Muscles - Histology

  • Created by: SummayaM
  • Created on: 24-12-19 15:25
Excitable cells capable of contraction are?
Muscle Fibers
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Which tissue is the most abundant tissue of the body?
Muscle tissue
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Components of external lamina?
Collage type 4 fibrils, glycoprotein laminin and proteoglycan perlecan
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Which muscle cells do not have external lamina?
Cardiac muscle cells
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Dartos muscle of scrotal skin is of which muscle type?
Smooth muscle cells
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Where are longest smooth muscle fibers found?
In the walls of pregnant uterus
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Nucleus of smooth muscle cells?
Rod shaped and central
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What is responsible for corkscrew appearance of nucleus of smooth muscle cells?
Contraction of the muscles during the process of fixation
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What is cytoskeleton of smooth muscles made up of?
Desmin intermediate fibers usually, vimentin intermediate fibers in blood vessels
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Where are organelles in a smooth muscle cell located?
Around the nucleus mostly, especially at its poles
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Function of caveolae?
To organize signaling molecules in sarcolemma and regulate movement of Ca ions
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What do caveolae contain?
Receptors, Ion channels, pumps
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What do dense bodies contain?
Alpha actinin
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Where are intermediate filaments in smooth muscle cells inserted?
Dense bodies
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Describe nerve fibers of smooth muscle cells
Post ganglionic and unmyelinated
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What are the types of smooth muscle fibers?
On basis of innervation, multi unit and unitary fibers.
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Examples of multi unit smooth muscle cells?
Muscles of iris and ductus deferens
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Which smooth muscle type acts as a syncytium and how?
Unitary fibers because of presence of gap junctions
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Examples of unitary smooth muscle cells?
Muscles of most hollow viscera, blood vessels.
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Function of ciliary muscles?
To control curvature of lens, accommodating near and far vision.
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When do smooth muscles in seminal vesicles and prostrate gland contract?
During ***********
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Epimysium has which kind of connective tissue?
Dense irregular
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Composition of endomysium?
Fine collagenous fibers embedded in proteoglycan matrix
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Name the smallest skeletal muscle?
Stapedius muscle of middle ear
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Function of external lamina?
Binds each muscle fiber to its endomysium
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Nucleus of skeletal muscles?
Ovoid and peripheral, clear cytoplasm around it
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Development of skeletal muscle fibers embryologically?
Due to fusion of mononucleated myoblasts
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Define sarcomere?
Basic contractile unit of muscle fiber
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Composition of thick myofilaments?
200-300 Molecules of myosin 2, an actin binding protein
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Structure of myosin 2 molecule?
One pair of heavy chains twisted around each other to form the tail and perpendicular heads. 2 pairs of light chains, each pair associated with one head.
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Heads have binding sites for what?
Actin and ATP
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Function of Titin?
Serves as molecular spring, responsible for passive elasticity of muscles. Binds myosin 2 to Z disks.
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Composition of Z discs?
Alpha actinin plus nebulin
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Structure of actin filament?
Two F actin polymers wound around each other in a helix. Each polymer made up of globular subunits of G actin
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Where is troponin attached?
On tropomyosin
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Structure of troponin?
Complex of three globular proteins: TnT, TnC, TnI
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Smallest subunit of troponin?
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Which enzyme is located in globular head?
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How many thin filaments surround a thick filament?
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Describe Z discs
Zigzag structure, bisected by an amorphous material called Z matrix
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Function of nebulin?
Helps alpha actinin in anchoring thin filaments
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Composition of M line?
Myosin binding protein called myomesin and creatine kinase
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Describe sarcoplasmic reticulum
A special type of smooth endoplasmic reticulum found in striated muscle cells
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What happens to SR at level of H zone?
Lateral anastomoses between longitudinally disposed tubules form a perforated collar around the myofibrils
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What happens to SR at the level of AI junction?
1. Longitudinal tubules join terminal cisternae present in the form of rings around the myofibrils 2. T tubule invaginates
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What is a triad?
Two terminal cisternae plus one T tubule.
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How many triads in one sarcomere?
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Do T tubules undergo branching?
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Are there junctions between T tubules and terminal cisternae?
Yes, at some places
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Function of SR?
Reservoir of Ca ions
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What kind of channels are present in SR?
gated Ca release channels (ryanodine receptors)
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Where are voltage sensor proteins present?
In T tubules
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What restores Ca ion concentration in SR?
Ca ion membrane pumps (SERCA) located in SR membrane
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Describe motor nerve fibers supplying skeletal muscles
Fibers originate from alpha motor neurons located in anterior gray horn of spinal cord or brainstem
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Define motor unit.
A motor neuron and the muscle fibers it innervates
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What are muscle spindles?
A special variety of sensory nerve endings that receive sensory (afferent) fibers
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What is the function of muscle spindles?
Convey information regarding degree of muscle tension/stretch to CNS
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Composition of endomysium of cardiac muscle cells?
Collagen and reticular fibers
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Nucleus of cardiac muscle cells?
Single (some cells may be binucleated), large, pale staining, oval located centrally
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Where is lipofuscin found?
Cardiac muscle cells of old people
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What is lipofuscin?
Fine yellow brown granules composed of lipid-containing residues of lysosomal digestion
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Location of mitochondria in cardiac muscle cells?
Normal size: beneath sarcolemma and perinuclear region. Large size: between myofibrils
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Unique feature of sarcoplasm of atrial muscle fibers?
Sarcoplasm contains membrane bound atrial granules containing Atrial Natriuretic Factor, a peptide hormone.
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Function of Atrial Natriuretic Factor?
Inhibits reabsorption of sodium by kidney tubules inducing diuresis
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Location of intercalated discs?
At level of Z lines
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Junctions present in intercalated discs and their functions?
Fasciae adherents and desmosomes (mechanical attachment), gap junctions (provide electrical coupling)
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What allows cardiac muscle to behave as a syncytium?
Gap Junctions allowing spread of electrical impulses between cells
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Difference between T tubules of cardiac and skeletal muscles?
Cardiac T tubules have a greater volume and lie at the level of Z discs (in skeletal muscles they lie at AI junctions)
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Instead of Triad, what is present in cardiac muscle cells?
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Regenerative capability of Smooth Muslce Cells?
Great. Occurs because of smooth muscle mitotic division or pericyte differentiation into SM in blood vessels
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Regenerative capability of Skeletal Muscle Cells?
Limited. Satellite cells may become active in times of injury but usually not enough. Injured site repaired by fibroblasts.
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What are satellite cells?
Mononucleated cells lying between skeletal muscle fibers and external lamina. They are dormant myoblasts.
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Regenerative capability of Cardiac Muscle?
None. Replaced by scar tissue consisting of collagen fiber produced by fibroblasts.
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Other cards in this set

Card 2


Which tissue is the most abundant tissue of the body?


Muscle tissue

Card 3


Components of external lamina?


Preview of the front of card 3

Card 4


Which muscle cells do not have external lamina?


Preview of the front of card 4

Card 5


Dartos muscle of scrotal skin is of which muscle type?


Preview of the front of card 5
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