Sense Organ

1
Sense Organ
Jun Zhou (??), M.D. Ph.D.
School of Medicine, Zhejiang University
20131216
2

• LEARNING METHODS
• Listen attentively and think actively during the
  lecture.
• Preview and review the textbook and atlas as much
  as you can.
• NEVER passing by a word without knowing its
  definition.
• To understand the structure and function of each
  organ, not just memorize them.
• Email zhjjwm300_at_zju.edu.cn

3
Special sense receptors

• Responsible for the five special senses taste,
  smell, seeing, hearing, feeling
• Tranduce stimuli from the environment into
  electrical impulses

4

• Specialized diffuse receptors
• Two important sensory organ
• The eye
• The ear

5
Specialized diffuse receptors

• Free nerve terminals
• -- feel cold, hot, pain and slight touch
• Encapsulated nerve ending
• --have CT capsule
• Pacinian corpuscle
• Meissner corpuscle
• Proprioceptive receptors

6
Free nerve ending
7

• Meissner corpuscle
• Ellipsoid, encapsulated receptor
• Located in the dermal papillae of thick skin
• Fine touch perception

8

• Pacinian corpuscle
• Large ellipsoid encapsulated receptor
• Located in the dermis. hypodermis, mesenteries
• Multilayer capsule surrounds inner unmyelinated
  nerve terminal
• Perceive pressure, vibration

9

• Proprioceptive receptors
• 3-12 small encapsulated
• intrafusal muscle fibers
• Sense differences in muscle length and tension

10
Two special sensory organs
The eye is a complex sensory organ that provides
the sense of sight.In many ways, the eye is
similar to a digital camera.It capture and focus
light, convert the light image into neuronal
impulse, then transmit to the brain via the optic
nerve. The ear is a three-chambered sensory organ
that functions as an auditory system for sound
perception and as a vestibular system for balance.

• Eyes visual organ
• Ears the organ of hearing and equilibrium.

11
THE EYE
12
Fibrous layer
Walls
Vascular layer
eyeball
Retina
eye
ContentAqueous humor?Lens?
Vitreous body
Accesory structureEyelid?Muscles of the
eye?Lacrimal gland
13
(No Transcript)
14
Eyeball Walls
Fibrous layer, includes the cornea, covers the
anterior one sixth of the eye,the transparent
portion. It has a prominence or convexity. The
sclera is composed of dense fibrous connective
tissue that provides attachment for the extrinsic
muscles of the eye.The sclera has a slightly blue
in children because of its thinness and is yellow
in the eldly because of the accumulation of
lipofuscin. Blood vessels and melanin pigment
give the choriod an intense dark-brown
color.Provides nutrients to the retina.The
anterior forms the ciliary body and iris.The
ciliary body is a ringlike thickening that
extends inward.The iris is a contractile
diaphragm that extends over the anterior surface
of the lens. The central circular aperture is the
pupil. The retina consists largely of
photoreceptors cells,forming visual impulses
along optic nerve.
Cornea 1/6
Fibrous layers Eye ball
Vascular layers
Retina
Sclera 5/6
Choroid 2/3
Ciliary body
Iris
15
Cornea
The transparent cornea is only 0.5mm thick at its
center and about 1mm thick peripherally.It
consists of three cellular layers ,which are
separated by two homogeneous membrane.

• Colorless, transparent
• 5 layers
• epithelium
• Bowmans membrane
• Stroma
• Descemets membrane
• endothelium

16
Cornea

• a.epithelium
• Non-keratinized stratified squamous epi.
• 5-6 layers
• Numerous mitotic figures
• No vessels.
• Free nerve ending
• b.Bowmans membrane( anterior basement membrane)
• An acellular homogeneous membrane
• (collagen fibrils)
• Binds Epi. to C.T.
• No regeneration

17

• C. Stroma or substantia propria
• Several lamellae of fine collagen f.network
• Flattened fibroblasts
• G.S.rich in chondroitin sulfate
• D. Descemets membrane (posterior limiting
  lamina)
• Acellular homogeneous membrane
• Can be repaired by endothelial cells
• E.Endothelium
• Like mesothelium in its morphology
• Regulate the water content of the stroma ?
  maintain transparency

