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Histo Lecture 4: Muscle Tissue:

Terms in this set (73)

fibers
muscle cells are also called muscle ____
skeletal and cardiac
which types of muscle cells are striated?
smooth
which is not?
...
come back to this!
...
and this!
true!
T/F: there are lots of mitochondria in skeletal muscle:
hundreds, flat and on the periphery
avg. # and arrangement of nuclei in skeletal muscle cells:
mesenchymal cells
where are skeletal muscles derived from?
myoblasts
what do mesenchymal cells give rise to?
fuse to form multinucleate myotubes which elongated
what do myoblasts then do:
mesenchymal cells --> myoblasts --> (fuse into) multinucleate myotubes
summary of skeletal muscle beginnings:
the muscles themselves can't divide, but have stem cells called satellites adjacent to the muscle cells that give rise to new muscle cells when needed

(mature muscle cells can't divide!!)
imp. thing about skeletal muscles:
the sarcoplasm
which part of the skeletal muscle contains a lot of mitochondria?
glycogen granules (for energy) and myoglobin (for oxygen)
what else is in the sarcoplasm? (2 things in addition to mitochondria)
a bunch of fascicles (groups of skeletal muscle cells/fibers)
-fascicle bundles grouped to form muscles
what is a skeletal muscle actually composed of?
a bunch of muscle cells (fibers)
what are fascicles composed of?
a bunch of myofibrils
what is each muscle cel composed of?
myofilaments
what are myofibrils made up of?
myofilaments make up --> myofibrils make up --> muscle cells (fibers) make up --> fascicles make up --> skeletal muscle
REVIEW:
connective tissue
what surrounds the cells, fascicles, and entire muscle?
ENDOmysium, PERImysium, and EPImesium (inside to outside)
3 different connective tissue coatings based on location:
surrounds each muscle cell (fiber)
what does endomysium surround? (a delicate connective tissue)
each fascicle (bundles of skeletal fibers)
what does perimysium surround?
surrounds the entire muscle
what does epimysium surround? (dense)
myofibrils
smallest unit of skeletal muscle that has a banding pattern
myofilaments
what makes up myofibrils?
actin (thin filaments) and myosin (thick filaments)
what are myofilaments made up of?
sarcomere (composed of actin and myosin myofilaments)
smallest unit of contraction that does the contracting and relaxing for the whole muscle
z-lines
name for the ends of the sarcomeres:
- they are what the actin filaments attach to
- a sarcomere is defined as running from z-line to z-line
more about the z-lines:
for the myosin (the thick, middle part) to attach to actin and pull the myosin heads together and shorten the sarcomere
what is the whole purpose of the sarcomere?
shortens: the sarcomere

doesn't shorten: actin and myosin
what actually shortens in this contraction? what does not?
the actin filaments pull close together and sometimes even overlap during contraction. Space between the actin disappears and the space between the actin disappears and the z-lines come together
talk through the process:
calcium!
- uncovers the binding sites on actin and makes them visible to the myosin heads
- opens up the binding sites and then the myosin binds to it
what mineral mediates the whole process? how?
myofibril, bands
the sarcomeres in each ___ are aligned with those adjacent so their ___ are also aligned
- A-band
- I-band
- Z-disc
- H-zone
names of the different bands/zones in the sarcomere:
runs from one end of a myosin filament to the other (encompasses the entire myosin filament)
where does the A-band run?
contains only light (actin) filaments
- bridges two sarcomeres to each other
where does the I-band run?
...
skeletal muscle with A-band, I-band, and z-line:
starts at the Z disc and runs towards the center
where does the actin start?
only contains actin (light band)
why is the I-band so pale?
where the actin and myosin overlap
where is the A-band darker?
the H-zone
what disappears as you contract the sarcomere and the z-lines move together?
the center of A bands
- lie between the free ends of the thin filaments
H bands are located at...
M lines (where adjacent thick filaments connect)
what bisect the H bands
myosin
the H-zone contains only
actin
the I-band contains only
bisect I bands
what do Z lines bisect?
myosin and overlapping actin filaments
A-band contains
-sarcomere shortens
- H-zone disappears
summary: what shortens/disappears when muscles contract?
- Z-lines move together
- actin filaments are pulled together
- I-zones shrink
what just moves closer together?
sarcoplasmic reticulum
name for the smooth endoplasmic reticulum in muscle cells:
- sequesters and releases calcium ions for muscle contraction
- binds calcium and holds it ("a ready resource")
- surrounds each myofibril w/in muscle cells
function of sarcoplasmic reticulum?
Transverse (T) tubules
- name for projections into the cell membrane at each A-I band junction
- a tubular invagination of the sarcolemma
- penetrates the muscle fiber and lies next to the surface of myofibrils
allows electrical charge to go through them and triggers the release of calcium
special job of T-tubules:
...
pretty picture of the whole deal
true!
T/F: cardiac muscle has the same contraction mechanism as skeletal muscle
cardiac:
- one nuclei per celll
- has intercalated discs (connecting the muscle cells together end-to-end)
- cells run in diff. directions (branched) to "ring out" the blood of the heart when they beat
- sparse sarcopasmic reticulum
a couple differences between cardiac and skeletal muscle:
- fascia adherens
- macula adherens (spot desmosomes)
- gap junctions
cell-to-cell junctions in intercalated disks (3 of them!)
macula adherens
junctions that prevents cardiac muscle fibers from tearing apart during attraction (attachment)
gap junctions
junctions that allow electrical stimuli/ions to be passed from cell to cell (connection)
-arranged in a step-wise arrangement connecting the fascia adherens together/allowing communication
fascia adherens
junction that anchors actin filaments (attachment)
- meant to act like a z-disk connecting the sarcomeres
- actin filaments insert into it and it holds the T-cells together
more about fascia adherens:
- walls of HOLLOW ORGANS (such as intestine and uterus)
- present in WALLS of LARGER BLOOD VESSELS (ex. arterioles) and in the EYE
common places where smooth muscle is present:
produce collagen, elastin, and proteoglycans
another job of smooth muscle:
- fusiform (spindle)-shaped
- single central nucleus
- packed together tightly
- 2 pointy ends
- no striations
qualities of smooth muscle:
- LOTS of mitochondria, some rough ER, and large Golgi complex
- each cell is surrounded by a thin layer of reticular fibers (coating that keeps the cells in place and anchors them)
- thin (actin) and thick (myosin) filaments are not tightly arranged by just crisscross through cell
- sarcomeres present here and there throughout the cell
even more qualities of S.M.:
dense body
- anchoring point in smooth muscle for adjacent cells
- anchor sites for actin-myosin filament bundles
- comparable to Z-disks of skeletal and cardiac muscle
- located along inside of sarcolemma and scattered throughout cytoplasm
False (it just absorbs calcium as it needs it)
T/F: there is voltage involved in smooth muscle contraction
whole cell
when the sarcomere shortens, the ___ ___ contracts
smooth muscle (muscle fibers undergo mitosis themselves and replace damaged tissue)
which muscle tissue has the ability to regenerate all on its own?
cardiac muscle (if you have a heart attach, it is replaced by dense connective tissue scar)
which can't regenerate at all?
skeletal muscle (stem cells called satellite cells are inactive myoblasts that become activated and proliferate and fuse after injury)
which undergoes limited regeneration?
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