20110103 01 muscle notes.txt
From Iusmhistology
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*If Ca+ is low, then tropomyosin will inhibit myosin to bind to thin filament. | *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. | **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 | + | *If Ca+ rises to 1 micromolar or greater, then Ca binds to TnC (troponin subunit of thin filament). |
- | *TnI and TnT (parts of | + | *TnI and TnT (parts of troponin) then are involved in conformational change. |
**TnI binds actin. | **TnI binds actin. | ||
**TnT binds tropomyosin. | **TnT binds tropomyosin. |
Revision as of 17:53, 2 February 2011
- started here on 01/03/2011 at 2PM
What is this course
- Structure-function correlation
- Structural foundation for physiology and pathology.
- Mescher writes the text book; he's at the Bloomington campus.
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.
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.
Lecture
Classes of Tissue in Histo
- Muscle (for contraction), nearve (for conduction), epithelium (for barriers, for glands), connective tissue (for holding things together and up).
Slide
Muscle
- Skeletal muscle
- cardiac muscle
- Smooth muscle
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
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.
Myofibrils
- They are surrounded by sarcoplasmic reticulum.
- Skeletal muscle cells have a basement membrane on the outside of the sarcolemma, too.
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.
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).
EM of Muscle
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.
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).
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.
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.
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.
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.
- Facial adherens
*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?
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.
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.
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.
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
Lab
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.
- Hematoxylin stains blue
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.
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.
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.
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