BE ABLE TO IDENTIFY:
anterior and posterior chambers
Bowman's, Bruch's, and Descemet's membranes
canal of Schlemm
ciliary muscle, process, and retina (= ciliary body)
conjunctiva (bulbar and palpebral)
corneal endothelium, epithelium, and stroma (= cornea)
sphincter pupillae muscle
irideal retina and stroma (= iris)
cone and rod outer segments
ganglion cell layer
limiting membranes (internal and external)
nuclear layers (inner and outer)
plexiform layers (inner and outer)
optic disk, nerve, and papilla
Slide #58 (Monkey eye) Before you start looking at the eye with the microscope, hold the slide in front of a piece of white paper and look at the section of the eye. You can use one of your eyepieces as a magnifying glass. Compare what you see on the slide with a diagram of the eye in either your atlas or textbook. Bring your text, did ya?
Then find the following items on the slide:
1. The Cornea and Sclera together form the Fibrous Tunic, which is the outermost covering of the eye. Note the orientation of the eye (the cornea is anterior).\
2. In the Anterior half of the eye, the Limbus, Anterior Chamber, Posterior Chamber, Iris, Lens, Ciliary Body, and Ora Serrata.
3. In the posterior half of the eye, the Sclera, Choroid, Retina, Vitreous Body, Fovea, and Optic Nerve. The Fovea and Optic Nerve may not be visible on your particular slide - borrow one that has them or look at a demonstration.
DON'T SKIP THIS ORIENTATION!!!! - You will save time in the long run.
There are three Tunic (Coats) of the Eye. From the outside inward they are the Fibrous Tunic (Tunica Fibrosa cosisting of the Cornea & Sclera), the Vascular Tunic (Tunica Vasculosa, Uvea, Choroid), and the Tunic Interna (Retina). All three of the tunics or coats are considered to be a complete covering of the eye (except for the pupillary opening). So if you follow the sclera forward from the posterior eye (around the periphery) you pass into the limbus (corneo-scleral junction) and the cornea. The anterior continuation of the choroid (vascular; tunic) becomes the ciliary body and stroma (front) of the iris. The retina is the innermost coat of the eye and is a sensory layer posterior to the Ora Serrata. The retina continues anteriorly as an epithelium two cells thick covering the Ciliary Processes (the Ciliary Retina) and the back of the Iris (The Iridial Retina). This anterior extension of the retina is not sensory, and contains melanin pigment.
Fibrous Tunic (Sclera, Limbus and Cornea)
Examine this outermost layer of the eyeball and be sure you can identify its three parts. (See microgaph below)
The Sclera consists of a dense C.T. coat about 0.5 mm. thick covering the posterior four fifths of the eye. It is white in the living state and is continuous anteriorly with the limbus. The collagen fibers in the sclera branch and anastomose giving this layer great strength. The tendons of the six extrinsic muscles of the eye attach to the sclera. Where the nerve fibers from the retina converge to form the optic disk (or papilla), the sclera has perforations (Lamina Cribrosa). These perforations allow the retina nerve fibers to leave the eye and form the Optic Nerve.
Fibrous Tunic - Cornea,Limbus & Sclera - The Limbus is the junction of the sclera with the cornea. It is an important landmark because it is situated over the Trabecular Meshwork (T.M.) and the Canal of Schlemm, which play a role in draining Aqueous Humor from the Anterior Chamber of the eye. Find these two structures on your eye slide.
The Cornea is the avascular, transparent, anterior one fifth of the fibrous tunic. On its anterior surface one finds a stratified squamous, non-keratinizing epithelium that sits on a thick specialization of corneal stroma called Bowman's membrane. This epithelium is continuous at the edge of the cornea with the conjunctival epithelium. Deep to these two outer layers is the Stroma, which forms the bulk of the cornea (90%). The collagen fibers are very regularly arranged in the stroma, which contributes to its transparency. On the inside of the cornea facing the Anterior Chamber there is an endothelium consisting of a single layer of cuboidal cells. This endothelium sits on the 10 micron thick acellular Descemet's membrane (i.e. D.M. is between the endothelium and the stroma). What makes the cornea transparent? Why aren't corneas rejected after transplantation?
The Vascular Tunic (Uvea or Choroid)
The Vascular Tunic or Choroidm is a pigmented layer beneath the sclera in the posterior portion of the eyeball. The choroid is situated between the sclera on the outside and the retina on the inside of the eyeball. Follow the choroid anteriorly to the ciliary body (see above). Identify the ciliary muscle. What is the function of this muscle? Also, identify the pigmented epithelium covering the wavy outline of the ciliary processes. The outer layer (closest to the sclera) is pigmented. The inner one is not. (See image below) This is the continuation of the retina anterior to the ora serrata called the ciliary retina that was described above. This epithelium continues forward to the back of the Iris Where it is called the Iridial Retina.
