A&p.skeletal.muscle.histology,3

Front 1

what percentage of body weight does muscle tissue account for?

Back 1

50%

Front 2

what is skeletal tissue?

Back 2

-striated
-moves the body by pulling on bones of the skeleton (how we walk, dance, etc);
-voluntary and subconscious movement
-Have multiple nuclei

Front 3

what type of movement is involved?

Back 3

voluntary and subconscious

Front 4

what is cardiac tissue?

Back 4

-striated
-move blood through blood vessels
-Only in the heart
-Interconnected at intercellular junctions called intercalated discs

Front 5

what are intercalated discs?

Back 5

intercelluar junctions

Front 6

what is smooth muscle tissue?

Back 6

-non-striated
-organs; move fluids and solids along the digestive tract and regulate the diameters of small arteries
-Example: blood vessels, hair follicles
-Found throughout the body

Front 7

what are the seven functions of skeletal muscle?

Back 7

1. produces whole body movements
2. stabilizes body positions- posture muscles are constantly contracted
3. storing and moving substances within- example: heart, veins
4. generating heat
5. support soft tissues
6. guard entrances and exits
7. provide nutrient reserves

Front 8

what is muscle tissue specialized for?

Back 8

contraction

Front 9

how does the skeletal muscle generate heat?

Back 9

-thermogenesis: shivering
-muscle contractions require energy that sometimes gets turned into heat

Front 10

what are the four properties of skeletal muscle?

Back 10

1. electrical excitability
2. contractility
3. extensibility
4. elasticity

Front 11

what is contractility?

Back 11

ability to contract forcefully

Front 12

what is electrical excitability?

Back 12

responding to a chemical

Front 13

what is extensibility?

Back 13

ability to stretch without damage (stomach, heart)

Front 14

what is elasticity?

Back 14

ability to return to original length after being stretched

Front 15

what is the subcutaneous layer?

Back 15

(superficial fascia)
-separates muscle from skin
-areolar and adipose
-nerve,blood, and lymph vessels

Front 16

what give functions does the subcutaneous layer provide?

Back 16

1. insulation
2. nourishment
3. cushion
4. protection
5. shock absorption

Front 17

what is the fascia?

Back 17

-covers surface of muscle
-dense irregular CT
-holds muscles with similar functions together
-nerve, blood, and lymph vessels

Front 18

what three layers extend from fascia?

Back 18

1. epimysium
2. perimysium
3. endomysium

Front 19

what is the epimysium and what two things does it do?

Back 19

-dense irregular CT of collagen fibers
1. surrounds/wraps around the entire muscle
2. separates muscle from surrounding tissues and organs

Front 20

what is the perimysium and what does it do?

Back 20

-dense irregular CT
-it divides the skeletal muscle into series of compartments called fascicles

Front 21

what are fascicles?

Back 21

a series of compartments that the skeletal muscle gets divided into by the perimysium

Front 22

what is the perimysium a continuation of?

Back 22

its a continuation/extension of the epimysium

Front 23

what does the perimysium contain?

Back 23

blood vessels and nerves that maintain the blood flow and innervate muscle fibers

Front 24

what is the endomysium and what do things does it do?

Back 24

-areolar CT
1. surrounds the individual skeletal muscle cells
2. loosely interconnects adjacent muscle fibers

Front 25

what is a tendon?

Back 25

attaches muscle to a specific point on a bone

Front 26

what is an aponeurosis?

Back 26

provides attachment over a broad area that may involve more than one bone

Front 27

where are tendons and aponeuroses formed?

Back 27

at the end of the skeletal muscle when the collagen fibers merge together to form these bundles

Front 28

what is the diameter of a skeletal muscle cell?

Back 28

10-100um

Front 29

what is the length of a skeletal muscle cell?

Back 29

4-12in

Front 30

what are skeletal muscle cells developed by?

Back 30

multinucleated cells

Front 31

what are multinucleated cells formed by?

Back 31

fusion of more than or equal to 100 mesodermal myoblats

Front 32

what are myoblasts?

Back 32

groups of embryonic cells

Front 33

how big are mature muscle fibers?

Back 33

enormous

Front 34

what causes muscle growth?

Back 34

hypertrophy which is when each muscle cell/fiver gets bigger

Front 35

what is hypertrophy?

Back 35

each muscle cell/fiber gets bigger by 1. human growth hormone, and 2. testosterone

Front 36

what are the eight organelles that make up a muscle fiber?

Back 36

1. sarcolemma
2. sarcoplasm
3. nebulin
4. t-tubules
5. sarcoplasmic reticulum
6. myofibrils
7. sarcomeres
8. titin

Front 37

where do unfused myoblasts remain?

