Sensation and Perception Ch. 14

glomerulus

Any of the spherical conglomerates containing the incoming axons of the olfactory sensory neurons. Each OSN converges onto two of this (one medial, one lateral)

olfactory bulb

A blueberry-sized extension of the brain just above the nose, where olfactory information is first processed. There are two of these, one in each brain hemisphere, corresponding to the left and right nostrils.

cribriform plate

A bony structure riddled with tiny holes, at the level of the eyebrows, that separates the nose from the brain. The axons from the olfactory sensory neurons pass through tiny holes of this to enter the brain

pheromone

A chemical emitted by one member of a species that triggers physiological or behavioral response in another member of the same species. Pheromones are signals for chemical communication and do not need to have any smell.

vomeronasal organ (VNO)

A chemical sensing organ at the base of the nasal cavity with a curved tubular shape. the VNO evolved to detect chemicals that cannot be processed by the olfactory epithelium, such as large and/or aqueous molecules, the types of molecules that constitute pheromones. Also called Jacobson's organ.

odorant

A molecule that is defined by its physicochemical characteristics, which are capable of being translated by the nervous system into the perception of smell. The odorant methyl salicylate has the odor of wintergreen mint.

olfactory cleft

A narrow space at the back of the nose into which air flows and where the olfactory epithelium is located

primer pheromone

A pheromone that triggers a physiological (often hormonal) change among conspecifics. This effect usually involves prolonged pheromone exposure

chemosignal

Any of various chemicals emitted by humans that are detected by the olfactory system and that may have some effect on the mood, behavior, hormonal status, and/or sexual arousal of other humans

releaser pheromone

A pheromone that triggers an immediate behavioral response among conspecifics

entorhinal cortex

A phylogenetically old cortical region that provides the major sensory association input into the hippocampus. This also receives direct projections from olfactory regions.

staircase method

A psychophysical method for determining the concentration of a stimulus required for detection at the threshold level. This is an example of a method of limits. A stimulus is presented in an ascending concentration sequence until detection is indicated, and then the concentration is shifted to a descending sequence until the response changes to "no detection." This ascending and descending sequence is typically repeated several times, and the concentrations at which reversals occur are averaged to determine the threshold detection level of that odorant for a given individual. Also called "reverse _____ method"

olfactory epithelium

A secretory mucous membrane in the human nose whose primary function is to detect odorants in inhaled air. Located on both sides of the upper portion of the nasal cavity and the olfactory clefts, this contains three types of cells: olfactory sensory neurons, basal cells, and supporting cells.

accessory olfactory bulbs (AOB)

A smaller neural structure located behind the main olfactory bulb that receives input from the vomeronasal organ.

triangle test

A test in which a participant is given three odorants to smell, of which two are the same and one is different. The participant is required to state which is the odd odor out. Typically, the order in which the three odorants are given (same, same, different. same, different, same...) is manipulated and the test is repeated several times for greater accuracy

vibration theory

An alternative to shape-pattern theory for describing how olfaction works. Vibration theory proposes that every odorant has a different vibrational frequency, and that molecules that produce the same vibrational frequencies will smell the same.

tufted cell

Any of a secondary class of output neurons in the olfactory bulb.

G protein-coupled receptor (GPCR)

Any of the class of receptors that are present on the surface of olfactory sensory neurons. All GPCRs are characterized by a common structural feature of seven transmembrane alpha helices.

cilium

Any of the hairlike protrusions on the dendrites of olfactory sensory neurons. The receptor sites for odorant molecules are on the cilia, which are the first structures involved in olfactory signal transduction.

mitral cell

Any of the main projective output neurons in the olfactory bulb.

binaral rivalry

Competition between the two nostrils for odor perception. WHen a different scent is presented to each nostril simultaneously, we perceive each scent to be alternating back and forth with the other, and not a blend of the two scents.

gestation

Fetal development during pregnancy

stereoisomers

Isomers (molecules that can exist in different structural forms) in which the spatial arrangements of the atoms are mirror-image rotations of one another, like a right and left hand.

supporting cell

One of the three types of cells in the olfactory epithelium. Supporting cels provide metabolic and physical support for the olfactory sensory neurons.

basal cell

One of the three types of cells in the olfactory epithelium. These are small neurons located beneath a watery mucous layer in the epithelium. The cilia on these dendrites contain the receptor sites for odorant molecules.

