PSYC 212: Chemical Senses

Physical Senses

Audition, vision, touch

Chemical Senses

Taste (gustation), smell (olfaction), and the Trigemenial System

Senses and the Outside World

The outside world interacts with sensory organs via physical contact, and we perceive our environment via physical and chemical interactions (physical interactions happen outside, chemical interactions happen internally)

Taste (Gustation)

Perceived via the interaction between soluble solutions and gustatory receptors located in the taste buds on our tongue

The Five Detectable Tastes

Sweet, sour, salty, bitter, umami (savory)

Smell (Olfaction)

Perceived via olfactory receptors located in the olfactory mucosa in the upper naval cavity, which we can use to distinguish between millions of odors

Trigeminal System Function

Provides motor (movement) and sensory information for different aspects of your head and face using processes like chemesthesis

Chemesthesis

A third chemosensory system, next to smell and taste, used to evaluate pain or thermal sensations such as tingling, itchiness, or irritation and is located on trigeminal fibers in the nasal/oral mucosa

Taste Bud Location

Found on the papillae on the mucosa of the tongue and along the oral cavity

Types of Papillae

Filiform, fungiform, foliate, circumvallate

Taste Bud Pathway

They use different cranial nerves to get to the solitary nucleus of the brainstem

Taste Map

A debunked urban myth, we can taste all qualities of flavor everywhere on the tongue

Taste Processing

From the solitary nucleus to the VPM of the thalamus, to the insula and parietal cortex, which is the critical spot for gustatory processing

Nostril Anatomy

Relatively narrow at first and goes far up, with the septum completely separating both nasal cavities until reaching the pharynx in the throat. At the back of the nose lies the vermonosal organ.

Nostril Symmetry

Highly asymmetrical

Olfactory Receptor Neurons (ORNs)

Neurons situated in the roof portion of the nasal cavity located in cilia hair cells, with one ORN per receptor, which can be activated by all sorts of substances as per it's olfactory code

Olfactory Code

A hypothesis that odor is stimulated by a distinct set of receptor cells and its associated receptor proteins which can be mixed in a near infinite number of combinations

Neural Olfaction I

ORN axons pass through the cribriform plate of the ethmoid bone and reach the olfactory bulb, to which they snyapse.

Neural Olfaction II

All ORNS converge onto one glomerulum within the olfactory bulb

Olfactory Processing Areas (In order)

Olfactory Bulb + Tract, primary olfactory cortex, pirifirm cortex, amygdala, endoterminal cortex, secondary olfactory cortex: ACC + Insula

Olfactory Processing Direction

Ipsilateral processing (e.g left nostril, left hemisphere) with no relay in the thalamus

Olfactory Processing Response

Will stimulate areas of emotion, learning, memory, and perception of reward

Proust Phenomenon

The power of odors to elicit memories that are especially old and vivid caused by hippocampal processing)

Orthonasal vs retronasal olfaction

The first involves smelling outside scents that go through the nose to he olfactory epithelium, the latter involves the scent entering through the mouth and throat to the epithelium

Olfaction Functions

Warning, nutrition, and social communication

Olfactory Dysfunction

Hyposmia

Anosmia

Phantosmia

Parosmia

Ansomia

The complete loss of smell (5%)

Hyposmia

An impaired sense of smell (15%)

Parosmia

An abnormal or perverted sense of smell (30% of hyposmiacs)

Phantosmia

The sensation of an odor that isn't there

Olfaction & Gustation Confusion

Most people with olfaction issues confuse it for gustation issues

Causes of Olfactory Dysfunction

Disease, neurodegenration, traumatic brain injury, Alzheimer's, chronic sinuitis (spinonasal disease)