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The Sensory Organs
Liu jiao
Binzhou Medical University
Department Of Anatomy
The Sensory Organs
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The sense organs are actually extensions of the
nervous system that respond to changes in the
internal and external environment and transmit
action potentials (nerve impulses) to the brain.
It is through the sense organs that we achieve
awareness of the environment, and for this reason
they have been described as “windows for the
brain.”
The Sensory Organs
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A stimulus must first be received before the
sensation can be interpreted in the brain and the
necessary body adjustments made.
A sensation is an awareness of a bodily state or
condition that occurs whenever a sensory impulse
is transmitted to the brain. The interpretation of a
sensation is referred to as perception.
Perceptions are the creations of our brain; in other
words,we see, hear, taste, and smell with our brain.
The Sensory Organs
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In order to perceive a sensation, the following conditions
are necessary.
A stimulus sufficient to initiate a response in the nervous
system must be present.
• A receptor must convert the stimulus to a nerve impulse.
A receptor is a specialized peripheral dendritic ending of a
sensory nerve fiber or the specialized receptor cells
associated with it.
• The conduction of the nerve impulse must occur from the
receptor to the brain along a nervous pathway.
• The interpretation of the impulse in the form of a
perception must occur within a specific portion of the brain.
The Sensory Organs
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our perceptions allow us to interact effectively
with our environment and are of obvious
survival value.
The Sensory Organs
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Sensory organs include the receptors and
accessory organs. The receptors may be divided
into three kinds:
The exteroceptors: receive stimuli such as touch,
temperature, pain, light and sound from the external
environment
The interoceptors: pick up information about
internal environment
The proprioceptors: Proprioception means
"sense of self". In the limbs, the proprioceptors are
sensors that provide information about joint angle,
muscle length, and muscle tension, which is
integrated to give information about the position of
the limb in space.
The Visual Organ 视器
Composition: eyeball and
accessory organs of eye
Shape of eyeball
 Has anterior and posterior
poles
 Equator: an imaginary line
encircling the eyeball,
midway between anterior
and posterior poles
 Axis of eyeball: a line
joining the two poles
 Optic axis: a line joining
the center of the pupil to the
fovea centralis
Walls of eyeball
Cornea
Fibrous tunic of eyeball
Sclera
Iris
Vascular tunic of eyeball
Cilliary body
Choroid
Pars iridica retinae
Retina
Pars caeca retinae
Pars ciliaris retinae
Pars optica retinae
Fibrous tunic of eyeball (outer)
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Cornea : anterior 1/6, a
nonvascular structure,
transparent portion, richly
supplied by nerves; because it
is curved, the cornea helps
focus light
Sclera (white of eye, opaque
portion):
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posterior 5/6, consisting of
fibrous connective tissue that
forms a tough protective
covering for eyeball,
Contains sinus venosus
sclerae which lies beneath the
junction of cornea and sclera
Vascular tunic of eyeball (middle)
Iris
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Thin contractile membrane
anterior to ciliary body, with a
central opening, the pupil
Contains sphincter pupillae
(circular fibers) and dilator
pupillae (radial fibers)
Cornea and iris meet to form
the iridocorneal angle
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Cilliary body
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Body a ring-shaped
thickening anterior to
equator, containing
smooth muscle fibers
called ciliary muscle
Ciliary processes : a
series of some 60~80
projections producing
aqueous humor
Ciliary ring
Sinus venosus sclerae
Ciliary Muscle
Iridocorneal angle
Dilator Pupillae
Sphincter Pupillae
Lens
ciliary zonule
Ciliary Processes
Ciliary ring
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Choroid
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Thin, highly vascular in
posterior 2/3 of eye
Contains brown
pigmented cells and
dense capillary plexus
Retina
It is the neural sensory stratum
lining the inner surface of the
vascular tunic
Pars caeca retinae
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Pars iridica retinae
Pars ciliaris retinae
Pars optica retinae
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Lines the
choroidsComposed of two
layers
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An outer pigment cell layer
Inner neural layer (four
layers)
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The fourth layer consists photoreceptor cells
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Cone cells are color receptors that function best during the day
Rod cells are dark-light receptors that function best at night and in dim
light
The third layer consists of bipolar neurons
The second layer is formed ganglion cells, whose axons form optic
nerve
The first layer consists of nerve axons that collect at the optic disk
and pass through the sclera to form the optic nerve
Ganglion cells
Bipolar neurons
Rod cells
Cone cells
Pigment cell layer
Optic disc (blind spot), located
medial to posterior pole of eye,
and consists of optic nerve fibers
and central artery of retina
Macula lutea
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Lies lateral about 3.5 mm to optic
disc, a shallow depression, it is
completely free of blood vessels
and is yellowish in color
Fovea centralis, aera of greatest
visual acuity (concentration of
cones), at its center
The pigmentted layer absorbs
light that passes completely
through the anterior layer,
preventing backscatter (blurring
of vision)
Contents of eyeball
