Other Biology Concepts - NCLEX-PN

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 sensation of taste is carried to the brainstem by three cranial nerves: the facial nerve (CN VII), the glossopharyngeal nerve (CN IX), and the vagus nerve (CN X). The facial and glossopharyngeal nerves both communicate sensation from the tongue, while the vagus nerve transmits sensory information from the epiglottis. The trigeminal nerve (CN V) is not directly involved in the sensation of taste, though there is evidence that it is involved in the senses of "heat" and "coolness" experienced while eating spicy or minty foods.

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.

In addition to the taste receptors in the mouth and pharynx, taste receptors are located in many other areas of the body. These including the lung (which has taste receptors for bitter flavors, possibly as a mechanism to protect against airborne toxins), the pancreas, the small intestine, the stomach, the brain, and the testis. While the function of taste receptors in the testes is not well known, some research indicates that testicular taste receptors may play an important role in male fertility.

Sweet, umami, and bitter taste are all correlated with receptors for guanine nucleotide-binding proteins, also known as G proteins. Taste bud receptors that transmit information about saltiness are triggered by sodium ion channels in the cell wall.

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.

The four types of lingual papillae are fungiform (mushroom-shaped), filiform ("thread-like"), circumvallate, and foliate.

Filiform papillae are the most numerous, covering the majority of the anterior two-thirds of the tongue. Fungiform papillae are scattered along the surface of the tongue, but are more concentrated on the tip and sides of the tongue. Foliate papillae are located on the sides and back of the tongue, and circumvallate papillae are the large, round papillae visible in a row on the posterior aspect of the tongue, just anterior to the foramen cecum and sulcus terminalis.

Filiform papillae, the most numerous of the lingual papillae, is the only type that does not contain taste buds. Rather, they serve to move food toward the esophagus, cleanse the interior of the mouth, and spread saliva onto food and mucus membranes.

Sour flavor taste bud receptors are triggered in the presence of hydrogen ions (thus acidic foods often have a sour taste). Sodium triggers receptors for salty flavor, while glutamate and gustducin (a guanine nucleotide-binding protein, or G protein), are associated with umami, sweet, and bitter flavors.

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.