20110103 01 muscle notes.txt

From Iusmhistology

  • started here on 01/03/2011 at 2PM


Contents

[edit] What is this course

  • Structure-function correlation
  • Structural foundation for physiology and pathology.
  • Mescher writes the text book; he's at the Bloomington campus.

[edit] Communication

  • Lecture slides posted on ANGEL
  • Only 21 or 22 lectures.
  • Three unit exams.
    • Very thorough assessment.
    • Exams are not cummulative.
  • Last exam is NBME.
    • Usually pretty reasonable.

[edit] Lab

  • 109-116
  • Good place for studying
  • Leo Thompson (MS 108)
    • Fixes microscopes
  • Alphabet starts in 114-116: A-O'Banner, then 109-110.
  • Find your name in the lab, find your drawer, find your paper, key, and slides.
    • Key on drawer goes on key ring; the other one stays in the drawer and opens the microscope cabinet.
  • Ability to learn is a function of how well you use your microscope, so let them help you learn.

[edit] Lecture

[edit] Classes of Tissue in Histo

  • Muscle (for contraction), nearve (for conduction), epithelium (for barriers, for glands), connective tissue (for holding things together and up).

[edit] Slide

[edit] Muscle

  • Skeletal muscle
  • cardiac muscle
  • Smooth muscle

[edit] Skeletal muscle

  • Long
  • A form of striated muscle (like cardiac)
  • Have more than one nucleus
    • Located at periphery
  • Each muscle cell = a muscle fiber; interchangable.
  • Myofibril (not a fiber) is an individual contractile intracellular organelle.
  • Myofibrils are surrounded by the sarcoplasmic reticulum.
    • Sarco from greek Sarcs = flesh.
  • Cytoplasm = sarcoplasm.
  • Sarcolemma = cell membrane

[edit] Image

  • Striations are clear in longitudinal cut of striated muscle.
  • Nucleus is at the periphery.
  • Myofibrils can separate a bit within a cell.
  • Human RBC = 7 micrometers across.
  • Sections are 5-7 microns thick and are cut with a knife.
    • This means there are some artifacts.

[edit] Myofibrils

  • They are surrounded by sarcoplasmic reticulum.
  • Skeletal muscle cells have a basement membrane on the outside of the sarcolemma, too.

[edit] Muscle cuts

  • Fasicles are bundles of many muscle cells.
  • Within a whole muscle lies individual cells which are held together by endomyseum.
  • Bundles are defined by perimyseium.
  • The epimyseum lies around an entire muscle.

[edit] Myofiber in detail

  • Myofibrils are visible.
  • The sarcomere is the contractile unit that is repeated to generate myofibrils.
  • Thick and thin filaments make up the sarcomere and generate the striations.
  • There is area where there is no thick filaments: called I bands because they don't change the orientation of polarized light.
  • A bands are where thick filaments exist; they do change orientation of light.
  • Z lines are where the thing filaments are anchored.
  • The M line (may or may not be visible in EM) is where thick filaments are anchored.
  • The H zone is where thick filaments don't overlap; surrounds M line.
  • We should be able to identify all of these on an EM (electron micrograph).

[edit] EM of Muscle

[edit] Myofilaments in detail

  • Thin filaments made of globular actin (which polymerizes to form filamentous actin).
  • Thin filaments also have troponin complex and tropomyosin.
  • Thick filaments are made of myosin.
  • Thick filaments have a sort of long tail with two heads that come off like pineapple fruit.
  • Myosin walks along the thin filament, pulling the thick filaments along the thin.

