Lecture 18: Nose And Olfaction

Question 1

Where are olfactory receptors found? What is this?

Answer 1

Olfactory epithelium. This is a specialized area of nasal mucosa covering portions of the ethmoid bone (cribiform plate) in the superior nasal cavity

Question 2

Chemically, how are odors perceived?

Answer 2

The olfactory sense is triggered by a chemical stimulus, the odorant, that attaches to a receptor in the nasal mucosa

Question 3

Is the olfactory nerve (CN1) considered a true nerve, why or why not?

Answer 3

No. Structurally and functionally it is already part of the CNS. Anatomically it is made up of numerous olfactory axons that are collectively called the “fila olfactoria”

Question 4

What is the path that olfactory information follows?

Answer 4

It is carried via the main olfactory bulb and olfactory tract to the paleocortex in the temporal lobe, along the olfactory stria near the uncus

Question 5

What is the paleocortex?

Answer 5

The phylogenetically oldest portion of the cortical mantle of the cerebral hemisphere and develops in association with the olfactory system. Comprised of the piriform complex and the parahippocampal gyrus

Question 6

What creatures posses a main olfactory bulb (MOB)?

Answer 6

All vertebrates except aquatic mammals

Question 7

What creatures posses an accessory olfactory bulb (AOB) ?

Answer 7

Most vertebrates but absent in old world monkeys, apes and humans

Question 8

What is the vomeronasal organ and what is another name for this?

Answer 8

A second area of olfaction present in many mammals. Aka the organ of Jacobson

Question 9

How do the stimuli that the main olfactory epithelium (MOE) and the vomeronasal organ (VNO) respond to differ?

Answer 9

MOE-thought to receive sensory input via volatile, airborne stimulus (aromatic molecules)
VNO- receives nonvolatile aromatic stimulus called pheromones

Question 10

Are the olfactory epithelium functionally separate?

Answer 10

Not really!

Question 11

Do the MOE and VNO use the main or accessory olfactory bulbs?

Answer 11

VNO used the accessory olfactory bulbs

MOE uses the main olfactory bulb

Question 12

Among mammals and other vertebrates, humans have what kind of expression of genes responsible for olfactory receptors associated with the VNO?

Answer 12

Low expression of V1R and V2R genes associated with the VNO

Question 13

Despite having low expression of genes responsible for the olfactory receptors associated with the VNO, humans do exhibit this and are known to respond to olfactory signals from pheromones. What are some examples of these?

Answer 13

• female menstrual synchronization
• dimorphic activation of brain activity when exposed to pheromones leading to hormonal responses
• human pheromones found in apocrine glands, saliva, seminal and vaginal secretions and urine

Question 14

What is the septal organ of masera (SOM)?

Answer 14

• small area of olfactory epithelium located in the nasal mucosa posterior to the nasopalantine ducts that connect the oral and nasal cavities
• known in rodents but not identifies in primates
• alert/alarm pheromone reception

Question 15

What is the gruenberg ganglion (septal organ of gruenberg) (GG)?

Answer 15

Found in rodents

Maternal and/or alarm pheromone reception

Question 16

Where do strepsirrhines have scent glands?

Answer 16

On wrists, elbows, throat and/or genital area

Question 17

What type of strepsirrhines engage in “stink fights” by wafting tails?

Answer 17

Lemur catta (ring-tailed lemur)

Question 18

What is olfaction important for in strepsirrhines and platyrrhines specifically?

Answer 18

Protection of young, engaging in competition for mates, etc

Question 19

Where do platyrrhines have scent glands?

Answer 19

In throat and/or genital area

Question 20

Where do catarrhines have scent glands?

Answer 20

On chest and genital area in some species

Question 21

Mandrillus (mandrils) and vervet monkeys are examples of old world monkeys that use what to communicate with conspecifics?

Answer 21

Scent marking

Question 22

What is the external anatomy of the human nose?

Answer 22

It is a dry skin covered structure that protrudes from the viscerocranium, situated between the nasal and maxillary bones of the skull. External cartilaginous portions define individual nose structure

Question 23

What is the inside of the nasal cavity covered in? What divides the left and right cavities?

Answer 23

Mucosa

Left and right cavities divided by cartilagenous nasal septum

Question 24

What creates the nasal turbinate bones (nasal conchae)?

Answer 24

Scroll-like bony features of the maxilla and ethmoidal elements

Question 25

Where do the paranormal sinuses open into the nasal cavity?

Answer 25

Beneath the turbinate mucosa

Question 26

What is the rhinarium?

Answer 26

Moist, naked surface surrounding the nasal openings/nostrils of most mammals; sensitive to touch but no olfactory receptors

Question 27

What is thought to be the function of the rhinarium?

Answer 27

Probably assists in delivering pheromone molecules to the VNO

Question 28

What is the philtrum?

Answer 28

A fold of skin that attaches the rhinarium to the mucus membranes of the premaxilla

Question 29

Which primates are “wet-nosed” and which are “dry-nosed”?

Answer 29

Wet-nosed=strepsirrhine

Dry-nosed=haplorine

Question 30

What are the two types of haplorhines, side-facing nostrils family and downward facing nostril family?

Answer 30

Side-facing nostrils=platyrrhines

Downward facing nostrils= catarrhines

Question 31

What classification would humans fall in, in regards to noses?

Answer 31

Catarrhines (downward facing nostrils) and haplorhine (dry-nosed)

Question 32

What is the “trade-off” hypothesis?

Answer 32

Rivalry between smell and vision for dominance, visual parts of brain developed/evolved at the expense of the olfactory parts in the forebrain. The idea is that specialization of one sensory function will impair another

Question 33

What evidence is used to support the “trade-off” hypothesis in OWM vs NWM?

Answer 33

OWM use visual cues in reproductive behavior and have emphasized vision over olfaction while NWM seem to rely more on olfaction

**Darwin also emphasized the importance of vision in humans and other primates compared to other mammals

Question 34

What does new molecular data suggest for the “trade-off” hypothesis?

Answer 34

New ways in which reliance on pheromones has been reduced in promotes and the shift toward reliance on trichromatic vision