Physio Lecture 1
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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
What is it called when one muscle contracts and a whole group of muscles contract together?
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
Single unit vs. multi-unit: which one is more similar to the skeletal muscle?
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
Muscle cell= myo_____
- IMPORTANT: If you're talking about the even small component, it's fibrils
______connects muscle to bone;
______connects bone to bone
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
Compare to other cells:
Sarcolemma is to_______
Sarcoplasm is to ______
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
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
What are myofilaments made of?
Individual myofilament proteins-thin and thick filaments
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
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?
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
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.
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
Refer to Figure 12.6
Think filaments are composed of protein _____
Thin filaments are composed of protein_____
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
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'
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
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
What kind of structural protein lies around the outside of z-line and m-line regions around the sarcomere?
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?
What is a support protein for the fibrils?
Dystrophin (right underneath the sarcolemma)
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
What do satellite cells and stells cells do?
Repair of damaged myofibers (but may not recover from muscular dystrophy)
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
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.
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
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
Sliding filament theory devised by Huxley-
___band doesn't change length during state of contraction
___band dissappears at full contraction
- 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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