Anatomy of nose
The nose contains 10-100 million receptors for the sense of smell, present in the olfactory epithelium. the olfactory epithelium occupies the superior portion of nasal cavity. the olfactory epithelium consist of 3 types of cells:-
- olfactory receptors- they are the neurons for olfaction. It is a bipolar neuron having a knob-shaped dendrite. the olfactory hairs are the main receptors for olfaction
- supporting cells- these are the columnar epithelial cells of the mucous membrane lining the nose. they provide nourishment, physical support and electrical insulation to the receptors.
- Basal cell- these are the stem cells present between the bases of the supporting cells.
within the connective tissue which supports the olfactory epithelium, are the olfactory glands. these glands produces the mucous which is carried to the epithelium by the ducts.
Physiology of olfaction
All odorous materials gives off the volatile molecules which are carried in the nose through the inhaled air. when they dissolve in the mucous, they stimulate the olfactory chemoreceptors. the air entering the nose is warmed and the convection current carries the air to the nasal cavity. Sniffing increases the no. of olfactory receptors stimulated and thus provides the sense of smell. The sense of smell may affect the appetite. If the odour is pleasant, the appetite is improved.
Inflammation of the nasal mucosa prevents the odorous substances from reaching the olfactory area of the nose. This prevents the loss of sense of smell.
Anatomy of tongue
Like olfaction, gustation or taste is also a chemical sense. The receptors for the sense of taste are located in the test buds. Nearly 10,000 test buds are present on a adult tongue, but some of the taste buds are also present on the soft palate, pharynx and epiglottis. The no. of taste buds decreases by age.
Each taste bud is a oval shaped body which consist of 3 types of epithelial cells-
- Supporting cells:- each supporting cells surrounds about 50 gustatory receptor cells
- Gustatory receptor cells:- gustatory cells consist of a single, long microvillus known as the gustatory hair; which projects from the taste pore, an opening in the taste bud
- Basal cells:- these are the stem cells, found in the periphery of the taste bud.
Taste buds are found in the elevations on the tongue called as the papillae. three types of papillae are present:-
- Vallate papillae:- these are about 12 large papillae which forms an inverted V- shaped row at the back of the tongue.
- Fungiform papillae:- these are mushroom shapes elevations present on the entire surface of tongue. it contains 5 taste buds each.
- Foliate papillae:- these are located on the lateral margins of the tongue.
Physiology of Gustation
There are 4 fundamental sensation of taste- sweet, sour, bitter and salt. it is known as all the taste buds are stimulated by all the tastes. Substances can only be taste when they are in a solution and not dry.
sense of taste and smell are nearly similar. taste triggers the salivation and secretion of gastric juice. Sense of taste also have a protective function, eg:- when the foul tasting food has been eaten, reflex actions stimulates and induces vomiting.
Multiple choice questions(MCQs)
1. The olfactory epithelium occupies which portion of nasal cavity?
A. superior portion of nasal cavity
B. posterior portion of nasal cavity
C. anterior portion of nasal cavity
D. inferior portion of nasal cavity
2. which types of cells are considered as the neurons of olfaction?
A. supporting cells
B. olfactory receptor cells
C. basal cells
D. both A and C
3. what is the function of supporting cells of olfaction?
B. provides support
C. electrical insulation
D. all of the above
4. How is the mucous produced by the olfactory glands reaches the olfactory glands?
5. Which of the following statement is NOT true?
A. gustation stands for sense of taste
B. receptors for smell are present in olfactory epithelium
C. olfactory receptors are bipolar neurons
D. all the taste buds are present on the surface of tongue
6. where are the basal cells of gustation present?
A. periphery of taste bud
B. posterior of taste bud
C. in front of taste bud
D. behind the taste bud
7. Match the following-
a) Vallate papillae 1. Contains no taste buds
b) fungiform papillae 2. Present on the lateral margins
c) foliate papillae 3. Five taste buds in each papillae
d) filiform papillae 4. Twelve taste buds in each papillae
8. which type of cells are not present in the taste bud?
A. gustation receptors
B. supporting cells
C. basal cells
D. none of the above
9. how many taste buds are enclosed in each fungiform papillae?
10. which of the following papillae forms the V- shaped rows?
A. fungiform papillae
B. vallate papillae
C. foliate papillae
D. filiform papillae
1. superior portion of nasal cavity
2. olfactory receptor cells
3. all of the above
5. all the taste buds are present on the surface of tongue
6. periphery of taste bud
7. a) – 4 b) – 3 c) – 2 d) – 1
8. none of the above
10. vallate papillae
REFERENCES: 1. Ross and Wilson-Anatomy and physiology in health and illness; 12th edition; page no.-: 205-207.
2. Gerard J. Tortora -Principles of anatomy and physiology; edition twelfth ; page no.-: 599-602.