18
The reasons of cornea transparent

• No blood vessels pigments
• Basal membrane of epi. is plane
• Uniform spacing of collagen fibrils and lamellae
  in stroma
• G.S. with transparent nature maintains proper
  water

19
Retina

• In the neural retina, two regions or portions
  that differ in function are recognized
• The nonphotosensitive region (nonvisual
  part),located anterior to the ora serrata, lines
  the inner aspect of the ciliary body and the
  posterior surface of the iris.
• 2) The photosensitive region (optic part) lines
  the inner surface of the eye posterior to the ora
  serrata except where it is pierced by the optic
  nerve.

• Two regions
• The nonphotosensitive region (nonvisual part)
• Located anterior to the ora serrata, no
  photoreceptors.
• The photosensitive region (optic part)
• Lines the inner surface of the eye posterior to
  the ora serrata (except the optic papilla)

20
Retina
The retina, is the innermost of the three
concentric layers of the eye.It consists of two
basic layers 1)RPE, the outer layer that rests
on and is firmly attached through the Bruchs
membrane to the choriocapillary layer of the
choriod 2)Neural retina or retina proper, the
inner layer that contains the photoreceptors A
potential space exists between the two layers of
the retina. The two layers may be separated
mechanically in the preparation of histologic
specimens. Separation of the layers, retinal
detachment, also occurs in the living state as a
result of eye disease or trauma.

• 4 layers of cells
• Pigment cells
• Optic cells
• Bipolar cells
• Ganglion cells

21

• Junctional complex consisting of gap junctions
  and elaborate zonulae occludentes and adherentes.
  This junctional complex is the site of the
  blood-retina barrier.
• 2) Processes project for a short distance between
  the photoreceptors of the rods and cones.
  Numerous elongated melanin granules are present
  in many of these processes.They aggregate on the
  side of the cell nearest the rods and cones and
  are the most prominent feature of the cells.
• The RPE serves several important functions
  including
• Absorption of light passing through the neural
  retina to prevent reflection
• 2) Isolation the retinal cells from blood-borne
  substances.It serves as a major component of the
  blood-retina barrier via tight junctions between
  RPE cells.
• 3) Phagocytosis and disposal of membranous discs
  from the rods and cones of the retinal
  photoreceptor cells.
• 4)Participation in restoration of
  photosensitivity to visual pigments that
  dissociated in response to light. The metabolic
  apparatus for visual pigment resynthesis is
  present in the RPE cells.

Pigment epithelium

• Structure
• 1) Simple cuboidal epi. Attached to choroid and
  easy separated from retina (detachment of retina)
• 2) Junctional complex ,
• 3) Melanin granules
• 4) Processes (contain pigment granules)
• Function
• absorb light,protect rod and cone from strong
  light
• Blood-retina barrier
• 3) Phagocytize the membranous discs from retinal
  photoreceptor cells
• 4) Store vitamin A to assist in forming rhodopsin

22
Optical cells
The rod and cones are the outer segment of
photoreceptor cells .The light that reaches the
photoreceptors must first pass through all of the
internal layers of the neural retina.The rods and
cones are arranged in a palisade manner
therefore, in the light microscope, they appear
as vertical striation.

• bipolar neurons
• The rods and cones
• Glial cells(Müller cell)

23
Rod cell
Outer segment of the photoreceptor is roughly
cylindrical,(hence, the descriptive name
rod). With the TEM, 600 to 1000 regularly spaced
horizontal discs are seen in the outer
segment. The membranous discs are formed
repetitive transverse infolding of the plasma
membrane in the region of the outer segment near
the cilium.Rods form new discs throughout their
life span. Discs are formed in cones in a similar
manner but are not replaced on a regular
basis. Rod discs lose their continuity with the
plasma membrane from which they are derived soon
after they are formed, eventually shed and
phagocytosed by the pigment epithelial
cells. Rhodopsin in rod cells initiates the
visulal stimulus when it is bleached by light. It
is a derivative of vitamin A. Thus, an adequate
intake of vitamin A is essential for normal
vision. Prolonged dietary deficiency of vitamin A
leads to the inability to see in dim light (night
blindness)

