93 terms

DAT Bootcamp - Muscular System

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what are the 3 types of muscle?
smooth; cardiac; skeletal
where is smooth muscle found?
walls of organs, airways, and blood vessels
smooth muscle contracts and relaxes _____
involuntarily
smooth muscle is _____, so it lacks _____
not striated, sarcomeres
smooth muscle cells are _____, and they have _____ nucleus/nuclei per cell
short & tapered; 1
sarcomeres
give muscles a striated appearance
cardiac muscle is found in the heart, and it contracts _____
involuntarily
cardiac muscle is _____, and it contains _____ nucleus/nuclei per cell
striated (has sarcomeres); 1
intercalated discs are found in _____ muscle
cardiac
intercalated discs hold adjacent cardiac muscle cells (_____) together, which allows for the heart _____
cardiomyocytes; syncytium
what are the components of an intercalated disc?
desmosomes and gap junctions
_____ cells are long, multinucleate, and striated
skeletal muscle
skeletal muscles are under _____ control
voluntary
what are the "levels of bundles" in skeletal muscles?
muscle belly --> fascicles --> muscle fibers --> myofibrils
what is the protective sheath encasing all the fascicles contained in a muscle belly?
epimysium
what is the protective sheath found between the fascicles of a muscle belly?
perimysium
what is the protective sheath found between muscle fibers of an individual skeletal muscle fascicle?
endomysium
_____ are skeletal muscle cells
muscle fibers
what is the plasma membrane of a muscle fiber called?
the sarcolemma
what is the cytoplasm of a muscle fiber called?
the sarcoplasm
muscle fibers contain an array of organelles arranged in parallel, what are they called?
myofibrils
myofibrils contain protein _____
myofilaments
myofibrils are composed of many repeating functional units, called _____
sarcomeres
what are the main myofilament proteins of a myofibril?
actin and myosin
sarcomeres are the functional unit of a muscle fiber, which _____ to facilitate muscle contraction
shorten
sarcomeres contain _____
myofilaments (actin and myosin)
the _____ model explains how myofilaments slide past one another to shorten the sarcomeres of a muscle fiber
sliding filament
do myofilaments shorten during contraction?
no, the sarcomere shortens because myofilaments slide past each other
what is the space between the presynaptic motor neuron and postsynaptic muscle fiber called?
neuromuscular junction
what neurotransmitter is released into neuromuscular junctions?
acetylcholine
acetylcholine facilitates the opening of _____ channels on the muscle fiber
ligand-gated Na+
_____ allow action potentials to spread through muscle fibers quickly, coordinating the contraction
t-tubules
what is the specialized smooth endoplasmic reticulum (ER) found in muscle fibers?
the sarcoplasmic reticulum (SR)
the stores _____ ions
Ca2+
what causes voltage-gated Ca2+ channels to open on the sarcoplasmic reticulum (SR)?
a wave of depolarization traveling down t-tubules
where does Ca2+ flow after it leaves the SR?
the sarcoplasm
what is the resting state of a muscle?
contracted
_____ covers actin's binding site for myosin when muscle fibers are not stimulated
tropomyosin
_____ hold tropomyosin in place over actin's binding site for myosin
troponin complexes
how does troponin move tropomyosin?
Ca2+ released from the SR binds to troponin-C, which triggers a shape change that moves troponin and therefore tropomyosin
myosin heads are _____ (enzymes)
ATPases
a _____ occurs when myosin (thick myofilaments) bind to actin (thin myofilaments) after muscle fiber stimulation
cross-bridge
cross-bridges form when myosin ATPases _____ and enter their high-energy state
hydrolyze ATP
the power-stroke occurs myosin _____ to enter a low energy conformation
releases ADP + Pi

