Histology test 3 review questions

When observing the glial cells in a section of grey matter, you confirm you are looking at an astrocyte. What type of astrocyte is it? How did you come to this conclusion?

- If confirmed correctly that it is an astrocyte it must be a protoplasmic astrocyte becasue you are looking at a grey matter section. Fibrous astrocytes are located in white matter. The functional difference between the two is not known they differ in strcuture. Protoplasmic astrocytes have shorter processes that branch profusely in comparison to the fibrous astrocyte which has thinner and longer processes that have less branching. In addition, while both astrocytes have hardly any organelles present in their processes, fibrous astrocytes have fewer present than protoplasmic.

Explain the histological signs of a nonfatal myocardial infarction and why it appears that way.

-Both hypertrophied and necrotic myofibrils will be present with fibrous connective tissue near the hypertrophied and/or necrotic myofibrils. -The hypertrophied myofibrils are caused from an increased load on the heart typically due to hypertension pathology. The necrotic myofibrils are caused from a decrease in nutrients to the myofibrils due to a blockage of the blood vessels that deliver the nutrients to the muscle. The presence of fibrous CT is a result of only 0.1% of cardiac cells being able to undergo mitosis; therefore, to fill the space left by the resorption of necrotic cardiac tissue, the heart produces fibrous CT.

How can you distinguish histologically between dense regular CT and peripheral nervous tissue?

-In peripheral nervous tissue, the staining is lighter than dense regular CT because of the presence of myelin in nervous tissue which doesn't take up much stain compared to the extensive extracellular matrix found in dense regular CT which takes up a lot of stain. There will also be a higher nucleus:ground substance ratio in nervous tissue than in dense regular CT, and dark lines which are axons and nodes of Ranvier can also be seen in peripheral nerves which will be absent in dense regular CT.

what are the basic steps of SM relaxation?

1. Free Ca in cytosol decreases when Ca is pumped out of the cell or back into the sarcoplasmic reticulum 2. Ca unbinds from CaM 3. Myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity 4. Less myosin ATPase results in decreased muscle tension

What are the basic steps of smooth muscle contraction?

1. Stimulation of VG ion channels or mechanically gated (stretch), RyR channel opening in SR, or IP3 channel opening - all allows calcium in (a lot of it) 2. Calcium binds to calmodulin (CaM) 3. Activates myosin light chain kinase (MLCK) 4. MLCK phosphorylates light chain in myosin heads and increase myosin ATPase activity 5. Active myosin heads create cross bridges and contraction (muscle tension) occurs

Briefly describe the components of the sacromere and what happens to each during contraction.

1. Z-disk = attachment/anchoring site of aactin filaments; during contraction, the distance becomes closer to the A band. 2. A-band = contains mostly thick filaments with some amounts of thin filaments; during contraction, the length does not change. 3. I-band = contains only thin filaments and surrounds the Z-disk; during contraction, the length shortens. 4. H-zone = contains only thick filaments and no actin; during contraction, the H zone shorten. 5. M-line = attachment site for thick filaments and bisectes A band; during contraction, the M-line doesn't change

Distinguish histologically between a muscle fiber, myofibril, and a motor unit.

A muscle fiber can also be identified as a muscle cell. It is a multinucleated cell with visible striations, and its nuclei are located just underneath the sarcolemma, which is the plama membrane of the cell. Muscle fibers contain bundles of longitudinally arrayed myofibrils. These are the structural and functional subunit of the muscle cell. Myofibrils contain bundles of myofilaments, which are the contractile units of muscles. The bundles of myofilaments are surrounded by the sarcoplasmic reticulum. Finally, a motor unit is the combination of a neuron along with the muscle fibers it innervates.

What would one see looking at a neuromuscular junction in EM?

The most notable thing would be the presence of the junctional folds of the muscle cell in the synaptic cleft. The axon may also be surrounded by a Schwann cell and myelinated. One would also see a large number of mitochondria and synaptic vesicles, which would be holding acetylcholine.

Explain the role of an intercalated disc and its appearance under Light microscopy and TEM.

