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Single unit of smooth muscles are also refered to as____
It has a lot of ________
- Visceral smooth muscles
- Gap junctions between each individual smooth muscle cells
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What is it called when one muscle contracts and a whole group of muscles contract together?
Functional synctytium
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What kind of smooth muscle cells are associated with iris of the eye and with the smooth muscles wrapped around the blood vessels?
Multi-unit smooth muscles
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Single unit vs. multi-unit: which one is more similar to the skeletal muscle?
Multi-unit
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What is the most common striated, long cylindrical fiber that is multi-nucleated?
- Skeletal muscle. with these characteristics:
- Nuclei located right under the sarcolemma of the cell,
- on the outside around the myofiber
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Muscle cell= myo_____
- myofiber
- IMPORTANT: If you're talking about the even small component, it's fibrils
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______connects muscle to bone;
______connects bone to bone
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The structure of a skeletal muscle
- Superficial fascia (1st layer of connective tissue)
- ---->A second layer of connective tissue: epimycium
- ---->Perimycium, another connective tissue surrounding bundles called fascicles
- ---->Inside each fascicles: individual myofibers
- ----->3rd layer of connective tissue: endomycium: surroudning each myofiber
- --->ind. myofilaments inside the myofiber
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Compare to other cells:
Sarcolemma is to_______
Sarcoplasm is to ______
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Location of the multi-nucleated nuclei in the muscle cell
Below the surface of the sarcolemma, outside or eccentrically placed in the myofiber, long cylindrical fibers
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1. What innervates the myofiber?
2. What is this connection called?
3. Where are those connections located?
- 1. One branch of an alpha motor neuron.
- 2. Neuromuscular junction
- 3. In the belly or center region of the muscle
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What are myofilaments made of?
Individual myofilament proteins-thin and thick filaments
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What are the two distinct locations and functions of the mitochondria in skeletal muscle?
- 1. One layer runs right below the surface of the sarcolemma
- The primary purpose is to maintain Na+/K+ active transport pump and concentration gradiens, which require energy (the same gradient we saw in the nerve)
- 2. The other layer is spread throughout/in between all of the myofibrils-
- The purpose of these mitochondria is to produce ATP to provide energy necessary for the sliding of the filaments that actin over the thick myosin filament
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Refer to Figure 12.15:
1. On the outside of the sarcolemma, the holes are open to_____?; following this space, they wrap themselves around each one of the myofibrils
2. What are the green tubes?
3. Describe what the triad of t-tubules are?
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Do muscle contractions change the concentration gradient of extracellular fluid?
What about the concentration gradient in the t-tubules? And why?
A muscle cell contracts a large number of times, it isn’t changing the concentration gradient of extracellular fluid to a large extent,but in the t-tubule, with Na+/K+ pumps active and concentration gradients are changing in that small volume within the t-tubule
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Describe the mechanism of K+ induced membrane potential
So if K+ is leaving the sarcoplasm and entering the t-tubule all of a sudden the K+ concentration of the extracellular fluid is elevated inside the t-tubule. The action potential is going to spread across the surface, but it also spreads across the t-tubule membrane with equal speed to get inside the cell to induce the contraction mechanisms for all of the myofibrils as near simultaneously as possible.
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Can the contractions of the myofibrils happen at different times?
No, they are near simultaneous as possible- can't have them go out of sync
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Refer to Figure 12.6
Think filaments are composed of protein _____
Thin filaments are composed of protein_____
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Draw a sarcomere-It extends from ___ to ____
1. __ band the light area/ __band is the dark area
2. What is the central lighter region called where the M line is?
3. Give the lay-out of the different bands
- Z-disk to the next z disc
- 1. I band/ A band
- 2. H band
- 3. I band (light area)---A band the really dark area(includes H band in the middle, including the M line)----I band
- *Also, realize that in 3 dimentions, the z line is actually a disk
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What protein are z disks made with and what is its primary function?
What is the smallest function unit in contraction?
- Alpha actinin, and to serve as anchor to the action filament'
- Sarcomere
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i. How do you add length to a myofiber?
ii. How do you increase the cross-sectional diameter of the myofiber?
- i. Add sarcomeres
- ii. add more thin and thick myofilament proteins
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What are the two primary functions of titin?
- 1. Elastic coil of muscles to help them return to their resting length during muscle relaxation
- 2. Aid in centering thick filamnent equidisitant between actin thin filaments
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What kind of structural protein lies around the outside of z-line and m-line regions around the sarcomere?
Obscurin
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What kind of protein is within the filament itself and is thought to give more cytoskeletal structure within the cell and maintain filaments in appropriate alignment?
Nebulin
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What is a support protein for the fibrils?
Dystrophin (right underneath the sarcolemma)
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What is the consequence of a mutation in dystrophin?
- -Many forms of muscle dystrophy
- -Make sarcolemma more easily damaged
- -Leads to necrosis of the cell
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What do satellite cells and stells cells do?
Repair of damaged myofibers (but may not recover from muscular dystrophy)
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1. What happens if the axon of the somatic motor neurons gets cut or damaged?
2. What is the medical condition called?
- 1. No more Ach being released and stimulating the cholinergic receptors at the site
- The membrane starts to flatten out and Ach receptors start to drift out along the sarcolemma asway from the damaged region
- 2. Disuse Atrophy- this is experienced also by astronauts in outerspace with little gravity
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Describe the synaptic action of the motor end-plate
- 1. Action potential travels down sarcolemma into the t-tubules down into the cell where it results in the release of Ca2+ that will initiate the contraction. Ventralhorn gives rise to large alpha motor neurons and branches.
- 2. Ach receptors on the motor end-plate and Ach in
- synaptic vesicles. When an action
- potential comes down, Ca2+ permeability changes, Ca2+ comes into the cell
- results in tubular formation that results in migration of neurotransmitter
- vesicles to pre-synaptic membrane where they are exocytosed, Ach drifts across
- neuromuscular synaptic cleft and binds to receptors.
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What is a motor unit?
- One somatic motor neuron and all of the myofibers
- it innervates is referred to as a motor unit
- Motor end-plate is only the specialized,
- post-synaptic region of the sarcolemma that is part of the neuromuscular
- junctions and does not include the terminal button of the axon
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How do you increase muscle strength?
- Adding more motor units to contraction. This is depended on the RECRUITMENT by the CNS to decide how many myofibers to recruit
- -Another way is to send action potentials more rapidly to give a summation effect
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Sliding filament theory devised by Huxley-
___band doesn't change length during state of contraction
___band dissappears at full contraction
Conclusion:
- A band
- I band
- The I band dissapears because the myosin thick filament was pulling the actin over it, leading to the shortening of each myofibril within each myofiber
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