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force of contraction is affected by:

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Biology

11th

22 Terms

1

force of contraction is affected by:

  • number of muscle fibers stimulated to contract

  • relative size of muscle

  • degree of prestretch

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2

muscle tissue is one of the _____ primary body tissues

four

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3

muscle tissue accounts for almost _____ the body’s weight

half

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4

muscle tissue is the dominant tissue of the _______________

heart and other visceral organs

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5

muscle functions:

  • maintain posture

  • stabilize joints

  • generate heat

  • produce movement

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6

smooth muscle tissue:

  • found in walls of visceral organs (other than the heart)

  • spindle-shaped fibers

  • single, centrally located nucleus

  • no striations

  • involuntary

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7

cardiac muscle tissue:

  • makes up the walls of the heart

  • fibers are branched and striated

  • single, centrally located nucleus

  • intercalated disks - fusion of adjacent membranes

  • involuntary

  • bifurcated

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8

skeletal muscle tissue:

  • comprises muscles that are attached to bones

  • fibers are long cylinders w/ tapered ends

  • multinucleated

  • dark striations

  • voluntary

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9

sarcoplasmic reticulum:

  • consists of a network of interlocking tubules that form a network over the sarcomere

  • near the i-bands tubules fuse to form cisternae which occur in pairs

  • function- to store calcium

  • t-tubules

  • calcium triad

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10

sliding filament hypothesis:

  • myosin cross bridges attach to actin

  • cross bridges pull actin over myosin and the sarcomere shortens

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11

muscles grow by:

  • stretching as bones grow in length

  • increasing in diameter due to the addition of actin and myosin filaments in already existing fibers

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12

tension develops when:

  • actin and myosin filaments interact and attempt to slide past one another within the sarcomeres

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13

slow twitch:

  • slow speed of contraction

  • thin with a rich blood supply (gives red color)

  • aka: red fibers

  • contracts for long time but generates little power

  • less actin/myosin

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14

fast twitch:

  • fast contracting fibers

  • large diameter

  • pale in color

  • aka: white fibers

  • contract powerfully but “poop out” quickly

  • a lot of actin/myosin

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15

how is muscle tissue irritated?

stimulus provided by a motor neuron

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16

single twitch contraction:

  • simple contraction resulted from a single electric shock

  • most basic form of a muscle contraction

  • phases: latent period, contraction phase, relaxation phase

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17

summation contraction:

  • contraction of great magnitude

  • results from a second stimulus before end of a contraction

  • phases: absolute refractory period, relative refractory period

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18

tetanus contraction:

  • results from a series of stimuli in rapid succession

  • muscle remains in constant contraction

  • types: incomplete, complete

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19

all muscle contractions that move body parts are __________

complete tetanus contractions

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20

steps of muscle contraction:

  • nerve impulses travel down motorneurons to a neuromuscular junction

  • acteylcholine is released from the motor neuron, crosses the synaptic cleft, and bands to sarcolemma

  • the binding stimulates the release of calcium from the SR inside the muscle fiber

  • released Ca binds with troponin, a protein associated with actin

  • this causes tropomyosin (a ribbon-like protein around actin) to shift and expose myosin binding sites

  • myosin heads bind to these sites, forming cross-bridges

  • cross bridges pull actin over the myosin and the sarcomere shortens

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21

events at the neuromuscular junction:

  • action potential reaches axon terminal of motor neuron

  • calcium channels open and ca enters the axon terminal

  • ca entry causes some synaptic vessels to release their contents (acetylcholine, a neurotransmitter) by exocytosis

  • acetylcholine diffuses across the synaptic cleft and binds to the receptors in the sarcolemma

  • ach binds and channels open that allow simultaneous passage of na into the muscle fiber. more na ions enter than k ions leave and this produces a local change in the electrical conditions of the membrane (depolarization), which eventually leads to an action potential

  • ach effects are ended by its breakdown in the synaptic cleft by the enzyme acetylcholinesterase

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22

creatine phosphate cycle:

CP → muscle contraction → free creatine → stimulates production of RNA → myosin/actin → added to muscle → stronger contraction → more CP → (repeat)

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