Anatomy PowerPoint- Special Senses

Essentials of Human Anatomy & Physiology

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Slides 8.1 – 8.19

Seventh Edition

Elaine N. Marieb

Chapter 8

Special Senses

Lecture Slides in PowerPoint by Jerry L. Cook and Melissa Scott

This presentation contains copyright protected materials

The Senses

∙ General senses of touch (tactile)

∙Temperature- thermoreceptors (heat)
∙Pressure- mechanoreceptors (movement)
∙Pain- mechanoreceptors

∙ Special senses

∙Smell- chemoreceptors (chemicals)
∙Taste- chemoreceptors
∙Sight- photoreceptors (light)
∙Hearing- mechanoreceptors
∙Equilibrium- (balance) mechanoreceptors

The Eye and Vision
∙ 70 percent of all sensory receptors are

in the eyes

∙ Each eye has over a million nerve fibers

∙ Protection for the eye

∙Most of the eye is enclosed in a bony orbit
made up of the lacrimal (medial), ethmoid
(posterior), sphenoid (lateral), frontal
(superior), and zygomatic and maxilla
(inferior)

∙A cushion of fat surrounds most of the eye

Accessory Structures of the Eye

∙ Eyelids-

brush
particles
out of eye
or cover
eye

∙ Eyelashes-

trap
particles
and keep
them out of
the eye

Accessory Structures of the Eye

∙ Ciliary glands –

modified
sweat glands
between the
eyelashes-
secrete acidic
sweat to kill
bacteria,
lubricate
eyelashes

Accessory Structures of the Eye

∙ Conjunctiva

∙Membrane that lines the eyelids
∙Connects to the surface of the eye- forms a seal
∙Secretes mucus to lubricate the eye

http://neuromedia.neurobio.ucla.edu/campbell/eyeandear/wp_images/175_conjunctiva.gif

CONJUNCTIVITIS

- Inflammation of the conjunctiva

- Caused by bacterial or viral infection

- Highly contagious

http://www.healthseva.com/images/eye/conjunctivitis.jpg

Accessory Structures of the Eye

∙ Lacrimal

apparatus

∙Lacrimal gland –
produces lacrimal
fluid

∙Lacrimal canals –
drains lacrimal
fluid from eyes

Accessory Structures of the Eye

∙Lacrimal sac –
provides
passage of
lacrimal fluid
towards nasal
cavity

Accessory Structures of the Eye

∙Nasolacrimal
duct – empties
lacrimal fluid into
the nasal cavity

Function of the Lacrimal Apparatus

∙ Properties of lacrimal fluid

∙Dilute salt solution (tears)

∙Contains antibodies (fight antigens- foreign
substance) and lysozyme (enzyme that
destroys bacteria)

∙ Protects, moistens, and lubricates the

eye

∙ Empties into the nasal cavity

Extrinsic Eye Muscles
∙ Muscles attach to the outer surface of

the eye

∙ Produce eye movements

When Extrinsic Eye Muscles Contract

∙Superior oblique- eyes look out and down

∙Superior rectus- eyes looks up

∙Lateral rectus- eyes look outward

∙Medial rectus- eyes look inward

∙Inferior rectus- eyes looks down

∙Inferior oblique- eyes look in and up

http://www.esg.montana.edu/esg/kla/ta/eyemusc.jpg

Structure of the Eye

∙ The wall is composed of three tunics

∙Fibrous tunic –
outside layer

∙Choroid –
middle
layer

∙Sensory
tunic –
inside
layer

The Fibrous Tunic
∙ Sclera

∙White connective tissue layer
∙Seen anteriorly as the “white of the eye”
∙Semi-transparent

The Fibrous Tunic
∙ Cornea

∙Transparent, central anterior portion
∙Allows for light to pass through (refracts, or
bends, light slightly)
∙Repairs itself easily
∙The only human tissue that can be
transplanted without fear of rejection

http://www.phys.ufl.edu/~avery/course/3400/vision/eye_photo.jpg

Choroid Layer
∙ Blood-rich nutritive tunic
∙ Pigment prevents light from scattering

(opaque- blocks light from getting in,
has melanin)

Choroid Layer
∙ Modified interiorly into two structures

∙Cilliary body – smooth muscle (contracts to
adjust the shape of the lens)
∙Iris- pigmented layer that gives eye color
(contracts to adjust the size of the pupil-
regulates entry of light into the eye)

∙Pupil – rounded opening in the iris

Sensory Tunic (Retina)
∙ Contains receptor cells (photoreceptors)

∙Rods
∙Cones

∙Signals leave the retina toward the brain
through the optic nerve

Sensory Tunic (Retina)

∙ Signals pass from photoreceptors via a

two-neuron chain

∙Bipolar neurons and Ganglion cells

http://www.uams.edu/jei/patients/retina_services/images/retina.jpg

VISUAL PIGMENTS

Rhodopsin- visual purple, in high concentration in RODS

-Composed of opsin and retinal (a derivative of vitamin
A) proteins

-When light hits the protein it “bleaches”- turns yellow
and then colorless. It straightens out and breaks down
into opsin and retinal.