Aqueous humor
Lens
Vitreous body
Aqueous humor
Chamber of eye － lies between
cornea and lens, and divided
by iris into anterior and
posterior chambers
Aqueous humor
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A clear watery fluid that fills
chamber of eye
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Continuously secreted by
ciliary body into posterior
chamber
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Passes through pupil into
anterior chamber
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Then it filters though
iridocorneal angle into sinus
venosus sclerae, this sinus
drains via anterior ciliary
veins into ophthalmic veins
Production and circulation of aqueous humor
Ciliary body
Posterior chamber
Iridocorneal angle
Pupil
Sinus venosus sclera
Ophthalmic vein
Functions
• Helps focus light
• Helps maintain constant pressure in eyeball
• Helps nourish the lens and cornea
Anterior chamber
Anterior ciliary vein
Lens
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Transparent biconvex structure, covered by an elastic transparent capsule
Located between iris and vitreous body, and suspended behind pupil by
ciliary zonule
Shape changed by the ciliary muscle: for near vision, the ciliary muscle
contracts and the lens rounds up, while for distant vision the lens flattens out,
so that the eye may be focused on distant objects
Vitreous body
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Consists of colorless,
transparent jelly-like
substance in which there is a
meshwork of fine fibrils,
occupies the vitreous
chamber, the space between
lens and retina
Helps maintain the shape of
eyeball and supports the
retina
Refractive media of eye
Bend entering light waves and
focus them on the retina
 Cornea
 Aqueous humor
 Lens
 Vitreous body
Accessory organs of eye
Eyelids
Conjunctiva
Lacrimal apparatus
Ocular muscles
Connective tissue in the orbit
Eyelids
（from without inwards ）
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Skin, extremely thin
Subcutaneous areola
tissue, loose and delicate
Muscular layer: orbicularis
oculi
Tarsus, formed by dense
connective tissue in which
the tarsal glands
embedded
Lined by palpebral
conjunctiva Function: to
protect, open, and close
eye
Tarsus
Conjunctiva
Three parts
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Palpebral conjunctiva :
lining inner surface of
eyelids
Bulbar conjunctiva :
lining anterior part of sclera,
up to corneal margin
Conjuntival fornix
(superior and inferior): line
of reflection of bulbar and
palpebral conjunctiva
Conjunctival sac
Lacrimal apparatus
Lacrimal gland
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Oval 2-cm, occupies fossa
for lacrimal gland
Ducts (6~10 in number):
empty into anterior region
of superior fornix of
conjunctiva
Secrets tears, which move
across eyeball to medial
angle,protect and moisten
eye
Lacrimal passages
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Lacrimal puncta opening
to lacrimal ductules, one
on each eylid margin near
medial angle
Lacrimal ductules : one
in each lid, pass medially,
join and enter lacrimal sac
Lacrimal sac within fossa
for lacrimal sac, opening
into nasolacrimal duct
Nasolacrimal duct
courses 2 cm inferiorly and
opens into inferior nasal
meatus
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Tear is produced by
lacrimal gland
Passes through superior
conjunctival fornix into
conjunctival sac
Then it is drained through
lacrimal punctum, lacrimal
ductule, lacrimal sac and
nasolacrimal duct into
inferior nasal meatus.
Ocular muscles
Muscle
Action
Nerve supply
levator palpebrae
superioris
Raises upper eyelid
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Superior rectus
Turns eyeball superomedially
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Inferior rectus
Turns eyeball inferomedially
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Medial rectus
Turns eyeball medially
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Lateral retus
Turns eyeball laterally
Ⅵ
Superior obliquus
Turns eyeball inferolaterally
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Inferior obliquus
Turns eyeball superolaterally
Ⅲ
Ocular muscles 眼球外肌
Connective tissue in the orbit
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Sheath of eyeball
:
a thin membrane, which
surrounds the eyeball from
optic nerve to
corneoscleral junction,
permits the eyeball to
move in the orbit without
friction
Adipose body of orbit :
lies between sheath of
eyeball and the orbit acts
as a protective cushion
and shock sorber for the
eyeball
Vessels of eye
Ophthalmic artery
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Branch of internal
artery
Branches－central
artery of retina Enters
optic nerve, passes
toward the optic disk
and then fans out to
supply the retina
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Four branches: superior
and inferior nasal or
temporal arteriole of
retina
Ophthalmic vein
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Superior ophthalmic vein
communicates with facial
vein anteriorly, exits
posteriorly via superior
orbital fissure to drain into
cavernous sinus
Inferior ophthalmic vein
lies on floor of orbit and
communicates with
pterygoid plexus, exits via
superior orbital fissure to
drain into cavernous sinus
The Vestibulocochlear Organ
Liu jiao
Binzhou Medical University
Department Of Anatomy
General features
Three parts
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External ear : collects
sound waves
Middle ear : transmits
sound waves
Internal ear : contains the
vestibulocochlear organ
concerned with equilibration
and hearing
External ear
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Auricle
External acoustic meatus
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Tympanic membrane
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Auricle
External acoustic meatus
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A slender canal that extends
from external acoustic pore to
tympanic membrane
Two parts
 Cartilaginous part－
lateral 1/3
 Bony part－medial 2/3
Lined by a layer of thin skin.
