EYE and EAR

Zhang Xi-Mei

Introduction:

Eyes: the visual organ.

Ears: the organ of hearing and equilibrium.

Eye

Retina Iris Vascular layer Ciliary body Walls Choroid Fibrous layer Cornea Sclera

Lens Content Aqueous humor Vitreous body

Retina

Cornea

Iris

Ciliary body

Choroid

Sclera

Lens

Aqueous humor

Vitreous body

Visualaxis

Ⅰ. Fibrous layer

Cornea: anterior 1/6

Sclera: posterior 5/6

Limbus: transition zone

Function: protect inner structure & maintain eyeball shape.

A. Cornea: Colorless & transparent.

5 layers

Epithelium Anterior limiting membrane

Stroma

Posterior limiting membrane

Endothelium

1. Epithelium Non-keratinized stratified squamous

epithelium. 2. Anterior limiting membrane (Bowman’s) An acellular homogeneous membrane.

3. Stroma Several lamella of fine collagen fibrils.4. Posterior limiting membrane

(Descement’s) Acellular homogenous membrane.5. Endothelium Simple squamous epithelium.

B. Sclera:

• Mainly D.C.T with blood vessels and melanocytes.

Sclera

Ⅱ.Vascular layer:L.C.T, rich in b.v. & melanocytes.

A. Iris: A circular membrane with a pupil.

3 layers:

a. Anterior border layer:

discontinuous layer of

fibroblasts & melanocytes

b. Stroma: L.C.T. & rich in b.v.

& melanocytes.

c. Epithelium:

(i) anterior layer: smooth

muscle (sphincter & dilator),

regulate the size of pupil.

(ii) posterior layer: cuboidal

cells rich in melanin granules.

sphincter

dilator

B. Ciliary body: L.C.T surrounding the ciliary muscle. Triangle in cross-section. ciliary processes: anterior 1/3. ciliary zonules: from processes to lens.

ciliary zonules

Structure: 1. ciliary muscles: smooth muscle cells. 2. ciliary stroma: L.C.T. rich in b.v. 3. ciliary epithelium: 2 layers of cuboidal cells. outer layer: highly-pigmented. inner layer: un-pigmented.

C. Choroid:C. Choroid:

L.C.T. rich in b.v. & pigments. L.C.T. rich in b.v. & pigments.

Function:Function: provide nutrients to retina. provide nutrients to retina.

Ⅲ. Retina10 layers of histological structures4 layers of cells:

Ganglion Cells

Bipollar Cells

Optic Cells

PigmentCells

A.Pigment epithelial cells 1 layer, columnar, rich in melanin granules.

B. Photoreceptor cells (optic cells) including: rod cells

cone cells

Rod cells ： (1) photosensitive bipolar neurons.(2) a body, two opposite processes. (3) outer process: Inner segment: rich in Mt, rER, r. Outer segment: flattened membranous disks (visual purple or rhodopsin). Sensitive to low intensity light, (for night vision). Lack of Vitamin A leads night blindness.

(4) inner process: the endknob synapses with the dendrite of bipolar cells.

Cone cells:

Differ from rods in: (1). Outer segments: pyramidal disks continuous with covering cellular membrane. (2). 3 types of cones contain variety photopigments (iodopsin) on disks, sensitive to red, green, & blue light. (3). Sensitive to high intensity light & colors (day vision & color distinguishing), visual acuity is

better than rods. Lack of them leads to color blindness.

Innerprocess

Body

Innersegment

Outersegment

C. Bipolar cells:An axon & a dendrite,

they synapse with ganglion cells & photoreceptor cells respectively.

D. Ganglion cells:

The dendrites synapse with bipolar cell.

The axons concentrate together to form optic nerve.

Müller cells

Neuroglia, extend entire thickness of retina; support, nourish and insulate the retinal neurons and fibers.

E. Optic papilla & Fovea:

Optic papilla: Optic nerves pass through, & absent

photoreceptor cells (blind spot).

Fovea: At the posterior pole of the optical axis, with

very thin retina in the center, only pigment layer & cones present, high acuity of vision.

Ears

• External ear & middle ear receive transmit sound waves;

• Internal ear: responsible for equilibrium & hearing.

• Inner ear

bony labyrinth

membranous labyrinth

1. Bony labyrinth: there are 3 portions:Osseous semicircular ducts, vestibule and cochlea. filled with perilymph.

2. Membranous labyrinth:

Suspends in perilymph & filled with endolymph. Consist of 4 parts (Membranous semicircular ducts, utricle, saccule, and cochlear duct).

3. Cochlear duct & the organ of Corti

A. Cochlear duct:Triangular shape

filled with endolymph.

Roof: vestibular membrane.

Outer wall: stria vascularis, rich in blood capillaries (secrete endolymph)

Floor: osseous spiral lamina & basilar membrane. The organ of Corti locates on the membrane.

B. The organ of Corti

Locate on the basilar membrane.

A tectorial membrane covers on the Corti.

There are auditory strings (collagenous fibrils) in basilar membrane . The length of fibrils is responsible for sound frequencies.

a. Supporting cells:Pillar cells: Inner & outer. Tall columnar with wide broad

base & contacted apices. A inner tunnel between them.

Phalangeal cells: At inner & outer sides of pillar cells respactively. The apex : finger-like process for supporting hair cells.

b. Hair cells: Inner (1 row) &

outer (3-5 rows) . On inner & outer

phalangeal cells respectively.

Stereocilia touch with the tectorial membrane.

Nerve ending of cochlear N. synapses with hair cells.

Homework

• Explanation of rods, cones, optic papilla, fovea, Müller cells.

• Describe the structure of the organ of Corti.