Vet histology readings pg 191-211
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What are generally considered the 3 types of muscle
Describe skeletal muscles
- Very long multinucleated cylindrically shaped with striations upon them
- Has a sarcolemma surrounding them
What is a group of muscle fibers called? What is it surrounded by?
WHat makes up the inside of a muscle fiber?What would the contractile units of thes ebe called?
- myofibrils composed of thick myosin and thin actin filaments
Are thick and thin filaments attached directly?
No they interdigitate betweek eachother
Which filament has a globular head? Where does it point too? Which proteins is it associated with mostly?
- Myosin has the globular head
- towards f actin
What seperates sarcomeres?
Z discs or lines
Which part of the Z disc do the thin filaments attach to
The alpha actinin
Light bands are called? Dark bands are called?
What is the sarcoplasm?
Cytoplasm of muscle fibre
What is the sarcoplasmic reticulum? What does it do?
- Mitochondria and cisternae of smooth ER
- Calcium sequestration and release
At each sarcomere What will we find (Hint: has to do with Sarcoplasmic reticulum) What do they come in contact with? What is the purpose of this?
- Terminal cisterns of SR
- a deep invagination of sarcolemma called the T tubule
- Forms a triad that triggers Ca2+ release when the sarcolemma is depolarized
What has to happen to allow the myosin head to bind to the actin subunit? This forms what?
- calcium binding to the troponin causes tropomyosin to change shape.
- Cross bridges between thick and thin filaments
Once myosin heads are bound to actin how does contraction actually happen
ATP hydrolysis pivots the head sliding the two filaments along eachother
With both Ca and ATP present for the contraction what do we see occur?
A contraction cycle ensures where myosin heads repeatedly attach pivot detach and return causing shortenting of the sarcomere
When membrane depolarization ends describe what happens?
Ca is sequestered thus binding of tropomyosin ends thus covering the actin binding sites and stopping contraction allowing muscles to relax
What do you call the synapse of a motor neuron and a skeletal muscle? (3 names)
- Motor end plates
- Neuromuscular junctions
- Myoneural junctions
What is the primary neurotransmitter between neurons and skeletal muscle
Do motor axons only innervate one muscle fiber? What do you call the unit?
- No often they will end with many motro end plates on many different muscle fibers
- All the fibers a nerve innervates is call the motor unit
Differentiate between muscle spindles and tendon organs? What is the same about them?
- They are both used to detect tension on the muscle
- The difference is muscle spindles are miny muscle bundles that attach to sensory proprioceptors while the tendon organs are nerves that attach to tendons to test the same thing
Where do tendon organs penetrate?
Into the collagen bundles at the myotendionous junction
So in muscle spindles the proprioceptors wrap around what? What about in tendon organs?
- Intrafusal fibers
- Myotendinous collagen bundles
Describe the three types of skeletal muscle fibers?
- Type 1: Slow oxidative
- Type 2 (a): Fast intermediate oxidative-glycolytic
- Type 3 (2b) : Fast glycolytic
Are cardiac muscles smooth?
No still striated
Describe the difference in cell size between cardiac and skeletal muscle
Cardiac is not all one big muscle, it is long normal muscle cells with normally 1 nucleus
How do cardiac muscle cells attach
Via intercalated discs
Does the sarcomere differ in the cardiac muscle from the skeletal muscle
Does the brain have input into the cardiac muscle?
No its control is intrinsic at nodes of impulse generating pacemaker fibers
Describe the shape of a smooth muscle cell?
Tapering as compared to cigar shaped, so tweedles off into a twindle
How are smooth muscle linked?
Via numerous gap junctions
Are there striations in smooth muscle? How does the sarcomere differ?
What does actin attach to if there is no sarcomere in the smooth muscles?
Dense bodies spread out around cell in sarcoplasm and sarclemma
Do smooth muscle cells contract together or individually?
Individually then they tell the next too, so it makes a sort of Squeezing motion
What differs about the T tubule system in the smooth muscle?
It doesn't exist
There is a lack of troponin in smooth muscles So what protein controls the sliding of filaments?
Myosin light-chain kinase (MLCK) as well as calmodulin
Why don't smooth muscle cells need t tubules?
Cause they contract individually and don't need that adaptation
What does troponin do?
Blocks binding site for myosin head
Why can skeletal muscle repair and regenerate?
- Because of the reserve satellite cells hanging out on it
- They can proliferate and fuse to form new muscle fibers
Can cardiac cell regenerate? Why?
Can smooth muscle cells regenerate? Why?
- Cause each one is relatively small and relatively less differentiated which can allow for renewed mitotic division
Cardiac muscle cells are bound together by whatÉ
What is the sarcoplasmic reticulum analogous to in a normal cell?
What is the sarcoplasm in a normal cell?
What is a sarcolemma in a normal cell?
What type of muscle do we see satellite cells in?
Differentiate between epi, endo and perimysium
- Epi = external
- Peri = inbetween fascicle
- Endo = between muscle cells
What is a bundle of muscle cells called (the unit surrounded by perimysium)
What is the junction of the tapering skeletal muscle and the continuing tendon?
an A band is?
Dark band where myosin is seen
The I band is?
Light band where only actin and titin is
Differentiate between F action and G actin
- F is the long chain of actin globules
- G is the individual globule
- G = globule
Myosin is a complex containing how many of each chain?
2 heavy chains making up tail and 4 light chains (2 pairs) making up heads
Differentiate between tropomyosin and troponin
- Tropomyosin is the long polypeptide coild sitting in the actin groove to stop myosin binding
- Troponin is the complex of three subunits controlling the tropomyosin
What makes up the Troponin complex
- TnT = attaches to tropomyosin
- TnC = binds Ca
- TnI = Regulates actin myosin interactions
What does titin do?
Connects the myosin to the Z disc
What Is nebulin
- Large accessory protein
- binds each thin myofilament laterally
What is myomesin
part of the M line that holds thick filaments in place
What are two proteins on the M line
Myomesin and creatine kinase
What is the purpose of creatine kinase on the M line?
catalyzes transfer of phosphate groups from phosphocreatine (Phoasphate storage molecule) to ADP to supply the muscle with ATP
When the myosin binds actin it forms a crossbridge and causes what else?
actomyosin ATPase activity (catalyzing energy release)
What is triad?
two terminal cisterns of the sarcoplasmic reticulum on either side fo the T tubule
What is a terminal cistern
expanded cisterns of the SR on the side of a T tubule
How does rigor mortis occur?
In the absence of ATP after deatht he myosin and actin crossbridges become stable and the muscle is stuck in contraction
What causes the release of the myosin head from the actin binding site so that it can make another pivot?
ATP breaking down to ADP and P
What removes acetylcholine from the synaptic cleft?
The sarcolemma at the neuromuscular junction is in what shape? Why?
- Junctional folds
- Increase SA so to transmit impulses better
What is an intrafusal fiber
- thin muscle fibers found surrounding a muscle spindle along with flattened cells
- (essentially modified perimysium)
Where would we find myoglobin most likely?
In muscles that have slow extended contractions cause they tend to do more oxidatitive phosphorylation and myoglobin has iron and stores lots of oxygen easily
What two things make up intercalated discs? Why does this make sense?
- Desmosomes and fascia adherents
- Cause if joining muscle together has to be all about strength
What structure allows cardiac cells to have ionic contiuity and essentially communicate contraction signals between eachother
Another name for smooth muscle?
What are calveolae
short membrane invaginations of smooth muscle
in smooth muscle what replaces troponin?
Calmodulin and Ca sensitive myosin light-chain kinase
does cardiac muscle contract individually?
Does it have T tubules?
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