5. Axons of olfactory bulb neurons broaden posteriorly furthermore, structure the olfactory tract.
6. A portion of the axons of the olfactory plot undertaking to the essential olfactory region of the cerebral cortex.
7. The essential olfactory region is where cognizant consciousness of smell starts.
8. Olfactory sensations are the main vibes that arrive at the cerebral cortex without in the thalamus.
9. Different axons of the olfactory plot venture to the limbic framework and nerve center.
10. These associations represent our profound and memory receptors and their problems.

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