Histology Exam 2: Smith Lecture 5 (Muscle)

Transcription

1 Histology Exam 2: Smith Lecture 5 (Muscle) What are the three types of muscle? Skeletal: morphology and functionality? Cardiac: morphology and functionality? Smooth: morphology and functionality? Skeletal muscles are innervated by what type of neurons? Cardiac and smooth muscles are innervated by what type of neurons? What are the three types of connective tissue found in muscles? What is their function? What are the three types of skeletal muscle cells? Can all three types be present in a single muscle? What can change a fiber's type? 1. skeletal 2. cardiac 3. smooth -striated -voluntary -striated -involuntary -non-striated -involuntary -somatic motor neurons -visceral motor neurons 1. epimysium: surrounds and entire muscle 2. perimysium: surrounds fascicles 3. endomysium: surrounds individual muscle cells 1. red (slow) 2. white (fast) 3. intermediate -yes -a change in innervation Page 1

2 Explain. Describe the general shape of skeletal muscle cells. What are they enveloped by? What is their cytoplasm called? What is their plasmalemma called? What does the sarcolemma form? What does every muscle cell possess? What are myofibrils? What features are found within every myofibril? -if a red fiber is denervated and its innervation replaced with that of a white fiber, the red fiber will become a white fiber -long -cylindrical -multinucleated -endomysium -sarcoplasm -sarcolemma -deep tubular invaginations called transverse (T) tubules -myofibrils -longitudinally arranged, cylindrical bundles of thick and thin myofilaments -Z disk -H band -I band -A band -M lines What do A bands contain? -actin/thin and myosin/thick filaments that overlap and interdigitate What do I bands contain? -actin/thin filaments only What do H bands contain? -myosin/thick filaments only Where is it found? Where are M lines found? What are Z disks? What is found between two Z disks? -in between the A band -at the center of H bands -dense regions bisecting each I band -a sarcomere Page 2

3 What is the sarcomere? What modified smooth ER is found in muscle cells? -the functional unit of contraction in skeletal muscle -the sarcoplasmic reticulum (SR) What is the role of the SR? -regulates muscle contraction by sequestering calcium ions (relaxation) or releasing calcium ions (leading to contraction) What special SR formations are found in muscle? Where are these located? What are triads? Where are they found? What is their role? What specialized regenerative cells are found within skeletal muscle? What is their role when damage to muscle takes place? What specialized anchoring proteins are found within myofibrils? What is the role of alphaactinin? What is the role of desmin? How are peripherally located Z discs anchored -dilated pairs of terminal cisternae -surrounding the myofibrils at the junction of each A and I band -specialized complexes consisting of a narrow central T tubule flanked on each side by terminal cisternae of the SR -at the A-I junction in mammalian skeletal muscle cells -help provide uniform contraction throughout the muscle cell -satellite cells -differentiate, fuse with one another, and form skeletal muscle cells when the need arises -alpha-actinin -nebulin -desmin -vinculin -titin -binds Z discs to thin/actin filaments with the assistance of nebulin -anchors myofibrils together at Z disks -by vinculin Page 3

4 to the sarcolemma? What is the role of titin? What are thin filaments composed of? What does each G-actin monomer possess? F-actin exhibits one very important feature. Explain what this is. Describe the overall structure of tropomyosin? Where is it found? What is troponin associated with? How many subunits does it possess? What is the function of each? One subunit possess what important binding sites? What is myosin composed of? What feature is notable on the heavy chains? Summarize the overall organization of skeletal muscle. What attached muscle to -connects the Z disk to the M line (to which myosin filaments are anchored) -F-actin -tropomyosin -troponin -associated proteins -an active site that can interact with myosin -polarity: each has a plus and minus end -two-stranded alpha-helical coiled coil protein -it is located in the grooves of the F-actin helix -each tropomyosin molecule 1. TnT: binds troponin complex to tropomyosin 2. TNC: possesses four binding sites for calcium 3. TnI: binds to actin, covers its active site -One subunit (TnC) possesses four binding sites for c -two identical heavy chains -two light chains -a globular head -myofibrils fill muscle fibers/cells -muscle fibers/cells are bundled into sub-fascicles -sub-fascicles are bundled into fascicles -fascicles form muscle -tendon Page 4

