nose & sense of smell
TRANSCRIPT
Nose & Sense of smell
Sarita Sharma Assistant professor Department of pharmacology Mumbai
The nose is the organ responsible for the sense of smell.
The cavity of the nose is lined with mucous membranes that have smell receptors connected to the olfactory nerve.
The smells themselves consist of vapors of various substances. The smell receptors interact with the molecules of these vapors and transmit the sensations to the brain.
The sense of smell is sometimes temporarily lost when a person has a cold.
Dogs have a sense of smell that is many times more sensitive than man's.
The visible part of the human nose is the protruding part of the face that bears the nostrils.
The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils.
The nasal root is the top of the nose, forming an indentation at the suture where the nasal bones meet the frontal bone.
The anterior nasal spine is the thin projection of bone at the midline on the lower nasal margin, holding the cartilaginous center of the nose.Adult humans
have nasal hairs in the anterior nasal passage.
Nose
Bony framework
Cartilaginous or inner
framework
Physiology of Olfaction
Olfactory mucus Membranelies in the superior part of each nostril
In each nostril, the olfactory membrane has a surface area of about 2.4 square cm
Olfactory Cells – The Olfactory receptor cells for the smell sensation - bipolar nerve cells derived originally from the CNS
--10 to 20 million receptor cells-Each olfactory receptor is a neuron
Composition of Olfactory epitheliumEach neuron has a
thick dendrite with an expanded end called olfactory rod
-From rods cilia project to the mucous surface
-Each receptor neuron has 10-20 cilia
-Axons of olfactory receptor neurons pierce cribriform plate of ethmoid bone and enter olfactory bulbs
- The mucosal end of the olfactory cell forms a knob from which 4 to 25 olfactory hairs (also called olfactory cilia), project into the mucus that coats the inner surface of the nasal cavity
- cilia react to odors in the air and stimulate the olfactory cells
- Spaced among the olfactory cells - Bowman’s glands that secrete mucus onto the surface of the olfactory membrane.
- Olfactory cells are constantly being replaced with a half-time of a few weeks
Mucus producing GlandsOlfactory mucous
membrane is constantly covered by mucus
-Mucus is produced by Bowman’s glands, placed just under the basal lamina of the membrane
Olfactory BulbsAxons of receptors
contact the primary dendrites of mitral cells.
-Forming complex globular synapses called olfactory glomeruli.
Mitral cells are neurons that are the part of oflactory
system. Located into oflactory bulb.
The receives the information from axons of oflactory
receptors neurons and transfer it to brain.
How It All Works/physiology of smell
Like the sense of taste, it's a chemical sense. They are called chemical senses because they detect chemicals in the environment,:
1. Vaporized odor molecules (chemicals) floating in the air reach the nostrils and dissolve in the mucus (which is on the roof of each nostril).
2. Underneath the mucus, in the olfactory epithelium, specialized receptor cells called olfactory receptor neurons detect the odor. These neurons are capable of detecting thousands of different odors.
3. The olfactory receptor neurons transmit the information to the olfactory bulbs, which are located at the back of the nose.
4. from the olfactory bulbs, the sensations are carried through olfactory tract to olfactory area in the temporal lobe of cerebral cortex.
5. These brain centers perceive odors and access memories to remind us about people, places, or events associated with these olfactory sensations.
Functions of nose1. breathing2. Air conditioning of inspired air3. Protection of lower airway4. Ventilation and drainage of p.n.s.5. Olfaction6. Nasal resistance
AbnormalitiesAnosmia – absence of sense of smell
Hyposmia – diminished olfactory sensitivity
Dysosmia – misleading/false sense of smell
More than 75% of humans over the age of 80 have an impaired ability to identify smells