Skeletal Muscle Cell Biology Flashcards
What are the 4 basic tissues?
Nervous, epithelial, Connective tissue and muscle
WHat are the 3 different types of muscle and which types are volunturay vs involuntary?
skeletal=voluntary
cardiac =involuntary
smooth=involuntary
what are skeletal muscle cells called?
muscle fibers, myocytes
describe the structure of skeletal muscle
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highly strucutered in a hierarchical fashion
- gross muscle
- fasicles
- myocytes
- myofibrils
- myofilament
- myofibrils
- myocytes
- fasicles
how many nuclei do skeletal myocytes have?
100s of nuclei at cell periphery, if in the center=pathology
What are the 3 layers of CT investing skeletal muscle
epimysium (deep fascia): entire muscle
perimysium: invests fasicles (groups of myocytes. continuous wiht the CT at the myo-tendon junction
Endomysium: invests individual myoctes, adjacent to basal lamina
WHat is the unit of contraction and what is seen on light microscopy for muscle
- Z lines demarcate the sarcomere which is the unit of contraction. Z line to Z line.
- Z lines connect I bands
- Nuclei are peripheral
- striated: alternating A bands (dark) and I bands (light)
WHat bisects the I band? What bisects the A band?
I band: Z line
A band: bisected by H-zone/M-line (contains MM-CK)
What do myofibrils contain?
Myofibrils contain myofilaments
- Thick and thin
- Thick: A-bands only
- myosin
- THin: I-bands and A-bands
- actin, 3 troponins, tropomyosin
- Thick: A-bands only
What are T tubules and what is SR?
T (transverse) tuules: invaginate “sarcolemma”
SR=sarcoplasmic reticulum envelopes each myofibril
perpendicular to eachother
What is the strucutre of a Neuromuscular (myoneural) Junction Component?
- pre-synaptc
- cleft
- post-synaptic
- Pre-synaptic
- Ca chananels
- synaptic vesiles (with Ach)
- Cleft: AchE
- Post-synaptic:
- AcHRs facing the cleft
- Na channels in folds (Ach binds, Na channel open and depolarization occurs)
How does an NMJ propogate action potential?
- nerve AP leads to Ca entering the neuron
- synaptic vesicle fuses to pre-synaptic membrane
- Ach is released into cleft
- Ach binds AchReceptor on myocyte
- the above actions are cblocked by succinylcholine or by curariform drugs
- Na enters myocyte which leads to muscle AP
How does skeletal muscle excitation occur?
depolarization of the T tubules releases Cav1.1 which then binds RyR in SR membrane which leads to Ca efflux from the SR into the cytoplasm of the skeletal muscle cell. when Ca levels are higher in the skeletal muscle then contraction can occur.
How does contraction occur?
- Ca binds troponin C which causes tropomyosin to move out of the way.
- ATP i shydrolyzed to ADP and Pi and myosin binds actin
- a power stroke occurs, when thin filaments move into the A-band and the sarcomere shorts. this is contraction
How does the length of the A band change during contraction? How about the length of th I band?
length of the A band is uncahnged
length of the I band is shortened
How does muscle relaxation occur?
- Ca is pumped back into the SR via SERCA. this rewuires phospholamban phosphorylation (phospholamban binding inhibits SERCA; but when phosphoplamaban in phosphorylated it dissociates itself from SERCA freeing SERCA)
WHat is rigor mortis?
in the absence of ATP, myosin stays bound to actin; therefore relxation cant occur, hence “stiffening” occurs
What is malignant hyperthermia and what causes it ?
- volatile anesthetics
- gain of funtion gene mutations
- CACNA1S gene (encodes Cav1.1)
- RYR gene (encodes ryanodine receptor)
- RYR=Ca channel in SR that promotes Ca release
- intervention: dantrolene
- muscle relaxant; inibits Ca release via RYR
WHat is the thick to thin myofibril ratio?
6:1
What are “slow twitch” muscle fibers
- continous contraction (oxidative) aerobic
- red fibers: due to enrichment of myoglobin and mitochondria
- generates ATP from serobic respiration
- susbstrate fatty acids
- used by marathoners
WHat are type II fibers?
“fast twitch” glycolytic
- white fibers due to enrichemnet of glycogen
- generates ATP from anaerobic glycolysis
- susbstrae: glycogen
- used by sprinters
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where can energy for muscle contrction be derived from besides aerobic and anaerobic respiration?
creatine phosphate
what are satellitle cells?
aka skeletal myoblasts
- adult stem cells
- reside in a “niche” inbetween sarcolemma (cell membrane) and basal lamina
- activated from Go after insult to basal lamina
skeletal muscle can regenerate the whole muscle. How does this occur?
- Insult: damage to basal lamina
- Proliferation of “satellite cells”
- satellite cells released from injured basal lamin and they proliferate
- compete with invadinf fibroblasts
- clone: daughter cells cease mitosis
- Fusion: myotube formation (immature muscle cells)
- day 21 there are new skeletal muscle cells
What is myostatin?
- growth factor secreted by skeletal myocytes
- inhibits satellitle cell proliferation
- likely via up-regulation of p21
- KO of myostatin gene=skeletal muscle hypertrophy
- target for inhibition in muscular dystrophy patients
How do you get Duchenne Muscular Dystrophy?
dystrophin mutation.
- treatment: cellular therapy w skeletal myoblasts
- gene therapy w advenovirus-dystrophin cDNA
- drugs
- prednisone
- PTC 124
- gentamicin
- OdN