gustation

The sense of taste

ipsilateral

Referring to the same side of the body (or brain)

receptor adaptation

THe biochemical phenomenon, occurring after continual exposure to an odorant, whereby receptors stop responding to an odorant and detection ceases.

amygdala-hippocampal complex

THe conjoined regions of the amygdala and hippocampus, which are key structures in the limbic system. This complex is critical for the unique emotional and associative properties of olfactory cognition

nasal dominance

The asymmetry characterizing the intake of air by the two nostrils, which corresponds to differing sensitivity to odorants between the two nostrils This alternates nostrils throughout the day, but there is no predictability about when the nostrils alternate.

learned taste aversion

The avoidance of a novel flavor after it has been paired with gastric illness. The smell, not the taste, of the substance is key for the learned aversion response in humans.

olfactory tract

The bundle of axons of the mitral and tufted cells within the olfactory bulb that sends odor information to the primary olfactory cortex.

aromatherapy

The contention that odors can influence, improve, and alter mood, performance, and well-being, as well as the physiological correlates of emotion such as heart rate, blood pressure, and sleep.

shape-pattern theory

The current dominant biochemical theory for how chemicals come to be perceived as specific odors. This theory contends that different scents- as a function of the fit between odorant shape to OR shape- activate different arrays of olfactory receptors in the olfactory epithelia. These various arrays produce specific firing patterns of neurons in the olfactory bulb, which then determine the particular scent we perceive.

limbic system

The encompassing group of neural structures that includes the olfactory cortex, the amygdala, the hippocampus, the piriform cortex, and the entorhinal cortex. THe limbic system is involved in many aspects of emotion and memory. Olfaction is unique among thh senses for its direct and intimate connection to the this.

trigeminal (V) nerves

The fifth pair of cranial nerves, which transmit information about the "feel" of an odorant (mint is cool, cinnamon is warm), as well as pain and irritation sensations (ammonia feels burning)

olfactory (I) nerves

The first pair of cranial nerves. The axons of the olfactory sensory neurons bundle together after passing through the cribriform plate to form the olfactory nerve, which conducts impulses from the olfactory epithelia in the nose to the olfactory bulb.

tip-of-the-nose phenomenon

The inability to name an odor, even though it is very familiar. Contrary to the tip of the tongue phenomenon, one has no lexical access to the name of the odor, such as first letter, rhyme, number of syllabus and so on. THis is an example of how language and olfactory perception are deeply connected.

Specific anosmia

The inability to smell one specific compound amid otherwise normal smell perception

odor hedonics

The liking dimension of odor perception, typically measured by ratings of an odors's perceived pleasantness, familiarity, and intensity

primary olfactory cortex or piriform cortex

The neural area where olfactory information is first processed. It comprises the amygdala, parahippocampal gyrus, and interconnected areas; and it interacts closely with the entorhinal cortex.

main olfactory bulb (MOB)

The olfactory bulb; the first region of the brain where smells are processed. In humans we refer simply to "olfactory bulb(s)"; in animals with accessory olfactory bulbs, we distinguish between "main" and "accessory".

orbitofrontal cortex (OFC)

The part of the frontal lobe of the cortex that lies behind the bone (orbit) containing the eyes. This is responsible for the conscious experience of olfaction, as well as the integration of pleasure and displeasure from food; and it has been referred to as the secondary olfactory cortex and the secondary taste cortex. This is also involved in many other functions, and it is critical for assigning affective value to stimuli- in other words, determining hedonic meaning.

cognitive habituation

The psychological process by which, after long-term exposure to an odor, one no longer has the ability to detect that odor or has very diminished detection ability.

cross-adaptation

The reduction in detection of an odorant following exposure to another odorant. Cross-adaptation is presumed to occur because the two odorants share one or more olfactory receptors for their transduction, but the order in which odorants are presented also plays a role.

olfactory receptor (OR)

The region on the cilia of olfactory sensory neurons where odorant molecules bind.

psychophysics

The science of defining quantitative relationships between physical and psychological (subjective) events

olfaction

The sense of smell

anosmia

The total inability to smell, most often resulting from sinus illness or head trauma

odor

The translation of a chemical stimulus into a smell sensation. "That cakes has a chocolate odor"