Sense Organ

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Sense Organ Jun Zhou ( 周俊 ), M.D. & Ph.D.

School of Medicine, Zhejiang University

20131216

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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: [email protected]

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Special sense receptors

Responsible for the five special senses: taste, smell, seeing, hearing, feeling

Tranduce stimuli from the environment into electrical impulses

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Specialized diffuse receptors

Two important sensory organ The eye The ear

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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

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Free nerve ending

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Meissner corpuscleEllipsoid, encapsulated receptor

Located in the dermal papillae of thick skin

Fine touch perception

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Pacinian corpuscleLarge ellipsoid encapsulated receptor

Located in the dermis. hypodermis, mesenteries

Multilayer capsule surrounds inner unmyelinated nerve terminal

Perceive pressure, vibration

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Muscular spindles

Proprioceptive receptors

3-12 small encapsulated

intrafusal muscle fibers

Sense differences in muscle length and tension

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Two special sensory organsTwo special sensory organs

Eyes: visual organ

Ears: the organ of hearing and equilibrium.

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THE EYE

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eyeball

Accesory structure:Eyelid 、 Muscles of the eye 、 Lacrimal gland

Walls

Content ： Aqueous humor 、 Lens 、

Vitreous body

Fibrous layer

Vascular layer

Retina

eye

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Ciliary body

Eyeball Walls

Fibrous layers

Eye ball Vascular layers

Retina

Cornea 1/6

Sclera 5/6

Choroid 2/3

Iris

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.

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.

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Cornea

Colorless, transparent

5 layers:

epithelium

Bowman’s membrane

Stroma

Descemet’s membrane

endothelium

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Corneaa.epithelium: Non-keratinized stratified squamous epi. 5-6 layers Numerous mitotic figures No vessels. Free nerve ending

b.Bowman’s membrane( anterior basement membrane)

An acellular homogeneous membrane (collagen fibrils) Binds Epi. to C.T. No regeneration

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C. Stroma or substantia propria Several lamellae of fine collagen f.network Flattened fibroblasts G.S.rich in chondroitin sulfate

D. Descemet’s 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

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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 prop

er water

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Retina

Two regions:The nonphotosensitive region

(nonvisual part)

Located anterior to the ora serrata, n

o photoreceptors.The photosensitive region (opti

c part)

Lines the inner surface of the eye posterior to the ora serrata (except the op

tic papilla)

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Retina

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

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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 ：

1) absorb light,protect rod and cone from strong light

2) Blood-retina barrier

3) Phagocytize the membranous discs from retinal photoreceptor cells

4) Store vitamin A to assist in forming rhodopsin

Pigment epithelium

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Optical cells

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

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Rod cell Thin,elongated cells ， about 120 million rods A body and two opposite processes Outer segment and inner segment separated discs ,shed disc phagocytized by pi

gment cells rhodopsin (visual purple) Function: sensitive to low intensity light Night vision (lack of vitamin A leads night bli

ndness)

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cone cell

About 7 million cells Located in posterior part of retina,especially in f

ovea Outer and inner segments (conical) Continuous discs & not renewed Function 1 ） sensitive to high intensity light 2 ） color distinguishing （ red 、 blue 、 green io

dopsin ）

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Bipolar cells

An axon & a dendrite

Synapse with photoreceptor

cells and ganglion cells

Müller cellsExtend entire thickness of retinaNeuroglia

Horizontal cellsAmacrine cells

Interconnected cells—providing greater visual acuity

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Ganglion cells

The dendrite synapse with bipolar cells

The axons concentrate together form optic nerve

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Specilized regions of the retina Ora serrata ： neural layer ends anteriorly at ciliary body,pigment cells ext

end to cover posterior iris Macula lutea:directly on eye’s posterior pole. “yellow spot”,mostly cones Fovea centralis: central pit of macula,only cones, vision acuity straight on Optic disc:blind spot,no rods or cones,optic nerve exits,medial and inferior t

o fovea centralis.

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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

10 layers

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Visual pathways

light cornea chamber lens vitreous body retina

pigment epithelium rods and cones bipolar cells

ganglion cells optic nerve fibers

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Ear

External, middle, internal ear

•External and middle ear:

gathers and funnels sound waves

•Internal ear:

sensory of hearing and balance

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External ear ：• auricle

• external acoustic meatus

• tympanic membrane (eardrum)

Middle ear ：• tympanic cavity

• auditory tube

• mastoid process

(auricle)Mastoid process

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Internal ear Bony labyrinth

Membranous labyrinth

Bony labyrinth ：•Semicircular canals

•Vestibule

•Cochlea

Menbranous labyrinth ：•Cochlear labyrinth•Vestibular labyrinth

three semicircular ducts

Utricle and saccule

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Six sensory regions of the membranous labyrinth:

Three crista ampullaris

Two maculae(maculae of utricle, maculae of saccule)

The spiral organ of Corti

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Crita ampullaris

three ， located in the membranous ampullae of the semicircular ducts

Composition ：

Supporting cells ： support ， forming cupula

Sensory hair cells ： with stereocilia and kinocilium are embedded in the cupula

Function ：sensors of angular acceleration of the head

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Maculae of utricle and saccule ：

•Located in the vestibule

•Sense the position of the head and its linear movement

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Note ：• The position of cochlear duct within the bony cochlea

• The scala vestibuli and the scala tympani, containing perilymph

• The scala media containing endolymph

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Schematic diagram of the cochlea:

Scala vestibuli

Scala tympani

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Corti’s organ ： sensor of sound vibration

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

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Sounds Pathway1) Sound comes

2) Hits tympanic membrane to vibrate

3) three auditory ossicles vibrate

4) vibration at tympanic (oval) window

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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

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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.

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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.

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cornea

lens

irisCiliary body

sclera

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Sclera

Choroid

Retina

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Scala vestibuli

Scala tympani

Scala media

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Choice: Select the single most appropriate answer.

1.The posterior wall of eyeball from outside inward containsA.fibrous layer,vascular layer and retinaB.retina,choriod and scleraC.choriod,sclera and retinaD.cornea,iris and retinaE.Retina, vascular layer and fibrous layer

2. The Müller cells of retina belong toA.sensory neuronsB.neuroglial cellsC.interneuronsD.photoreceptorsE.motor neurons

3.The cells used color perception and fine visual acuity areA. ganglion cells B. Müller cellsC. bipolar cells D.rodsE. cones

( A)

( B )

( E )

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4.The optic nerve fibers are constituted by axons of A.ganglion cellsB.Müller cellsC.Bipolar cellsD.rodsE.Cones

5.The receptor of hearing is located onA.Vestibular membraneB.Crista ampullarisC.Maculae sacculeD.Maculae utricleE.Organ of Corti

( A )

( E )

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Final score of Histology & Embryology (2013) ： Attendance and picture drawing ： 10% Quiz ： 15% （ each quiz 5% ） LAB Test ： 25% Final written examination ： 50% Histology ： 35-40% Embryology ： 10-15%

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