An intercalated disc represents the attachment site between cardiac muscles cells. In light microscopy the intercalated discs appear like densely stained linear structures. In TEM the transverse and lateral components of the disc are visible. The major constituent in the transverse component are Fascia adherens and Gap junctions are the major constituents in the lateral component. Desmosomes are found in both the lateral and transverse component.

List some histological differences between arteries, veins, and capillaries.

Arteries have a much thicker tunica media leading to a narrower lumen. Veins have a larger lumen, but a thinner tunica media. The thickest layer of a vein is the tunica adventitia. In veins, the tunica intima is likely folded to form valves. Capillaries are made up of only endothelium and is only wide enough to allow one red blood cell to pass.

Describe the four types of central neuroglia.

Astrocytes: morphologically heterogeneous cells that provides physical and metabolic support for neurons of the CNS Oligodendrocytes: small cells that are active in the formation and maintenance of myelin in the CNS Microglia: inconspicuous cells with small, dark, elongated nuclei that possess phagocytotic properties. They normally account for about 5% of all glial cells in the adult CNS. Ependymal cells: columnar cells that line the ventricles of the brain and the central canal of the spinal cord. They form a single layer of cells that have the the morphologic and physiologic characteristics of fluid-transporting cells.

Explain the path of blood flow through the heart (include major valves involed, arteries, and veins).

Blood enters through the right atrium from the superior and inferior vena cavae. It flows through the atrioventricular valve into the right ventricle, and contraction of the right ventricle (due to mainly the Purkinje fibers at the apex of the heart) pushes blood through the pulmonary valve opening it. From here, blood flows into the pulmonary trunk. Once blood is in the pulmonary trunk, it is distributed by right and left pulmonary arteries to the lungs. At the lungs, CO2 and O2 are exchanged (CO2 "leaves" the RBC, and O2 "gets on" the RBC). Now, blood returns from the lungs via the pulmonary veins to the left atrium. Blood flows into the left atrium, through the left atrioventicular valve, and into the left ventricle. Contraction in the left ventricle via Purkinje fibers forces the aortic valve to open. Blood flows out of this valve into the ascending aorta. From here, the blood in the aorta is distributed to every organ in the body (CO2/O2 exchange happens again at this site). The cycle repeats when blood is returned to the heart via the vena cavae.

What are the structural components of blood vessels and their histological characteristics?

Blood vessels are composed of 3 layers that are modified according to the vessel's function. From innermost to outermost, they are the tunica intima, tunica media, and tunica adventitia. The tunica intima is a simple squamous endothelium supported by a thin layer of CT. In some vessels such as arteries, an internal elastic lamina is also present at the junction with the tunica media. The tunica media is composed of varying amounts of smooth muscle and elastic CT oriented circularly around the vessel. In larger arteries, there may be an external elastic lamina or membrane at the junction with the tunica adventitia. The tunica adventitia is composed of fibrous CT that often blends with surrounding CT, making the outer limit of the vessel difficult to see.

When viewing a heart section, you can easily identify the myocardium, but are having trouble distinguishing between the epicardium and endocardium. What are some key histological differences you should search for?

Both display a simple squamous layer and supportive CT, making them hard to dealinate. However, the endocardium, specifically within the subendocardial layer (the layer nearest the myocardium), can contain Purkinje fibers if the section was taken from either ventricle. Purkinje fibers appear lighter staining, almost bubbly (due to being larger and dilated), and are often binucleate. Their strange appearance makes them stick out, so noticing them confidentally places one in the enodcardium. Even without the presence of Purkinje fibers, the endocardium appears to have raised ridges, called trabeculae carrea (if in ventricles) or pecntinate muscle (if in atria). These ridges do not appear in the epicardium. Finally, epicardium typically harbors adipose tissue, while the endocardium would not (at least in any noticeable amounts).

Explain the histological difference in appearance and functional differences between the three types of capillaries:

Continuous: No fenestrae present tight junctions prevent very little leakage occurs and allows regulated material exchange. In TEM they appear to be in cross-sections. Fenestrated: In TEM small circular holes called fenestrae are present and visible. It allows more molecular exchange across the endothelium to occur. Found in (kidney, intestine and endocrine glands). Sinusoid (discontinuous): Under TEM fenestrae can be observed as well as a discontinuous basal lamina and a lack of pinocytotic vesicles. The capillaries appear to have large holes under TEM. Allow the exchange of macromolecules as well as cells between tissue and blood. (liver, spleen, and some endocrine glands)

What role does dystrophin play in a properly functioning sarcomere, and what would likely occur if it was absent or otherwise defunct?

