Download Sense of Smell - Manasquan Public Schools

Sense of Smell
Suzanne D'Anna
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Olfactory Organs
lie in nasal epithelium mucous
membrane
 total area of olfactory epithelium is less
than 1 square inch
 located in superior portion of nasal
cavity
- superior nasal conchae
- part of nasal septum

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Olfactory Epithelium

Consists of three types of cells:
- olfactory receptors
- supporting cells
- basal cells
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Olfactory Receptors
10 - 100 million
 lifespan about 30 days

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Olfactory Receptors
(cont.)
bipolar neurons with knob-shaped
dendrite at distal end
- cilia called olfactory hairs protrude
from dendrite
- cilia are sites of olfactory transduction
 respond to chemical stimulation of an
odorant molecule
 single axon projects into olfactory bulb
at proximal end
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Supporting Cells
columnar epithelial cells of mucous
membrane lining the nose
 surround and support olfactory receptors
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Basal Cells
located around supporting cells
 stem cells that produce new olfactory
receptors (neurons)
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Olfactory Glands
also called Bowman’s glands
within connective tissue that supports
epithelium
 produce mucus
- moistens surface of olfactory epithelium
- dissolves odorant gasses
- continued production clears surface area
and prevents continued stimulation by same
odor

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Physiology of the Sense of
Smell
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Olfactory Stimulation

Primary scents:
- floral
- pungent
- musky
- minty
- putrid
- camphoraceous
- etheral
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Olfactory Stimulation
(cont.)
irritating odors also stimulate lacrimal
and nasal receptors producing tears
and sniffles
 Example:
- onions

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Olfaction or Transduction

chemical interaction with receptor sites
- sodium channels open leading to
depolarization which causes action potential
in axon leading to olfactory bulb

low threshhold - only a few molecules of a
substance in the air are necessary to
stimulate olfactory receptors
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Adaptation
decreasing sensitivity to odors
 occurs rapidly; about 50% in the first
second after stimulation and very slowly
thereafter
 even though adaptation to one odor has
occurred, sensitivity to other odors
remains unchanged

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Olfactory Pathway
olfactory receptors
 olfactory nerves
 olfactory bulbs
 olfactory tract
 prepyriform cortex and limbic system
 frontal lobes

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Taste
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Taste Buds
about 10,000 are located on surface of
tongue, throat, and epiglottis
 Oval body consisting of three kinds
of epithelial cells:
- supporting cells
- gustatory receptor cells
- basal cells

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Supporting Cells
form capsule supporting gustatory
receptor cells
 inside capsule - gustatory receptor cells

Gustatory Receptor Cells

single hair-like gustatory hair projects from
each bud to external surface through taste
pore
- hairs make contact with stimuli
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Basal Cells
found at periphery of taste bud near
connective tissue layer
 produce supporting cells which develop
into receptor cells whose life-span is
about 10 days

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Papillae
elevations on tongue
 contain taste buds
 give tongue rough appearance
 Types of papillae:
- circumvallate
- fungiform
- filiform

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Circumvallate
largest
 form v-shaped row on posterior surface
of tongue

Fungiform
mushroom-shaped
 found on tip and sides of tongue

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Filiform
thread-like
 cover anterior 2/3 of tongue
 contain no taste buds
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Taste Sensations
Four basic:
 sour - lateral edges of tongue
 salty - anterior portions of tongue
 bitter - posterior portions of tongue
 sweet - anterior portions of tongue

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Gustatory Pathway
(once a chemical is dissolved in saliva)
contact is made with plasma membrane
of gustatory hairs (site of transduction)
 gustatory receptors - release
neurotransmitter
 nerve impulses arise in neurons that
synapse with gustatory receptors
 sensory fibers become part of three
cranial nerves

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Gustatory Pathway

Three cranial nerves:
- facial (VII)
- glossopharyngeal (IX)
- vagus (X)
taste impulses conduct from taste buds
along cranial nerves to medulla
oblongata
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Gustatory Pathway

From medulla:
- some taste fibers transmit impulses to
hypothalamus and limbic system
(emotional memory responses)
- some taste fibers transmit impulses to
primary gustatory area in parietal lobes
of cerebral cortex (taste perception)
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Somatic and Special Senses
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Senses
constantly provide us with information
about our surroundings
 Grouped into two major categories:
- general senses
- special senses

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Sensory Pathway

Includes:
- receptors
- sensory neurons
- sensory tracts
- sensory area
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Receptors
detect stimuli
 specific with respect to changes to which
they respond

Sensory Neurons
transmit impulses from receptors to
central nervous system
 found in both spinal and cranial nerves
(each carries only one type of receptor)

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Sensory Tracts
white matter in spinal cord or brain
 transmit impulses to a specific part of brain

Sensory Areas
most are in cerebral cortex
 feel and interpret sensations
 learning to interpret sensations begins in
infancy without awareness and continues
throughout life

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General Senses
Somatic:
- tactile - touch, pressure, vibration, itch, etc.
- thermal - hot and cold
- pain - acute and chronic
- proprioceptive - muscle, tendon, joint
 Visceral
- distension of viscera - internal organs
- chemical composition of extracellular fluid

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Special Senses
Somatic:
- visual - sight
- auditory - hearing
- equilibrium - static and dynamic
equilibrium
 Visceral:
- olfactory - smell
- gustatory - taste

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Skin Receptors
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Tactile Sensations

Touch receptors:
- root hair plexuses
- tactile discs
- type II cutaneous mechanoreceptors
- corpuscles of touch - (Meissner’s
corpuscles)
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Root Hair Plexuses
dendrites arranged around hair follicles
 receptors that rapidly adapt to detect
movements when hair is disturbed

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Tactile Discs
expanded (flattened) nerve endings
 slowly adapting touch receptors for
discriminative touch
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Type II Cutaneous
Mechanorecptors
also called end organ for Ruffini
 expanded nerve endings
 embedded in dermis
 receptors that adapt slowly to heavy
and continuous touch

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Corpuscles of Touch
(Meissner’s Corpuscles)
small, oval, encapsulated nerve endings
 rapidly adapting touch receptors
 recognize exactly what point to which
body is touched
 abundant in hairless portions of skin

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Corpuscles of Touch
(cont.)
rapidly adapting receptors that respond
to low frequency vibrations
 also respond to pressure and touch
stimuli

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Tactile Sensations

Pressure and vibration receptors:
- corpuscles of touch (Meissner’s)
- lamellated corpuscles (Pacinian)
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Lamellated Corpuscles
(Pacinian)
oval structures
 composed of connective tissue
 layered like an onion
 enclose a dendrite
 rapidly adaptive receptors that respond
to pressure and high frequency
vibrations

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Tactile Sensations
(itch and tickle receptors)

free nerve endings are receptors for
both tickle and itch sensations
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Thermal Sensations
(thermoreceptors)
heat receptors most sensitive to
temperatures above 25oC (77oF) and
become unresponsive at temperatures
above 45oC (113oF)
 cold receptors most sensitive to
temperatures between 10oC (50oF) and
20oC (68oF)

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Thermal Sensations
(cont.)
intermediate temperature sensory input
from combination of cold and heat
receptors
 both heat and cold receptors rapidly
adapt to continuous stimulation
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Pain Sensations
(Nociceptors)
free, naked nerve endings
 located between cells of epidermis
 respond to all types of stimuli

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Referred Pain
pain that feels as if it originated from a
part other than site being stimulated
 Example:
- pain from heart attack (myocardial
infarction) may be felt in left shoulder or
inside of left arm
- pain from gallstones may be felt in
right shoulder

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