Download The Special Senses

Biology 211
Anatomy & Physiology I
The
Special
Senses
Special Senses
1. Receptors all located
in the head
2. Highly specialized cells
form those receptors
3. These specialized
receptor cells are
located in highly
specialized
sensory organs
4. All special senses reach the brain
through cranial nerves
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
Let’s start with taste
Specialized
Receptor Cells
Specialized
Organ. . .
Gustatory Cells
Taste Buds
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 palate and the
oropharynx,as far down as the epiglottis
Each taste bud contains three types of cells:
Gustatory cells (50-100)
Supporting cells
Basal 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 which form part of a
cranial nerve
Gustatory cells within taste buds can detect thousands of
different types of molecules, but these are grouped into five
general categories:
a) Sweet tastes: sugars (glucose, fructose,
lactose, sucrose)
saccharin, aspartame,
sucralose, xylitol, etc.
b) Salty tastes: sodium, potassium, lithium,
many others
c)
Sour tastes: citric acids, carbonic acid,
hydrochloric acid, malic acid,
tartaric acid, many others
d) Bitter tastes: quinine, fatty acids, many others
e) Umami taste: 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.
We used to think that taste buds on
certain regions of the tongue were
specialized for particular tastes, but we
now know that taste buds with gustatory
cells for different types of tastes are
located in all regions of the tongue.
Each gustatory cell has a separate threshold:
concentrations below this do not stimulate the receptors.
In general: Sweet & salty substances
have high thresholds
Sour and umami substances
have moderate
thresholds
Bitter substances have low
thresholds
Taste signals from the anterior
part of the tongue travel in the
facial nerve.
Taste signals from the posterior
part of the tongue travel in the
glossopharyngeal nerve.
Taste signals from the palate and
pharynx travel in the vagus nerve.
Taste signals in all three nerves
reach a nucleus in the medulla
oblongata, then get sent to the
thalamus
From the thalamus, these signals get relayed to the
“gustatory region” on the parietal lobe of the cerebral cortex.
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 .
TASTE:
Gustatory Cells
Taste Buds
SMELL:
Olfactory Cells
Olfactory
Epithelium
VISION:
Rods & Cones
Eye (Retina)
HEARING:
Hair Cells
Cochlea
EQUILIBRIUM:
Hair Cells
Vestibular
Apparatus
Olfactory receptor cells are part of the olfactory
epithelium (mucosa) 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) form the
olfactory nerve which passes through the cribriform plate
to synapse with neurons in the olfactory bulb of the brain.
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.
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:
a) The thalamus and the
olfactory cortex on the
medial surface of the
temporal lobe.
This provides conscious perception and interpretation
of smells
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:
b) The hypothalamus and
the limbic system.
This provides reflexes
(salivation, avoidance, etc.) and "associative responses"
(activation of autonomic pathways, sexual responses,
emotional responses, etc.)
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
Anterior view of the eye
Sclera
Medial angle
(canthus)
Lateral angle
(canthus)
Iris
Pupil
The eyeball has three layers or "tunics:
Fibrous Tunic: Sclera and cornea
Strong connective tissue
Protects the eye
Holds shape of eye
Insertion of extraoccular muscles
Vascular Tunic: Choroid, ciliary body, iris
Contains blood vessels
Pigmented
Smooth muscle cells in ciliary body &iris
Sensory Tunic: Retina
Contains rod and cone cells
and
Other neurons to transmit visual
information to brain
Layers ("tunics") of the eyeball
Fibrous Layer
Iris
Cornea
Vascular Layer
Ciliary
Body
Sensory Layer
Sclera
Choroid
Retina
Internal Structure of the Eye
Vitreous
Humor
Aqueous
Humor
Lens
Suspensory
Ligaments
("Zonules")
Ciliary
Body
Focus:
Majority of light refraction
(bending) occurs in cornea.
Not adjustable
"Fine tuning" of light refraction
occurs in lens:
Thicker lens = more refraction
Thinner lens = less refraction
Rods: ~ 6 million
Cones: ~ 20 million
Detect black , white, gray
Detect color
Highly sensitive in
low-light conditions
Less sensitive in
low light conditions
Low resolution
High resolution
Detect motion
The cornea and lens focus
light onto the macula lutea and
fovea centralis, which has only
cones. This provides high
resolution and color vision but
requires brighter light.
Other regions of the retina
have mostly rods. This
provides black/white/gray
vision in dimmer light, and
detects movement.
Optic
Chiasm
Optic Nerve
Optic Tract
Optic
Radiations
Optic nerve
Optic chiasm
Optic tract
Next: Hearing
Specialized
Receptor Cells
HEARING
Hair Cells
Specialized
Organ .
Cochlea
Located in inner ear.
Outer ear and middle
ear transmit and
regulate the volume
of sound reaching the
inner ear.
Auricle or
Pinna
Inner Ear
Outer Ear
Middle
Ear
The outer ear
channels air
vibrations
(sound) to the
tympanic
membrane
(eardrum).
The inner ear contains two
complex fluid-filled structures,
the bony labyrinth
and the membranous
labyrinth, which
are embedded
in the
temporal
bone.
The middle ear is an air-filled
chamber containing three
ossicles, the malleus, the incus,
& the stapes, which transmit
vibrations to the inner ear.
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 inner ear.
The inner ear is fluid-filled.
Therefore:
Vibrations of air (sound)
in the outer ear vibrate
the tympanic membrane
Which makes the
ossicles vibrate
Which makes the
oval window vibrate
Which makes the fluid 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 inner ear actually consists of two sets of tubes, one
inside the other.
The outer tube, or bony labyrinth, is filled with a fluid
called perilymph, while the inner tube, the membranous
labyrinth, is filled with fluid called endolymph.
At one end of inner ear,
these two tubes (one
inside the other) coil about
2 & 2/3 times to form the
cochlea.
Vibrations of the oval
window make the
perilymph vibrate.
This must be transmitted to the endolymph within the
cochlea before the hair cells can detect it.
Scala vestibuli
(perilymph)
Cochlear duct
(endolymph)
Scala tympani
(perilymph)
Structure of cochlea if it could be uncoiled
Vibration of oval window causes vibration of perilymph
of scala vestibuli and scala tympani, which causes
vibration of endolymph in cochlear duct
Vibration of the endolymph in the cochlear duct causes
bending of hair cells in the spiral organ of Corti.
When these hair cells bend, they send electrical signals
through the vestibulocochlear nerve to the brain
Vestibulocochlear
nerve
Hair cells
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:
Hair Cells
Vestibular
Apparatus
The parts of the membranous labyrinth responsible for
equilibrium are the saccule, the utricle, and three
semicircular canals which lie at right angles to each other.
Semicircular
Canals
Utricle
Saccule
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 macula
The tips of these hair cells project into a gelatinous mass
called the otolithic membrane, in which are embedded
small crystals of calcium carbonate called otoliths.
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 (“dynamic equilibrium”) when hair cells of the
semicircular canals bend.
Semicircular
Canals
Each semicircular canal has an enlargement, or ampulla,
at one end where the hair cells (receptors) are located
Ampullae of
Semicircular
Canals
The tips of these hair cells in an ampulla of a semicircular
canal project into a gelatinous mass called the cupula, in
which otoliths 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.
That’s all, folks