Dystrophin attaches the actin of the Z-line to the sarcolemma via laminins, as well as sarcoglycans and destroglycans, which are integral membrane proteins capable of signal transduction. It essentially attaches the sarcomere to the sarcolemma; consequently, muscle cells can maintain proper shape since the sarcolemma is not deformable during muscle contraction. Without dystrophin, the sarcomere cannot properly attach to the sarcolemma, so the muscle cells eventually lose their mechanical strength and die. As a result, one would experience extreme muscular fatigue and the inability to maintain skeletal muscle stiffness. Additionally, cell signaling would be disrupted since dystrophin links to the sarcoglycans and destroglycans in the sarcolemma.

What are the main components of a neuron and their function?

Each neuron has a cell body (or soma) that contains a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components. The cell body connects to the dendrites and the axon. It receives a signal from dendrites and then relays that signal to the axon. Dendrites are branch-like structures extending away from the cell body, and their job is to receive messages from other neurons and allow those messages to travel to the cell body. An axon is a tube-like structure that carries an electrical impulse from the cell body to the structures at opposite end of the neuron (axon terminals), which can then pass the impulse to another neuron. The cell body contains a specialized structure, the axon hillock, which serves as a junction between the cell body and the axon. The synapse is the chemical junction between the axon terminals of one neuron and the dendrites of the next. It is a gap where specialized chemical interactions can occur, rather than an actual structure.

Describe the Histological features of an Elastic Artery.

Elastic arteries are the largest arteries. They contain high amounts of elastic fibers within all three layers of their walls inorder to compensate for the pressure alterations that occur due to high pressure from ventricles pumping blood into their lumina and low pressure due to emptying in chambers of the heart. The layer which lines the lumina is called the tunica intima which is composed of a endothelium, subendothelial and internal elastic lamina layer this layer is thin compared to the other two layers of the artery wall. The next layer out from the tunica intima is the tunica media which is very thick. Tunica media is composed of smooth muscle and concentrically arranged elastic laminae. The outer layer is the tunica adventitia which is thinner than the tunica media but thicker than the tunica intima.the tunica adentitia is composed of collagenous connective tissue, fibroblast, elastic fibers, smooth muscle cells and vasa vasorum.

Give the histological features of the 3 layers of the heart.

Endocardium = single layer of squamous endothelial cells on a thin layer of loose connective tissue, also contains some smooth muscle cells, and also elastic and collagen fibers. Myocardium = flatten cells that are within loose endomysial connective tissue, contains cardiac muscle fibers and capillaries Epicardium = simple squamous epithelium supported by connective tissues, contains nerves, veins, lymphatics, and adipocytes

How and why do ventricles differ histologically from atria?

For starters, Purkinje fibers are localized in the ventricles rather than the atria. These fibers help the heart's conduction system create synchronized contractions that maintain the heart rhythm. The myocardium component of the ventricles is also much more prominent than in the atrium. Both are characteristic of the ventricles because the ventricles are responsible for pumping blood through the pulmonary and systemic circulations, whereas the atria receive blood from large veins and dump it into the ventricles, a low pressure process. It is important for the ventricles to be innervated and very muscular in order to generate higher pressure required for pumping the blood.

What are specific histological characteristics of the dorsal root ganglion that you may note under the light microscope?

In the dorsal root ganglion, the cell bodies and nucleus of pseudounipolar neurons would be visible. Immediately surrounding the cluster would be satellite cells, as well. Towards the periphery of the slide would be nerve fibers running longitudinally, and these axons may be quite clear. The cell bodies tend to look as if it is along a "bump" in the DRG, with the axons flowing underneath. At the edge of the ganglion, connective tissue may also be noted.

Describe the histology of intercalated discs in both EM and light microscopy.

