7.8

• On the tongue, taste receptor cells typically occur in clusters of 50 to 100 called taste buds.
• Taste buds are often located around protuberances called papillae.
• The 50 to 100 receptor cells that compose each taste bud is said to be one of three types: (1) cells that detect bitter, sweet and umami (savory); (2) cells that detect sour; and (3) cells that detect salty.
• In each taste bud, only one of the receptor cells, the presynaptic cell, synapses onto the neuron carrying signals away from the bud; communication among the other cells of a taste bud appears to occur via gap junctions.
• In each taste bud, only one of the receptor cells, the presynaptic cell, synapses onto the neuron carrying signals away from the bud; communication among the other cells of a taste bud appears to occur via gap junctions.
• True or False, gustatory receptor cells survive only a few weeks before being replaced by new cells.

  True
• Taste transduction for sweet, umami, and bitter is mediated by metabotropic receptors.
• two metabotropic receptors for sweet,
• one for umami
• about 25 for bitter
• Taste transduction for salty and sour is mediated by ionotropic receptors.
• Sour is transduced by three different ionotropic receptors
• salty is mediated by two ionotropic receptors
• facial (VII) --> front of the tongue
• glossopharyngeal --> back of the tongue
• vagus (X) cranial nerves --> back of the oral cavity
• These fibers all terminate in the solitary nucleus of the medulla, where they synapse on neurons that project to the ventral posterior nucleus of the thalamus.
• The gustatory axons of the ventral posterior nucleus project to the primary gustatory cortex, which is in the insula, an area of cortex hidden in the lateral fissure
• True or False, a different area of primary gustatory cortex represents each taste.

  True
• Secondary gustatory cortex is in the orbitofrontal cortex.