There are three different other opsins beside rhodopsin,
with absorption for yellowish-green (photopsin I), green
(photopsin II), and bluish-violet (photopsin III) light.

Neurons of the Retina and Vision

∙ Rods

∙Most are found towards the edges of the
retina

∙Allow dim light vision and peripheral vision
(more sensitive to light, do not respond in
bright light)

∙Perception is all in gray tones

http://www.webvision.med.utah.edu/imageswv/PKCrodb.jpeg

http://webvision.med.utah.edu/imageswv/rod-GC.jpeg

ROD CELLS

Neurons of the Retina and Vision

∙ Cones

∙Allow for detailed color vision

∙Densest in the center of the retina

∙Fovea centralis – area of the retina with
only cones

∙Respond best in bright light

∙ No photoreceptor cells are at the

optic disk, or blind spot

http://blc1.kilgore.cc.tx.us/kcap2/images/retina%20100x%20b%20fireworks.jpg

http://www.yorku.ca/eye/rod-cone.gif

http://www.secretbeyondmatter.com/ourbrains/theworldinourbrains_files/11-1.jpg

Cone Sensitivity
∙ There are three

types of cones

∙ Different cones are

sensitive to different
wavelengths
- red- long
- green- medium
- blue- short

∙ Color blindness is

the result of lack of
one or more cone
type

How do we see colors?

• To see any color, the brain must compare the

input from different kinds of cone cells—and
then make many other comparisons as well.

• The lightning-fast work of judging a color

begins in the retina, which has three layers of
cells. Signals from the red and green cones in
the first layer are compared by specialized
red-green "opponent" cells in the second layer.
These opponent cells compute the balance
between red and green light coming from a
particular part of the visual field. Other
opponent cells then compare signals from blue
cones with the combined signals from red and
green cones.

COLORBLINDNESS

- An inherited trait that
is transferred on the
sex chromosomes (23rd
pair)- sex-linked trait

- Occurs more often in
males

- Can not be cured or
corrected

•Comes from a lack of one
or more types of color
receptors.

•Most are green or red or
both and that is due to a
lack of red receptors.

•Another possibility is to
have the color receptors
missing entirely, which
would result in black and
white vision.

http://www.geocities.com/Heartland/8833/coloreye.html

COLORBLINDNESS TEST PLATES

Lens
∙ Biconvex

crystal-like
structure

∙ Held in place

by a
suspensory
ligament
attached to
the ciliary
body

∙ Refracts light

greatly

Internal Eye Chamber Fluids
∙ Aqueous humor

∙Watery fluid found in
chamber between the
lens and cornea

∙Similar to blood
plasma

∙Helps maintain
intraocular pressure

∙Provides nutrients for
the lens and cornea

∙Reabsorbed into
venous blood through
the canal of Schlemm

Refracts light
slightly

Internal Eye Chamber Fluids
∙ Vitreous humor

∙Gel-like substance behind the lens

∙Keeps the eye from collapsing

∙Lasts a lifetime and is not replaced

http://faculty.washington.edu/kepeter/119/images/eye3.jpg

Refracts light
slightly

Holds lens and
retina in place

Lens Accommodation

∙ Light must be focused to a

point on the retina for
optimal vision

∙ The eye is set for distance

vision
(over 20 ft away)

∙ 20/20 vision- at 20 feet,

you see what a normal eye
would see at 20 feet
(20/100- at 20, normal
person would see at 100)

∙ The lens must change

shape to focus for closer
objects

Nearsightedness, or myopia is the difficulty of
seeing objects at a distance.
Myopia occurs when the
eyeball is slightly longer
than usual from front to
back. This causes light
rays to focus at a point
in front of the retina,
rather than directly on
its surface.
Concave lenses are used
to correct the problem.

MYOPIA

Hyperopia, or
farsightedness, is
when light entering
the eye focuses
behind the retina.

