Lecture 17 9/20/23 Flashcards
What is the term for a muscle cell?
muscle fiber
What are the characteristics of muscle fibers?
-multiple nuclei
-many mitochondria and other organelles
What is the sarcolemma?
-the outer membrane around the muscle fiber
-equivalent to the plasma membrane of other cells
How many motor neurons innervate each muscle fiber?
one
Why does each muscle fiber only have one innervation?
so that the muscle fiber can only be triggered to move in one direction at any one time
What are the parts of a sarcomere?
-Z line
-I band
-A band
-H zone
-M line
What is the Z line?
periphery of sarcomere where thin actin filaments attach
What is the I band?
light area containing only actin
What is the A band?
dark area where actin and myosin overlap
What is the H zone?
center light zone with only myosin
What is the M line?
middle of the sarcomere, within the H zone
What are the characteristics of actin?
-thin protein filaments
-intertwines with tropomyosin
-intermittently bound troponin
What are the characteristics of myosin?
-thick filaments
-intertwined helices with globular heads
-binds ATP and actin
What are the characteristics of the sarcoplasmic reticulum?
-surrounds the myofibrils
-stores calcium at rest
-releases calcium rapidly during an action potential
Why are the transverse tubules important?
they allow for better signal transmission and faster movement of Ca2+
What are the steps of an action potential/muscle contraction?
-Ach released at NMJ
-nicotinic Ach receptors on sarcolemma activated
-voltage-gated Na+ channels opened
-action potentials spread
-Ca2 released from sarcoplasmic reticulum
-contraction initiated
How is the DHP receptor involved with action potentials/muscle contraction?
-action potential in T-tubule alters DHP rec. conformation
-DHP rec. opens Ca2+ ion channels in SR, allowing Ca2+ to enter cytoplasm
-Ca2+ binds to troponin, allowing actin-myosin binding
What are the characteristics of milk fever?
-semi-paralysis in dairy cows
-hypocalcemia
-less Ach released
-less depolarization of sarcolemma
-unable to contract muscles/too weak
What are the characteristics of puerperal tetany?
-hypocalcemia after whelping (dogs)
-muscle rigidity
-hyper-contraction due to more permeable Na+ channels and hyper-depolarization
What are the steps of excitation-contraction coupling?
-increased calcium in sarcoplasm
-additional calcium binds to troponin
-tropomyosin moves, exposing the myosin-binding site on actin
What are the steps of shortening the sarcomere?
-ATP binds myosin head
-myosin no longer bind actin
-enzymes on myosin head hydrolyze ATP
-ADP and Pi change myosin’s conformation so it strongly binds actin again (cross-bridging)
-ADP and Pi released from myosin
-myosin head flexes, pulling actin towards center
What are the characteristics of riger mortis?
-shortening of muscle fibers w/o action potentials
-not enough ATP to release myosin head from actin
What are the characteristics of fast twitch/type II fibers?
-larger
-extensive SR/rapid Ca2+ release
-fewer mitochondria
-less extensive blood supply
-quick fatigue
-more powerful
What are the characteristics of slow twitch/type I fibers?
-darker color due to more myoglobin
-rich blood supply
-more mitochondria
-more aerobic
-longer-lasting energy
What are the two subdivisions of type II fibers?
-type IIA: intermediate between slow and fast twitch
-type IIB: traditional fast twitch
How do muscle fibers differ between dogs?
-endurance athletes have more type 1 muscle fibers
-sprint athletes have more type II muscle fibers
What nutrient supplies dogs’ muscles with energy?
fats