• Thin,elongated cells,
• about 120 million rods
• A body and two opposite processes
• Outer segment and inner segment
• separated discs ,shed disc phagocytized by
  pigment cells
• rhodopsin (visual purple)
• Function
• sensitive to low intensity light
• Night vision (lack of vitamin A leads night
  blindness)

24
cone cell
Outer segment of the photoreceptor is roughly
conical.(hence, the descriptive name cone). Discs
are formed in cones in a similar manner but are
not replaced on a regular basis. Discs within the
cones retain their continuity with the plasma
membrane. The specificity of the cones provides a
functional basis to explain color blindness.True
color-blind individuals (almost all are male) are
dichromats and are believed to have a defect in
either the red-, green-, or (much less commonly)
blue-sensitive cones.

• About 7 million cells
• Located in posterior part of retina,especially in
  fovea
• Outer and inner segments (conical)
• Continuous discs not renewed
• Function
• 1)sensitive to high intensity light
• 2)color distinguishing(red?blue?green iodopsin)

25
Bipolar cells
Interconnected cells is reduced to provide
greater visual acuity. Four types of conducting
cells---bipolar,horizontal, interpexiform and
amacrine cells.

• An axon a dendrite
• Synapse with photoreceptor
• cells and ganglion cells
• Müller cells
• Extend entire thickness of retina
• Neuroglia
• Horizontal cells
• Amacrine cells

Interconnected cellsproviding greater visual
acuity
26
Ganglion cells
These nerve cells have lightly staining round
nuclei with prominent nucleoli and have Nissl
bodies in their cytoplasm. Axonal process passes
into the nerve fiber layer, then goes into the
optic nerve.

• The dendrite synapse with bipolar cells
• The axons concentrate together form optic nerve

27

• Specilized regions of the retina
• Ora serrata neural layer ends anteriorly at
  ciliary body,pigment cells extend to cover
  posterior iris
• Macula luteadirectly on eyes posterior pole.
  yellow spot,mostly cones
• Fovea centralis central pit of macula,only
  cones, vision acuity straight on
• Optic discblind spot,no rods or cones,optic
  nerve exits,medial and inferior to fovea
  centralis.

Macula lutea is the area surrounding the fovea,
is yellowish because of the presence of yellow
pigment.Here, the retinal cells and their
processes, especially the ganglion cells, are
heaped up on the side of the fovea so that light
may pass unimpeded to this most sensitive area of
the retina.
28
10 layers
1 pigmented epithelium 2 layer of
photoreceptors 3 external limiting membrane 4
outer nuclear layer 5 outer plexiform layer,
where photoreceptors synapse 6 inner nuclear
layer of bipolar neurons 7 inner plexiform
layer, where bipolar neurons synapse with
ganglion cells 8 ganglion cell layer 9 optic
nerve layer 10 internal limiting membrane
The specific arrangement and association of the
nuclei and processes of these cells result in the
retina being organized in ten layers that are
seen with the light microscope. The ten layers of
the retina, from outside inward, are 1.RPE the
outer layer of the retina 2.contains the outer
and inner segments of photoreceptor cells 3.the
apical boundary of mullers cells 4.contains the
cell bodies(nuclei) of retinal rods and
cones 5.contains the processes of retinal rods
and cones and processes of the horizontal.amacrine
and bipolar cells that connect to
them. 6.contains the cell bodies of horizontal,
amacrine, bipolar and mullers cells. 9.processes
of ganglion cells that lead from the retina to
the brain 10.composed of the basal lamina of
Mullers cell.
29
Visual pathways

• light cornea chamber lens
  vitreous body retina
• pigment epithelium rods and cones
  bipolar cells ganglion cells optic
  nerve fibers

