A&P chapter 11

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characteristics of muscle tissue

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1

characteristics of muscle tissue

  • excitability

  • conductivity

  • contractility

  • extensibility

  • elasticity

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The plasma membrane is called the

sarcolemma

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3

The cell’s cytoplasm is referred to as the

sarcoplasm

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4

The sarcoplasm contains

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

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5

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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9

Myoglobin is a protein that

stores oxygen

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10

Myoglobin gives muscles their

red color

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11

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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13

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

terminal cisternae

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14

The terminal cisternae stores

calcium

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15

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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19

Myofibrils make up this much of muscle fiber volume

80%

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20

Myofibrils contain the

sarcomere

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21

Myofibrils are made up of

myofilaments

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22

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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38

Defects in this protein lead to muscular dystrophy

dystrophin

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39

Muscular dystrophy results in

the destruction of muscle cells and the replacement with scar tissue

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40

Someone diagnosed with muscular dystrophy has a life expectancy of about

20 years

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41

The striations seen on muscle cells are due to

actin and myosin (thick and thin filaments)

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42

A bands consist of

both thick and thin filaments

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43

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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46

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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48

Sliding filament theory states that muscles contract when

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

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49

structural hierarchy

knowt flashcard image
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50

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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52

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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54

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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63

Muscle and nerve cells are

electrically excitable

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64

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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68

The sodium-potassium pump resets

the action potential system

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69

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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71

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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81

Warmer temperatures increase… because there is…

contraction strength… increased enzyme activity

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82

Hydrated muscles increases… because there is…

contraction strength… proper spacing between thick and thin filaments

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83

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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85

Two enzyme systems control phosphate transfers in muscle cells

  1. myokinase

  2. creatine kinase

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86

This enzyme transfers Phosphate from one ADP to another, converting the latter to ATP

myokinase

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This enzyme obtains Phosphate from a phosphate-storage molecule creatine phosphate (CP) and gives it to ADP

creatine kinase

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88

Excess postexercise oxygen consumption is also known as

oxygen debt

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89

The loss of contractility due to prolonged use of muscle is known as

muscle fatigue

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90

Muscle fatigue in high-intensity exercise results from

  • potassium accumulation in the ECF which reduces excitability of the muscle fiber

  • excess ADP and phosphate which slow cross-bridge movements (actin and myosin interaction)

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Muscle fatigue in low-intensity exercise results from

  • fuel depletion as glycogen and glucose levels decline

  • electrolyte loss through sweat which can decrease muscle excitability

  • central fatigue = when fewer motor signals are issued from the brain

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Muscular strength depends on

  • fascicle arrangement

  • size of motor units

  • multiple motor unit summation

  • temporal summation

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93

Muscle conditioning will

  • increase muscle size (by increasing the number of myofibrils and forming more actin-myosin cross-bridges)

  • increase muscle endurance

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Types of muscle conditioning

  • resistance training - builds strength only (ex: weightlifting)

  • endurance training - builds endurance only (ex: aerobic exercise)

  • cross-training - combines resistance and endurance training

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2 major classes of muscle fibers

  • slow-twitch → long-term motion

  • fast-twitch → short-term motion

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Differences between fiber types

knowt flashcard image
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97

Contributing factors to involuntary muscle spasms:

  • too few electrolytes

  • dehydration

  • stress-induced muscle fatigue

  • excessive caffeine or other stimulants

  • lack of sleep/exhaustion

  • poor muscle condition

  • low blood sugar

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98

Functional properties of cardiac muscle:

  • contracts with regular rhythm

  • works in sleep or wakefulness, without fail, and without conscious attention

  • highly resistant to fatigue

  • muscle cells of a given chamber must contract in unison

  • contraction must last long enough to expel blood

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99

Cardiac muscle is made of cells called

cardiocytes/myocariocytes

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100

Cardiocytes are joined by

intercalated discs

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