[edit] Contraction in detail

  • Myosin has an ATPase site in each head which burns ATP down to ADP and Pi.
    • The units are not released immediately after burn, though.
  • If Ca+ is low, then tropomyosin will inhibit myosin to bind to thin filament.
    • So ADP and Pi will be held on myosin but bind and contraction are not occurring.
  • If Ca+ rises to 1 micromolar or greater, then Ca binds to TnC (troponin subunit of thin filament).
  • TnI and TnT (parts of troponin) then are involved in conformational change.
    • TnI binds actin.
    • TnT binds tropomyosin.
  • Calcium binding on troponin changes the conformation of troponin such that TnI comes up off actin which allows tropomyosin to move about 5 minutes around the clock face of the actin.
  • This allows the head of myosin to bind in on the thing filament.
  • Upon binding to actin, the Pi is released from myosin. This causes a conformational change--the power stroke.
  • After the conformational change, the ADP is released.
  • Release of ADP and Pi makes myosin high affinity for ATP such that it binds and gets burned causing a release of myosin from actin (hence rigor mortis).

[edit] Sarcoplasmic reticulum and calcium transport

  • Rise in Ca+ causes contraction.
  • But these cells are huge, so how do we cause such an increase in an ion?
    • In a normal cell we could just open the calcium channels and let it flow in, but it muscles it would take a long time for calcium to diffuse throughout.
    • So we have a sarcoplasmic reticulum to deliver the Ca+ throughout the cell.
  • The nerve signal comes from the outside the cell and depolarizes the membrane. But how does it talk to the sarcoplasmic reticulum?
    • Via transverse tubules (T tubules)
    • These stretch from cell membrane into the cell to touch the Sarcoplasmic reticulum via terminal cisternae.
    • Two terminal cisternae with a A-I junction in between is called the triad.
  • T tubules have a bit of basememnt membrane that dives into the cell along with the T cell.
  • Note that mammals have T tuble going to A-I jxn whereas in others it goes to the Z line.

[edit] Getting signal to muscle cell

  • Motor neuron brings the signal.
  • Neuron and muscle jxn = synapse = nerve plate.
  • One axon may innervate one myofiber or dozens.
  • A motor unit is a single neuron and all the muscles it innervates.
    • Motor units are either all or none; all cells contract when signaled.
    • In the eye, we get fine motion and control becuase we have one nerve axon per myofiber.
    • In the back, we have many myofibers per neuron because we don't need fine movement.

[edit] Cardiac Muscle

  • Striated like skeletal muscle with some unique structures.
  • Cardiac has branched cells; ;which are joined physically and electrically.
    • Skeletal cells may be connected physically but not electrically.
    • Skeletal don't pick up signal to fire from neighbors, but cardiac cells do, via electrical connection.
  • Cardiac muslce have centrally located nuclei and only 1 or 2 nuclei.
  • Something different about sarcolemma, too.
  • Cardiac structures have intercalated disks which connect them to one another.
  • Cardiac muscle is highly vascular but skeletal is much more limited.

[edit] Intercalated disks

  • Allo cardiac cells to bind end to end.
  • Have three junctions:
    • Facial adherens
      • Where thin filaments are joined together.
      • A bit like zonula adherens.
      • Where thin filaments joined to function as one between cells.
    • Macula adherens
      • Just a desmosome
      • Where thick filaments pass between cells (?).
    • Gap juctions
      • Electrical connections.
      • membranes come together very close at gap jucntions
      • Don't physically hold cells together because they don't affect cytoskeleton.
      • Occur along the longitudinal axis of the muscle cells, generally.
*Diads occur in cardiac cells...don't see one of the things of the triad; don't know what it was.
*ANP atrial naturetic peptid is released by what?

[edit] Smooth muscle

  • All the cells are spindle shaped--a rod with tapered ends.
  • Central nuclei.
  • Much smaller than cardiac cells.
  • In a cross section the cells are cut at different levels because of their tapering.
What is a "typical HNE cut"?
  • Smooth muscles have thick and thin filaments but they are not organized into sarcomeres.
    • They are also attached to intermediate filaments made of desmin and vimentin.
  • Thin and intermediate filaments are linked by cytoplasmic dense bodies and membrane by membrane dense bodies.
    • These cause dark bodies on the membrane and out in the cytoplasma.
    • Dense bodies are where contractile skeleton connects to cytoskeleton.

