HISTOLOGY LAB V - NERVOUS TISSUE

 

BE ABLE TO IDENTIFY:

axon and dendrite
axon hillock
cells-- neuroglia, neuron, satellite, and Schwann
central canal
endo-, epi-, and perineurium
ganglion (including spinal and autonomic)
gray and white matter
myelin sheath
Nissl Body
node of Ranvier
peripheral nerve
roots (dorsal and ventral)
Schmidt-Lantermann cleft
synapse (EM only)
synaptic cleft (EM only)

 

In this lab you will be examining nervous tissue. Now, this might be accomplished at this point in time by simply looking at each other. However, we have something else in mind. First, you will look at slides of peripheral nerves cut in various planes. Next, two types of ganglia will be studied until you are reasonably sure you can tell one from the other. Last of all, you will take a look at the central nervous system i.e. spinal cord, cerebellum, and cerebrum. You should try to get familiar with the GENERAL microscopic features of the last three items. The specifics of the central nervous system will be covered in detail in a course given later called Neuroanatomy where---Oh boy!---will you get FAMILIAR with them!

The Neuron

 

 

Slide #145 (spinal cord). The neurons in this slide are stained blue to lavender and vary greatly in size. The largest cells you find are ventral motor neurons. You should see that they contain a large nucleus with a prominent nucleolus, have a number of processes evident (multipolar), and are heavily stained with the basic dye used. What is staining in the cytoplasm? In the nucleolus?

 

 

 

 

Peripheral Nerves

Slide #120 (Sciatic Nerve). This is a longitudinal cut of a piece of peripheral nerve. About all you can expect to do on this slide is differentiate the connective tissue (orangey-pink) from the nerve (bluer-pink) and to see some foamy looking myelin sheaths with a dark line running down the middle. If you look around and focus up and down, you might see a few nodes of Ranvier. Nodes of Ranvier can be seen well on slide #146, teased nerve. Most of the nuclei you see in the nerve are Schwann cell nuclei although there may be a few fibroblasts in there too (endoneurium, remember?).

 

Slide #100 (two sections) One is peripheral nerve in cross-section and the other a nerve in longitudinal-section. Look at the cross-section first. Notice how the axons are darkly stained and the myelin sheaths are even more foamy than in the last slide! In fact, some of them are just spaces where the myelin used to be. You should be able to see fairly clearly which nuclei belong to the Schwann cells. Using a longitudinal section see if you can find some nodes of Ranvier.

 

 

 

Slide #120 (Longitudinal) Arrow indicates node of Ranvier.

 

 

 

 

 

 

 

 

Slide #21. Can you tell the nerve axon from the artery or vein? NO? Go back to the beginning and start over! Yes? Well, congratulations!! You can proceed to see if you can tell whether these nerves contain mostly myelinated or unmyelinated nerves.

 

Ganglia (Singular, ganglion)

Slide #108 (Spinal {alias, sensory or dorsal root} Ganglion). Look around at medium power. You should see some fibers and some rather round neurons with nuclei containing a prominent nucleolus. Some of the cells contain and orange-brown pigment. The pigment is called lipo-fuchsin. It is an aging pigment which is probably a collection of secondary lysosomes. Go to high dry objective and locate satellite cells. What are they there for? See any myelin sheaths in the bundles of nerve fibers? Would you find very many synapses in this ganglion of you looked at it in an Electron Microscope? Cells are pseudounipolar, SENSORY, NEURONS!!

 

 

Slide #121 (Autonomic Ganglion). Compared to the cells of the spinal ganglion, the cell bodies are a lot smaller, they are not as round, and the nuclei in these neurons are more often eccentrically located. In addition you may see binucleate neurons. Find any thick myelin sheaths here? You do? START OVER!! Do not pass Gross and collect no $200.00. These fibers do have very thin myelin sheaths that would not show up in the light microscope. These pre ganglionics leave cord myelinated.

 

 

 

 

Sensory Nerve Terminations

 

Slides #123, #92, and #93 Try to find Pacinian corpuscles and Meissner's corpuscles or wait until we do skin. Muscle spindle will be on demonstration.

