Biology 211
Anatomy & Physiology I
Special Senses
Special Senses
1. All confined to head
2. All special senses reach the central nervous system
through cranial nerves
3. Consist of highly specialized cells which serve as
receptors
4. These specialized receptor cells housed in sensory
organs which are also specialized for a particular
function.
Special Senses
Specialized
Receptor Cells
Specialized
Organ.....
TASTE:
Gustatory Cells
Taste Buds
SMELL:
Olfactory Cells
Olfactory
Epithelium
VISION:
Rods & Cones
Eye (Retina)
HEARING:
Hair Cells
Cochlea
EQUILIBRIUM:
Hair Cells
Vestibular
Apparatus
Special Senses
Specialized
Receptor Cells
Specialized
Organ.....
TASTE:
Gustatory Cells
Taste Buds
SMELL:
Olfactory Cells
Olfactory
Epithelium
VISION:
Rods & Cones
Eye (Retina)
HEARING:
Hair Cells
Cochlea
EQUILIBRIUM:
Hair Cells
Vestibular
Apparatus
Most, but not all, taste buds are located on projections
from the surface of the tongue called papillae
Some taste buds are also located on the cheeks, the
palate, and the oropharynx
Each taste bud contains three types of cells:
Each taste bud also
has a small hole, or
taste pore, on its
free surface (facing
the inside of the
mouth)
Each gustatory cell has long microvillus, called a gustatory
hair, which extends out of the taste pore into the saliva of the
mouth.
This gustatory hair
contains receptors on
its plasma membrane
which can detect
specific chemicals in
the saliva.
At the other end,
each gustatory cell
is surrounded by
dendrites of sensory
neurons
Gustatory cells within taste buds can detect thousands of different
types of molecules, but these are grouped into five general categories:
a)
: sugars (glucose, fructose, lactose, sucrose, etc.)
saccharin, aspartame, sucralose, xylitol, etc.
b)
: sodium, potassium, lithium, many others
c)
: citric acids, hydrochloric acid, carbonic acid,
malic acid, tartaric acid, many others
d)
: quinine, fatty acids, many others
e)
: glutamate
Substances must be dissolved in saliva or other liquid
before they can stimulate the gustatory cells.
Each gustatory cell can respond to only one substance
(sodium, glucose, etc.) BUT each taste bud contains many
different types of gustatory cells.
Taste buds with gustatory cells
for different types of tastes are
located in all regions of the
tongue, but certain regions are
more sensitive to specific tastes
Each gustatory cell has long microvillus, called a gustatory hair, which
extends out of the taste pore into the saliva of the mouth.
This gustatory hair
contains receptors on its
plasma membrane which
can detect specific
chemicals in the saliva.
At the other end, each
gustatory cell is
surrounded by dendrites
of sensory neurons
Each gustatory cell has a separate threshold:
concentrations below this do not stimulate the receptors.
In general: Sweet & Salty substances have high thresholds
Sour substances have moderate thresholds
Bitter substances have low thresholds
These afferent neurons carry information for conscious
perception of tastes.
They also form afferent limbs of reflexes whose efferent
limbs stimulate saliva production,
secretion of enzymes by stomach, liver,
pancreas
if necessary, gagging
vomiting
Special Senses
Specialized
Receptor Cells
Specialized
Organ.....
Gustatory Cells
Taste Buds
VISION:
Rods & Cones
Eye (Retina)
HEARING:
Hair Cells
Cochlea
EQUILIBRIUM:
Hair Cells
Vestibular
Apparatus
TASTE:
SMELL:
The olfactory epithelium (mucosa) is located high in the
nasal cavity, just inferior to the cribriform plate of the
ethmoid bone.
Each olfactory cell has long microvillus, called an olfactory
hair, which extends into a layer of mucous on its free surface
This olfactory hair contains receptors on its plasma
membrane which can detect specific chemicals in the
mucous.
The axons of these olfactory cells (neurons) pass through
the cribriform plate to synapse with neurons in the olfactory
bulb. These axons are the olfactory nerve (C.N. I)
Substances must dissolve from the air into the mucous
before they can stimulate the olfactory cells.
Each olfactory cell appears to be able to respond to many
different substances.
Each olfactory cell has a separate threshold, but these are
generally very low: just a few molecules of a substance
may stimulate the olfactory cells.
Olfactory Pathways:
Axons of olfactory receptor cells pass through the cribriform
plate of the ethmoid bone as the olfactory nerve, then
synapse with afferent neurons in the olfactory bulb which
lies just superior to it.
Axons of these afferent neurons pass through the olfactory
tract to:
- The thalamus and the olfactory cortex on the medial
surface of the temporal lobe. This provides conscious
perception and interpretation of smells
- The hypothalamus and the brainstem. This provides
reflexes (salivation, avoidance, etc.) and "associative
responses" (activation of autonomic pathways, sexual
responses, emotional responses, etc.)
