The Gustatory (Taste) System
The Human Tongue
The human tongue contains four kinds of papillae, three of which (highlighted in blue) contain taste buds.
Foliate papillae - a series of folds on the sides of the tongue in the back
Circumvallate papillae - are organized in an inverted V at the back of the tongue
Fungiform papillae - are found scattered across the top front and middle of the tongue
Filiform papillae - are found across the top of the tongue
Fungiform Papilla, close up
The taste buds (shown in yellow) are located at the surface of these papillae
Foliate Papillae, close up
The taste buds (shown in yellow) are located deep in the folds of these papillae
Circumvallate Papilla, and Filiform Papillae, close up
The taste buds (shown in yellow) are located deep in the trenches of the circumvallate papillae.
The small, pink cone shapes in the background are the filiform papillae.
Taste Bud, close up
The smallest functional unit of taste, taste buds can be found on the tongue within three different kinds of papillae, as well as the back of the throat and the roof of the mouth.
Each taste bud contains several taste receptor cells (shown in peach and yellow).
Taste compounds interact with the tops of these specialized cells, which then transmit taste information through a nerve to the brain.
The Olfactory (Smell) System
Olfactory Bulb Location
Olfactory bulbs are located at the base of the brain and at the top of the nasal cavity. There is one located at the top of the left side of the nose, and one at the top of the right. Here, the area containing the left olfactory bulb (outlined in yellow) is shown in cross-section.
Olfactory Bulb, close up
The olfactory bulb is a bundle of olfactory neurons. These neurons extend through a porous bone and interact with the odor compounds in the nasal cavity. This point at which this interaction occurs is highlighted in yellow.
Olfactory neuron, close up
A portion of each olfactory neuron extends into the nasal cavity. This portion of the neuron (highlighted in yellow) interacts with any odor compounds present and transduces, or converts, the odor compounds into a neural signal that then carries odor information to the brain. Unlike most neurons in your body, olfactory neurons actually regenerate throughout your lifetime. It is speculated that this is necessary since the neurons interact with environmental chemicals and can be damaged over time.
Although there is not a Chemesthetic System per se, the trigeminal nerve (shown in light brown) conveys a great deal of information about the presence of irritating and painful stimuli (like the burn from chili peppers) to the brain. Chemesthetic sensations are perceived by free nerve endings in the tissue and then transmitted to the brain, often through the trigeminal. Different branches of this nerve go the corneas, the nose, the tongue and the teeth, and each relays information about stinging, prickling, burning, and pain in these locations. The trigeminal nerve also conveys information about temperature, like the cooling sensations that arise from the menthol in mouthwash.