Back 37

in the endomysium

Front 38

what happens at multinucleate cells begin differentiating into skeletal muscle fibers?

Back 38

they enlarge and begin producing the proteins involved in muscle contraction

Front 39

what do the genes in the nuclei of skeletal muscle cells control?

Back 39

the production of enzymes and structural proteins required for normal muscle contractions

Front 40

what happens as more copies of the genes in the nuclei are produced?

Back 40

the faster the proteins can be produced

Front 41

what is the sarcolemma?

Back 41

-the plasma membrane of the skeletal muscle fiber
-separates sarcoplasm from surrounding interstitial fluid

Front 42

what does the sarcolemma have the ability to do?

Back 42

change the transmembrane potential with its selective permeability

Front 43

what is the transmembrane potential?

Back 43

uneven distribution of charges on either side of the sarcolemma

Front 44

what is the sarcoplasm of a skeletal muscle fiber?

Back 44

-muscle cell cytoplasm surrounding the myofibrils

Front 45

what does the sarcoplasm store and for what?

Back 45

glycogen for energy

Front 46

what does the sarcoplasm consist of?

Back 46

1. glyocen for energy
2. myoglobin

Front 47

what is myoglobin and what do you need it for?

Back 47

a specialized protein that binds to oxygen and is needed for energy and metabolism

Front 48

what is nebulin and what may it regulate?

Back 48

-its a non-elastic protein that runs the length of the thin filament anchoring it to the z-disc during development
-it may regulate the length of the filament

Front 49

what does the nebulin do?

Back 49

it holds the F-actin strand together

Front 50

what are t tubules?

Back 50

(transverse tubules) narrow tubes that are continuous with the sarcolemma and form passageways through the muscle fiber for action potential

Front 51

what are t-tubules filled with?

Back 51

extracellular fluid

Front 52

what are t-tubules, what do they encircle, and what do they wrap around?

Back 52

-they are invagination of the sarcolemma which carry AP
-they encircle each sarcomere and wraps around the myofibrils

Front 53

what is significant about where the tubule wraps around myofibrils?

Back 53

it is where is the tubule is tightly bound to the membranes of the SR

Front 54

what is the sarcoplasmic reticulum related to and what does it form?

Back 54

-(SR) related to the smooth ER
-consists of triads
-it forms a tubular network around each individual myofibril and terminal cisternae (expanded chambers) at the T-tubules

Front 55

how is the sarcoplasmic reticulum related to the smooth ER?

Back 55

it forms a tubular network around each individual myofibril

Front 56

what do the terminal cisternae at the T-tubules formed by the sarcoplasmic reticulum store and what do they start?

Back 56

Ca2+ and they begin muscle contraction when they are released int o the sarcoplasm

Front 57

what is a triad and where are they found?

Back 57

-its a combination of a pair of 2 terminal cisternae + 1 T-tubule
-found in the sarcoplasmic reticulum

Front 58

how do Ca2+ ions move from the sarcoplasm into the SR?

Back 58

by ion pumps in the membrane of the SR which triggers muscle contraction

Front 59

what are myofibrils?

Back 59

they are contractile organelles and extend the entire length of the cell

Front 60

where are myofribrils found?

Back 60

in the sarcoplam of the muscle fiber

Front 61

what do myofibrils consist of?

Back 61

-numerous mitochondria
-myofilaments

Front 62

what six things make up a myofibril?

Back 62

(p. 284)
1. zone overlap
2. A-band
3. I-band
4. H-band
5. M-line
6. Z-line

Front 63

what is the zone overlap?

Back 63

where thin filaments are interspersed among the thick filaments

Front 64

what is the A-band?

Back 64

contains the thick filaments

Front 65

what is the I band?

Back 65

contains thin filaments, but no thick filaments

Front 66

what is the H band?

Back 66

contain thick filaments, but no thin filaments

Front 67

what is the M line?

Back 67

it connects the central portion of each thick filament

Front 68

what is the Z line?

Back 68

interconnects thin filaments and mark the boundaries between them

Front 69

what interconnects the thin filaments in the Z-line?

Back 69

protiens called actinins

Front 70

what are myofilaments?

Back 70

-contractile proteins

Front 71

what do myofilaments consist of?

Back 71

-thin filaments
-thick filaments
-repeating functional units called sarcomeres

Front 72

what are the most abundant myofilaments and what do they consist of?

Back 72

thin filaments composed primarily of actin

Front 73

what are thick filaments primarily composed of?

