ICL 3.2: Histology of Muscle Flashcards
what are the layers of a muscle?
muscle –> fascicle –> muscle fibers/myocyte –> myofibril –> myofilaments (thick and thin)
what are thick and thin myofilaments also called?
thin = thin actin filaments
thick = thick myosin filaments
what are the boundaries of a sarcomere?
z line to z line is a sarcomere
what is the I band composed of?
ONLY actin thin filament
the Z band is also in the I band
what is the H band composed of?
ONLY myosin thick filament
the M line is also in the H band so think M and M
what is the sarcolemma?
the membrane surrounding a muscle fiber/myocyte
what is the function of the sarcoplasmic reticulum?
storage of calcium
it’s a network inside of a muscle fiber the goes in-between all the myofibrils in the sarcoplasm
what is the terminal cisternae?
a dilation of the sarcoplasmic reticulum that hug T tubules
T tubules are an invagination of the sarcolemma which allows depolarization to get to all the myofibrils
what is a muscle triad?
a T tubule + 2 cisternae
located at the AI junction
what is the connective tissue covering the layers of muscle?
- epimysium = covers the entire muscle
- perimysium = covers each fasicle
- endomysium = covers individual muscle fibers
what does skeletal muscle look like on histology slides?
you can see fascicles arraigned in parallel fashion
you can also see a clear/lighter pink epimysium
skeletal muscle also has a lot of peripheral nuclei!
what is thick filament made of?
myofibrils are either thick or thin – thick filaments are often called myosin
so thick filament is made up of multiple myosin molecules
1 myosin molecule = 4 light chains and 2 heavy chains
what is thin filament made of?
myofibrils are either thick or thin – thin filaments are often called actin
1 thin filament = actin + tropomyosin + troponin
what are the 3 components of troponin?
Tc = binds calcium
Tt = binds tropomyosin
Ti = binds actin
Ca binds and changes configuration of troponin so the myosin binding sites on actin get exposed so that myosin can bind
what are the 2 types of skeletal muscle fibers?
type I and type 2
what are type I skeletal muscle fibers?
- fatigue-resistant
- large amounts of myoglobin and mitochondria
- aka red muscle
- use oxidative phosphorylation
ex. postural muscles
what are type II skeletal muscle fibers?
- they use anaerobic glycolysis
- fatigue-prone but they’re the fast muscles for quick precise movement
- large number of glycolytic enzymes
- aka white muscle
what is dystrophin?
it’s found in the sarcolemma of a muscle fibers and it helps to anchor actin to transmembrane proteins
what happens when there’s a dystrophin mutation/deficiency?
duchenne and becker’s muscular dystrophy –> duchenne is more severe and is a frameshift mutation
they result from defective dystrophin proteins formation which inhibits muscle regeneration
patients often have giant calves
what is a cardiac diad?
T tubule + 1 terminal cisternae
the diad is located at the z-line1/2020-1/2021
how many nuclei does cardiac muscle fiber have?
1 nuclei
skeletal muscle usually has multiple
what does cardiac muscle look like on histology?
branching muscle fibers; not as parallel as muscle fibers
nuclei are centrally located
there are intercalated discs too
what are the two types of smooth muscle?
- multi-unit
2. visceral (main type)
what is multi-unit smooth muscle?
it is found only in a select few areas of the body, e.g. ciliary muscle, muscles of iris, and arrector pili muscle of the skin
what is visceral smooth muscle?
more abundant that multi-unit smooth muscle
it is found in the walls of most viscera of the body, including the gastrointestinal tract, bile ducts, ureters, uterus, and many blood vessels
what are dense bodies?
smooth muscles don’t have z-disks, they have dense bodies but they serve the same function
what are caveolae?
they take place of T tubules in smooth muscle
smooth muscle fibers are smaller so we don’t need the extensive invagination as we see in the T tubules in skeletal and cardiac muscle
what does smooth muscle look like histologically?
TONS of nuclei all throughout the cytoplasm
what are the striations, nucleus, T-tubules, type of innervation and cell-to-cell junction seen in skeletal muscles?
striations = present
nucleus = multiple, peripheral
T-tubules = present
innervation = voluntary
cell-to-cell junction = none
what are the striations, nucleus, T-tubules, type of innervation and cell-to-cell junction seen in cardiac muscles?
striations = present
nucleus = one or a few, centrally located
T-tubules = present
innervation = involuntary
cell-to-cell junction = intercalated discs
what are the striations, nucleus, T-tubules, type of innervation and cell-to-cell junction seen in smooth muscles?
striations = absent
nucleus = single, centrally located
T-tubules = absent
innervation = involuntary
cell-to-cell junction = gap junctions
how does smooth muscle contract?
actin filaments of smooth muscle slide in opposite directions due to arrangement of myosin heads
this allows smooth muscle to contract really really well which we need like in our GI!
what’s the difference in the thick filament of the different muscles?
skeletal and cardiac muscle have bipolar thick filament which makes them limited in their movement and they can only go to the M line
smooth muscle on the other had has side-polar thick filament which can contract all the way to opposing sides which allows it to contract stronger
when skeletal muscle contracts, do the following structures shorten, stay the same length, or elongate?
Sarcomere H band I band A band M line Myofilaments
Sarcomere = shortens
H band = shortens
I band = shorten
A band = stay the same length
adjacent M lines = shorten; get closer together
myofilaments = stay the same length
during marathon training, percentage of what would increase?
type I muscle fibers!
the i band is bisected by what?
z line
the M line is located in the middle of what structure, band or line?
A band, H band and sarcomere!
