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Tissues of the eye
Transcript of Tissues of the eye
however not to colour Phototransduction in rods A light photon hits the retinal in a photoreceptor (rods or cones)
Retinal changes to a unstable conformation due to the photon, and splits the molecule in half
The GTP still attached to the alpha subunit causes a enzyme to activate, which causes the conversion of cGMP to GMP, which lowers the concentration of cGMP and closes the sodium channels
Potassium is still allowed in through channels, which and because of this hyperpolization the voltage gated calcium channels also close
As calcium drops, the neurotransmitter glutamate drops, which causes a depolarization on the on center bipolar cells -> increased firing rate ganglia cells Phototransduction Major components of the eye The human eye is made up of three coats:
Outer Layer - cornea and sclera
Middle Layer - choroid, aqueous humor, ciliary body, lens and iris
Inner Layer - retina and vitreous humor Three transparent structures are found within the coats:
Aqueous humor, vitreous chamber and lens Cornea - The cornea is the transparent coating at the front of the eye which covers the iris, aqueous humor and pupil
-Major refractory component of the eye
- No blood flow within cornea
- Oxygen diffuses into the tears, and then into the cornea
- Nutrients also reach the cornea through tear diffusion, and through diffusion from the aqueous humor
- Covered in nerve ending which are highly sensitive to touch, temperature, and chemicals Five corneal layers: 1. Corneal epithelium
- six layers of fast growing and easily regenerate cells
2. Bowman's layer
- tough layer composed of irregularly arranged collagen I fibers
3. Corneal stroma
- composed of regularly arranged collagen I fibrils and keratocytes (Repair cells)
4. Descemet's membrane
- acellular, and composed of collagen IV fibrils
5. Corneal endothelium
- squamous monolayer of mitochondria-rich cells, used to regulate fluid and solute transport to the cornea tissues The Lens Function
-The lens, along with the cornea, helps to refract light to the retina Structure
-a smooth, transparent basement membrane that completely surrounds the lens. The capsule is elastic and is composed of collagen.
-composed of a single layer of cube like cells with large, spherical central nuclei. The epithelium functions to regulate osmolarity and volume by using Na+/K+ pumps to pump ions out of the lens as ions, nutrients and liquid enter from the aqueous humor.
-long, firmly packed, thin, transparent cells that make up the bulk of the lens The lens lacks, nerves, blood vessels, or connective tissue Capsule Epithelium Fibers Vitreous Humor - The transparent, colorless gel that functions to fill the space between the lens and the retina of the eye and maintain the shape of the eye - Produced by the cells in the ciliary body
-Its composition is similar to the cornea but contains very few cells.
Phagocytes which remove cellular debris
Hyalocytes on the surface which reprocess hyaluronic acid
- no blood vessels
- composed of 98-99% water and 1-2% salts, sugars, collagen, proteins and hyaluronic acid
- has a refractive index of 1.337 Choroid The vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. - The Choroid is composed of layers of blood vessels and capillaries that provide oxygen and nourishment to the retina Sclera The white of the eye Function
- Maintains the shape of the globe
- Protects the inner eye
- Provides an attachment site for muscles and is perforated by nerves and blood vessels
The sclera is covered with a clear mucus membrane and capillaries
Four layers of connective tissue:
episclera - loose, fibrous, elastic tissue
stroma - tough connective tissue
lamina fusca - pigmented connective tissue
endothelium - thin layer of epithelial cells Cone Photoreceptor Cells Photoreceptor cells are found in the retina; they allow the conversion of light into signals
The photoreceptor cells include rods and cones. There are three types of cones and a single type of rod cell in mammalian retina. The 3 different cones are sensitive to different ranges of wavelengths.
The outer segment of the cone contains stacks of membranous discs
In cones the discs are attached to the outer segment membrane.
The inner segment is filled with mitochondria to provide ATP The cell body is located below the inner segment
The axon runs from the cell body to the synaptic terminal
The synaptic terminal releases neurotransmitters
Cones are most highly concentrated in the fovea of the retina ("center" of the retina). Aqueous Humor or Anterior Chamber - Transparent
- Gelatinous fluid
- Secreted from the the ciliary epithelium
- Filled with numerous amino acids Functions - Provides nutrition (Amino acids, glucose, ect.) to cornea, lens, and other non vascular eye tissues
- Allows for inflation and expansion of cornea for increased protection
- Maintains pressure for the eye, keeps the eye inflated/rigid
- Immune defense Cornea 5 Layers of the cornea - Firstly, light passes through the cornea. This causes the light to refract from a wide beam into a more narrow beam - After light passes through the cornea, it enters the liquid chamber of the eye known as the anterior chamber, or aqueous humor. -Next light then enters the lens
- This is where the fine focus of the light beam is achieved through the use of muscles which contort the lens - Finally light passes through
the vitreous humor and shines
on the retina, which is covered
in photochemical cells Pathway of light through the eye Cornea Anterior Chamber - The passage of light
through the fluid causes
some extra refraction. Lens Retina Rod Photoreceptor Cells There is only one type of rod cell that exists in the retina.
Rods are a lot more sensitive to light than cones.
Rods only have one type of light-sensitive pigment - unlike cones which have 3 - and therefore are not involved in "seeing" colour.
The structure of rods and cones is very much alike: the main difference lies in the outer segment.
Rod cells have a slower response time when activated by light
Rods are most highly concentrated in a ring around the fovea Retinal Pigment Epithelium The retinal pigment epithelium lies between the outer membrane of the photoreceptor cells, and the blood-supplying choroid.
It is composed of tightly-packed, hexagonal single-layered cells which are rich in pigment granules and digestive organelles. Functions One of the main functions of the RPE is to absorb excess (scattered) light coming into the eye.
The absorption of light causes an increase in temperature to about 40 degrees C in the choroid/RPE system.
The RPE supplies the photoreceptor cells with small molecules.
The epithelium also contains the Vitamin-A derived chromophore called retinal.
The RPE phagocytoses old membrane discs of photoreceptor outer segments.
The overall role of the RPE is to protect the retinal system from the outside environment. Bipolar Retinal Cells Located between photoreceptors and ganglion cells
They transmit signals from rods & cones to the ganglion cells
They are made up of a cell body with two processes extending in each direction.
There are "ON" (metabotropic) bipolar cells and "OFF" (ionotropic) bipolar cells.
They communicate via graded potentials (unlike most neurons which use action potentials) - The photochemical cells interpret the light and send a signal to the brain Ganglion Cells Ganglion cells are the last neuron cells in the retinal system.
They transmit visual info form the photoreceptors to the brain
One ganglion cell can communicate with as little as 5 photoreceptors to as many as 1000
Ganglion cells fire action potentials at a base rate while at rest.
There are 5 major classes of ganglion cells which respond to different conditions
The ganglion axons collectively make up the optic nerve. depressed firing rate increased firing rate These three layers, in addition to the cornea, are the transparent mediums that light passes through to reach the retina Cones Rods Questions?