Hyperoptic eyes
are shorter than
normal.

Hyperopia is
treated using a
convex lens.

http://web.mountain.net/~topeye/images/hyperopia.jpg

HYPEROPIA

Images Formed on the Retina

If the image is focused at the spot
where the optic disk is located,
nothing will be seen. This is known as
the blind spot. There are no
photoreceptors there, as nerves and
blood vessels pass through this point.

Visual Pathway

∙ Photoreceptors of

the retina

∙ Optic nerve

∙ Optic nerve crosses

at the optic chiasma

Visual Pathway

∙ Optic tracts

∙ Thalamus (axons

form optic radiation)

∙ Visual cortex of the

occipital lobe

Eye Reflexes

∙ Internal muscles are controlled by the

autonomic nervous system

∙Bright light causes pupils to constrict
through action of radial (iris) and ciliary
muscles
∙Viewing close objects causes
accommodation

∙ External muscles control eye movement

to follow objects- voluntary, controlled at
the frontal eye field

∙ Viewing close objects causes

convergence (eyes moving medially)

The Ear

∙ Houses two senses

∙Hearing (interpreted in the auditory
cortex of the temporal lobe)

∙Equilibrium (balance) (interpreted in the
cerebellum)

∙ Receptors are mechanoreceptors

∙ Different organs house receptors for

each sense

Anatomy of the Ear

∙ The ear is divided into three areas

∙Outer
(external)
ear
∙Middle
ear
∙Inner
ear
∙(Add C. “INNER
EAR” to notes)

The External Ear

∙ Involved in

hearing only

∙ Structures of

the external ear

∙Pinna (auricle)-
collects sound
∙External
auditory canal-
channels
sound inward

The External Auditory Canal

∙ Narrow chamber in the temporal bone-

through the external auditory meatus

∙ Lined with skin

∙ Ceruminous (wax) glands are present

∙ Ends at the tympanic membrane

(eardrum)

The Middle Ear or Tympanic Cavity

∙ Air-filled cavity within the temporal bone

∙ Only involved in the sense of hearing

The Middle Ear or Tympanic Cavity
∙ Two tubes are associated with the inner

ear

∙The opening from the auditory canal is
covered by the tympanic membrane
(eardrum)

∙The auditory tube connecting the middle ear
with the throat (also know as the eustacian
tube)

∙Allows for equalizing pressure during yawning
or swallowing

∙This tube is otherwise collapsed

Bones of the Tympanic Cavity

∙ Three bones

span the cavity

∙Malleus
(hammer)

∙Incus (anvil)

∙Stapes (stirrip)

http://www.ghorayeb.com/files/STAPES_on_a_Penny_375_SQ.jpg

http://medicine.wustl.edu/~oto/bbears/images/ossic.jpg

Bones of the Tympanic Cavity

∙ Vibrations from

eardrum move
the malleus

∙ These bones

transfer sound
to the inner ear

Inner Ear or Bony Labyrinth

∙ Also known as

osseous labyrinth-
twisted bony
tubes

∙ Includes sense

organs
for hearing and
balance

∙ Filled with

perilymph

Inner Ear or Bony Labyrinth

∙Vibrations of the stapes push and pull
on the membranous oval window, moving
the perilymph through the cochlea. The
round window is a membrane at the
opposite end to relieve pressure.

http://www.neurophys.wisc.edu/h&b/auditory/animation/animationmain.html

Inner Ear or Bony Labryinth

∙ A maze of bony chambers within the

temporal bone

∙Cochlea

∙Upper chamber
is the scala
vestibuli

∙Lower chamber
is the scala
tympani

∙Vestibule

∙Semicircular
canals

Organ of Corti

∙Located within the cochlea

∙Receptors = hair cells on the basilar membrane

Scala tympani

Scala vestibuli

∙Gel-like tectorial membrane is capable of
bending hair cells (endolymph in the
membranous labyrinth of the cochlear duct
flows over it and pushes on the membrane)

Organ of Corti

Scala tympani

Scala vestibuli

Organs of Hearing
∙ Organ of Corti

∙Cochlear nerve attached to hair cells
transmits nerve impulses to auditory cortex
on temporal lobe

Scala tympani

Scala vestibuli

Mechanisms of Hearing

∙ Vibrations from

sound waves
move tectorial
membrane (pass
through the
endolymph fluid
filling the
membranous
labyrinth in the
cochlear duct)