LM: dark transverse band EM: transverse component (right angle to myofibrils) which contain desmosomes and adherens junctions lateral component (parallel to myofibrils) contain gap junctions

Describe the different layers of the cerebral cortex

Molecular layer - Can also be called the plexiform layer - Mostly where you have neuroglial cells - Dendrites and end of processes of the lower layers External granular layer - Where you find the small pyramidal cells - Pretty dense in terms of distribution of cells External pyramidal cell layer - Medium pyramidal cells - Layer tends to be thicker - Really dense in number of nuclei present Internal granular layer - Lots of granular cells - Small and dense Ganglionic layer - Internal pyramidal layer - Large pyramidal cells Multiform cell layer - Diverse shapes of cells here

What are lymphatic vessels? Describe them structurally and functionally.

Lymphatic vessels bring fluids from the tissues to the bloodstream, serving as adjuncts to the blood vessels. They are unidirectional. The smallest of these capillaries are especially common throughout loose connective tissues under the epithelium of skin and mucous membranes; they converge into larger vessels known as lymphatic vessels. Capillaries remove protein-rich fluids from the intracellular spaces, and they also take up inflammatory molecules, dietary lipids, and immune cells. This fluid becomes the "lymph" as it passes through lymph vessels and nodes. When passing through lymph nodes, lymph is exposed to immune cells. The lymphatic capillaries are endothelial tubes that lack a basal lamina, which allows for their high permeability. Anchoring filaments extend between the incomplete basal lamina and the perivascular collagen. In order to prevent any backflow, lymphatic vessels also posses valves. The lymph moves in one direction and slowly; the movement is driven by compression of the vessels from skeletal muscles as well as from the contraction of a smooth muscle layer that surrounds the vessels.

Briefly explain the difference between myelinated and unmyelinated nerves.

Myelinated axons have their nerve processes surrounded by myelin sheath that are produced by Schwann cells while unmyelinated axons have their nerve processes enveloped in the membrane and cytoplasm of Schwann cells. Myelinated axons have fast nerve impulses that require a fewer number of ATP and have nerve impulses jump from node to node in a process of saltatory conduction while unmyelinated axons have slow impulses due to the nerve impulse having to travel the entire length of the axon in a continuous wave in a process called continuous conduction.

Describe the structural organization of a myofibril.

Myofibrils are made up of bundles of myofilaments, which are polymers of myosin II protein and actin protein. Myosin II molecules come together to form thick filaments and actin molecules form think filaments. The thick and thin filaments are arranged in a staggered manner, which gives the myofibril a cross-striated appearance. They have the primary duty of muscle cell contraction. The myofilaments that form the myofibril are surrounded by the sarcoplasmic reticulum.

Explain the major differences between single unit-SM and multi-unit SM.

Single-unit SM cells are connected electrically via gap junctions, while multi-unit SM cells are not linked electrically, they are individual cells. The neuron varicosity that innervate the smooth muscle cells is found on the "outside of" the single-unit SM. When the neuron releases its NT, it attaches to receptors on the outside of the SM layer, sending a signal into one cell, eventually leading to all of the muscle cells contracting simultaneously. In a multi-unit SM, the cells are not electrically linked, therefore they have neurons running between the cells, innervating each of the muscle cells individually.

What are the main proteins that are found to help aid in Schwann cells sticking to axons so tightly?

Nrg-1 (neuroegulin-1) helps aid in sticking the Schwann cells directly to the axon of a neuron. Other proteins such as P0 and MBP are charged proteins found in the cytoplasm that create a strong bond to the negatively charged phospholipid head groups, ultimately creating a major dense line that appears dark when viewing histologically. The extracellular space creates an intraperiod line, which appears lighter when viewing histologically. PMP22 is an integral protein that also helps to aid in sticking the layers of the myelin together.

Histologically differentiate purkinje fibers from cardiomyocytes.

Purkinje fibers are located in the subendocardium located above the myocardium in the ventricles. Purkinje fibers are larger in size and stain lighter than cardiomyocytes. They take up stain differently becasue there are fewer myofibrils in purkinje fibers becasue they transport electrical signals. In addition, the bulk of the sarcoplasm is glycogen which in most histological preperation is not preserved which yields their empty appearance. In TEM purkinje fibers would have a larger number of mitochondria than cardiaomyocytes so that they can conduct electrical impulses through the heart.

