Muscles Flashcards
Myocyte
= muscle fiber
individual muscle cell
sarcoplasm
muscle cytoplasm
sarcolemma
plasma membrane or plasmalemma
what are the 3 types of mucles?
- skeletal
- smooth
- cardiac
all mesodermally derived
skeletal muscle
responsible for movement, voluntary moto control
syncytia
skeletal muscle cells are multinucleated to form this
myoblasts undergo fusion into i
multinucleated myotube
myotubes
synthesize contractile proteins which assemble into sarcomeres
What happens to nuclei when it migrates to periphery of cell
lose ability to proliferate
endomysium
Individual muscle fibers surrounded by connective tissue
fascicles (= fasciculi)
“bundles”
fibers bound together
perimysium
- Fascicles surrounded by connective tissue perimysium
- many fascicles together form muscle
epimysium
Entire muscle surrounded by epimysium, continuous with tendinous attachment
what do blood vessels and neurons tend to follow in connective tissue?
epi- and perimysia for support
two major types of biers in skeletal muscles
- slow twitch
2. fast twitch
Type I, Slow Twitch Fibers
- “Slow” myosin
- Small fibers with large amount of myoglobin
- Use 1’ aerobic respiration for oxidative metabolism
- Large # of mitochondria (=> ATP for energy)
- Resistant to fatigue, but generate only moderate M tension
- Common in peripheral limbs
Type II, Fast twitch, fibers
- “Fast” myosin
- Largefibers with less myoglobin & fewer mitochondria
- Use 1’ anaerobic glycolysis for energy production
- Abundant glycogen
- Extensive sarcoplasmic reticulum for rapid Ca release
- Fatigue rapidly, but generate high M tension for short bursts of activity
Intermediate fibers consists of what tyoes?
Type IIA and Type IIB
Type IIA
oxidative & fatigue resistant
Type IIB
glycolytic & fatigue sensitive
intermediate metabolites (e.g., lactic acid)
- During peak periods of exertion, both Type I & Type II fibers metabolize glycogen via anaerobic glycolysis to produce ATP
- Results: precipitate as crystals in Mm => tearing of Mm fibers & pain after heavy exertion
Oxygen debt
ischemia& Mm cramps, even cell death
rhabdomyolysis
breakdown of actin and myosin
myoglobinuric nephrosis
subsequent kidney failure
Extremem exertion may lead to what?
rhabdomyolysis and myoglobinuric nephrosis
during normal exercise, muscle fibers delvelop___
micro tears
hypertrophy
With exercise, Mm cells ↑in size
- Due to ↑in # of mitochondria, & ↑in volume of contractile proteins; splitting/ branching of individual Mm fibers
- Production of new Mm fibers relatively rare
atrophy
With disuse, Mm cells ↓in size
- Due to immobilization (e.g., splint, cast), denervation(N damage => Mm atrophy)
sarcopenia
With ↑age, also get progressive loss of skeletal Mm fibers
-not replaced => ↓# & ↓Mm mass
muscle size changes due to 2 possibilities
- hypertrophy
- atrophy
- Age
Response to injury for skeletal muscles?
- limited ability to regenerate following injury
- Regeneration 1’ due to satellite cells, small myogenic cells adjacent to sarcolemma
- Proliferate following injury, differentiate into myoblasts
intrafusal fibers
Modified skeletal Mm fibers associated with modified Nerve endings
- neuromuscular spindles
- neurotendinous spindles
Neuromuscular spindles
(= muscle spindles)—located within belly of Mm; sensitive to changes in length
Neurotendinous spindles
(=Golgi tendon organs)—located within tendon; sensitive to changes in tension
postural reflexes
Both prevent overstretching & tearing of Mm
Ultrastructure
- Individual Mm fibers composed of myofibrils
- Actin & myosin present in ~ 2:1 ratio in skeletal Mm
myofibrils
composed of numerous myofilaments, or contractile proteins, in parallel bundles
2 types of myofilaments:
- Actin (thin)
2. Myosin (thick)
