what are odorants?

Ans- Odorants—volatile chemicals that are
perceived as odors—are

what are odors?

Ans- volatile chemicals

how are odors detected?

Ans- olfactory sensory neurons

where are they detected?

Ans-nose.

where are olfactory sensory neurons located?

Ans- olfactory epithelium

what is the role of olfactory epithelium?

Ans- The olfactory sensory neurons are embedded in a specialized olfactory epithelium

what does olfactory epithelium line?

Ans- part of nasal cavity

what other cells are associated with olfactory epithelium?

Ans- glia-like supporting cells

what kind of nerve cell is olfactory sensory neuron?

Ans- bipolar nerve cell.

Single dendrite extends form which end to end?

Ans- extends from the apical end to the epithelial surface

What happens at the epithelial end?

Ans- where it gives rise to numerous thin cilia

What is mucus function in nasal cavity?

Ans-coats the nasal cavity

What role does cilia play in the nasal cavity?

Ans- protrude into the mucus

what do cilia recognize and how?

Ans- odorants as well as the transduction machinery

Why is transduction machinery needed?
Ans- to amplify the sensory signals and transform them into electrical signals in the neuron’s axon

How many different odorant receptors do humans have?

Ans- 350

How many different odorant receptors do mice have?

Ans- 1,000

Odorant receptors belong to which family?

Ans- the G protein-coupled receptor superfamily

Single odorant receptors recognizes how many odorants?

Ans- A single odorant receptor can recognize multiple odorants

How is an odorant recognized?

Ans-one odorant is recognized by a specific combination of different receptors

Where does odorant binding occur?

Ans-occurs in a pocket in the transmembrane region

Transmembrane region is formed by?

Ans-a combination of the transmembrane domains.

Which receptors are expressed in olfactory epithelium?

Ans- A second, smaller family of chemosensory receptors is also expressed in the olfactory epithelium.

What are TAARs?

Ans-trace amine-associated receptors (TAARs), are G protein-coupled

What is special about TAARs protein sequence?

Ans- their protein sequence is unrelated to that of odorant receptors.

TAARs are encoded by?

Ans-a small family of genes present in humans and mice as well as fish

What do TAARs recognize?

Ans- volatile amines

What happens when odorant binds to odorant receptor?

Ans- Binding of an odorant causes the odorant receptor to interact with Gαolf, the α-subunit of a

heterotrimeric G protein.

What does the interaction of Galphaolf lead to?

Ans- causes the release of a GTP-coupled Gαolf, which stimulates adenylyl cyclase III, leading to an increase in cAMP.

What happens when there is elevated levels of cAMP?

Ans- The elevated cAMP in turn induces the opening of cyclic nucleotide-gated cation channels,

causing cation influx and a change in membrane potential in the ciliary membrane

What happens when depolarization spreads to the cell body?

Ans- depolarization spreads to the cell body of the olfactory sensory neuron, causing action

potentials that are actively conducted in the axon to the olfactory bulb

What are the two mechanisms by which different receptors encode for different odarants?

Ans-each olfactory sensory neuron expresses only one odorant receptor gene and therefore one type of receptor.

• each receptor recognizes multiple odorants, and conversely each

odorant is detected by different types of receptors.

How does distinctive pattern of signals occur?

Ans-each odorant is detected by a unique constellation of receptors and thus causes a distinctive pattern of signals to be transmitted to the brain.

why a slight change in the structure of an odorant can alter its perceived odor?

Ans-highly related odorants have different receptor codes

What can change percieved odor?

Ans-change in concentration of an odorant, slight change in the structure of an odorant

What happens when the concentration of odour is increased?

Ans-additional receptors with lower affinity for the odorant are recruited into the response and change the receptor code

How many receptor types are there in one zone?

Ans- Each receptor type is expressed in approximately 5,000 neurons that are confined to one Zone

How are neurons with different receptors interspersed?

Ans- Neurons with the same receptor are randomlyscattered within the zone so that neurons with different receptors are interspersed.

How is a specific odorant recognized by receptors in several different zones?

Ans-Although one zone may have more receptors for a particular odorant compared to other zones, all zones contain a variety of receptors, so that a specific odorant

may be recognized by receptors in several different zones.

