Capsaicin, found in cayenne peppers and other species of plants in the genus Capsicum, is used in topical analgesic creams to reduce joint and muscular pain. It is thought to work by depletion of substance P in the sensory nerves.

The brain stem consists of the medulla, the pons, and the midbrain. The cerebellum is an outgrowth posterior to the pons. The corpus callosum is the broad bundle of neural fibers that attaches the left hemisphere of the brain to the right hemisphere.

Olfaction is form of chemoreception, or a translation of a chemical signal into an action potential. Smells are triggered by molecules of volatile chemicals that trigger chemoreceptors in the epithelium of the olfactory cleft. 

The olfactory nerves travel through the cribiform plate of the ethmoid bone. The grooves of the cribiform plate support the olfactory bulb, and the bone is perforated by many tiny foramen for transmission of the olfactory nerves from the epithelium of the nasal cavity to the olfactory bulb.

The other structures listed are all bony features of the ethmoid bone, but they do not allow the passage of olfactory nerves.

Olfactory receptor neurons require 7-8 molecules of a volatile odorant to trigger an action potential, and approximately 40 action potentials must be triggered in an olfactory receptor neuron in order for a smell to be detected. 

There are three types of cells embedded in the olfactory epithelium: basal cells, supporting cells, and olfactory sensory neurons. All three of these cells play a significant role in the sense of smell, though the olfactory sensory neurons are the only cell type that actually respond to chemical stimuli. 

The olfactory perception is managed by several parts of the brain, the primary areas being the piriform cortex, the insula, and the orbitofrontal cortex. Other lesser involved areas of the brain include the anterior olfactory nucleus, the amygdala, the entorhinal cortex, and the olfactory tubercle.

The arcuate nucleus is an area of the hypothalamus that is involved in regulation of hunger and satiety. 

The olfactory epithelium is located at the roof of the nasal cavity in a relatively large area that includes the superior turbinate and the superior portion of the nasal septum. There are no specialized olfactory cells on the inferior turbinates, and no olfactory receptors in either the sphenoid sinus of the eustachian tube. 

The human tongue can detect bitter flavors at concentrations as low as 8 micromolars per liter. In comparison, in the average person the detection threshold for sucrose is 10 millimoles per liter. The reason for the extreme sensitivity of the human tongue to bitter flavors may be protective, as many poisonous or toxic substances have a bitter taste.

Taste buds are located in the papillae of the tongue, a group of structures lining the surface of the tongue from the apex to the base. These papillae are also present in the cheek, the soft palate, the epiglottis, and the upper esophagus. They are not present in the palatoglossal arch.