Back 73

myosin

Front 74

what are sarcomeres?

Back 74

repeating functional units in myofilaments

Front 75

what is actin?

Back 75

-it is the binding site for myosin
-located in thin filaments

Front 76

how big are thin filaments

Back 76

8 nm

Front 77

what is myosin?

Back 77

-its motor proteins
-located in thick filaments

Front 78

how big are thick filaments?

Back 78

16 nm

Front 79

what are the two regulatory proteins?

Back 79

1. tropomyosin
2. troponin

Front 80

what are the two structural proteins?

Back 80

1. titin
2. nebulin

Front 81

what do the structural proteins provide?

Back 81

alignment, stability, elasticity, and extensibility

Front 82

what four different proteins do thin filaments consist of?

Back 82

1. F-actin
2. nebulin
3. tropomyosin
4. troponin

Front 83

what is F-actin?

Back 83

-2 strands of intertwined beaded proteins
-major protein of the thin filament

Front 84

what does F-actin contain?

Back 84

binding sites for myosin called G-actin

Front 85

what is G-actin?

Back 85

binding sites for myosin

Front 86

what is tropomyosin?

Back 86

regulatory, rope-like protein wrapped around the F-actin blocking the binding sites (G-actin) for myosin, preventing actin-myosin interaction

Front 87

what does tropomyosin prevent?

Back 87

actin-myosin interaction

Front 88

what is troponin?

Back 88

regulatory molecule that's attached (chemically bonded) to the tropomyosin and the actin proteins

Front 89

what does troponin have a third attachment site for?

Back 89

calcium ions

Front 90

what two proteins regulate the binding of myosin?

Back 90

tropomyosin and troponin

Front 91

what do thick filaments contain?

Back 91

-titan
-bundles of myosin fibers around titan core

Front 92

what is titan?

Back 92

the core of the thick filament

Front 93

what are the three structural properties of a myosin molecule?

Back 93

1. 2 intertwined elongated tails with globular heads
2. tails that point toward the M-line
3. heads project outward toward one of the 6 thin filaments

Front 94

what is every thick filament followed by and where?

Back 94

6 actin/thin filaments in a cross section

Front 95

when is the sliding filament mechanism?

Back 95

when thin and thick filaments slide past eachother and form a contraction in the skeletal muscle fiber

Front 96

what are the 6 steps of the sliding filament mechanism?

Back 96

1. myosin heads pull thin filaments toward M-line
2. H and I bands get smaller
3. Zones of overlap get larger
4. Z discs move closer together
5. sarcomere shortens due to the shortening of the myobrils
6. entire muscle fiber shortens

Front 97

what happens to the length of the filaments in the sliding filament mechanism?

Back 97

they do not change

Front 98

what is a neuromuscular junction?

Back 98

(NMJ) the site where each skeletal muscle fiber is controlled by the nervous system

Front 99

how many neuromuscular junctions (NMJ) does each fiber have?

Back 99

only one

Front 100

what is acetylcholine?

Back 100

(ACh) a neurotransmitter chemically released by a neuron to change the permeability or other properties of another cell's membrane

Front 101

where is ACh located?

Back 101

in the vesicles of the synaptic terminal's cytoplasm

Front 102

what is Acetylcholinesterase?

Back 102

(AChE) the enzyme that breaks down ACh

Front 103

where is AChE located?

Back 103

in the synaptic cleft and the sarcolemma

Front 104

what type of process is the excitation-contraction coupling and what does it do?

Back 104

-a cyclic process
-triggers contraction of the muscle fiber

Front 105

what are the seven steps of the excitment stage of the excitation-contraction coupling process?

Back 105

1. begins with the excitation cycle
2. excitatory stimulus (action potential) from the somatic motor
3. each muscle cell is innervated by one neuron
4. synaptic transmission occurs
5. action potential travels along t-tubule to triads
6. calcium ions bind to troponin
7.** release of actin active site begins contraction cycle

Front 106

what is the somatic motor system?

Back 106

stimulus comes from the brain or spinal cord out to your muscle or PNS

Front 107

what happens when synaptic transmission occurs?

Back 107

neurotransmitters (ACh) are released into the synaptic cleft and binds to receptors which opens sodium ion channels

Front 108

what happens when the AP travels along the T-tubule to the triads?

Back 108

it releases calcium ions from the terminal cisternae of the SR

Front 109

what are the four steps required for relaxation of a muscle fiber?

Back 109

1. acetylcholinesterase (AChE) breaks down ACh
2. calcium release channels close so Ca2+ active transport pumps move calcium back into SR
3. troponin-tropomyosin complexes cover myosin binding sites
4. muscle fiber relaxes

Front 110

what is exocytosis of ACh triggered by?

