Ch. 9: Smell/Olfaction

How many different odorants can humans discriminate between?

1 trillion

How much can the expression of different odor receptors differ between any 2 people?

by 30%

Where does inhalation bring odorants to?

the olfactory epithelium that lines nasal cavities and nearby regions

Different types of cells found on the olfactory epithelium?

olfactory receptor cells (6 million), supporting cells, and basal cells

Cells involved in adult neurogenesis (for the olfactory neurons)

olfactory neurons regenerated from basal cells

What do olfactory receptor neurons have?

dendrite to olfactory mucosa with cilia extending from the dendritic knob, unmyelinated axon to olfactory bulb, and metabotropic receptors on cilia and knob; are bipolar (have 2 projections from their cell body)

How many types of olfactory receptors can each olfactory neuron express?

1

How many different olfactory receptors are there?

1000 different olfactory receptors, each of which belong to 1 of 4 subfamilies, only 400 receptors are functional

Olfactory receptor signaling pathway

odorant binds metabotropic receptor → G-protein activated → adenylyl cyclase activated and makes cAMP (2nd messenger) → cAMP causes cation (Ca2+, Na+) channels to open → voltaged gated Cl- channels open to further depolarize the cell → action potential

What allows us to be able to distinguish between so many different smells?

population coding

Where do olfactory neuron axons synapse onto?

mitral cells in the olfactory bulb that are clustered into glomeruli

Glomeruli

a sphere of cells

How are glomeruli organized in the olfactory bulb?

separated by function

Cells from which a glomerulus in the olfactory bulb receives information from

from olfactory neurons with the same receptor type

Olfactory components/cells that are located in the olfactory bulb

mitral cell, glomerulus

Where do the dendrites of one mitral/tufted cell go to?

to only one glomerulus

Cranial nerve involved in smell and where it exits from?

cranial nerve I, the olfactory nerve, exits from the olfactory bulb

Piriform cortex

the primary olfactory cortex

Where does information from the olfactory bulb go to?

Go to the piriform cortex

Why can smell trigger memories?

Because information from the piriform cortex can go directly to the hippocampus

mitral cell firing rate

slow to fire (slow-spiking), transfer info slower

tufted cell firing rate

fast to fire (fast-spiking), transfer info fast

What type of receptors are olfactory receptors?

are all metabotropic

Which parts of the brain do the mitral cells synapse onto?

anterior olfactory nucleus, olfactory tubercle, piriform cortex, amygdala, and entorhinal cortex

What do tufted cells synapse onto?

anterior olfactory nucleus, olfactory tubercle, and the piriform cortex

Where can information along the olfactory tract go to?

anterior olfactory nucleus, olfactory tubercle, piriform cortex, and amygdala (amygdala projects to the hypothalamus)

Where is there converging information from the olfactory bulb projection?

the thalamus and frontal cortex