5 bone? What is skeletal muscle formed by? What are satellite cells? Describe the innervation of muscle cells. Where are the nuclei of mature muscle cells located? Skeletal muscle fiber types. What model is used to explain the contraction of skeletal muscle? What are the major tenets of the model? Outline the initiation of contraction. In the resting state, how are actin and myosin positioned? Describe the conformational change that results from calcium -the fusion of a large number of myoblasts -residual myoblasts in mature muscle -each muscle fiber is connected to a single nerve -at the periphery -memorize chart -the sliding filament model 1. during contraction, thick and thin filaments do not shorten but increase their overlap 2. thin filaments slide past thick filaments and penetrate more deeply into the A band, which remains constant in length 3. I bands and H bands shorten as Z disks are drawn closer together -neurons release NT, which bind to receptors on the muscle cell -sodium channels on muscle cell open up, leading to depolarization -T-tubules carry wave of depolarization to the myofibrils -dihydropyridine (DHP) receptors alter their conformation -ryanodine receptors are mechanically linked to DHP receptors, which causes a change in their conformation -ryanodine receptors mediate the release of calcium from the SR -myosin binding sites on actin filaments are partially covered by tropomysoin -troponin I is also bound to actin and hinders myosin-actin interaction -calcium binds to troponin C -this breaks the troponin-actin bond -tropomyosin shifts its position slightly and uncovers the myosin Page 5

6 binding. What type of protein is responsible for removing calcium from the cytosol when contraction is no longer required? Outline the contraction cycle in muscle cells. What actually results in muscle contraction? Most muscles are composed of what percentage red/slow twitch fibers vs. white/fast twitch fibers. This results in what type of pattern in slides. When is a checkerboard pattern not present? Explain why this occurs. binding sites (now in active state) -a calcium-atpase pump in the SR 1. ATP binds to myosin and is hydrolyzed by ATPase into ADP and phosphate. The energy released by this process activates the myosin head and cocks it into a high-energy, extended position. 2. The cocked myosin head binds to a newly exposed active site on the thin filament, generating a cross-bridge between actin and myosin. 3. Myosin releases the ADP and phosphate and returns to a lowenergy position, pulling the thin filament along, and this movement is called a power stroke. 4. The binding of ATP destabilizes the myosin-actin bond, allowing myosin to detach from actin. -the collective bending of numerous myosin heads, all in the same direction -most are a "checkerboard" pattern -when a patient suffers from a neuro-muscular degenerative conditions -some diseases result in successive rounds of denervation and reinnervation -when a muscle become denervated, a neighboring neuron can sprout new fibers and re-innervate this fiber Page 6

7 -this muscle can be converted from a slow twitch fiber to a fast twitch fiber or vice versa What causes duchenne muscular dystrophy? What type of protein is dystrophin? Where is it normally present? What its role? What is the inheritance pattern of this disease? What is the main impact of this disease? Main symptoms? What does a slide that shows duchenne muscular dystrophy feature? What do these features reveal? What structure functions as stretch receptor in skeletal muscles? What is the muscle spindle bounded by? What does the external capsule enclose? What type of muscle fibers are these? -the inability synthesize dystrophin -an actin binding protein -in small amounts within the sarcolemma -it acts as a link between the cytoskeleton and the extracellular matrix -X-linked -skeletal muscle fibers undergo necrosis and are ultimately replaced with adipose and connective tissue -muscle weakness -fatigue -centrally placed nuclei: fibers are immature (satellite cells have just replaced a necrotic fiber) -many nuclei of macrophages: macrophages are degrading necrotic fibers -abnormally high amount of connective tissue: some CT replaces regions where muscle fibers have been degraded -the muscle spindle -a connective tissue capsule known as the "external capsule" -a fluid-filled periaxial space and 8-10 modified skeletal muscle fibers -"intrafusal fibers" Page 7

8 What surrounds the muscle spindle? What two types of intrafusal fibers are found within the muscle spindle? Each fiber receives what two types of innervation? What does the muscle spindle detect? Which fibers actually "record" the rate and duration of the stretching? -normal skeletal muscle fibers/extrafusal fibers 1. nuclear bag fiber 2. nuclear chain fiber 1. group II sensory fibers (afferent) 2. static gamma motor neuron (efferent) -the rate and duration of stretching -the group II sensory fibers What records contraction? -nothing, the body is unable to detect muscle contraction What must be done when your muscle contracts? How is it re-set? How are cardiac muscle cells stimulated to contract? What general shape are cardiac muscle cells? How many nuclei do cardiac muscles have? In what part of the cell are the nuclei found? What type of granules do cardiac muscle cells contain? Do cardiac muscle cells regenerate? -muscle spindle must be re-set -alpha motor neurons tell the gamma static neurons that contraction has occurred, group II sensory fibers are re-set -they aren't, they contract spontaneously -branched -one, occasionally two, nuclei -they are centrally placed -glycogen granules -no Page 8