 

Pacinian Corpuscles (P)

 

 

 

 

 

 

 

Meissner's Corpuscle

 

 

Central Nervous Tissue

Slides #145 & #16, (Spinal Cord). These two slides have been stained differently, #145 is stained for Nissl substance. In other words you will be looking at neuron cell bodies. Orient yourself to ventral and dorsal by remembering that the ventral surface of the cord a prominent fissure extending inward toward the central canal. You should be able to identify the following items: Gray and white matter, ventral motor neurons, and the central canal. You might be able to see where either or both the dorsal and ventral roots come off the cord depending on the section you have. Slide #16 has been stained with silver which stains nerve fibers very well and leaves the cell bodies unstained. Find all the same structures in this slide that you found in #145. See--! You really don't have to depend on colors!!

Slide #144, (Cerebrum). Notice that the white and gray matter locations are reversed in the brain from what they were in the spinal cord. In the brain the gray matter is on the outer surface and the white matter inside. compare these sections with the illustrations in Wheater pp 370-373 (309-315). Look for Pyramidal cells in the Cerebral cortex.

Glial Cells!! We have some demo slides of glia which will be available for examination. Be sure you know the text material on glial cells. Brain tumors are usually GLIAL CELL tumors! Do you know why?

 


 

 

 

HISTOLOGY LAB V - MUSCLE

 

BE ABLE TO IDENTIFY:

A, H, I, and Z-bands
Muscle - skeletal, cardiac, and smooth,
endo-, epi-, and perimysium
intercalated disk
motor end plate (EM only)
Purkinje fiber
sarcomere

 

This lab is devoted to the study of the 3 types of muscle. The first section deals with smooth muscle, found in many places in the body. The slides listed need not limit you. Any slide of any portion of the gut will show two layers of smooth muscle. Look at slides #179 & #180. One layer will be cut in transverse or cross-section and the other in longitudinal section. You should be able to identify smooth muscle in either situation. Another good place to find examples of smooth muscle is around small blood vessels (arterioles and venules) in almost any slide you pick of any organ. Try to identify any epithelial layers you find while looking at these slides. It's a good review exercise.

I. Smooth Muscle (SM - called "Visceral Muscle" in some texts)

 

 

Slide #167 (Smooth Muscle Teased) This slide may be good in some slide boxes and bad in others--trade and share. On this slide, the individual SM cells have been teased apart so you can see their shape. Remember that while all SM cells have the same shape with tapered ends, they may vary considerably in length. Unlike skeletal muscle, each smooth muscle cell has only one centrally located nucleus and the contractile proteins (actin and myosin) are more randomly arranged in the cytoplasm. They do however, manage to contract quite nicely.

 

 

 

 

 

 

 

 

Smooth Muscle in Transverse (Cross) Section - Note that the profiles (cross sections) of the smooth muscle cells vary in size. Nuclei are found in the largest cross sections (Arrows).

 

 

 

 

 

 

 

 

 

 

Slide #30 (lower esophagus showing Smooth Muscle) Notice how Smooth Muscle looks when cut in different planes. Remember that smooth muscle cell profiles vary in diameter in cross-sectioned bundles. What would cause that?

Slide #50 and #70 (Gall Bladder and Uterus) Both of these slides show smooth muscle bundles running in various directions and thus, cut in various planes of section. Try to get used to what smooth muscle looks like in many planes of section.

II. Skeletal Muscle (SKM)

Slide #27 (Striated Muscle in Tongue) There are many profiles of skeletal muscle (SKM) on this slide. Some show the muscle in cross section (A), some in longitudinal section (B). Notice how the muscle cells (fibers) are arranged in bundles, and their profiles are roughly the same diameter. Note also that the cells are multinucleate and the nuclei are located at the periphery (just inside of the sarcolemma) of the cells. Using your Hi-Dry (40X) objective, try to make out bands on the longitudinally sectioned SKM.

 

 

 

 

 

 

 

 

 

Slide #169 (Skeletal Muscle (SKM)) The section on this slide is very thin (1.5 microns) so there is not as much contrast as most others. However, the detail of the muscle banding shows up great. The banding is the result of the regular arrangement of the contractile protein filaments within the SKM cells (FIBERS). Look at this slide with your 40X and oil immersion (100x) objective. Locate the A, I, and Z bands of the muscle sarcomeres. Relate what you see to the sliding filament model of muscle contraction. What is the chemical nature of the A and I bands?


