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69 Cards in this Set

  • Front
  • Back
3 cell types in Skeletal Muscle:
1. Myocytes
2. Endothelial cells (of vascular supply)
3. Fibroblasts
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)
What other muscle type is skeletal muscle similar to? How?
Cardiac - both are striated
How are cardiac and skeletal muscle unique?
Skeletal is multinucleated - has hundreds of nuclei per cell.
Where are nuclei normally located in skeletal myocytes?
At the periphery
What invests the whole gross muscle?
Deep fascia called EPIMYSIUM
What invests each fascicle?
What invests each myocyte?
Endomysium - the gray within the fascicle.
What is the endomysium continuous with?
The most INTIMATE investment of each muscle cell, the BASAL LAMINA
Do all muscle cells have a basal lamina?
What is the overall feature to remember about Muscle CT investments?
They are all continuous - even with the myotendon junction that connects the muscle to bone.
What feature of skeletal muscle indicates pathology or injury?
If the myocyte nuclei which should be peripheral, are located centrally.
What is the area between z-lines?
The sarcomere
What does the Z-line contain?
The protein alpha actinin
Why are myocytes striated?
Due to alternating light bands and dark bands
What do we call the light bands?
Dark bands?
Light bands = I bands

Dark bands = A bands
What bisects the I bands?
Z lines
What does the M-line contain?
MM-creatine kinase
2 types of myofilaments in myofibrils:
Why are I bands light?
Only contain thin filaments
Why are A bands dark?
They contain overlapping thick and thin
What are the major thin filament proteins?
Troponin (3 kinds)
What is the function of alpha actinin?
Binds actin to the z line
Major protein in thick filaments:
2 membrane systems in myocytes:
-Transverse tbules
-Sarcoplasmic reticulum
Where do the 2 membrane systems confront each other?
At the A-I junction
What are t-tubules?
Invaginations of the sarcolemma
Function of T-tubules:
To carry depolarization waves deep into the myocyte.
Where T-tubules go deep into the myocyte, what does the SR do?
Envolops each myofibril.
What is the configuration of the 2 membrane systems at the AI junction?
A TRIAD - 2 SRs each on either side of the T-tubule.
How does striated muscle contract?
By excitation contraction coupling
Excitation phase (4 steps):
1. Depolzn wave traverses sarcolemma
2. Travels deep via t-tubules
3. Depolarizes SR at triad
4. Opens SR storage of Ca
What happens when the SR releases calcium?
It binds troponin-C
What does Troponin-C do?
Causes Troponin I to move off the myosin-binding sites on Actin.
What happens when Myosin's binding sites are freed up?
It binds to actin and results in the power stroke.
How can myosin just do the power stroke spontaneously?
It has already hydrolyzed ATP and cocked its head for it.
What happens to the thin filaments during the power stroke?
They get PULLED INTO the A-band.
How does skeletal muscle relax?
Calcium gets pumped back into SR.
What happens if ATP is absent?
Rigor mortis
What is Malignant Hyperthermia?
The inability of anesthetized patients who have a rare gene mutation to resequester calcium.
What is the result of being unable to pump Ca back into the SR?
sustained muscle contractions - generate lots of heat.
What is bigger; myofiber or myofibril?
Myofiber - it is the muscle cell, and yes it contains many little fibrils.
What is the ratio of Thin:Thick filaments in the myofibril?
4 energy storage forms in skeletal muscle:
-Creatine phosphate
-Fatty acids
What type of energy do
-sprinters use?
Glycogen - sprinters

Fatty acids - marathoners
2 types of muscle fibers:
Type I - red
Type II - white
Why are type I fibers red?
They contain lots of myoglobin for fatty acid oxidation
Are type I fibers slow or fast?
Slow oxidative
What do Type I fibers have lots of?
What type of fibers do muscles in the body contain; I or II?
So the Sprinter type of fiber:
Type II - Fast glycolytic - white
Muscles are mixed
The Marathoner type of fiber:
Type I - Slow oxidative
lots of mitochondria
How does skeletal muscle regenerate?
By Resident Adult Stem Cells
Where are stem cells for myocyte regeneration located?
In adult stem cell niches between the SARCOLEMMA and BASAL LAMINA of each myocyte.
What are these adult stem cells called?
Satellite cells (but misnamed)
What phase are Satellite cells resting in during normal situations?
What induces Satellite cells to re-enter the cell cycle in G1?
Damage to the basal lamina which releases Growth Factor signals.
What happens after Satellite cells enter G1 and multiply?
They form myotubes
What happens to the nucleus of satellite cells in going from resting stage in niches to myotubes?
They go from being mononuclear -> division -> multinuclear myotubes.
How do the multinuclear myotubes form?
By fusion of the multipled satellite cells.
What are 2 clinical uses (or attempts anyway) at using satellite cells to regenerate muscle tissue?
1. Cardiac insufficiency
2. Duchenne muscular dystrophy
What is the purpose of injecting myosatellite cells into the heart?
To bolster ejection fraction
What is the mutated protein gene in Duchenne muscular dystrophy?
Function of Dystrophin?
Stabilizes the myocyte cytoskeleton
What happens in the absence of dystrophin?
The sarcolemma breaks down, myocyte tries to repair, then dies.
How big is the dystrophin gene?
What does mutation to the dystrophin gene do?
Introduces premature stop signals for transcription.
What population is affected most by DMD? Why?
Males - 1/3500 - because the disease is X-linked (remember from med interviewing)
What are drugs for DMD directed at doing?
Normalizing the readout of genes to overcome the premature stop of translation and transcription.