Where does the The axons of olfactory sensory neurons terminate?

Ans- terminate on the dendrites of olfactory bulb neurons within bundles of neuropil

called glomeruli

What happens in glomerulus?

Ans- the sensory axons make synaptic connections with three types of neurons:

What are the three types of neurons in glomerulus?

Ans-mitral and tufted relay neurons, which project axons to the olfactory cortex, and

periglomerular interneurons

How does 100- fold decrease occur in number of transmitting signals to the brain from nose?

Ans-In each glomerulus the axons of several thousand sensory neurons converge on the dendrites of approximately 40 to 50 relay neurons which results

What kind of synapses do dendrites of gabaergic neurons have?

Ans- reciprocal excitatory-inhibitory synapses with secondary dendrites of relay neurons

Which dendrite are thought to provide negative feedback?

Ans-The dendrites of GABAergic granule cells are thought to provide negative feedback to relay neurons that shapes the odor response.

Glomerulus is encircled by?

Ans- periglomerular interneurons

periglomerular interneurons receive what kind of input and from where?

Ans-receive excitatory input from sensory axons

Relation of periglomerular interneurons with tufted and mitral interneurons?

Ans-form inhibitory dendrodendritic synapses with mitral and tufted celldendrites in that glomerulus.

How does sharpening the contrast between important and irrelevant sensory information before its transmission take place?

Ans- The lateral inhibition afforded by these connections is thought to dampen signals from

glomeruli and relay neurons that respond to an odorant only weakly,

How are neurons with the same receptors placed in zones?

Ans- olfactory sensory neurons with the same odorant receptor are randomly scattered in

one epithelial zone, their axons converge in a few glomeruli at two spots, one on either side of the olfactory bulb.

How many inputs does each glomerulus receive and from where?

Ans- Each glomerulus, and each mitral and tufted relay neuron connected to it, receives input from just one type of odorant receptor.

Glomerulus or mitral or tufted is activated by?

Ans- activated by more than one odorant.

What does odorant activate in olfactory bulb?

Ans-Because each odorant is recognized by a unique combination of receptor types, each odorant also activates a particular combination of glomeruli in the olfactory bulb.

Through which tract does information get passed to the cortex?

Ans- lateral olfactory tract

The axons of which neuron passes signal to the cortex?

Ans- The axons of the mitral and tufted relay neurons of the olfactory bulb

The olfactory cortex comprises of how many areas?

Ans- five main areas

Name the areas?

Ans- the anterior olfactory nucleus

(2) amygdala

(3) the olfactory tubercle

(4) part of the entorhinal cortex

(5) the piriform cortex, the largest and considered the major olfactory cortical area.

What happens in the pitiform cortex?

Ans-the axons of olfactory bulb mitral and tufted cells leave the lateral olfactory tract to form excitatory glutamatergic synapses with pyramidal neurons, the projection neurons of the cortex.

How does pyramidal neurons transmit directly and indirectly?

Ans- Pyramidal neurons in the olfactory cortex transmit information indirectly to the

orbitofrontal cortex through the thalamus and directly to the frontal cortex.

Single transmission of pyrimidal neurons is modulated by?

Ans- inhibitory inputs from local GABA-ergic interneurons as well as by excitatory inputs from

neighboring pyramidal neurons

What role does hypothalamus and amygdala play?

Ans-thought to mediate the emotional and motivational aspects of smell as well as many of the behavioral and physiological effects of odorants.Most areas of the olfactory cortex also relay information to the lateral hypothalamus, an area important in appetite.

What is specific anosmia?

Ans- An individual with a specific anosmia has lowered sensitivity to a specific odorant even though sensitivity to other odorants appears normal.

Most common aberration?

Ans- specific anosmia

What is general anosmia?

Ans- complete lack of olfactory sensation

What is hyposmia?

Ans- diminished sense of smell

How does hyposmia occur?

Ans- can result from damage to the olfactory epithelium caused by infections; from particular diseases, such as Parkinson disease; or from head trauma.

What is other name for hyposmia?

Ans- Chronic anosmia

What is cacosmia?

Ans- Olfactory hallucinations of repugnant smells

How does cacosmia occur?

Ans- as a consequence of epileptic seizures.

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