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
3. photosensitive cells
- Provides support for the outer part of the eye
- ovoid highly elastic structure
- PHOTOSENSITIVE CELLS
- 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
- Outer Layer (Tunica Fibrosa)
- Consists of...
- cornea (anterior) and sclera
- modified connective tissue
- Middle Vascular Layer
- This contains structures that comprise of the UVEAL TRACT
- ciliary body
- 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
- - 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
- CILIARY BODY
- 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
-absorbs light after photo. stimulation
- What are the layers of the neural retina?
- 1.outer layer of rods and cones
2.external plexiform layer
4.internal plexiform layer
- Outer layer of rods and cones
- dendrite - sensitive to light
inner and outer segments
- External Plexiform Layer
- 1. contains synapses btw rods and cones, and bipolar neurons
- Bipolar Neurons
- aka LINKING CELLS
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
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
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
- most obvious feature
convoluted elastic cartilage covered with skin
leads to EXTERNAL AUDITORY MEATUS
- 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
- 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
- MEMBRANOUS LABYRINTH
- 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
- SEMICIRCULAR CANALS
- 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
2) NO OTOLITHS
- 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
- ENDOLYMPHATIC DUCT AND SAC
- -absorb endolymph
-scavenge debris present in endolymph
- COCHLEAR DUCT
- 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?
- PILLAR CELLS
-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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