4. Why do we study taste and
smell together?
SENSORY INTERACTION: the principle that one sense may
influence another.
The senses of taste and smell have a very cooperative
working relationship.
Many of the subtle distinctions you may think of as
flavors really come from odors
Often, if you can’t smell the food, you can’t taste the
food.
both senses are strongly tied to primitive emotional and
behavioural functions of our nervous systems.
5. OLFACTION – Sense of Smell
Most primitive sense
Poorly understood
Poorly developed in humans
Only sensory modality that doesnot relay
in hypothalamus
6. Important for enjoyment &
selection of food .
Flavors are combinations of
taste and smell (smell
contribution is about 80 %)
Gives warning of harmful
substances or places
7. Primary Sensations of Smell
Based on psychological studies, one attempt to classify
these sensations is the following:
1. Camphoraceous - eucalyptus
2. Musky - musk
3. Floral - roses
4. Pepperminty - mint
5. Ethereal - pears
6. Pungent - vinegar
7. Putrid – rotten eggs
In recent years, specific studies of the genes that encode
for the receptor proteins, suggest the existence of at
least 100 primary sensations of smell
9. Many animals are macrosmatic
having a keen sense of smell that is
necessary for survival
Humans are microsmatic
a less keen sense of smell that is not
crucial to survive
11. VOMERONASAL SYSTEM
(Accessory Olfactory System)
“substances produced by an animal that act at a
distance to produce hormonal, behavioral, or
other physiological changes in another animal of
the same species are called Pheromones”
Vomeronasal organs have receptors for
pheromones
12. Pheromones influence:
- estrus cycles
- onset of puberty
- female for mating
- implantation of fertilized embryos
- new born to suckle
14. Structure of the Olfactory System
Olfactory mucosa is located at the top
of the nasal cavity
Odorants are carried along the
mucosa coming in contact with the
sensory neurons
Cilia of these neurons contain the
receptors
Humans have about 350 types of
receptors.
Signals are carried to the glomeruli
in the olfactory bulb
15. Structure of the Olfactory System - continued
Signals are sent to
Primary olfactory
(piriform) cortex in the
temporal lobe
Secondary olfactory
(orbitofrontal) cortex in
the frontal lobe
Amygdala deep in the
cortex
19. SPECIAL FEATURES OF OLFACTORY
EPITHELIUM
These neurons have a limited lifespan of up to several
months, but are continuously replenished from the pool of
precursor cells
New olfactory receptors are thus generated throughout
adult life, and their axons enter the olfactory bulb to form
new synapses with existing CNS neurons.
The regenerative capacity of the olfactory mucosa
gradually diminishes with advancing age.
Resulting in net loss of receptors and a slow decline in
overall sensory function
20. OLFACTORY BULB
is an elongated oval
structure that lies just
above the cribriform
plate.
It is continuous
posteriorly with the
olfactory tract through
which it is connected
to the base of the
cerebral hemisphere.
21. OLFACTORY PATHWAY
FIRST ORDER NEURON:
From olfactory epithelium to glomerulus
SECOND ORDER NEURON:
The olfactory bulb. where the second neurons
of the olfactory pathway (mitral and tufted
cells) are located.
The axons of these Second order neurons
pass centrally as the olfactory tract.
THIRD ORDER NEURON:
The prepiriform area (area 28) is considered
the primary olfactory cortex which contains
the third order neurons.
22. Neural connections of olfactory system
Asymmetric cortical
representation
No relay in
Hypothalamus
26. Odour Thresholds and Adaptation
chemical METHYL MERCAPTAN, which smells like
rotten cabbage and can be detected in
concentrations as low as 1/25 billionth of a milligram
per millilitre of air.
It is added to natural gas to detect gas leaks
Adaptation (decreasing sensitivity) to odors occurs
rapidly
