Download The Special Senses

The Special
Senses
Chapter 15
The Special Senses
• Chemical senses
– Taste (gustation)
– Smell (olfaction)
• Vision
• The ear
– Hearing
– Equilibrium
• ***NOTE: Touch is not part of special
senses, it is part of the NERVOUS SYSTEM
2
Sense of Taste
• Taste buds are the
sensory receptor
organs located in the
oral cavity.
– Approximately 10,000
with most in the
papillae of the tongue
Taste Buds
• Each consists of 50-100
epithelial cells
Receptor cells – also called
gustatory or taste cells
-Gustatory Hairs
Disolved molecules bind & induce
receptor cells to generate
impulses in sensory nerve
fibers
– Basal cells – act as stem cells
which divide and differentiate
into supporting cells (taste bud
cells are replaced every 7-10
days)
Five taste sensations
•
•
•
•
•
Sweet—front middle
Sour—middle sides
Salty—front side/tip
Bitter —back
“umami”—posterior
pharynx
M&M, Fig. 16.1
Taste Sensations
• Cravings are often related to needs such
as protein, sugar, salt or vitamin C
• Bitterness is often related to poisons and
spoiled food which is why we don’t find it
pleasant
Taste
• In order to taste, the food
must dissolve in saliva,
diffuse into the taste pore
and contact the gustatory
hair
• This then allows the taste to
be transmitted to the brain
• About 80% of taste is smell
• Mouth also contains
thermo-receptors and
mechanoreceptors
Cranial
Nerves of
Taste
Anterior 2/3 tongue: VII (Facial)
Posterior 1/3 tongue: IX Glossopharyngeal)
Pharynx:
X (Vagus)
M&M, Fig. 16.2
Sense of Smell
• Olfactory epithelium is
located on the roof of the
nasal cavity and similar
to taste buds is
composed of:
– Olfactory receptor cells
• Attached are olfactory cilia
that increase surface area
– Supporting cells
– Basal cells
Smell
• Humans can distinguish
between approximately
10,000 smells
• Smell also relies on
odor chemicals being in
solution to be
transmitted. Smells
dissolve in mucus in the
nose to be transmitted.
Smell Disorder
Anosmia: absence of the sense of smell
– Trauma
– Colds or allergies producing excessive
mucus
– Polyps causing blockage
– 1/3 are from zinc deficiency
Ear/Hearing
M&M, fig. 16.17
• 3 Parts to the Ear
• Outer Ear: auricle is elastic cartilage attached to dermis, gathers sound
• Middle ear: ear ossicles transmit and modulate sound
• Inner ear: cochlea, ampullae and semicircular canals sense sound and
equilibrium
Hearing
• Ear is composed of 3 main structures:
– Outer ear
• consists of the auricle and external auditory canal. The
auricle helps to direct sound while the external auditory
canal extends the sound to the eardrum or tympanic
membrane.
• External auditory canal also aids in keeping the ear clean
and free of foreign object through the secretion of cerumen
(ear wax)
• As sound enters, it causes the ear drum to vibrate which
transfers the sound to the middle ear
Middle Ear
• External auditory canal ends
at tympanic membrane
which vibrates against
malleus on other side
• Inside middle ear chamber
– malleusincus stapes
which vibrates on oval window
of inner ear
• Muscles that inhibit vibration
when sound is too loud
– Tensor tympani m. (inserts on
malleus)
– Stapedius m. (inserts on
stapes)
M&M, fig. 16.19
Sound in external acoustic meatus
hits tympanic membrane (eardrum) –
it vibrates
Pressure is equalized
by the
pharyngotympanic
tube (AKA eustachian
or auditory tube)
16
TM causes ossicles in air filled middle ear to move:
– Malleus (hammer)
– Incus (anvil)
– Stapes (stirrup)
These are 3 of the
smallest bones of the body
Ossicles articulate to
form a lever system
that amplifies and
transmits the vibratory
motion of the TM to
fluids of inner ear
cochlea via oval
window
17
Auditory pathway
18
Inner Ear/Labyrinth
• Static equilibrium, linear motion
M&M, fig. 16.20
– Utricle, saccule are egg-shaped sacs in center (vestibule) of labyrinth
• 3-D motion, angular acceleration
– 3 semicircular canals for X,Y,Z planes
• Sound vibrations
– Cochlea (“snail”)
Auditory Nerve (Acoustic) VIII
receives stimulus from all to brain
Vestibular n.—equilibrium
Cochlear n.—hearing
Hearing
– The inner ear
• Also known as the labyrinth because of the shape
• Made up of 2 divisions: the bony labyrinth and the
membranous labyrinth
– Bony labyrinth is made up of the:
» Vestibule: contains the saccule and utricle sacs that are
related to equilibrium
» Cochlea: contains the spiral organ of Corti which is related to
hearing
» semicircular canals: contains ampulla on semicircular ducts
that respond to equilibrium
– Membranous labyrinth is a continuous series of sacs and ducts
within the bony labyrinth
• The bony labyrinth is filled with perilymph while the
membranous labyrinth floats in it
Sound
• Sound is a pressure
disturbance. Alternations
between high and low
pressure creates vibrations
which in turn create sound
waves.
• The sound waves are able to
travel through the ear where
they eventually excite hair
cells in the organ of Corti.
These send the transmission
to the brain.