Explain what Purkinje fibers, and describe them histologically.

Purkinje fibers are muscle fibers found in bundles along the ventricle wall. They are specifically found in the subendocardial layer of the endocardium, associated with irregularly arranged connective tissue, blood vessels and adipocytes that separate the Purkinje fibers from the myocardium. Cardiac muscle fibers tend to be stained darker than Purkinje fibers. In cross-sectioned fibers, the myofibrils are seen at the periphery of the cell; the cytoplasm appears as if it were unstained. Nuclei are clearly visible. Intercalated discs can be seen in longitudinally sectioned fibers. Purkinje fibers are specialized conducting cells within the ventricles. These fibers are larger and contain more glycogen than cardiac muscle cells. These fibers conduct impulses from the AV node along the ventricular septum and into the ventricular walls, and they are responsible for the final distribution of the electrical stimulus to the myocardium.

Describe the function and histological characteristics of satellite cells:

Satellite cells are small cells that can blend in with the muscle sacroplasm. They are found between the sarcolemma and external lamina in skeletal muscle. In a transverse section, they surround muscle fibers. They are responsible for the generative capacity of muscle, yet still have limitations in this capacity.

When viewing a slide of a dorsal root ganglion, you notice many eosinophilic cuboidal cells forming a layer around the soma of ganglia. These cells do not seem to be pathologic. You also do not see any myelination occurring. What are they, and what is their likely function?

Since there is no noticeable pathologic effect stemming from these cells, these are likely satellite cells. Satellite cells are cuboidal and stain eosinophilicly in H&E. They tend to surround the soma of ganglia to provide support via controlling the microenvironment as well as metabolic exchanges. These cells do not myelinate, which explains the absence of myelin in the slide.

Compare and contrast small, medium, and large veins.

Small veins have a diameter of about 0.1 to 1mm. Medium veins have a diamter as much as 10mm. Large veins have a diameter greater than 10mm. All three types of veins contain all three tunics, but the thickness of each varies. For instance, the tunica adventitia of large veins is the thickest layer of the vessel wall. Also, as the size of the vein increases, the components of each layer start to contain more parts. For instance, the tunica adventitia of medium veins contains collagen fibers and elastic fibers, whereas the tunica adventitia of large veins contains those same things, but also contains smooth muscle cells and vasa vasorum

Name three structural differences between smooth and skeletal muscle.

Smooth muscle contains only a endomysium sheath composed of reticular fibers that surround individual muscle fibers where as skeletal muscle contains epimysium which surrounds the entire muscle and is composed of fibrous elastic tissue, a perimysium which is a thicker sheath of connective tissue which surrounds groups of muscle fibers to form muscle fasicles and a endomysium which is composed of reticular fibers and surrounds individual muscle fibers. Smooth muscle contain caveolae for regulating contraction. Caveolae function to sequester calcium due to lower amounts of sarcoplamsic reticulum within smooth muscle. Skeletal muscle on the other hand contains a T-tubule system to regulate contraction. Smooth muscle has longer actin and myosin filaments and lacks striations unlike skeletal muscle which has shorter actin and myosin filaments and is heavily striated due to presences of the contractile unit sarcomere.

Describe some characteristics of smooth muscle

Smooth muscle is found predominantly in walls of hollow organs and tubes. In a smooth muscle twitch, contraction and relaxation occur more slowly than skeletal muscle. Smooth muscle uses less energy to generate a given amount of force and can maintain force for long periods. It has low O2 consumption rates yet can sustain contractions without fatiguing. Smooth muscle lacks striations and has less organized contractile fibers than skeletal muscle. It is involuntary and is controlled by the autonomic nervous system and hormones. Smooth muscle also has only one central nucleus and lacks specialized motor end plates. Moreover, gap junctions connect the cells in smooth muscle.

You are looking at a slide you believe to be a section from the ventricle of the heart, what histological elements would confirm this?

The biggest histological aspect that is present in the ventricles are purkinje fibers. These modified cardiac cells are present in the ventricles to help conduct the electrical impulses through the heart.These fibers are found between the endocardium and myocardium. and appear larger than normal cardiac muscle, stain lighter than cardiac muscle, and often times Purkinje fibers have 2 nuclei present as well.