Start with Vision:
Specialized
Receptor Cells
Specialized
Organ.....
VISION:
Other structures of eye regulate amount of light reaching
retina and focus it on rod and cone cells.
The eyeball has three layers or "tunics:
Strong connective tissue
Protects the eye
Holds shape of eye
Insertion of extraoccular muscles
Contains blood vessels
Pigmented
Contains smooth muscle cells
Contains rod and cone cells
and
Other neurons to transmit visual
information to brain
Layers ("tunics") of the eyeball
Fibrous Layer
Vascular Layer
Sensory Layer
Focus:
Majority of light refraction
(bending) occurs in cornea.
Not adjustable
"Fine tuning" of light
refraction occurs in lens:
Thicker = more refraction
Thinner = less refraction
Rods:
Cones:
Special Senses
Specialized
Receptor Cells
Specialized
Organ.....
TASTE:
Gustatory Cells
Taste Buds
SMELL:
Olfactory Cells
Olfactory
Epithelium
VISION:
Rods & Cones
Eye (Retina)
HEARING:
Hair Cells
Cochlea
EQUILIBRIUM:
Hair Cells
Vestibular
Apparatus
Next: Hearing
Specialized
Receptor Cells
Specialized
Organ.....
HEARING
Located in inner ear.
Outer ear and middle ear
serve to transmit and
regulate the volume of
sound
The inner ear contains a
complex fluid-filled structure,
the membranous
labyrinth, which
is embedded
in the
temporal
bone.
Outer ear
channels air vibrations
(sound) to the tympanic
membrane (eardrum)
The middle ear is an air-filled
chamber containing three
ossicles: the malleus, the
incus, & the stapes
Malleus
Incus
Stapes (attaches
to oval
window
of inner
ear)
Tympanic
membrane
The tympanic membrane is attached to the malleus,
which is attached to the incus, which is attached to the
stapes, which is attached to the oval window of the
membranous labyrinth of the inner ear. The membranous
labyrinth is fluid-filled.
Therefore:
Vibrations of air (sound) vibrate the tympanic membrane
Which makes the ossicles vibrate
Which makes the oval window vibrate
Which makes the fluid of the membranous labyrinth
of the inner ear vibrate
This is how the vibrations get transmitted from the air of
the outer ear to the receptor cells of the cochlea in the
inner ear
The membranous labyrinth of the inner ear actually
consists of two sets of tubes, one inside the other.
The outer tube is filled with a fluid called
, while
the inner tube is filled with fluid called
At one end of inner ear, these two tubes (one inside the
other) coil about 2 & 2/3 times to form the
Vibrations of the oval window actually make the perilymph
vibrate. This must be transmitted to the endolymph within
the cochlea before the hair cells can detect it.
Structure of cochlea if it could be uncoiled
Vibration of oval window causes vibration of perilymph
of
and
which causes
vibration of endolymph in
Vibration of the cochlear duct causes bending of hair
cells within it.
When these hair cells bend, they send electrical signals
through the vestibulocochlear nerve to the brain
Hearing involves two aspects of bending hair cells:
Which hair cells bend determines the pitch of the sound
How far hair cells bend determines volume of the sound
The membranous labyrinth of the inner ear also houses
the specialized receptor cells for equilibrium - both
position of the head ("static equilibrium") and movement
of the head ("dynamic equilibrium").
Special Senses
Specialized
Receptor Cells
Specialized
Organ.....
TASTE:
Gustatory Cells
Taste Buds
SMELL:
Olfactory Cells
Olfactory
Epithelium
VISION:
Rods & Cones
Eye (Retina)
HEARING:
Hair Cells
Cochlea
EQUILIBRIUM:
The parts of the membranous labyrinth responsible for
equilibrium are the
the
and three
which lie at right angles to each other.
The saccule and the utricle are responsible for detecting
the position of the head ("static equilibrium").
Each of them contain a region of hair cells called a
The tips of these hair cells project into a gelatinous mass
called the
in which are embedded small
crystals of calcium carbonate called
When the head changes position, gravity pulls on the
otoliths, which causes the otolithic membrane to bend
the hair cells (receptors)
When these hair cells
bend, they send
electrical signals to the
brain through the
vestibulocochlear
nerve, telling it the
new position of the
head
A very similar situation tells your brain about movement of
the head when hair cells of the semicircular canals bend.
Each semicircular canal has an enlargement, or
at one end where the hair cells (receptors) are located
The tips of these hair cells in an ampulla of a semicircular
canal project into a gelatinous mass called the
in
which
are also embedded
When the head moves in any direction, movement of the
endolymph in the semicircular pulls on the otoliths, which
causes the cupula to bend the hair cells (receptors)
When these hair
cells bend, they
send electrical
signals through the
vestibulocochlear
nerve to the brain,
telling it which
direction the head
moved.