Glossary of NJDS Histology - EYE AND EAR

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The Eye
Photosensitive organ partially surounded by orbits
How is the eye derived?
- Surface ectoderm

- Outpocketing of prosencephalon
What are the anatomic components of the eye?
1. globe
2. lens
3. photosensitive cells
4. neurons
Provides support for the outer part of the eye
ovoid highly elastic structure
Receives visual stimuli and found in the retina
Transmit visual information to the brain (neurons coalesce into optic nerve)
What are the three structural layers of the eye?
1. Outer Layer (tunica fibrosa)
2. Middle (vascular) layer
3. Inner
Outer Layer (Tunica Fibrosa)
Consists of...
- cornea (anterior) and sclera
- majority
- modified connective tissue
Middle Vascular Layer
This contains structures that comprise of the UVEAL TRACT
- choroid
- ciliary body
- iris
Inner Layer
- This layer consists of the retina
- The retina posterior to the ora serrata is sensitive to light
What are the three components of the eye?
1. Anterior Chamber
2. Posterior Chamber
3. Vitreous Space
Anterior chamber
This compartment is...
- found between the cornea, and iris and lens
- filled with aqueous humor
Posterior Chamber
This compartment is...
- between the iris, ciliary body, zonule, and lens
- filled with aqueous humor
Vitreous Space
This compartment...
- is bounded by lens and retina
- is the largest
- contains gelatenous vitreous body which maintains eye shape and protects retina from tauma due to rapid movements
What are the components of the tunica fibrosa?
1. Sclera
2. Cornea
- known as the "whites of the eyes"
- composed of dense fibrous CT where many are multidirectional collagen bundles parallel to eye surface
- This component is the outer surface of the sclera
- It is made of loose CT
This eye component...
- is the anterior, transparent part of globe
- is a multilayered avascular structure
- has outer nonkeratinized SSE
- has lots of mitotic activity
- is richly innervated
Vascular supply of Cornea
- This vascular supply lies along the periphery
- Vessels merge into SCHLEMM'S CANAL
Schlemm's Canal
This structure...
- drains the anterior chamber of aqueous humor
- empties into regional venous system
deeply pigmented (many melanocytes)
many blood vessels
loose connective tissue - contains many collagen and elastic fibers and leukocytes
Choriocapillary layer
very vascular
provides nutirtion of retina
damge can cause extensive retinal damge
widening of choroid next to lens, triangular in c. sexn
- contains loose CT encasing CILIARY MUSCLE
Ciliary Muscle
smooth muscle
- inserted on both sclera and ciliary body
- allow for stretching of choroid amd releasing tension on lens
- causes proper visual accomodation
Ciliary Processes
evaginations of ciliary body
- loose CT core with simple columnar epithelium covering
- cells create AQUEOUS HUMOR
Oxytalan (zonule) Fibers
from cilary processes insert on lens capsule
holds lens in place
projection of choroid that partially covers the lens leaving aperture
-rough anterior surface covering CT with melanocytes
-below is highly vascularized CT
-Posterior surface is smooth with 2 layers of epithelium
1) Inner Layer - melanocytes and pigmented
2) Outer Layer -myofilaments creating DILATOR PUPILLAE
Dilator Pupillae
along with melanocytes
regulate light that enters pupil (adaptation)
What are three parts of the lens?
1. Lens Capsule
2. Subcapsular Epithelium
3. Lens Fibers
Subcapsular Epithelium
simple columnar or cuboidal found only on ANTERIOR SURFACE
Lens Fibers
majoroty of lens
found below epithelium
elongated subcapsular epithelium cells w/o organelles
contain proteins (CRYSTALLINS)
RETINA (Inner Layer)
photosensitive elements in posterior portion
What are the 2 distinct layers of the retina?
1. Pigment epithelium
2. neural (optical) retina
Pigment Epithelium
simple columnar
-transmit Vitamin A to photo. cells
-produce melanin
-absorbs light after photo. stimulation
What are the layers of the neural retina?
1.outer layer of rods and cones
2.external plexiform layer
3.bipolar neurons
4.internal plexiform layer
5.ganlion cells
Outer layer of rods and cones
dendrite - sensitive to light
inner and outer segments
nuclear region
synaptic region
External Plexiform Layer
1. contains synapses btw rods and cones, and bipolar neurons
Bipolar Neurons
integrate rods and cones with ganglion cells
Internal Plexiform Layer
contains synapses btw bipolar neurons and ganglion cells
Ganglion Cells
neurons whose axons form OPTIC NERVE
-may be diffuse or monosynaptic
Path of light in retina
1. ganglion cells (closest to vitreous body
2. bipolar neurons
3. rods and cones
What are the cells of the retina?
1. Rods
2. Cones
3. Diffuse bipolar cells
4. monosynaptic bipolar cells
5. ganglion cells
6. horizontal cells
7. amacrine cells
8. supporting cells
-responsive to low light conditions
-light sensitive portion
-elongated outer segment contains many stacked membranous disks
-disks contain rhodopsin
In disks of rods
interaction with light is first step to vision
elongated conical process
-responsive to color and high intensity light
- less than 5% of photoreceptors
- disks formed by invaginations cell membrane
-thought to provide better visual perception than rods
Visual pigment of cones
sensitive to RGB light
Diffuse Bipolar Cells
synapse with 2 or more photoreceptors
Monosynaptic Bipolar Cells
synapse with one photoreceptor
Horizontal Cells
connect photorecptors together
Amacrine Cells
connect ganglion cells together
Supporting Cells
microglia, astrocytes, Muller Cells
Muller Cells
provide nutrition and structural support to cells of retina
highest visual acuity
What are the accessory structures of the eye?
1. Conjunctiva
2. Eyelids
3. Lacrimal Glands
mucous membrane covering cornea and inner surface of eyelid.
-stratified columnar w/ goblet cells
What are the three glands of the eyelid?
1. Meibomian glands
2. glands of Zeis
3. glands of Moll
Meibomian Glands
produces lipid rich surface that prefvents tear film evaporation
-does not enter into hair follicle
Glands of Zeis
sebaceous glands that enter into eyelash follicle
Glands of Moll
modified sweat glands that empty into eyeash follicles
Lacrimal Glands
secrete tears
-serous and rich in lysozyme (kills bacteria)
-compound tubuloacinar gland
The Ear
aka vestibulocochlear apparatus
-concerened with perception of sound and balance
What are the three general parts of the ear?
1. External ear
2. Middle ear
3. Inner ear
What are the components of the EXTERNAL EAR?
* collects sound waves
external auditory meatus
temporal bone
ceruminous glands
tympanic membrane
most obvious feature
convoluted elastic cartilage covered with skin
External Auditory Meatus
-outer third has supporting wall made of elastic caritlage
-remainder is temporal bone
-fibrous elastic CT
-lined on outer surface skin
lined on inner surface by simple cuboidal epithelium
-lined by hairy mucosa and contains CERUMEN GLANDS
Ceruminous glands
simple coiled tubular glands
secrete ear wax for protection
What structures make up the borders of the MIDDLE EAR?
1. tympanic membrane
2. temporal bone
3. inner ear
What two structures does the middle ear communicate with?
1. mastoid air cells (poseriorly)
2. nasopharynx (anteriorly
- via auditory (eustachian) tube
What are the two structures in the medial wall of the middle ear?
1. oval window
2. round window
*Both are membrane covered structures w/o underlying bone
What are the three ossicles and where are they located?
*bridging the tympanic membrane and the oval window