Back 110

it is triggered by permeability changes in membrane

Front 111

what happens during the exocytosis of ACh?

Back 111

exocytosis of ACh into the synaptic cleft and occurs as vesicles fuse with the membrane

Front 112

explain the myosin head in the "resting sarcomere"

Back 112

-each myosin head is already energized meaning its charged with the energy that will be used to power a contraction
-myosin head is "cocked"

Front 113

why does the myosin head in a resting sarcomere function as an ATPase?

Back 113

because cocking the myosin head requires energy which is obtained by the breakdown of ATP; ATPase is an enzyme that breaks down ATP

Front 114

in the beginning of the contraction cycle where is the ADP and P (breakdown products) bound?

Back 114

the myosin head

Front 115

what happens in a contracted sarcomere?

Back 115

-entire cycle is repeated several times
-calcium ions remain elevated as long as AP continues to pass through the T-tubules and stimulate the terminal cisternae

Front 116

what happens once the stimulus in the contracted sarcomere is removed?

Back 116

Ca2+ channels in the SR close and Ca2+ ions pull the Ca2+ from the sarcoplasm and stroe it within the terminal cisternae.
-Troponin molecules shift position, swinging the tropomyosin strands over the active sites and prevent further cross-bridge formation

Front 117

what is tension and when does it occur?

Back 117

it is a pull on the tendons at either end and occurs during contraction when the muscle shortens

Front 118

where are all Ca2+ released from and what does this result in?

Back 118

released from all triads in the muscle fiber resulting in the fiver either being "on"(producing tension) or "off"(relaxed)

Front 119

what does varying of tension production depend on?

Back 119

the fiber's resting length at the time of stimulation

Front 120

when sarcomeres are either stretched or compressed what happens to the tension production?

Back 120

it declines

Front 121

what three things prevents too much compression or stretching?

Back 121

1. arrangement of skeletal muscles
2. connective tissues
3. bones

Front 122

what is a twitch?

Back 122

a single stimulus-contraction-relaxation sequence in a muscle fiber

Front 123

what does the variance of twitches depend on?

Back 123

duration, muscle type and location, internal and external environmental conditions, and other factors

Front 124

what are the three stages of a twitch?

Back 124

1. latent stage
2. contraction stage
3. relaxation stage

Front 125

what is the latent period of a twitch contraction?

Back 125

-begins at stimulation when AP sweeps across the sarcolemma and Ca2+ are released
-lasts ~2msec

Front 126

what is the contraction phase of a twitch?

Back 126

-the tension rises to a peak and crossbridges are formed
-lasts 10-100msec

Front 127

what is the relaxation phase of a twitch?

Back 127

-Ca2+ levels are falling and going back into SR, binding sites are being covered by tropomyosin, cross-bridges are detaching, and tension decreases
-lasts 10-100msec
-involves a refractory period for ~5msec

Front 128

what two factors determines the amount of tension produced by a skeletal muscle?

Back 128

1. amount of tension produced by each stimulated muscle fiber
2. total number of muscle fibers stimulated at a given moment

Front 129

if a skeletal fiber is stimulated immediately after the relaxation phase has ended, what happens to the following contraction and how long will this continue for? what is this referred to?

Back 129

it will develop a slightly higher maximum tension and will continue over the first 30-50 stimulations
-referred to as teppe (like a staircase)

Front 130

do most muscles demonstrate treppe?

Back 130

no

Front 131

what is wave summation?

Back 131

if a second stimulus arrives before the relaxation phase has ended, a second more powerful contraction will occur

Front 132

what determines the maximum time available to produce a wave summation?

Back 132

the duration of a single twitch

Front 133

what is an incomplete tetanus?

Back 133

-when a muscle produces an almost peak tension during rapid cycles of contraction and relaxation
-the fiber is only partially relaxed and the contraction is sustained but wavering

Front 134

what is a complete tetanus?

Back 134

-a higher stimulation frequency eliminates the relaxation phase and the AP arrives so rapidly that the SR cannot reclaim Ca2+ ions causing the contraction to prolong, making it continuous
-individual twitches cannot be detected

Front 135

what is a wave summation called?

Back 135

a 'summation' of the contractile force

Front 136

at what rate is an incomplete tetanus stimulated at?

Back 136

at a rate of 20-30 times/asecond

Front 137

at what rate is a complete tetanus stimulated at?

Back 137

a rate higher than 80-100 times/second

Front 138

what is a motor unit?

