Question

WE HAVE THREE TYPES OF TASTE BUDS: SWEET SOUR AND BITTER THEN HOW DO WE GET THE TASTE OF SPICY FOOD ?

Answer 1

              Hotness, spiciness sensations

      The basic tastes are sweetness, sourness, saltiness, bitterness, and umami (appetitive taste).   There are taste buds (containing receptors) for sweetness, sourness, bitterness.  Saltiness is tasted using ion channels in the tongue.

  Glutamic acid is detected by G protein couple receptor that produces umami taste.  The taste receptors for sweet sensation are T1R2 and T1R3.  Those for sourness are PKD2L1.  Those for bitterness are TAS2R or T2R.

   But the spiciness sensation is different from the basic tastes.

       Chili peppers contain capsaicin compounds.  The spicy materials like peppers, ginger, radish, black peper etc cause a hot or spiciness or pungency or burning sensation on the tongue.  The sensation is called chemesthesis.   It is caused by a trigeminal nerve reaction along with a normal taste reception.  The receptors involved are TRP1 and TRPA1.  

    In chemesthesis the taste is not really due to the taste buds.  It is due to the separate nerves that carry the signals to the brain.  The spicy foods activate the nerve fibers (somatosensory fibres on the tongue) directly.   This is a similar sensation as that of sensation of heat (temperature + pain).