A&P chapter 11

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characteristics of muscle tissue

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characteristics of muscle tissue

  • excitability

  • conductivity

  • contractility

  • extensibility

  • elasticity

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The plasma membrane is called the

sarcolemma

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The cell’s cytoplasm is referred to as the

sarcoplasm

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The sarcoplasm contains

normal organelles but also myofibrils, glycogen, myoglobin, and lots of mitochondria

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Myofibrils are long cords made up of

protein

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Myofibrils are this of the fiber

functional unit

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Glycogen is a polysaccharide made up of

chains of glucose

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Glycogen is used during intense exercise and is stored in these

glycosomes

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Myoglobin is a protein that

stores oxygen

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Myoglobin gives muscles their

red color

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The role of the mitochondria in a muscle fiber is to

make ATP by combining sugar and oxygen

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The smooth ER that forms a network around each myofibril is called

the sarcoplasmic reticulum

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Dilated end-sacs of SR which cross the muscle fiber from one side to the other are called

terminal cisternae

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The terminal cisternae stores

calcium

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Tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side are called

T (transverse) tubules

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A triad is made up of

a T tubule and two associated cisternae

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Muscle fibers contain 100’s to 1000’s of

myofibrils

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Myofibrils run

parallel to muscle length

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Myofibrils make up this much of muscle fiber volume

80%

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Myofibrils contain the

sarcomere

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Myofibrils are made up of

myofilaments

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Myofilaments are made of

contractile proteins (actin and myosin) + regulatory proteins (troponin and tropomyosin)

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Thick filaments are made of

myosin

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The two heads on myosin contain

actin-binding sites and an ATP-binding site

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Thin filaments are mostly made of

actin

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A single subunit of actin is called

G (globular) actin

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A string of actin is called

F (filamentous) actin

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G actin contain

the active sites for myosin heads

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Two intertwined F actin filaments make up

the thin filaments

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Tropomyosin

stabilizes the actin filaments & covers the binding site between actin and myosin in a relaxed muscle

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Troponin

bonds the actin, tropomyosin, and calcium

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Titin is a large, elastic, kind of “springy”

protein

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Titin runs through the core of thick filaments and anchors it to

the Z disc and the M line

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Titin helps stabilize and position

the thick filament

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Titin prevents overstretching and

provides recoil to muscle

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A sarcomere is everything between

one Z disc and another Z disc

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These help link the myofibrils with the sarcolemma and to the bones

accessory proteins

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Defects in this protein lead to muscular dystrophy

dystrophin

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Muscular dystrophy results in

the destruction of muscle cells and the replacement with scar tissue

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Someone diagnosed with muscular dystrophy has a life expectancy of about

20 years

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The striations seen on muscle cells are due to

actin and myosin (thick and thin filaments)

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A bands consist of

both thick and thin filaments

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H bands are found

in the middle of the A band

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H bands consist of

thick filaments only

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M line is found

in the middle of the H band (where protein links thick filaments)

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I bands consist of

thin filaments only

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Z disc provides anchorage for

thin filaments and elastic filaments

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Sliding filament theory states that muscles contract when

thick and thin filaments pull on one another, shortening the sarcomere

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structural hierarchy

knowt flashcard image
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A synapse is any place where

a nerve fiber connects to another cell

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A neuromuscular junction is a type of

synapse

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One nerve fiber connects with the muscle fiber at

multiple positions, which increases the speed of the muscle contraction

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A swollen end of a nerve fiber is called

a synaptic knob

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The synaptic knob contains

synaptic vesicles with acetylcholine (ACh)

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The gap between the synaptic knob and the sarcolemma is called

the synaptic cleft

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The mat of collagen and glycoprotein that isolates the NMJ from surrounding tissue is called

the basal lamina

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The basal lamina contains

acetylcholinesterase (AChE)

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AChE breaks down

ACh, allowing fiber relaxation

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A nerve impulse causes the release of neurotransmitters (ACh) via

exocytosis

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Neurotransmitters diffuse across… and bind to receptors on…

the synaptic cleft… the surface of the sarcolemma

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These increase the surface area, giving more space for ACh receptors

junctional folds

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The binding of the neurotransmitter initializes… which causes…

an electrical signal on the sarcolemma… the contraction of the muscle fiber

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Muscle and nerve cells are

electrically excitable

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The membranes of muscles and nerves are

polarized

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The polarization of muscle and nerve membranes is due to

a difference in the ionic concentrations of the ICF and the ECF

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The process of moving toward equilibrium is known as

depolarization

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The process of returning to resting membrane potential is known as

repolarization

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The sodium-potassium pump resets

the action potential system

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4 major steps of the behavior of skeletal muscle fibers

  1. excitation

  2. excitation - contraction coupling

  3. contraction

  4. relaxation

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shortening of one leads to shortening of the other:

sarcomere → myofibril → muscle fiber → fascicle → muscle compartment → whole muscle

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Each muscle cell is supplied by

one neuron

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Each neuron supplies multiple

muscle cells

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One nerve cell and all its associated muscle cells is

a motor unit

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The average motor unit supplies

200 muscle fibers

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3-6 muscle fibers make up… which specializes in fine motor control

a small motor unit

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1000 muscle fibers make up… which specializes in strength

a large motor unit

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A quick cycle of contraction and relaxation when stimulus is at threshold or higher is called

a twitch

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Stimulating the nerve with higher voltages produces… because…

stronger contractions… higher voltages excite more nerve fibers which stimulate more motor units to contract

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The process of using more motor units to strengthen contraction is known as

recruitment/multiple motor unit (MMU) summation

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Higher frequency of stimulations increases… because higher frequency stimuli produce…

contraction strength… temporal (wave) summation

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Warmer temperatures increase… because there is…

contraction strength… increased enzyme activity

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Hydrated muscles increases… because there is…

contraction strength… proper spacing between thick and thin filaments

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ATP supply depends on availability of

oxygen and organic energy source (e.g. glucose and fatty acids)

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2 main pathways of ATP synthesis

  1. anaerobic fermentation

  2. aerobic respiration

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