[edit] Contraction

  • Regulated in part by assembly and disassembly of intermediate filaments.
  • Don't need T tubles to stimulate contraction because they are small.
  • Stimulation causes phos of myosin which causes them to assemble inot thick filaments, allowing contraction.
  • There is more regulation but we won't talk about it.
  • Contraction is stopped by activation of phosphatase which cleaves off phosphorous of myosin and depolymerization.
  • Smooth muscle contraction scrunches the cell into shorter and fatter, ball-like shape.
    • This can cause the nucleus to corkscrew.

[edit] Junctions in Smooth muscles

  • Can have gap jxns which means neighbors act in coordinate fasion: unitary smooth muscle
  • Multi-unit smooth muscle is more tightly controlled by individual neruons.

[edit] Regeneration of skeletal muscle

  • Because of satellite cells, we can regnerate some skeletal cells.
  • Most smooth muscle can dedifferentiate and generate new cells.
  • Cardiac cells cannot regenerate, only form fibrotic tissue.
  • Process of skeletal regen:
    • Satellite cells -> myoblasts -> myotubles (long, multiple cells bound together) -> myofibrillogenesis (fusion of cells) -> myofiber
    • Satellite cells
      • Reside just below basement membrane next to skeletal cells.
      • May look like peripheral nucleus or fibroblast in our slides.
    • Myoblasts
      • Don't look like muscle cells but have similar expressiokn patterns.
      • Can fuse to other myoblasts.
    • Myotubes
      • A syncitium of myoblasts.
    • Myofibrillogenesis
      • Formation of myofibrils of myotubes.
      • Pushes nuclei outward
      • Elongates cell.
    • Myofiber

[edit] Lab

[edit] Staining

  • H&E = hematoxylin and eosin
    • Hematoxylin stains blue
      • Hemotoxylin binds to acidic particles because it is basic.
      • Stains upon reaction with Fe and Al.
      • Stains chromatin, ribosomes,
    • Eosin stains red / orange.
      • Stains acidic particles.
      • Stains connective tissue, cytoplasm, collagen, muscle fibers, and mt.

[edit] Miscellaneous

  • Fats are dissolved away in fixation process leaving some areas vacant of tissue.
  • Because these specimens were "immersion fixed" there may be RBCs floating around.
    • RBCs are around 7 micrometers in diameter but around 10 micrometers when found in their normal environment--the vessel.
*Is the dark spot within the nucleus the nucleolus or the heterochromatin?
**It is the nucleolus.
**The difference between heterochromatin and euchromatin is a darkness thing; heterochromatin will be darker because it is condensed.  The size of the nucleus will not necessarily change with the difference in hetero and euchromatin.
  • Liver cells are typically 20-30 micrometers.
    • So a 6-8 micrometer slice will not capture it all.
  • Don't rely on color for identification.
  • Nuclei of all types of muscle may corkscrew upon fixation.

[edit] Smooth muscle

  • Uterus, appendix, bladder.
  • The appendix (and the rest of the GI tract) has an inner circumferential and outer longitudinal layer of smooth muscle.
    • The stomach is the opposite, though.
  • The uterus has interlaced bundles of smooth muscle.
  • The bladder has disparate bundles separated by connective tissue.
  • Connective tissue is often stained an intense red (from eosin) and has few (fibroblast) nuclei present.

[edit] Skeletal muscle

  • Soft palate, tongue,
  • The soft palate showed glandular tissue, too, I think.
  • There are transverse striations visible in skeletal muscle.
  • Nuclei are many and on the periphery.
Is there connective tissue at the angular connections of differently oriented striations?
  • Myofibrils appear as longitudinal striations in a longitudinal cut and as stippling in a cross-sectional cut.
  • Myofibers are surrounded by endomysium; muscle cell bundles are surrounded by perimysium; gross muscles are surrounded by epimysium.

[edit] Cardiac muscle

  • Striated
  • Heart
  • One or two nuclei per cell, centrally located.
  • Cardiac muscle has intercalated disks and branched muscle cells.


  • stopped here on 01/03/2011 at 5:35PM
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