Download The Special Senses

Biology 211
Anatomy & Physiology I
Dr. Thompson
The Special Senses
Special Senses
1. All located in the head
2. All special senses
reach the brain
through cranial
nerves
3. Highly specialized
cells form receptors
4. These specialized
receptor cells are
located 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
The last laboratory exercise dealt with vision and hearing
so
Let’s start with taste and smell
Special Senses
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) pass through the cribriform
plate to synapse with neurons in the olfactory bulb of the brain.
These axons are the olfactory nerve (cranial nerve 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.
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.)
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: Strong connective tissue
Protects the eye
Holds shape of eye
Insertion of extraoccular muscles
Vascular Tunic: Contains blood vessels
Pigmented
Contains smooth muscle cells
Sensory Tunic: 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 = more refraction
Thinner = less refraction
Rods:
Cones:
Black & white
Color
High sensitivity
Lower sensitivity
Low resolution
High resolution
Detect motion
Optic
Chiasm
Optic Nerve
Optic Tract
Optic
Radiations
Next: Hearing
Specialized
Receptor Cells
HEARING
Hair Cells
Specialized
Organ .
Cochlea
Located in inner ear. Outer
ear and middle ear serve to
transmit and regulate the
volume of sound
Auricle or
Pinna
Inner Ear
Outer
Ear
Middle
Ear
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) 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 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 perilymph, while the inner
tube 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.
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 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:
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.