What is the blood-brain barrier? What are its components and histological characteristics?

The blood-brain barrier protects the central nervous system from fluctuating levels of electrolytes, hormones, and tissue metabolites circulating in the blood vessels. It is primarily composed of endothelial cells with tight junctions between these cells, which are visible throughout TEM. TEM also suggests that there strong ties between the barrier and astrocytes, and these astrocytes' foot processes are associated with the endothelial basal lamina. This prevents simple diffusion of solutes and fluid into the neural tissue. Astrocytes release soluble factors that increase the barrier's properties and tight junction protein junction.

Name the two accessory proteins of the sarcomere and describe the functions of these proteins.

Titin is a huge, elastic molecule that stretches one Z disk to the neighboring M line during muscle contraction. It functions to stabilize the position of the contractile filament, anchors the thick filament to the Z disc, and the elasticity returns the stretched muscle to its resting length. Nebulin is a giant, inelastic protein that lies alongside the thin filament and attaches to the Z disc. It functions to align the actin filament on the sarcomere.

Explain the basic histology of the heart valves.

The core, fibrosa, is made up of dense irregular CT. Spongiosa, made up of CT that has more elastic fibers and GAGs, lines both sides. The outermost layer of atria ventricular valves, atrialis and ventricularis, are composed primarily of elastin. The base of the valves are attached to strong fibrous rings.

What are the 3 layers of CT in the brain and describe their location and function.

The three layers (outermost to innermost) are the dura mater, the arachnoid, and the pia mater. The dura mater is a thick layer of CT that is continuous with the periosteum of the skull. The dura mater contains venous sinuses lined by endothelium which are channels to bring blood from the brain to the heart. The arachnoid lies on the inner layer of the dura mater and has extensions called arachnoid trabeculae to the pia mater. The space which contains the trabeculae also contains CSF and is called the subarachnoid space. The pia mater is the innermost layer and is a very delicate layer of CT. It lies directly on the brain and is continuous with the perivascular CT sheath of blood vessels in the brain.

Explain the difference in size between the tunica mediae in arteries and veins.

The tunica media is larger in arteries than in veins because arteries play a larger role in maintaing blood pressure homeostasis than veins do. Veins function more to hold a volume of blood than to control the systemic blood pressure. In order to maintain blood pressure, arteries require a lot of concentric and longitudinal smooth muscle that can contract and relax depending on the needed reaction for blood pressure homeostasis. The enlarged tunica media in arteries is indicative of the presence of a lot of smooth muscle. This, on the contrary, is not necessary in the tunica media of veins.

Explain what the vasa vasorum is and why it is necessary.

The vasa vasorum is the a network of small blood vessels that have the function of removing waste products from the larger vessels and to transport oxygen and nutrients to the larger vessels. The network contains small arteries that enter the vascular wall of the large vessel and then divide into a network of arterioles and capillaries that supply the outer portion of the vascular wall. The vasa vasorum contains small veins that drain the capillaries and venules into larger veins. The inner part of the vascular wall is supplied by diffusion of nutrients from the lumen.

If you are looking at a slide of a myocardial infarction how would you know what it was based on the histological structure?

There are multiple stages of MI. The first stage being tissue death in which neutrophils are present. After roughly 3 days lymphocytes come into the area of the infarction. These lymphocytes will "eat" away the dead cells leaving empty spaces where they once were. Ultimately this fibrous space will be filled with scar tissue containing fibrous CT and no cardiac myocytes.

When observing smooth muscle in TEM bulb-like structures attached to the sarcolemma can be seen. What are they? What is their function?

These invaginations are caveloae. When attached to the sarcolemma they concentrate Ca2+ which is pivitol to smooth muscle contraction. The sarcoplasmic reticulum in SM is not as developed as in skeletal so caveolae are used to sequester Ca. They release the Ca2+ into the cell which then binds to calmodulin to activate the MLCK which phosphorylates the myosin head group. Crossbridges are formed to initiate the power stroke.

You see a fenestrated capillary present in the kidney. What is it, and how can you tell?

