1108 F24 4.01 Motor units and skeletal systems

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35 Terms

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Muscle contractions are analog

Graded

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Muscles require

antagonistic muscle groups

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One muscle fiber =

one muscle cell (multinucleate)

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Myofibril =

structure within muscle cell with repeating sarcomeres

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Sarcomere

contractile unit; alternating light/dark units

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A-C

one length of actin filament

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B-D

One length of myosin

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Two mechanisms for grading muscle contractions

number of cells that contract (number of active neurons) or cary the rate at which fibers are stimulated

<p>number of cells that contract (number of active neurons) or cary the rate at which fibers are stimulated</p>
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A twitch results from a

a single action potential in a motor neuron

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more rapidly delivered action potentials produce a graded contraction by

summation

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Tetanus

maximum contraction possible

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oxidative

oxidative phosphorylation generates ATP

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oxidative phosphorylation

requires lots of mitochondria, requires lots of oxygen (myoglobin) = red, slow but comparatively inexhaustible source of ATP

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glycolytic

glycolysis generates atp

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glycolytic

less mitochondria needed, less oxygen needed = white, fast but rapidly exhausted source of ATP

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fast twitch fibers; brief powerful contractions

glycolytic fewer mitochondria, rapid release, appear white due to low concentration of myoglobin (oxygen carrier) quick to fatigue; specialized for burst of activity

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slow twitch fibers

oxidative, slower release and uptake of Ca2+, appear red due to high myoglobin conc, slow to fatigue, specialized for endurance

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intermediate fibers- varying contractile properties

oxidative and glycolytic, appear pink to red, contractile properties carry, but are intermediate between fast and slow-twitch

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hydrostatic skeleton is the main type of skeleton in

cnidarians, flatworms, nematodes, and annelids

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exoskeleton is a

hard encasement deposited on the surface of an animal

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hydrostatic skeleton consists of

fluid held under pressure in a closed body compartment.

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exoskeletons are found in most

mollusks and arthopods

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exoskeletons are not composed

of cells and so must be shed for the animal to grow

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the exoskeleton constraints

the contraction size of the muscle

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an exoskeleton consists of

hard support elements such as bones, buried in soft tissue

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endoskeletons are found in

sponges, echinoderms, vertebrates/chordates

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a mammalian skeleton has more than 200 bones

some bones are fused; others are connected at joints by ligaments that allow freedom of movement

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antagonistic muscles in hydrostatic skeletons

-works by squeezing water, which moves the structure it surrounds
-longitudinal muscles run length of animal, circular muscles run circumference of animal
- longitudinal contracts while circular muscle relaxes and vice versa
- relaxed = stretched out. contracted = compressed
(think of movement as like an accordian)
found in invertebrates

<p>-works by squeezing water, which moves the structure it surrounds<br>-longitudinal muscles run length of animal, circular muscles run circumference of animal <br>- longitudinal contracts while circular muscle relaxes and vice versa <br>- relaxed = stretched out. contracted = compressed<br>(think of movement as like an accordian)<br>found in invertebrates</p>
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flexor

contracts to bring two bones in an arc towards each other

<p>contracts to bring two bones in an arc towards each other</p>
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extensor

contracts to straighten the bones out

<p>contracts to straighten the bones out</p>
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antagonistic muscles in endoskeletons

found in sponges, starfish, and chordates

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antagonistic muscles in exoskeletons

Found in arthopods and mollusks; same idea as in endoskeletons except not enough room for muscles to contract

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Unlike the action potentials that control them, muscle contractions are graded (a muscle can be contracted fully, not at all, or some degree in between). How is this accomplished?
Vary the number of activated myosin motor proteins (thick filaments)
Vary the number of activated motor units
Vary the amount of calcium released by the sarcoplasmic reticulum
Vary the frequency of action potentials in the motor neuron
Vary the number of T tubules depolarized
Vary the size of the action potential in the efferent neuron

Vary the number of activated motor units
Vary the frequency of action potentials in the motor neuron

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Compared to oxidative skeletal muscle fibers, those classified as glycolytic typically have _____.
more sensitivity to fatigue
a darker visual appearance
a higher density of mitochondria
a higher concentration of myoglobin
all of the above
none of the above

Fast-twitch - brief, rapid, powerful contractions
Glycolytic (fewer mitochondria)
Rapid release and uptake of Ca2+
Appear white due to low myoglobin concentration
Quick to fatigue; specialized for bursts of activity
Slow-twitch - long, sustained contractions
Oxidative (many mitochondria)
Slower release and uptake of Ca2+
Appear red due to high myoglobin concentration
Slow to fatigue; specialized for endurance

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Muscles generate force for moving the body, and muscles are arranged in antagonistic pairs in animals with endoskeletons, exoskeletons, and hydrostatic skeletons. This statement is:
True for all skeleton types (endoskeleton, exoskeleton, hydrostatic skeleton)
True for endoskeletons and exoskeletons, but not hydrostatic skeletons
True for endoskeletons only
False: Muscles are never arranged in antagonistic pairs, as their actions would then cancel each other and no net movement results

True for all skeleton types (endoskeleton, exoskeleton, hydrostatic skeleton)