This S-shaped passage
medially, at first forward and
upward, then backward and,
finally forward and downward.
Tympanic membrane
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A thin oval membrane
Two parts
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Flaccid part : upper 1/4
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Tense part : lower 3/4
Umbo of tympanic membrane
Cone of light
Middle ear
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Tympanic cavity
Auditory tube
Mastoid antrum and mastoid cells
Tympanic cavity
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An air-containing cavity
locates within petrous portion
of temporal bone
Walls
Roof
Medial wall
lateral wall
Posterior
wall
Anterior wall
Floor
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Walls
 Roof or tegmental wall formed by tegmen tympani,
separates tympanic cavity from middle cranial fossa
 Floor or jugular wall separates the cavity from superior
bulb of internal jugular vein
 Anterior wall or carotid wall separates tympanic cavity
from carotid canal, superiorly lies two openings:
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Upper opening for tensor tympani muscle
Lower opening for auditory tube, which communicates with
nasopharynx
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Posterior wall or mastoid wall
 Aditus of mastoid antrum
 Pyramid
lateral wall or membranous wall －tympanic membrane with
epitympanic recess superiorly
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Medial wall or labyrinthine wall
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Promontory
Fenestra vestibuli
Fenestra cochleae covered by secondary tympanic membrane
Prominence of facial canal
Acute otitis media
Perforation, inflammation or
trauma
Auditory ossicles
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Consists of chain of three
bones:
 Malleus
 Incus
 Stapes Articulate by
synovial joints
Transmit vibration of
tympanic membrane to
footplate of stapes in
fenestra vestibule.
Muscles of auditory ossicles
 Tensor tympani
 Stapedius
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Auditory tube
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About 3~4 cm long, extends
from nasopharynx posteriorly,
laterally, and upward to
tympanic cavity
Two parts
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Bony part: posterolateral 1/3
Cartilaginous part: medial 2/3
Functions to equalize air
pressure on either side of
tympanic membrane
In childhood, it is shorter,
wider and more horizontal
than in adult
Mastoid antrum and mastoid cells
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Mastoid antrum: a small
chamber between tympanic
cavity and mastoid cells
Mastoid cells: contain a
group of air cells within
mastoid process of
temporal bone
Internal ear
General features
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Lies within the petrous
portion of temporal bone
Key contents of internal ear
 Bony labyrinth contains
perilymph
 Membranous labyrinth
is filled with endolymph
and contains the sensory
organs
Bony labyrinth
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Cochlea
Vestibule
Bony semicircular canals
Cochlea
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It somewhat resembles a
snail’s shell
Consists of
 Modiolus
 Cochlear spiral canal
makes two and one-half
spinal turns around the
modiolus
 Osseous spiral lamina
 Scala vestibuli
 Scala tympani
Vestibule
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Hollow bony space
Contains utricle and saccule
Bony semicircular canals
(anterior, posterior, and lateral) posteriorly
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Semicircular duct in each
Canal at right angles to each other
Dilated ampulla in each canal，called bony ampullar
Membranous labyrinth
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Cochlear duct
Utricle and saccule
Semicircular ducts
Cochlear duct
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Contains spinal organ
(of Corti), the sound
receptors lies on
tympanic wall of
cochlear duct
Utricle and saccule
 Contain macular utricli and macular sacculi, end organs of
balance, which respond to linear acceleration and deceleration,
static of gravity
Semicircular ducts
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Each duct has a membranous ampullae
Containing crista ampullaris, receptors of balance that
respond to rotational acceleration in three different planes
Conduction of sound
Sound waves
Cochlear nerve
Air-conduction of sound
Bony- conduction of sound
Sound waves
Skull
Bony labyrinth
Endolymph within cochlear duct
Cochlear nerve
Perilymph
Spinal organ
Internal acoustic meatus
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Extends from internal
acoustic pore to fundus of
internal acoustic meatus
Facial, vestibulocochlear
nerves and vessles of
labyrinth pass through the
fundus of internal acoustic
meatus
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