Taste

Taste buds are the sense organs of taste. Each taste bud contains a number of taste cells which which are the taste receptors (gustatory receptors) مستقبلات الذوق Each receptor has microvilli on its apical end which protrude at the taste pore Taste buds are present in  (1) the walls of Fungiform and Vallate papilae of the tongue ( papillae are ridges and valleys in the tongue ) Apical end Basal end They are specialized to detect things that are sweet حلو, sour حامض, salty مالح or bitter مر.

& (2) in the mucosa of palate, pharynx and epiglottis. & (2) in the mucosa of palate, pharynx and epiglottis. The Basic Taste Modalities (1) Sweet ( tested by sucrose ) and is located mainly at the tip of the tongue. (2) Sour ( tested by acids, e.g., acetic acid ) and is located mainly along the edges of the tongue. (3) Bitter ( tested by quinine ) and is located mainly at the back of the tongue. (4) Salt ( tested by Na Cl ) and located mainly on the dorsum anteriorly. However, considerable overlap occurs.

The Taste Pathway Electrical impulses in the sensory fibers  (1) from the anterior 2 / 3 rds of tongue  are carried by chorda tympani branch of the Facial nerve (2) From the posterior 1/ 3 rd of tongue  travel via the Glossopharyngeal nerve Glossopharyngeal nerve (3) and From palate,pharynx and epiglottis  are carried in the Vagus nerve. in the Vagus nerve. These fibers synapse in nucleus of the solitary tract (NST, Nucleus Tractus Solitarius ) in the Medulla. From there, second-order neurns give rise to axons that cross the midline and join the Medial Lemniscus to end with fibers of touch, pain and temperature in the Ventrobasal Complex of the Thalamus. From the thalamus third-order neurons arise and project to the postcentral gyrus along with the other sensations ( touch and pressure ) from the mouth ). This cortical taste area is located at the foot of the postcentral gyrus

Smell

Olfactory ( taste ) receptor neurons are specialised. ciliated, nerve cells. They are not present all over the nasal mucosa, but present only in a small, 5 cm 2, yellowish-pigmented part of it called olfactory epithelium ( or olfactory mucous membrane ) 5 cm 2, yellowish-pigmented part of it called olfactory epithelium ( or olfactory mucous membrane ) This olfactory epithelium is located at the roof of the nasal cavity near the septum. Sniffing, by creating currents of air going up, helps in smelling odorant materials.

The cilia of the Olfactory receptor cells project into the mucus surrounding the olfactory epithelium. Unlike the ear hair-cell receptors, the olfactory receptors are themselves sensory neurons. The olfactory receptors send their axons up  through small ( foramina ) openings in the cribriform plate الصحن المثقّب of the ethmoid bone  to enter the cranial cavity

and then synapse on ilarge Mitral cells in the olfactory bulb ( which is present on the inferior surface of the frontal lobe ). ( which is present on the inferior surface of the frontal lobe ). The area where several axon terminals synapse on the dendrites of an individual mitral cell is calle Glomerulus The smell pathway has no relay in the thalamus. From there fibers go to the olfactory cortex in the Piriform area.