Olfaction/Gustation

Why are they called chemical senses and gatekeepers?

come into direct contact with chemicals; protect you/tell you what is good and bad

Why do receptors in both systems undergo a cycle of birth, development, and death so often?

neurogenesis → nose/mouth in constant contact with harsh chemicals, temperatures; receptors get damaged often

Functions of the olfactory system

lets you know if something is harmful, if chemicals have been added to natural gas, certain animals for reproduction (heat)

Macrosmatic vs Microsmatic

• Macrosmatic: keen sense of smell (dogs)

• Microsmatic: not keen sense of smell (humans)

How are human and dogs different with olfaction in terms of number and strength of receptors?

strength of receptors is same for both, but dogs have way more number of neurons than humans

Odor detection

when you can smell something there

Odor identification

can identify what the smell is specifically

Detection threshold for odor

smallest amount of odorant of chemical that you can detect

Difference threshold for odor

smallest difference between 2 odorants you can detect

Recognition threshold of odor

threshold at which you can identify/recognize that odorant identification

• 3x detection threshold

Why is odor identification difficult?

hard to describe smells

Olfactory mucosa

high in nasal cavity, includes cilia, olfactory sensory neurons

Cilia

jutting into airway, actual receptors for smell on cilia

Olfactory bulb

CN #1, 2 bulbs for 2 nostrils

Glomeruli

sections of the olfactory bulb

Convergence with the glomeruli

we send information from many more olfactory sensory neurons onto fewer glomeruli

Rules regarding zones on the olfactory mucosa and bulbs

• different zones on mucosa correspond to different zones on the bulbs

  • 1) smell usually only activates one zone

  • 2) usually more than 1 type of sensory neuron in a zone

  • 3) we have a particular type of olfactory sensory neuron exists in 1 zone

Primary olfactory cortex

• “Piriform cortex”

• ventral medial temporal lobe

  • lower middle part of temporal lobe

Secondary olfactory cortex

• “OFC”: Orbital Frontal Cortex

• frontal lobe

How is info presented in olfactory bulb vs. primary olfactory cortex?

• bulb: things separated by sections

• cortex: not neatly organized/scattered

Recognition profile of an odorant

different neurons fire in different patterns for different odorants

Process of taste

• papille: bumps on tongue

• taste buds: inside most papille

• taste cells: broken down from taste buds; neurons (go through neurogenesis)

• taste pore: top of taste cells; receptor sites for taste; where chemicals attach

How might distributed coding work in gustation?

different sensory neurons/taste cells can fire in different patterns for different chemicals

Flavor: how does smell and taste interact

combination of smell and taste

Retronasal route

odorant molecules go from mouth to nose backwards

Orbitofrontal cortex (OFC)

where smell and taste first combine in brain

• touch and vision send signals to OFC as well

Bimodal neurons

neurons that respond to more than one sense

What happened to the experiment on the moneys with cream and firing in the OFC

monkeys who consumed more cream started to not like it → as appeal for cream went down, firing in OFC also went down