30
The ear is a three chambered sensory organ,
functions as an auditory system for sound
perception and as a vestibular system for
balance. There are three divisions of ear. The
external and middle ear collect and conduct sound
energy to the internal ear, where auditory
sensory receptors convert that energy into
electrical impulses. The sensory receptors of
vestibular system are located in the internal
ear.These receptors respond to gravity and
movement of the head.
Ear

• External, middle, internal ear
• External and middle ear
• gathers and funnels sound waves
• Internal ear
• sensory of hearing and balance

31
Mastoid process
(auricle)

• External ear
• auricle
• external acoustic meatus
• tympanic membrane (eardrum)
• Middle ear
• tympanic cavity
• auditory tube
• mastoid process

External 1)auricle(pinna)oval,projects from the
lateral surface of the head.Its shape is
determined by internal supporting elastic
cartilage. 2)an air-filled tubular space that
follows a slightly S-shaped course 3)The tympanic
membrane separates the external acoustic meatus
from the middle ear. Middle 1)an air-filled
space, called typanic cavity, which are spanned
by three small bones. 2)The auditory tube
connects the middle ear to the nasopharynx.
Equalizing the pressure of the middle ear with
atmospheric pressure.It is common for infections
to spread from pharynx to the middle ear via the
auditory tube. 3)Mastoid bone is spongy bone.
32
Internal ear Bony labyrinth
Membranous
labyrinth
The internal ear consists of two labyrinthine
compartments, one contained within the other. The
bony labyrinth is a complex system of
interconnected cavities and canals in the petrous
part of the temporal bone. The vestibule is small
oval chamber located in the center of the bony
labyrinth.The semicircular canals extend from the
vestibule posteriorly, and the cochlea extends
from the vestibule anteriorly. The semicircular
canals are tubes within the temporal bone that
lie at right angles to each other. The cochlea is
a cone-shaped helix connected to the
vestibule. The membraneous labyrinth consists of
a series of communicating sacs and ducts
containing endolymph. It is suspended within the
bony labyrinth, and remaining space is filled
with perilymph. Endolymph has similar composition
to intracellular fluid.Perilymph similar to
extracellular fluid.

• Bony labyrinth
• Semicircular canals
• Vestibule
• Cochlea

• Menbranous labyrinth
• Cochlear labyrinth
• Vestibular labyrinth
• three semicircular ducts
• Utricle and saccule

33
Specialized sensory cells are located in six
regions in the membranous labyrinth. 1)cristae
ampullaris are located in the membranous ampullae
of the semicircular ducts.They are sensitive to
angular acceleration of the head. 2)Two
maculae,sense the position of the head and its
linear movement. 3)functions as the sound
receptor.

• Six sensory regions of the membranous labyrinth
• Three crista ampullaris
• Two maculae(maculae of utricle, maculae of
  saccule)
• The spiral organ of Corti

34
Crita ampullaris
Project from the wall of the membranous labyrinth
into the endolymphatic space. 1)cupula a
gelatinous protein-polysaccharide mass, attached
to the hair cells of each crista. 2)The
stereocilia and kinocilium of each hair are
embedded in the cupula. Rotational movement move
the semicircular canal and membranous
semicircular ducts.Deflection of the stereocilia
of the hair cells generates nerve impulses in the
associated nerve ending.
three,located in the membranous ampullae of the
semicircular ducts Composition Supporting
cellssupport,forming cupula Sensory hair
cellswith stereocilia and kinocilium are
embedded in the cupula Function sensors of
angular acceleration of the head
35
The maculae of the utricle and saccule are
oriented at right angles to one another.One is in
a horizontal plane, another one is in a vertical
plane.

• Maculae of utricle and saccule
• Located in the vestibule
• Sense the position of the head and its linear
  movement

36
The cochlea duct divides the cochlear canal into
three parallel compartment or scalae.The cochlea
duct itself is the scala media. The scala
vestibuli and scala tympani are the spaces above
and below, respectively.