 

 

 

 

 

 

 

 

This is an electron micrograph of a sarcomere of skeletal muscle. Look at the electron micrographs provided in the laboratory an compare them with this image and images in your text.

 

 

 

 

III. Cardiac Muscle

 

 

Slides #55, #56, & #125 (Heart Muscle, Human) Cardiac muscle has striations, but the fibers (cells) are branched (BR), vary in diameter, and have centrally located nuclei (N&NUC). The muscle bundles in the heart run in various directions, so by searching around you should be able to find cross and longitudinal sections. With luck you should see some intercalated discs (ICD) (try focusing up and down). What are they?

 

 

Slide #107 Find the Purkinje Fibers (PF). They don't look like regular cardiac muscle (CM) cells. They are much larger, pale staining, and very different. They have fewer myofibrils (MF) than Cardiac Muscle cells. What do they do? Why do they stain so lightly?

 

 

 

 


 


 

 

HISTOLOGY LAB VI - CARTILAGE, BONE, BONE DEVELOPMENT

 

BE ABLE TO IDENTIFY:

Cartilage
cells-- chondroblast, chondroclast, chondrocyte
cartilage-- hyaline, elastic, fibrous
isogenous group
lacuna
perichondrium
territorial and interterritorial matrix

Bone
canaliculi
canals-- central and Volkmann's
cells-- megakaryocyte, osteoblast, osteoclast, osteocyte, and osteoprogenitor
diaphysis and epiphysis
endosteum and periosteum
Haversian system (osteon)
Howship's lacuna
lacuna
lamellae (circumferential and interstitial)
spicule/trabeculum

 

I. Cartilage

There are three types of cartilage: hyaline, which is the most common, elastic, which looks a lot like hyaline unless it is specially stained for elastic fibers, and fibrous, which is not very common and is difficult to identify.

Slides # 49. You have seen these slides before when studying pseudostratified epith. #48 is a cross section of the trachea, which should exhibit a long piece of hyaline cartilage. These cartilaginous rings circle the trachea and keep it from collapsing. In Slide #49, you see a profile of a number of rings since this is a longitudinal section of the trachea.

The matrix of the cartilage is basophilic and will normally stain blue in most slides. The staining varies, however, and in some of your slides it may appear light purple to pink. Sitting in this clear matrix are lacunae (small lakes) containing the chondrocytes or cartilage cells. The matrix will stain heavier around lacunae. Usually, the lacunae are found in small groups called isogenous groups (same genes). Each isogenous group originated from one chondrocyte that divided a number of times. Notice that there are no blood vessels in cartilage. How do nutrients and O2 reach the chondrocytes? The C.T. immediately adjacent to the cartilage is called perichondrium.

 

Slide #10, (Developing Bone) Another example of hyaline cartilage.

 

 

Slide #8, (Epiglottis) The elastic fibers have been stained dark purple. Elastic cartilage looks a lot like hyaline cartilage unless the elastic fibers in the matrix are specially stained.

 

 

 

 

Slide #53 shows elastic cartilage in the external ear. This slide is not as good as slide #8, but if you close down the iris diaphragm of your condenser, you will see that the matrix is not as smooth as hyaline cartilage matrix. Elastic cartilage is flexible but strong. If you don't believe me, try to yank your ear off.

 

 

 

 

Slide #9 Fibrous cartilage appears to be a transition between dense connective tissue and hyaline cartilage. It is usually not very well demonstrated. Slide #9, is not the same slide in all slide boxes! If the predominant color on your slide is pink, find the hyaline cartilage, then find some dense C.T. In between, you should see a region where there are lacunae surrounded by collagen fibers (pink).

 

 

 

 

 

 

 

If the predominant color on your slide is blue and there are some little red things here and there, then look closely at the red things and you will see that they are lacunae with chondrocytes in them. The blue stuff is collagen. Try to see both types of slide by sharing with others. There will also be demonstration slides.