9 How are injuries to cardiac muscle repaired? Describe the diameter of cardiac muscle cells in cross section. What type of junctions connect adjacent cardiac muscle cells? What general shape are they? What three specializations are found at the transverse portions of the intercalated disks? In some places, the fasciae adherenes serves as a substitute for the...? As such, what is connected to the fasciae adherens? What three specializations are found within the lateral portion of intercalated disks? What do gap junctions facilitate? What do desmosomes facilitate? Thus, cardiac muscle behaves as...? What specialized cardiac -by the formation of fibrous connective (scar) tissue by fibroblasts -see wide range of diameters -due to all of the branching that is going on -intercalated disks -step-like -fasciae adherens -desmosomes -gap junctions -Z-line -actin filaments -desmosomes -numerous large gap junctions -ionic coupling between cells -aid in coordinating contraction -functional syncytium -purkinje fibers Page 9

10 muscle cells are located in the bundle of his? What are they specialized for? Where are the smallest cardiomyocytes found? Where are purkinje fibers found? Do purkinje fibers contain many myofibrils? What is the interior of most purkinje fiber cells filled with? What are the implications of this in terms of staining? What type of granules are found within atrial cardiac muscle cells? What do they contain? What is the role of atrial natriuretic peptide? What impact does this have on blood pressure? What is the general shape of smooth muscle cells? How many nuclei do they contain? Do they actively divide and regenerate? Smooth muscle fibers are surrounded by? -conduction -within the SA node -->the smallest fibers beat the fastest -run from the AV node down the interventricular septum and invade the walls of the two ventricles -no, they do not: they are specialized for conduction -glycogen and mitochondria -don't stain well with H&E -atrial granules -the precursor of atrial natriuretic peptide -increases sodium excretion -relaxes smooth muscle -lowers blood pressure -fusiform -only one -yes, they do -endomysium Page 10

11 And are organized into...? These fascicles are arranged into what type of arrays? Within cross sections, can you always see the nucleus of a smooth muscle cell? Explain. Where is smooth muscle found? What three types of filaments are found in smooth muscle? Are the contractile filaments organized into myofibrils? How then are they organized? What are these densities known as? These are the equivalent of what structures in skeletal muscle? Where are the intermediate filaments found? What facilitates the spread of excitation within smooth muscle cells? -fasicles -orthogonal arrays -no, you cannot, due to the orthogonal arrays of the fascicles -in walls of hollow viscera -in walls of blood vessels -in ducts of some glands -myosin/thick filaments -actin/thin filaments -intermediate filaments -no -they are attached to peripheral and cytoplasmic densities -dense bodies -z-disks -attached to cytoplasmic densities -gap junctions What are individual dense -networks of actin, desmin, and vimentin filaments Page 11

12 bodies linked by? The cytoplasmic structures in smooth muscle to which actin and intermediate filaments are anchored are known as...? What is the filamentous protein that blocks the binding of myosin to actin in skeletal muscle myofibrils? What is the outermost layer of connective tissue that surrounds a muscle? What are transverse tubules aligned with? What is the "triad" that is found in skeletal muscle formed by? Where specifically are they located? Does smooth muscle possess a sarcoplasmic reticulum? What is the layer of connective tissue surrounding an individual muscle fascicle? What calcium binding protein controls muscle contraction? Duchenne muscular -dense bodies -tropomyosin -epimysium -Z-disks -transverse tubules, flanked on each side by a terminal cisternae of the SR -at the junction of the A-band and I-band -yes, it does -perimysium -troponin -dystrophin Page 12

13 dystrophy is due to an inherited mutation in the gene for...? In skeletal muscle, what is ATPase activity associated with? Are more mitochondria found in slow twitch fibers or fast twitch fibers? What are three important histological features of a normal muscle fascicle? What are four important histological features of a pathological muscle fascicle? The region of the sarcomeres that contains predominately myosin filaments and no actin filaments is known as the...? -myosin -more mitochondria are found in slow twitch fibers -polygonal muscle fibers of uniform size -minimal connective tissue in between muscle fibers -peripherally arranged myonuclei in each muscle fiber -cross section with a wide variety of diameters of muscle fibers -vacuoles seen commonly within the cytoplasm -inflammatory cells are found within the perimysium -connective tissue, including cells and collagen fibers, occupy a great deal of space -H-band Page 13