Terminology, remember…
• Optic – refers to the eye
• Otic – refers to the ear
• Getting eyedrops and ear drops mixed up
is probably not a good idea
22
The Eye and Vision
The Eye and Vision
• Vision is the dominant sense in humans
• 70% of sensory receptors in humans are
in the eyes
• 40% of the cerebral cortex is involved in
processing visual information
• The eye (or eyeball) is the visual organ
– Diameter 2.5 cm (1 inch)
– Only anterior 1/6 visible
– Lies in bony orbit
– Surrounded by a protective cushion of fat
24
Sense of Sight
• Accessory structures include
–
–
–
–
–
Eyebrows
Eyelids
Conjunctiva
Lacrimal Apparatus
Extrinsic Eye Muscles
Sense of Sight
• Eyebrows
– Short, coarse hairs that shade the eye and
prevent sweat from trickling into the eye
• Eyelids (palpebral fissure— “eyelid slit”)
– Main function is to keep the eye from drying and
to keep out foreign objects
• This is largely accomplished via blinking;
• Eyelashes are related to this as well; any pressure will
trigger blinking
• Lacrimal caruncle
– Contains sudoriferous and sebaceous gland
that produces “sleep”, “sandman’s sand” or
“eye-boogers”.
• Orbicularis muscles encircle the eye; when they
contract the eye closes
• Upper eyelid is larger and more motile
• Eyelid muscles contract to blink every 3-7 seconds
– Clears eyes of debris
– Prevents drying out
Accessory Structures
eyelids cont….
• Eyelashes: rich in nerve
endings; anything that
touches them triggers
blinking
• Tarsal (Meibomian)
glands: posterior to the
eyelashes (on the
eyelid)
– Produce oily secretion
that lubricates eye
– Prevents lids from sticking
together
• Sebaceous glands
called ciliary glands lie
between the hair
follicles.
• Inflammation of these
glands results in a sty
Sense of Sight
• Conjunctiva
– A transparent mucous membrane that lines the eyelid and the
white area of the eye
– Prevents the eye from drying out by producing a lubricating mucus
– Pink Eye (Conjunctivitis)
Sense of Sight
• Conjunctiva
– A transparent mucous membrane that lines
the eyelid and the white area of the eye
– Prevents the eye from drying out by
producing a lubricating mucus
– Pink Eye (Conjunctivitis)
• Lacrimal Apparatus
– This is made up of the lacrimal gland and
ducts.
• Glands produce secretions (tears)
• Tears are spread across the eyeball
and drain into the lacrimal sac and
eventually nasolacrimal duct
• Tears (lacrimal fluid) contains mucus,
antibodies, and lysozyme
Accessory Structures
eyelids cont….
• Lacrimal Apparatus:
lacrimal glands and ducts
• Lacrimal gland; lies in
the orbit above the
eyeball
• Continually releases a
saline solution: tears
– Contains mucus,
antibodies and lysosomes
• Spread across eyeball
and drain into the
lacrimal punctum: little
red dots in the corner of
the eye
• Drain into lacrimal sac
and then into nasal cavity
–
stuffiness
Lacrimal Gland Infection
• http://bjo.bmj.com/content/suppl/2005/02
/22/89.3.DC1/893report.full
M&M, fig. 16.4
Movement
of eye
Sense of Sight
• Extrinsic Eye Muscles
– There are 6 eye muscles that work together to keep the
eye in orbit and allow movement of the eyeball.
•
•
•
•
•
•
Lateral Rectus
Medial Rectus
Superior Rectus
Inferior Rectus
Inferior Oblique
Superior Oblique
Eye Muscle Disorders
Diplopia:
double vision
(seeing one object as two)
Strabismus:
cross-eyed
• Amblyopia
Lazy eye
Sense of Sight
• The eyeball is a slightly irregular hollow
sphere with anterior and posterior poles
• The inside of the eyeball is filled with
liquids called humors and the wall of the
eyeball is made up of 3 tunics
– Fibrous tunic
– Vascular tunic
– Sensory tunic
Fibrous Tunic
• The outermost coat of the
eye composing the sclera
and the cornea
– Sclera is opaque white and
acts as a support for the
eyeball and anchor for the
extrinsic eye muscles
– Cornea is a transparent
bulge in the anterior region
of the sclera that allows light
to enter
IRIS
• Behind the cornea are
the iris and the pupil.
The iris is the colorful
part of the eye. When
we say a person has
blue eyes, we really
mean the person has
blue irises!
PUPIL
• The iris controls how much light goes
through the pupil. The pupil is the black
circle in the center of the iris, and it lets
light enter the eye. The pupils will get
smaller when a light shines near them
and they'll open wider when the light is
gone.
Eye as lens/optical device
M&M, fig. 16.7
Light path: Cornea  Pupil  Lens  Retina
Cataract (opaque lens)
Nearsightedness
Myopia
• An eye that is too long or a cornea that is too
steep causes myopia (or nearsightedness). In
nearsighted eyes, the image isn't focused
precisely inside the eye, causing blurring in the
distance. The more nearsighted you are, the
more blurred the distant object appears, and
the thicker your glasses need to be. Most
nearsighted people feel that their condition is
severe, due to their dependence on glasses
and contact lenses. In fact, only one in ten
nearsighted individuals are actually in the
"severe" or "extreme" categories.
Notice geese are clear but the
city is blurry.
Far-Sighted
• Hyperopia
• An eye that is too short, or a cornea that is not
steep enough causes hyperopia (or
Farsightedness). People with hyperopia see
blurry when looking at close objects. Young
people can slightly overcome hyperopia by
using their focusing muscles to make the
image clear. This gets harder as they get
older. Currently, there are restricted options to
correct hyperopia. Most operations are still
under development.
What is blurry this time?
Cow Eye Dissection