∙ Hair cells are bent

by the membrane

Mechanisms of Hearing

∙ An action potential

starts in the cochlear
nerve

∙ The signal is

transmitted to the
midbrain (for
auditory reflexes
and then directed to
the auditory cortex
of the temporal
lobe)

∙Continued stimulation can lead to
adaptation (over stimulation
to the brain makes it stop
interpreting the sounds)

Mechanisms of Hearing

Organs of Equilibrium

∙ Receptor cells are in two structures

∙Vestibule

∙Semicircular canals

Organs of Equilibrium
∙ Equilibrium has two functional parts

∙Static equilibrium- in the vestibule

∙Dynamic equilibrium- in the semicircular
canals

Static Equilibrium

∙ Maculae –

receptors in
the vestibule

∙Report on
the position
of the head
∙Send
information
via the
vestibular
nerve

Static Equilibrium

∙ Anatomy of the

maculae

∙Hair cells are
embedded in
the otolithic
membrane
∙Otoliths (tiny
stones) float in
a gel around
the hair cells

Function of Maculae

∙Movements cause otoliths to bend
the hair cells (gravity moves the
“rocks” over and pulls the hairs)

http://neuromedia.neurobio.ucla.edu/campbell/eyeandear/wp_images/177_macula_HP.gif

Dynamic Equilibrium

∙ Whole structure is the

ampulla

∙ Crista ampullaris –

receptors in the
semicircular canals

∙Tuft of hair cells

∙Cupula (gelatinous cap)
covers the hair cells

Dynamic Equilibrium

∙ Action of angular head

movements

∙The cupula stimulates the hair
cells

∙Movement of endolymph
pushes the
cupula over
and pulls the
hairs

∙An impulse is
sent via the
vestibular nerve
to the cerebellum

DYNAMIC EQUILIBRIUM STRUCTURES

http://www.faculty.une.edu/com/abell/histo/CristaAmp.jpg

http://neuromedia.neurobio.ucla.edu/campbell/eyeandear/wp_images/177_macula_crista.gif

Chemical Senses – Taste and
Smell

∙ Both senses use chemoreceptors

∙Stimulated by chemicals in solution

∙Taste has four types of receptors

∙Smell can differentiate a large range of
chemicals

∙ Both senses complement each other

and respond to many of the same
stimuli

Olfaction – The Sense of Smell
∙ Olfactory receptors are in the roof of the nasal

cavity

∙Neurons with long cilia

∙Chemicals must be dissolved in mucus for
detection

Olfaction – The Sense of Smell

∙ Impulses are transmitted via the olfactory nerve

∙ Interpretation of smells is made in the cortex

(olfactory area of temporal lobe)

http://asb.aecom.yu.edu/histology/labs/images/slides/A74_OlfactoryEpith_40X.jpg

The Sense of Taste

∙ Taste buds

house the
receptor
organs

∙ Location of

taste buds

∙Most are on
the tongue
∙Soft palate
∙Cheeks

The Tongue and Taste

∙ The tongue is covered

with projections called
papillae

∙Filiform papillae – sharp
with no taste buds

∙Fungifiorm papillae –
rounded with taste buds

∙Circumvallate papillae –
large papillae with taste
buds

∙ Taste buds are found on

the sides of papillae

http://neuromedia.neurobio.ucla.edu/campbell/oral_cavity/wp_images/96_fungiform.gif

http://www.esg.montana.edu/esg/kla/ta/vallate.jpg

Structure of Taste Buds
∙ Gustatory cells are the receptors

∙Have gustatory hairs (long microvilli)

∙Hairs are stimulated by chemicals dissolved
in saliva

Structure of Taste Buds

∙ Impulses are carried to

the gustatory complex
(pareital lobe) by
several cranial nerves
because taste buds are
found in different areas

∙Facial nerve

∙Glossopharyngeal nerve

∙Vagus nerve

http://www.biosci.ohiou.edu/introbioslab/Bios171/images/lab6/Tastebuds.JPG

Taste Sensations

∙ Sweet receptors

∙Sugars
∙Saccharine
∙Some amino acids

∙ Sour receptors

∙Acids

∙ Bitter receptors

∙Alkaloids

∙ Salty receptors

∙Metal ions

∙ Umami

∙Glutamate, aspartate
(MSG, meats)

http://instruct1.cit.cornell.edu/courses/psych431/student2000/mle6/tonguebig.gif

Developmental Aspects of the
Special Senses

∙ Formed early in embryonic development

∙ Eyes are outgrowths of the brain

∙ All special senses are functional at birth