The Stroma of the Iris is also a continuation of the Choroid. It contains the Sphincter and Dilator Pupillae muscles that contol the diameter of the pupil
Also, identify the pigmented epithelium covering the wavy outline of the ciliary processes. The outer layer (closest to the sclera) is pigmented. The inner one is not. This is the continuation of the retina anterior to the ora serrata called the ciliary retina that was pictured above. This epithelium produces aqueous humor from the plasma in the capillaries located within the ciliary processes. The Aqueous Humor is pumped into the Posterior Chamber. Where does it go after it is produced??
Z.F. = Zonular Fibers
The iris is the anterior continuation of the uvea. There is also a double epithelial layer on the surface facing the posterior chamber. This epithelium is the anterior continuation of the ciliary retina called the iridial retina. In this region, both of the cell layers are heavily pigmented, making it difficult to see two layers. The (anterior) outer layer becomes myoepithelial at the periphery of the iris and is called the dilator pupillae. The dilator is not very easy to see on some of these slides. Locate the smooth muscle fibers of the constrictor pupillae, which surround the pupillary opening. They will be cut in cross-section in this specimen (WHY?) Some of your eye slides will not show a pupillary opening so borrow one that does or use a demo that will be available. The less pigmented portion of the iris anterior to the pigmented iridial retina contains the sphincter muscle and is called the Stroma of the Iris. The Stroma contains the sphincter and dilator muscles, C.T. fibers, blood vessels, and some pigment cells. Posteriorly, this layer contained the ciliary muscle and behind that was the choroid. You should be able to discuss the role of the autonomic nervous system in the innervation of the sphincter pupillae, dilator pupillae, and cilial muscles. Observe the pigmented epithelium (iridial retina). What is its function? What is the function of the iris?
The lens is not too well preserved in most of our slides. Usually it looks sort of shattered. The lens is described in your text and is the focussing portion of the optical part of the eye. Look at the periphery of the lens for fibers that connect the lens to the ciliary body. These are called zonular fibers. Clouding of the lens is one type of cataract that used to be "repaired" by removal of the lens and the use of rather thick glasses. Now prosthetic lenses are implanted to replace the diseased lens, thus eliminating the thick glasses.
Retina (Tunica Interna)
Slides #58 & #119 You have already looked at the iridial and ciliary extensions of the retinal layer anteriorly. All of the rest of the retina is sensory and can be seen in these slides. This sensory portion of the retina is the most extensive and is called the Pars Nervosa of the Retina. The pars nervosa lines the inside of the eye posterior to the ora serrata.
Slide #119 (Mammalian retina) On this slide you should see a section of a small portion of the eye with the retina on one side (partly detached). Some of the choroid with its pigment cells and blood vessels is seen next to the retina. Some sclera may be seen on the other side of the choroid. A few of these slides have a piece of the optic nerve showing outside of the sclera.
Identify all the layers of the retina that you can: pigment epithelium, rod and cone outer segments, external limiting membrane, outer nuclear layer, outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion cell bodies, nerve fiber layer, and internal limiting membrane. The fovea centralis is present on very few slides. Why is the ganglion cell layer so thick immediately peripheral to the fovea?
Optic Papilla (exit of optic nerve fibers from the eye)
This structure is also called the "blind spot".
The sclera has a specialized sieve-like region called the Lamina Cribrosa through which the nerve fibers from the ganglion cells pass. After passing through the sclera the nerve fibers become mylinated and make up the optic nerve.
Lacrimal gland (Demonstration)
Take a look at this tubuloalveolar serous gland. It makes tears, necessary to keep the corneal surface lubricated. If there are no tears for even a short time the cornea will cloud up irreversibly! The cornea must be lubricated to stay clear and functional.
HISTOLOGY LAB X - THE EAR
BE ABLE TO IDENTIFY:
cochlear duct (scala media), nerve, and ganglion
endolymph and perilymph
hair cells (inner and outer)
membranes (basilar, tectorial, and vestibular)
organ of Corti
osseous spiral lamina
pharyngotympanic (Eustachian; auditory) tube
phylangeal cells (inner and outer)
scala media, tympani, and vestibuli
spiral (cochlear) ganglion
Slide #18 (Cochlea) Some of these slides show the cochlea rather poorly. Try slide #19, which may also have a good cochlea. THESE SECTIONS ARE VERY THICK, so focus up and down a lot. If neither slide is good for cochlea, then borrow one of these slides from another box.