• Note
• The position of cochlear duct within the bony
  cochlea
• The scala vestibuli and the scala tympani,
  containing perilymph
• The scala media containing endolymph

37
Schematic diagram of the cochlea
The scala media is the triangle space with its
acute angle attached to the modiolus.Both the
scala vestibuli and the scala tympani are filled
with perilymph, whereas the cochlear cduct is
filled with endolymph.The spiral organ of Corti
rests on the lower wall of the scala media. The
scala vestibuli and the scala tympani are
perilymph-containing spaces that communicate with
each other at the apex of the cochlea through a
small channel.
Scala vestibuli
Scala tympani
38
Cortis organsensor of sound vibration
The tectorial membrane extends from the spiral
limbus over the cells of the spiral organ of
Corti.And attaches to the stereocilia of the hair
cells. Between the inner pillar cells and outer
pillar cells, form a triangular tunnel.
On the lower wall of the scala media Tectorial
membrane Inner (close to spiral lamina)and outer
(farther from the spiral lamina) hair
cells Supporting cells inner and outer
phalangeal cells
pillar cells
39
High-frequency sounds cause maximal vibration of
the basilar membrane near the base of the
cochlealow-frequency sounds cause maximal
displacement nearer the apex.
Sounds Pathway 1) Sound comes 2) Hits tympanic
membrane to vibrate 3) three auditory ossicles
vibrate 4) vibration at tympanic (oval) window
40
5) Vibration in the perilymph of the scala
vestibuli to the scala media 6) Vibrates of
basilar membrane and tectorial membrane, and hair
cells attached to also vibrates 7) Vibrate the
stereocilia of the hair cells and initiate
neuronal transduction
41
Clinical Correlation

• Vertigo dysfunction of vestibular system
• Causes viral infections, certain drugs,
  tumors, excessive stimulation (seasickness,
  carsickness, or airsickness)
• Hearing loss
• 1)Conductive hearing loss sound waves are
  mechanically impeded from reaching the auditory
  sensory receptors within the internal ear, such
  as excessive accumulation of cerumen.
• 2)Sensorineural hearing impairment injury to the
  auditory hair cells or the cochlea nerve. May be
  congenital or acquired. Causes include
  infections, trauma (exposure to excessive noise),
  administration of certain antibiotics, aging.

42

• OBJECTIVES
• Know the general layers of the eye.
• Describe the structure of Cornea and its reason
  of transparency.
• Describe the structure of Retina and the function
  of pigment cell, rod cell and cone cell.
• Know the definition of Ora serrata, Macula lutea,
  Fovea centralis and Optic disc.
• Know the general structure of ear.
• Describe six sensory regions of the membranous
  labyrinth and their function.

43
cornea
Ciliary body
iris
lens
sclera
44
Sclera Choroid Retina
45
Scala vestibuli
Scala media
Scala tympani
46
Choice Select the single most appropriate
answer. 1.The posterior wall of eyeball from
outside inward contains A.fibrous layer,vascular
layer and retina B.retina,choriod and
sclera C.choriod,sclera and retina D.cornea,iris
and retina E.Retina, vascular layer and fibrous
layer 2. The Müller cells of retina belong
to A.sensory neurons B.neuroglial
cells C.interneurons D.photoreceptors E.motor
neurons 3.The cells used color perception and
fine visual acuity are A. ganglion cells
B. Müller cells C. bipolar cells
D.rods E. cones
( A)
( B )
( E )
47

• 4.The optic nerve fibers are constituted by axons
  of
• A.ganglion cells
• B.Müller cells
• C.Bipolar cells
• D.rods
• E.Cones
• 5.The receptor of hearing is located on
• A.Vestibular membrane
• B.Crista ampullaris
• C.Maculae saccule
• D.Maculae utricle
• E.Organ of Corti

( A )
( E )
48

• Final score of Histology Embryology (2013)
• Attendance and picture drawing 10
• Quiz15 (each quiz 5)
• LAB Test25
• Final written examination50
• Histology 35-40
• Embryology10-15

49
Thanks for your attention