(the power-stroke occurs after the initial formation of a cross-bridge)
what releases the cross-bridge after the power-stroke has occurred?
ATP binding to myosin
why does rigor mortis occur in dead animals?
no ATP is being produced, so cross-bridges cannot be released
when the brain stops sending nerve signals for contraction, contraction stops - what happens to Ca2+?
it re-enters the SR by active transport
the _____ represents the periphery (end) of each sarcomere
Z disk
the _____ represents the midpoint of each sarcomere
M line
_____ branch from the Z disk toward the M line
thin actin myofilaments
_____ branch from the M line toward Z disk
thick myosin myofilaments
_____ are areas where only actin is present (includes the Z disk)
I bands
_____ are areas where myosin and actin overlap
A bands
all bands and zones of a sarcomere shorten/disappear during a muscle contraction, with the exception of _____
the A band
the _____ is an area where only myosin is present
H zone
a _____ is all the muscle fibers innervated by 1 motor neuron
motor unit
describe the general concept of a small motor unit:
1 motor unit with few muscle fibers
_____ movements are created by small muscles with many small motor units
precision
describe the general concept of a large motor unit:
1 motor unit with many muscle fibers
_____ movements are created by large muscles with few large motor units
powerful
a _____ is a brief muscle fiber contraction after a single action potential stimulates an entire motor unit
twitch
describe the all-or-nothing principle of muscle contraction:
either the depolarization is above threshold (all fibers in the unit twitch) or it is below threshold (no fibers in the unit twitch)
what are the 3 phases of a twitch contraction?
latent; contraction; relaxation
describe the basics of what occurs during the latent phase of a twitch:
action potential --> t-tubules --> SR opens voltage gated Ca2+ channels
describe the basics of what occurs during the contraction phase of a twitch:
Ca2+ binds to troponin-C --> actin's binding sites are uncovered --> cross-bridges --> H-zone shrinking (sarcomere shortening)
describe the basics of what occurs during the relaxation phase of a twitch:
active pumping of Ca2+ back into the SR --> actin's binding sites are covered
the speed a twitch contraction occurs is related to _____
muscle fiber type
what are the 3 muscle fiber types?
slow oxidative fibers (type I); fast oxidative-glycolytic fibers (type II-a); fast glycolytic fibers (type II-b)
what are the general characteristics of slow oxidative (type I) muscle fibers?
dark red; aerobic; weak; efficient; fatigue resistant
what are the general characteristics of fast oxidative-glycolytic (type II-a) muscle fibers?
dark red; aerobic/anaerobic; strong; intermediate efficiency and fatigue resistance
what are the general characteristics of fast glycolytic (type II-b) muscle fibers?
white; anaerobic; strongest; inefficient and fatigue quickly
the force of a muscle twitch varies due to _____
summation mechanisms
what are the 2 types of summation?
wave (temporal) summation; motor unit summation
in _____, tension waves stack for a stronger contraction
wave summation
in _____ a twitch occurs before completion of a previous twitch
wave summation
twitches blend during _____, which means tension can no longer increase, and there is maximal motor unit stimulation
tetanus
twitches blend during tetanus, which means tension can _____, and there is _____
no longer increase; maximal motor unit stimulation
action potentials travel to different motor units at different times in _____
motor unit summation
describe the size principle of motor unit recruitment:
small motor units are recruited 1st, then larger units are recruited to achieve the proper tension
how does the size principle of motor unit recruitment avoid fatigue?
different motor units within the same muscle are being stimulated at different times, giving units a chance to relax
what is muscle tone (tonus)?
weak, involuntary twitches of small groups of motor units, which keeps muscles firm
_____ (muscle tone/tonus) creates flaccid muscles
hypotonicity
why might hypotonicity occur in a skeletal muscle?
damage to the peripheral nervous system or reduced electrolytes
what is an example of a condition that may cause hypotonicity in a skeletal muscle?
carpal tunnel (results in weakness/numbness)
_____ (muscle tone/tonus) creates spastic, rigid muscles
hypertonicity
why might hypertonicity occur in a skeletal muscle?
damage to the central nervous system
what is an example of a condition that may cause hypertonicity in a skeletal muscle?
stroke
what are the 2 main types of voluntary skeletal muscle contractions?
isotonic & isometric
what are the 2 types on isotonic contractions?
concentric and eccentric
what are the 3 main functional groups of skeletal muscles?
agonists (primary movers); antagonists; synergists
_____ are muscles involved in preforming a desired motion
agonists
_____ produce the opposite motion to agonists
antagonists
_____ are muscles that help primary movers and provide support to joints
synergists
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