 

 

 

 

 

 

 

 

 

II. BONE

Bone is tissue. Bones are organs. First, we will look at bone.

Slide #14 is ground bone. All the soft material, cells, collagen, blood vessels, etc. have been removed and you are looking at the mineral part of the bone. However, you can see the lacunae (where the cells were), the Haversian canal (where the blood vessels were), and the canaliculi (where tiny cell processes were). These structures all look black on this slide. Identify these structures and an Haversian system (osteon) made up of the canal, lamellae (L), and the structures listed above. Between osteons are isolated interstitial lamellae. These are remnants of old osteons. Remember that bone is constantly being remodeled. Think about it. Try to envision the process in 3-D. Haversian systems are cylinders.

All bone sections are thick, so focus up and down.

 

 

 

 

 

 

 

 

 

This higher magnification of ground bone shows lacunae and canaliculi. The bone matrix located between the two rows of lacunae is called a lamella and collectively lamellae. The canaliculi located in the lamellae contain protoplasmic processes from the osteocytes that reside in the lacunae. These processes contact one another in the middle of the lamella to allow for transport of nutrients and metabolites from one osteocyte to another. This is how the nutrients get from the Haversian canal to the outer lacunae and the metabolites move in the opposite direction.

 

 

 

 

 

 

Slide #12 is decalcified compact bone. In this slide, all of the minerals have been removed. You should be able to see the osteons, though. The canaliculi are not easily seen, but the Haversian canals with blood vessels and C.T. should be clear, as are the lacunae. The bright red stuff is collagen. There is lots of it in bone. The mineral part of the bone deposits on this collagen. The C.T. right next to the exterior surface of the bone is periosteum by definition (not seen in this image).

 

 

 

 

 

 

 

 

III. Bone Development

Slide #11 Intramembranous bone forms within mesenchymal connective tissue. Osteoblasts, (the bone forming cells) have a basophilic cytoplasm and are found lined up on the surface of brightly stained bone spicules that are forming in the C.T. You also may see a large multinucleate cell with an acidophilic cytoplasm. These are osteoclasts and are responsible for bone resorption and remodeling. They are more likely to be found on slide #10. If you don't see them on #11 don't waste time, look at #10. If you have a slide #22, look there also. Some of these slides are from a developing jaw (mandible) and may include a developing tooth, so, if you see a big weird structure that you cannot identify it is probably a tooth.

 

 

 

 

 

 

Slide #10 (Developing Cartilage Bone) This is the joint of a young developing animal and shows all the stages of bone development from a cartilage precursor (model). This type of bone development is called Endochondral Bone Formation.

 

Find the hyaline cartilage (nearest the joint!) and follow it into the region where the cells begin to proliferate and line up in rows (zone of proliferation). Further along in the process, the chondrocytes and their lacunae enlarge (zone of hypertrophy) and later the cells die and the cartilae cartilage becomes calcified (zone of calcification). This forms the framework upon which the osteoblasts will lay down new bone. Remember, the calcified cartilage is REPLACED by bone, it does not turn into (or become) bone. Color changes that will help you to identify the structures in the various stages are: cartilage matrix (pale blue-grey), calcified cartilage matrix (deep blue), early bone formation (pink), and compact bone (red).

 

 

 

 

 

 

Osteoclasts and chondroclasts look alike and are actively reabsorbing bone and calcified cartilage, respectively, during the process of endochondral bone formation. Don't confuse them with megakaryocytes, which are abundant in the bone marrow and resemble osteoclasts to the unpracticed eye. Osteoclasts have a pink cytoplasm and have more than one nucleus (2-8). Megakaryocytes have clear cytoplasm and only one nucleus. The megakaryocyte nucleus is very large, long and convoluted, so that it can look as if it has multiple nuclei.

 

 

 

 

 

 

 

 

Megakaryocytes are also larger than osteoclasts.

You should recognize osteoblasts by now. When they have surrounded themselves with bone matrix, they are called osteocytes. You will also see many developing and mature red and white blood cells in the marrow cavity.

Look around outside the bone for various connective tissue types (i.e. review C.T). Developing muscle will be found attached (or attaching) to the outside of the developing long bone.

 

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