Skeletal Muscle (Lecture 6) Flashcards
the important functions of skeletal muscle
locomotion, postural support, and heat production
3 layers of skeletal muscle (in order)
epimysium, perimysium, endomysium
epimysium
surrounds the entire muscle
perimysium
surrounds bundles of muscle fibers (fascicles)
endomysium
surrounds individual muscle fibers
satellite cells
play a role in muscle growth/repair, protein synthesis, and adaptions to strength training (hypertrophy)
the basic function unit of skeletal muscle
sarcomere
the part of the sarcomere that provides structural support to proteins to anchor them in place
M line
the part of the sarcomere that stabilizes and anchors actin
Z line
thick filaments of skeletal muscle
myosin
thin filaments of skeletal muscle
actin
myofibrils
contain contractile proteins (rod-like structures) actin and myosin
terminal cisternae
enlarged portion of SR that acts like a “middle-man”
sarcoplasmic reticulum (SR)
storage sites for calcium (Ca2+) that is responsible for coupling of excitation to contraction of muscle fibers
transverse tubules (T-tubules)
extend from the sarcolemma to SR to allow nerve impulses to be transmitted rapidly to individual fibers (throughout the cell)
signals release of Ca2+ from SR (excitation-contraction coupling)
triad
association of a T-tubule and 2 adjacent terminal cisternae
neuromuscular junction (NMJ)
the connecting point between the a-motor neuron and muscle fiber
motor unit
motor neuron and all fibers it innervates
motor end-plate
region/pocket formed around the motor neuron by sarcolemma
synaptic/neuromuscular cleft
short gap between neuron and muscle fiber
neurotransmitter in the NMJ
acetylcholine (Ach)
acetylcholine
neurotransmitter that is released from motor neurons, diffused through synaptic cleft, binds to receipts on motor end-plate, and causes end-plate potential (EPP)
end-plate potential (EPP)
depolarization of muscle fiber and signal to being the contractile process
excitation-contraction (E-C) coupling
depolarization of motor end-plate (excitation) coupled to muscular contraction
sliding filament model
muscle shortening from the movement of actin filament over myosin filament, causing formation of cross-bridges between actin and myosin filaments
power stroke
series of structural changes in the actin-myosin cross-bridge driven by hydrolysis of ATP
troponin and tropomyosin
proteins that regulate the interaction between actin and myosin (via Ca2+ binding)
the action of troponin/tropomyosin tropomyosin rest to exercise (contraction)
-Ca2+ released from SR
-Ca2+ binds to troponin
-tropomyosin moves away
-exposing the site for actin-myosin interaction
-cross-bridge is formed (contraction)
muscle fatigue
decline in muscle power output, force generation and shortening velocity
power = force x shortening velocity
causes of muscle fatigue in short duration, high intensity exercise (~60 seconds)
accumulation of H+, ADP, Pi, and free radicals (reduces cross bridges)
causes of muscle fatigue in long duration, low intensity exercise (2-4 hours)
muscle factors including accumulation of free radicals, electrolyte imbalance, and glycogen depletion
muscle fiber types
- slow, oxidative, type I
- fast, glycolytic, type II
biochemical properties of muscle fibers
- oxidative capacity
- myosin ATPase isoform type
- amount of contractile protein in fiber
contractile properties of muscle fibers
- maximal force production
- speed of contraction
- maximal power output
- muscle fiber efficiency