Back 138

all the muscle fibers controlled by a single motor neuron

Front 139

what is the size of a motor unit an indication of?

Back 139

how fine the control of movement can be

Front 140

what is recruitment?

Back 140

the smooth but steady increase in muscular tension produced by increasing the number of active motor units

Front 141

what is motor unit recruitment?

Back 141

process in which the number of motor units increases

Front 142

how can tension in a muscle be controlled?

Back 142

by controlling the number of motor units

Front 143

what motor units are stimulated first in a contraction?

Back 143

the smallest are activated worst; they're the weakest

Front 144

what happens when larger motor units are activated?

Back 144

(stronger, faster) tension is increased

Front 145

what two reasons do some motor units contract while others relax?

Back 145

1. to maintain contraction
2. preserve some motor units

Front 146

what is asynchronous motor unit summation?

Back 146

when some motor units contract while others relax

Front 147

what is muscle tone?

Back 147

the resting tension in a muscle

Front 148

what is resting tension in a muscle?

Back 148

when motor units contractions dont produce enough tension to cause movement

Front 149

what effect does muscle tone have on the resting rate of metabolism?

Back 149

the higher the muscle tone the higher the resting rate because activated muscle fibers use energy

Front 150

on what basis do we classify muscle contractions as isotonic or isometric?

Back 150

their pattern of tension production

Front 151

what happens in an isotonic contraction?

Back 151

tension remains constant and the muscle changes length

Front 152

what are isotonic contractions used for?

Back 152

body movements, moving objects

Front 153

what are the two types of isotonic contractions?

Back 153

1. concentric isotonic contraction
2. eccentric isotonic contraction

Front 154

what happens in a concentric contraction and when does it occur?

Back 154

flexion, the muscle shortens; occurs when the tension produced exceeds the load

Front 155

how does the speed/rate of muscle contraction vary with the load on the muscle during concentric contraction?

Back 155

inversely; if its a light load the contraction is quick; fastest when load=0

Front 156

in a concentric contraction, what produced the tension to overcome the load?

Back 156

cross-bridges

Front 157

what happens in an eccentric contraction and when does it occur?

Back 157

extension; the muscle lengthens in a controlled manor while continuing to contract; occurs when the peak tension is less than the load, causing elongation

Front 158

what is an example of concentric contraction?

Back 158

picking up a glass of water

Front 159

what is an example of eccentric contraction?

Back 159

putting a glass of water down

Front 160

what happens in an isometric contraction?

Back 160

-the muscle as a whole does not change in length and the tension produced never exceeds the load
-does not result in movement but does use energy

Front 161

why does an isometric contraction not result in movement?

Back 161

-because if the load equals peak tension, the load wont move when the muscle contracts
-since the muscle fibers cannot shorten any further than connective tissue, the tension does not exceed the load

Front 162

what are isometric contractions important for?

Back 162

to maintain posture and to support objects in a fixed position

Front 163

while you are doing isometric contractions what else is taking place?

Back 163

isotonic contractions are being done at the same time but in different areas of the muscles

Front 164

what is muscle tension equivalent to?

Back 164

contraction force

Front 165

what is always the same about AP's in neurons and muscles?

Back 165

size

Front 166

since the force of muscle fiber contraction varies, what three things does the force in a single muscle fiber depend on?

Back 166

1. rate of nerve impulses: free stimulation
2. amount of stretching before contraction
3. nutrient availability (includes oxygen)

Front 167

what does contraction force in a whole muscle depend on?

Back 167

the number of muscle fibers contracting in unison

Front 168

when does maximum muscle tension occur?

Back 168

when the overlap extens from the edge of an H zone to one end of thick filament

Front 169

what happens in stretched sarcomeres?

Back 169

the zone of overlap shortens; lost tension --> no tension

Front 170

what happens in shorter sarcomeres?

Back 170

the relationship with myosin alters

Front 171

where does both shorter and stretched sarcomeres lose efficiency?

Back 171

in the H zone

Front 172

what does a motor unit consist of?

Back 172

one somatic motor neuron + all skeletal muscle fibers it stimulates

Front 173

how many muscle fibers does 1 motor neuron come in contact with?

Back 173

average of 150 muscle fibers

Front 174

where are motor units found?

Back 174

they are dispersed throughout the muscle

Front 175

how do all muscle fibers in one motor unit contract?

Back 175

in unison

Front 176

when is movement made more precise?

Back 176

when there are less motor units

Front 177

what is the motor end plate of a single muscle fiber?

Back 177

-the region of the sarcolemma opposite the synaptic cleft
-neuromuscular junction