1. malleus
2. incus
3. stapes
What are the functions of the ossicles?
transmit vibratory stimuli to oval window and then to inner ear
What are structural characterisitics of the ossicles?
1. They have synovial joints
2. covered by simple SE
3. malleus and stapes
have muscle attachment
for regulating sound
What are the two labyrinths of the INNER EAR?
1. bony labyrinth
2. membranous labyrinth
Bony Labyrinth
casing within temporal bone housing membranous labyrinth
*contains widenin known as VESTIBULE
contains dilated utricle and saccule
simple squamous epi attached to peiosteum of bony labyrinth
What are the component parts of the membranous labyrinth?
1. saccule and utricle
2. semicircular canals
3. endolymphatic duct and sac
4. cochlear duct
Saccule and utricle
cavities containing neuroepithelial cells that communicate with vestibulocochlear nerve
What are the locations of the macula in the saccule and utricle respectively?
Sacule - floor
Utricle - lateral wall
* macula oriented perpendicular to each other
What are the macula composed of?
1) 2 kinds of receptor hair cells
2) supporting cells
3) efferent and afferent nerve endings
What are the components of the hair cells of the macula?
up to 80 sterocilia and 1 cilium
* a geltainous layer covers hair cells
What is the function of otoliths?
cause displacement when head changes acceleration, bends stereocilia and sends message to brain via VESTIBULOCOCHLEAR NERVE
helps determine body position
Where are the receptors in the semicircular canals located?
dilated areas adjacent to utricle
How are they arranged and what is their name?
They are arranged in long ridges
What are the 2 structural differences between the maculae and the ampullae?
1) thicker gelatinous layer and conical in shape
How do the semicircular canals function?
determines body position by movement of endolymph
tilts cupula, bends stereocilia, leads to signals depending on direction of tilt
-absorb endolymph
-scavenge debris present in endolymph
aka cochlea
-responsible for reception of sound
-has 3 spaces in cross sxn
What are the 3 spaces of the cochlea?
1. scala vestibuli
2. scala media
3. scala tympani
Scala vestibuli
superior, contains perilymph
Scala Media
contains endolymph, terminates at end of cochlea
Scala tympani
inferior, contains perilymph
What do the vestibuli and tympani connect?
oval window to round window
Describe the sturcture of the cochlear duct?
1. double layer of of simple SE separates vestibuli and media
2. lateral wall of media
- simple cuboidal epi
-transports and modifies endolymph
- No cilium
-long hair cells contact TECTORIAL MEMBRANE
What does the organ of Corti consist of?
hair cells and supporting cells
What are the 2 hair cell patterns in the organ of Corti?
1. outer layer
- 3-5 rows in cuved pattern of stereocilia
2. inner layer
- linear pattern of stereocilia
What are the innervations of the hair cells?
Afferent and Efferent
-parakaryons of afferent neurons make up spiral ganglion
What are the supporting cells of the cochlear duct?
-line inner tunnel (space important for sound transmission)
Describe the path of sound perception
External Ear > external auditory meatus > tympanic membrane > ossicles > oval window > perilymph of vestibuli > vestibular membrane > endolymph of scala media > perilymph of scala tympani > displacement of basilar membrane (under hair cells) > tectorial membrane > bending stereocilia > AP generated > cochlear branch of vestibulocochlear nerve

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