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69 Cards in this Set
- Front
- Back
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3 cell types in Skeletal Muscle:
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1. Myocytes
2. Endothelial cells (of vascular supply) 3. Fibroblasts |
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5 levels in the skeletal muscle hierarchy of organization:
(highest to lowest) |
1. Gross muscle (cm)
2. Fascicles (mm) 3. Myocytes (fibers) (10-100 um) 4. Myofibrils (1-2 um) 5. Myofilaments (nm) |
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What other muscle type is skeletal muscle similar to? How?
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Cardiac - both are striated
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How are cardiac and skeletal muscle unique?
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Skeletal is multinucleated - has hundreds of nuclei per cell.
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Where are nuclei normally located in skeletal myocytes?
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At the periphery
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What invests the whole gross muscle?
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Deep fascia called EPIMYSIUM
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What invests each fascicle?
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Perimysium
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What invests each myocyte?
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Endomysium - the gray within the fascicle.
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What is the endomysium continuous with?
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The most INTIMATE investment of each muscle cell, the BASAL LAMINA
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Do all muscle cells have a basal lamina?
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Yes
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What is the overall feature to remember about Muscle CT investments?
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They are all continuous - even with the myotendon junction that connects the muscle to bone.
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What feature of skeletal muscle indicates pathology or injury?
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If the myocyte nuclei which should be peripheral, are located centrally.
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What is the area between z-lines?
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The sarcomere
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What does the Z-line contain?
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The protein alpha actinin
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Why are myocytes striated?
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Due to alternating light bands and dark bands
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What do we call the light bands?
Dark bands? |
Light bands = I bands
Dark bands = A bands |
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What bisects the I bands?
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Z lines
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What does the M-line contain?
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MM-creatine kinase
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2 types of myofilaments in myofibrils:
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-Thick
-Thin |
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Why are I bands light?
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Only contain thin filaments
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Why are A bands dark?
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They contain overlapping thick and thin
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What are the major thin filament proteins?
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Actin
Tropomyosin Troponin (3 kinds) |
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What is the function of alpha actinin?
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Binds actin to the z line
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Major protein in thick filaments:
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Myosin
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2 membrane systems in myocytes:
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-Transverse tbules
-Sarcoplasmic reticulum |
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Where do the 2 membrane systems confront each other?
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At the A-I junction
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What are t-tubules?
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Invaginations of the sarcolemma
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Function of T-tubules:
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To carry depolarization waves deep into the myocyte.
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Where T-tubules go deep into the myocyte, what does the SR do?
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Envolops each myofibril.
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What is the configuration of the 2 membrane systems at the AI junction?
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A TRIAD - 2 SRs each on either side of the T-tubule.
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How does striated muscle contract?
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By excitation contraction coupling
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Excitation phase (4 steps):
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1. Depolzn wave traverses sarcolemma
2. Travels deep via t-tubules 3. Depolarizes SR at triad 4. Opens SR storage of Ca |
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What happens when the SR releases calcium?
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It binds troponin-C
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What does Troponin-C do?
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Causes Troponin I to move off the myosin-binding sites on Actin.
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What happens when Myosin's binding sites are freed up?
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It binds to actin and results in the power stroke.
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How can myosin just do the power stroke spontaneously?
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It has already hydrolyzed ATP and cocked its head for it.
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What happens to the thin filaments during the power stroke?
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They get PULLED INTO the A-band.
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How does skeletal muscle relax?
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Calcium gets pumped back into SR.
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What happens if ATP is absent?
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Rigor mortis
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What is Malignant Hyperthermia?
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The inability of anesthetized patients who have a rare gene mutation to resequester calcium.
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What is the result of being unable to pump Ca back into the SR?
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sustained muscle contractions - generate lots of heat.
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What is bigger; myofiber or myofibril?
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Myofiber - it is the muscle cell, and yes it contains many little fibrils.
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What is the ratio of Thin:Thick filaments in the myofibril?
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6:1
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4 energy storage forms in skeletal muscle:
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-ATP
-Creatine phosphate -Glycogen -Fatty acids |
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What type of energy do
-sprinters use? -Marathoners? |
Glycogen - sprinters
Fatty acids - marathoners |
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2 types of muscle fibers:
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Type I - red
Type II - white |
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Why are type I fibers red?
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They contain lots of myoglobin for fatty acid oxidation
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Are type I fibers slow or fast?
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Slow oxidative
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What do Type I fibers have lots of?
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Mitochondria
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What type of fibers do muscles in the body contain; I or II?
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Both
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So the Sprinter type of fiber:
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Type II - Fast glycolytic - white
Muscles are mixed |
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The Marathoner type of fiber:
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Type I - Slow oxidative
-Red lots of mitochondria |
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How does skeletal muscle regenerate?
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By Resident Adult Stem Cells
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Where are stem cells for myocyte regeneration located?
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In adult stem cell niches between the SARCOLEMMA and BASAL LAMINA of each myocyte.
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What are these adult stem cells called?
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Satellite cells (but misnamed)
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What phase are Satellite cells resting in during normal situations?
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Go
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What induces Satellite cells to re-enter the cell cycle in G1?
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Damage to the basal lamina which releases Growth Factor signals.
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What happens after Satellite cells enter G1 and multiply?
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They form myotubes
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What happens to the nucleus of satellite cells in going from resting stage in niches to myotubes?
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They go from being mononuclear -> division -> multinuclear myotubes.
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How do the multinuclear myotubes form?
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By fusion of the multipled satellite cells.
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What are 2 clinical uses (or attempts anyway) at using satellite cells to regenerate muscle tissue?
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1. Cardiac insufficiency
2. Duchenne muscular dystrophy |
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What is the purpose of injecting myosatellite cells into the heart?
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To bolster ejection fraction
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What is the mutated protein gene in Duchenne muscular dystrophy?
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Dystrophin
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Function of Dystrophin?
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Stabilizes the myocyte cytoskeleton
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What happens in the absence of dystrophin?
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The sarcolemma breaks down, myocyte tries to repair, then dies.
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How big is the dystrophin gene?
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BIG
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What does mutation to the dystrophin gene do?
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Introduces premature stop signals for transcription.
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What population is affected most by DMD? Why?
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Males - 1/3500 - because the disease is X-linked (remember from med interviewing)
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What are drugs for DMD directed at doing?
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Normalizing the readout of genes to overcome the premature stop of translation and transcription.
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