Physiology of Olfaction and Gustation

Question 1

two senses for perception of chemicals - what are they?

Answer 1

olfaction (smell)
gustation (taste)

Question 2

olfaction?

Answer 2

can detect very small amounts of many substances from a great distance

Question 3

gustation?

Answer 3

can detect larger amounts of relatively few substances in direct contact

Question 4

functions of olfaction?

Answer 4

detection of food, enemies, navigate terrain/detect territories and detection of potential mates

Question 5

olfaction developed early in vertebrate evolution - why?

Answer 5

required most complex processing in the brain

Question 6

mammalian neocortex developed from?

Answer 6

from olfactory sense and a large portion of the neocortex is still devoted to olfactory processing in modern mammals

Question 7

nostril have slits laterally to?

Answer 7

to direct airflow laterally to prevent interference with incoming smells - stereo nostrils allow directional smelling

Question 8

what do turbinates do?

Answer 8

they direct airflow - ventrally in normal breathing, dorsally when sniffing

Question 9

lamina transversa?

Answer 9

(absent in microsmatic species) is a bone that separates the olfactory recess from the main airway and traps scent molecules to enhance detection

Question 10

olfactory recess?

Answer 10

contains the ethmo-turbinates lined with olfactory epithelium containing all the olfactory receptors (3 x10(8))

Question 11

cribiform plate?

Answer 11

separates cranial cavity from nasal cavity - a perforated plate to allow olfactory cell processes to pass through and synapse with olfactory bulb mitral cells

Question 12

olfactory bulb?

Answer 12

processes olfactory information - 40 times greater percentage of brain devoted to olfaction in the dog vs. human

Question 13

what does the nasal cavity contain?

Answer 13

contains scroll-like bones called turbinates

Question 14

describe the turbinates in the rostral cavity:

Answer 14

these are highly vascularised and used for heat exchange

Question 15

describe the turbinates in the caudal nasal cavity?

Answer 15

these are covered in olfactory epithelium

Question 16

through which three main passage/meatuses can airflow be directed through?

Answer 16

either:
ventral meatus
middle meatus
dorsal meatus

Question 17

ventral meatus?

Answer 17

shortcut beneath the heat exchanger directly to the nasopharynx a.

Question 18

middle meatus?

Answer 18

leads air through the heat exchanger and to the caudal part of the olfactory epithelium before entering the nasopharynx

Question 19

dorsal meatus?

Answer 19

leads air above the heat exchanger and to the olfactory epithelium and then to the nasopharynx

Question 20

breathing at rest - airflow?

Answer 20

air flows mainly through the two more ventral meatuses

Question 21

what happens during sniffing?

Answer 21

air passes dorsal to the heat exchanger
the airflow through the nasal cavity becomes turbulent, which further increases the air that reaches the olfactory epithelium

Question 22

where does exhalation occur?

Answer 22

occurs mainly through the ventral meatus

Question 23

olfactory receptors respond only to?

Answer 23

only to substances in contact with olfactory epithelium and need to be dissolved in mucus

Question 24

olfactory adaptation?

Answer 24

over time, olfactory threshold increases so that more of a substance is required to elicit the same response

Question 25

adaptation/habituation of smell?

Answer 25

smell of odoriferous substance first detected much more noticeable
gradually becomes less noticeable

Question 26

what is olfactory adaption mediated by?

Answer 26

by Ca2+ ions

Question 27

degree of adaptation is measured by?

Answer 27

measured by rise in threshold concentration to activate olfactory receptors

Question 28

what does degree of adaptation vary depending on?

Answer 28

depending on the substance

Question 29

nasal pain fibres - what nerve?

Answer 29

trigeminal nerve (cranial nerve V)

Question 30

how many branches of trigeminal nerve for nasal pain fibres?

Answer 30

mandibular branch
maxillary branch
ocular branch

Question 31

many trigeminal pain fibres from the maxillary branch are found where?

Answer 31

found in olfactory membrane

Question 32

what are trigeminal pain fibres stimulated by?

Answer 32

by irritating substances

Question 33

what are trigeminal pain fibres responsible for?

Answer 33

for initiating sneezing, lacrimation and other reflex responses

Question 34

what is the vomeronasal organ?

Answer 34

it is a sensory organ located in the rostral palatine bone with similar functionality to the olfactory epithelium

Question 35

vomeronasal organ found in which animals?

Answer 35

early evolutionary organ found in amphibians, reptiles and mammals
absent in fish and lost in birds

Question 36

vomeronasal organ in mammals?

Answer 36

well-developed and functional in most mammals (latest evidence suggests present but rudimentary in humans)