SPECIAL SENSES

Dr Ambika Jawalkar

SOMATIC SENSES –

TACTILE, THERMAL,

PAIN, AND

PROPRIOCEPTION

SPECIAL SENSES—

SMELL, TASTE,

VISION, HEARING &

EQUILIBRIUM

Five Senses

Physical

Chemical

Touch

Hearing

Sight

Smell

Taste

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.

OLFACTION – Sense of Smell

Most primitive sense

Poorly understood

Poorly developed in humans

Only sensory modality that doesnot relay

in hypothalamus

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

Primary Sensations of SmellBased 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 encodefor the receptor proteins, suggest the existence of atleast 100 primary sensations of smell

www.emptynosesyndrome.org

Sniffing

Normal Breath

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

Animal Sense of Smell

Vomeronasal Organ

Olfactory Organ

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

Pheromones influence:

- estrus cycles

- onset of puberty

- female for mating

- implantation of fertilized embryos

- new born to suckle

PATHWAY

Vomeronasal organ

Accessory olfactory bulb

Lateral olfactory tract

Amygdala

hypothalamus

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

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

John C. Leffingwell, Ph.D. www.leffingwell.com

Organization of olfactory membrane,

olfactory bulb & connections to olfactory

tract

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

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.

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.

Neural connections of olfactory system

Asymmetric cortical

representation

No relay in

Hypothalamus

Olfactory Transduction

Olfactory Transduction

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

Applied Physiology

Anosmia – complete absence

Hyposmia – decreased

Dysosmia – distorted

Parosmia – perverted

Cacosmia - Inappropriately disagreeable odors

Kallmann's syndrome - a hereditary disorder,

usually X-linked, (hypogonadism & anosmia)