The cochlea is shaped like a snail and has three compartments running up the length of the spiral. Using the above micrograph, try to locate the Scala tympani, the Scala vestibuli, and the Scala media on your slide. Look in the Scala media (Cochlear duct) for the Organ of Corti, which sits on the Basilar Membrane. The other membrane delimiting the Scala Media is called Vestibular Membrane. . Try to find the Spiral Ganglion and some of the bundles of axons that form the Cochlear Nerve. The cochlear nerve runs through the center of the spiral.
A gelatinous projection called the Tectorial Membrane extends from the medial wall of the ScalaMedia and sits on top Hair Cells(inner and outer) of the Organ of Corti. Try to find the nerve fibers coming from the outer hair cells which will form part of the Cochlear Nerve. The cochlear nerve runs through the center of the spiral Cochlea.
Slide #19 (Crista ampullaris). This slide may or may
not have a good Crista Ampullaris
on it. Ditto for Cochlea. If you do find a good one somewhere
then compare it to the diagrams provided and see if you can find
the Cupula and Hair Cells. What is the function
of the Cristae?
BE ABLE TO IDENTIFY:
lymphatic nodule (w or w/o germinal center)
lymph node-- be able to identify this structure and the following components:
capsule and trabeculum
medulla, medullary cord, and medullary sinus
postcapillary venule (PCV)
subcapsular (marginal; cortical) sinus
spleen-- be able to identify this organ and the following components:
capsule and trabeculum
splenic (Billroth's) cord and splenic (venous) sinus
Peyer's patch-- be able to identify this structure and the following components:
Thymus-- be able to identify this organ and the following components:
cortex and medulla
thymic (Hassall's) corpuscle
Tonsil-- be able to identify
Slides #106 & 174 Examine lymph node architecture by low power objective. The differences between cortex and medulla should be obvious. If not, check someone else's slide, you have one of the bad slides (i.e., only part of a lymph node, showing just cortex). Be sure you can identify plasma cells, macrophages and P.C.V. on slide #174.
Cortex - You should be able to identify the thick connective tissue capsule and trabeculae (connective tissue that extends from the capsule into cortical tissue). Look for the marginal sinus just beneath the capsule. Afferent lymph vessels enter here at the periphery.
Slide #3 A stromal network of reticular fibers and reticular cells exists throughout the node upon which rest the numerous lymphocytes and macrophages. Therefore, the fibers and reticular cells are nearly impossible to identify without a special stain. Note large number of cortical nodules. What cells exist in the germinal center? Can you see any macrophages? Macrophages can be identified only by the presence of rust coloration in their cytoplasm (indication of intracellular iron). There should be more in the medulla and they are easiest to find in the thin-section.
Medulla - This part of the node consists of medullary cords (pieces of lymphatic tissue) separated by medullary sinuses (lymphatic channels). Macrophages are more abundant here! Scan the tissue outside the node to see examples of blood vessels, nerves, and adipose tissue.
Slides #63, #175 At low power, what differences do you note between spleen and lymph node? Does spleen have a cortex and medulla? The spleen also has a thick connective tissue capsule, which has a larger component of elastic fibers and smooth muscle cells. Trabeculae (mainly smooth muscle) can be found throughout the spleen parenchyma. Splenic nodules (white pulp) are scattered throughout the organ and are always associated with a central artery (usually positioned off to the side of the nodule). What makes up red pulp red? Give up already? Venous sinuses (engorged with erythrocytes) separated by Bilroth cords (arrays of lymphatic tissue) constitute red pulp. Don't bother trying to identify the components of red pulp. Just remember that all tissue between splenic nodules (white pulp) is red pulp, made up of venous sinuses and Bilroth cords. On slide 175, be sure you can identify macrophages, and mast cells.
Slide #184 Identify Peyer's patches in the wall of the ileum (specifically in the lamina propria and submucosa. These patches represent aggregates of lymphatic tissue. Often they show evidence of lymphatic nodule activation (as was seen in lymph node, i.e. nodules with germinal centers). Demonstrations will be available of Peyer's patches.
Slides #129, #64, #176 Thymus Gland
Is slide #129, an adult or an infant thymus? Identify cortical and medullary tissue in the adult slide. What are Hassall's (thymic) corpuscles? Scattered throughout the medulla are concentrically arranged cellular aggregates known as thymic or Hassall's corpuscles. Their functional significance is still unknown at this time. On slide #176 be sure you can identify macrophages and mast cells.
Hassall's (thymic) corpuscles
Scattered throughout the medulla are concentrically arranged cellular aggregates known as thymic or Hassall's corpuscles. Their functional significance is still unknown at this time. On slide #176 be sure you can identify macrophages and mast cells.
Thymic Corpuscles at high magnification. They are made up of epithelioid cells in a spherical arrangement. They vary in size but tend to be larger in thymuses from adults.
Slide #47 - (Tonsil) This lymphatic tissue also has lymphatic nodules with germinal centers. Can you identify the type of epithelium on the surface of this organ?
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