These types of capillaries are found in tissues where rapid interchange of substances occurs, such as the kidney, intestine, or endocrine glands. The arrows point to fenestrations, which allow for the rapid exchange. Other structural elements that can be used to identify this vessel are the endothelial cell nuclei and thin endothelial layer. Furthermore, only one red blood cell is present in this vessel, further confirming that it is a capillary.

This structure is present in the nervous system. What is it, and how can you tell? describe synapse

This EM micrograph exhibits a synapse. One way to correcly determine this structure is by looking at the small, circular strucutres that predominate in the image. These are synaptic vesicles containing neurotransmitters, which are released due in large part to an influx of calcium. Another way to determine that this structure is a synapse is by locating the electron dense area below the synaptic vesicles. This area is the synaptic cleft, which is where neurotransmitter is released and travels to bind receptors on the post-synaptic cell.

Name and describe three thin filament-associated proteins.

Tropomyosin- protein that consists of a double helix of two polypeptides. It forms filaments that run in the groove between F-actin molecules in the thin filament. In resting muscle, tropomyosin and its regulatory protein, the troponin complex, mask the myosin-binding site on the actin molecule. Troponin- complex of three globular subunits containing a troponin complex: Troponin-C, Troponin-T, and Tropnin-I. TnC binds Ca2+. TnT bind to tropmoyosin, achoring the complex. TnI binds to actin, inhibiting actin-myosin interaction. Tropmodulin- actin-binding protein that is attached to the negative end of the thin filament. It maintains and regulates the length of the actin filament in the sarcomere.

Explain the difference in appearance between myelinated and unmyelinated axons in EM.

When cut in a cross section, using an electron microscope the myelinated axons in the PNS appears clear with neurofilaments and neurotubules inside which appear dotted. Mitochondria within the axon are also visible. Surrounding the axon is a dark myelin sheath which appears to be multi-layered. A singular schwann cell can be seen in association with the axon. Unmyelinated axons when observed by TEM are much smaller than myelinated axons. They have single layered schwann cell sheath (say that 3x fast). The neurofilaments and neurotubules are still present as well as the mitochondria.

Describe the different layers of the nerve connective tissue wrappings as they would be seen in a c.s. under a microscope.

When looking at a cross-sectioned slide, you would be able to histologically identify the endoneurium as the loose connective tissue that wraps around a single axon (if looking at EM slide, because endoneurium is not identifiable in LM). (You would be able to identify the axon in c.s. because they look like tiny, black dots enclosed within a larger circle.) Also within the endoneurium are readily apparent collagen fibrils, fibroblasts, and endothelial cells, such as macrophages, capillaries, and mast cells. The endoneurium layer is poorly vascularized so you will not see blood vessels in this layer. In order to identify the perineurium, you would have to look for a specialized CT layer surrounding individual nerve fascicles. The perineurium layer is one or more cell layers thick, and the cells that compose this layer are squamous. Also within the perineurium are tight junctions used to provide the basis for the blood-nerve barrier. The next layer, most outer layer, the epinuerium, is a dense irregular tissue covering that surrounds the entire peripheral nerve . Histologically, it is difficult to tell the difference between the perineurium and the epineurium, but one thing you should be Able to identify is the space between the two layers, the myelin space. Adipose tissue is often associated with the epineurium layer, as well as larger nerve supply. These large blood vessels and nerves travel into the epineurium and branch and penetrate the perineurium.

Your friend is determined to check out some myelination in nervous tissue. He prepares a H&E stain, and goes to work with the light microscope. Explain to your friend why he might struggle seeing myelination, and offer alternative methods for better viewing.

While your friend's method might be useful to see some structures in nervous tissue (i.e. nuclei) , using H&E is not the best stain to view myelination of nerves because myelin is very hydrophobic, due to its high lipid content. Thus, myelin sheath will appear clear while using H&E. Osmium tetroxide would be much better suited for your friend's observation. Osmium tetroxide binds strongly to lipids, so myleniated nerve fibers will react strongly and appear much more visible than in H&E.

Give three facts about astrocytes: one function, one histological, one extra.

help form the BBB starlike shape contain GFAP others: most abundant glial cell in the CNS regulate tissue fluid composition fibrous