Transcript Olfactory sensory neurons

Sensory Receptors and signal
transduction
14.6.12
The Ear
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Sound enter pinna
Ear canal acts as resonator for 3000Hz frequency
Vibrates tympanic membrane
Set ossicles into vibration: Sound amplifiers
Transfer vibrations to oval window by piston action
of stapes
Perilymph of scala vestibuli
Organ of corti: Basilar and tectorial membrane
vibrates bending hairs of hair cells
Fluid of Scala tympani and finally round window
Transduction by Hair cells
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The deflection of the hair-cell stereocilia opens
mechanically gated ion channels that allow any small,
positively charged ions (primarily potassium and
calcium) to enter the cell.
Unlike many other electrically active cells, the hair cell
itself does not fire an action potential. Instead, the influx
of positive ions from the endolymph in Scala media
depolarizes the cell, resulting in a receptor potential.
This receptor potential opens voltage gated calcium
channels, calcium ions then enter the cell and trigger the
release of neurotransmitters at the basal end of the cell.
Transduction by Hair cells
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The neurotransmitters diffuse across the narrow
space between the hair cell and a nerve terminal,
where they then bind to receptors and thus trigger
action potentials in the nerve.
In this way, the mechanical sound signal is converted
into an electrical nerve signal. The repolarization in
the hair cell is done in a special manner. The
Perilymph in Scala tympani has a very low
concentration of positive ions. The electrochemical
gradient makes the positive ions flow through
channels to the Perilymph.
Loudness of sound and frequency of
action potentials
The louder the sound is, the greater height or
amplitude of the vibrations in the sound
waves, the more movement of hairs/stereocilia
of hair cells and thus more action potentials
 Greater the frequency of action potentials,
louder the sound is
 If you could hear someone talking, that means
the voice is loud enough to generate action
potentials in the sensory neurons of your ear.
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Loudness of sound and frequency of
action potentials
If they raise their voice, that causes an
increase in the APs to your brain. If they lower
their voice into a whisper, the frequency
decreases.
 If they lower their voice to the point where
you can’t hear them, then that means you’re
not even generating ONE action potential. So
if you can’t hear a sound, it doesn’t mean
there’s no sound in the room, it means the
sound is too soft for you to hear.
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Hearing Loss
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Hearing loss is typically described as being conductive,
sensorineural, or mixed.
Conductive hearing loss refers to an impairment
of one's ability to conduct airborne sound through the
middle ear to the inner ear. Scar tissue or otosclerosis,
the abnormal growth of bone within the middle ear,
can lead to restricted movement of the ossicles.
Sensorineural hearing loss refers to impairment of
the sensory unit consisting of the auditory nerve and
the hair cells that excite it.
Hearing Loss
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Sometimes the distinction between these two types
of hearing loss can be made with a simple tuning fork
test. If the tuning fork cannot be heard when
sounded in air, then the base of the tuning fork is
placed against the hard bone behind the ear.
If the person can now hear it by conduction through
the bone, then conductive hearing loss is indicated. If
it cannot be heard by either air or bone conduction,
then sensorineural loss is indicated.
Hearing Aids
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Sometimes a satisfactory level of hearing can be restored by a
hearing aid - a combination of a microphone to sense ambient
sound, an amplifier, and a tiny speaker that projects the
amplified sound into the ear canal.
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Sound goes in the Microphone.
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Sound gets amplified.
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Sound comes out the Speaker into your Ear
Types of hearing aids
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Body
Behind The Ear (BTE)
In The Ear (ITE)
In The Canal (ITC)
Completely In the Canal (CIC)
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Stimuli: All changes in the environment both
internal and external are known as stimuli
Receptors: Organs of the body that detect these
changes or stimuli are called “receptors” or “sense
organs”. Sensory receptors are specialized to
respond to only certain stimuli, which will activate
the receptor with weak or moderate levels of
intensity. Sensory receptors transduce the stimuli
into a graded potential caused by opening of
membrane channels
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The sensitivity range of a sensory organ is much
broader than the range of a single receptor cell
This is because individual afferent (sensory) fibers of
the sensory system cover different parts of the
sensitivity spectrum
Sensory neurons: If the receptor potential is strong
enough to reach threshold, sensory neurons fire
(generate action potentials
Sensation: Sensation arise when signals are detected
by sensory receptor cells and transmitted through the
nervous system to the designated parts of the brain
Components of sensation
Stimulation
 Transduction
 Conduction: The impulse must be conducted
along a neural pathway from the receptors to
the brain
 Translation: A region of the brain designated
for the specific stimulus or spinal cord must
translate the impulse into a sensation
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Five senses
Touch: includes contact, pressure, heat, cold
etc
 Taste: for certain substances in solution
 Smell: for volatile chemicals and gases in air
 Hearing: for vibrations in air, water or solid
 Sight: for light waves
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Chemical Senses
Olfaction:The sense of smell
 Gustation:The sense of taste
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The nose:
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Three cell types
Supporting cells: Provides metabolic and physical
support for the olfactory sensory neurons
Basal cells: Precursor cells to olfactory sensory
neurons
Olfactory sensory neurons (OSNs): The main
cell type in the olfactory epithelium » OSNs are
small neurons located beneath a watery mucous
layer in the epithelium
Olfactory receptor
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Cilia: Hairlike protrusions on
OSN dendrites
- Have receptor sites for odorant
molecules.
- structures for olfactory signal
transduction
- Takes seven or eight odor
molecules binding to a receptor
to initiate an action potential
- Very sensitive to stimuli
however they quickly become
fatigued. This explains the reason
why odours seem to go away after
being easily noticable
Tongue
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Detects sweet, sour,
salty, bitter, & amino
acids (umami)
Taste/Gustation
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Taste receptor cells
are modified epithelial
cells
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50-100 are in each
taste bud
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Each bud can respond
to all categories of
tastants
Taste/Gustation
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Salty & sour do not have receptors; act by passing through channels
10-29
Taste/Gustation
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Sweet & bitter have receptors; act thru G-proteins
10-30