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BIOL 319 > Lab 7: Muscle Structure & Function and Electromyography (EMG) > Flashcards

Lab 7: Muscle Structure & Function and Electromyography (EMG) Flashcards

1
Q

list the general steps of how a signal is translated into a digital display during a power lab

A
  • use transducer to convert signal to analog voltage
  • signal is modified through signal conditioning
  • analog voltage is sampled at regular intervals and converted to digital form
  • digital signal is transmitted to the computer where it is displayed
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2
Q

define transducer

A

device that converts the signal of interest (blood pressure, body temperature, etc.) into an analog voltage

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3
Q

define signal conditioning

A

modifies the analog voltage by amplifying, filtering, and zeroing

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4
Q

define zeroing

A

the removal of unwanted steady offset voltage from a transducer’s output

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5
Q

what does the hardware do during the power lab

A
  • signal conditioning: amplifying, filtering, and zeroing
  • analog voltage is sampled at regular intervals and converted to digital form
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6
Q

define a power lab unit

A
  • basic hardware
  • recording instrument that measures electrical signals through the inputs on its front panel
  • generates output signals
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7
Q

define frequency

A

number of occurrences of a repeating event per unit time

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8
Q

define amplitude

A

height of the wave from baseline to crest

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9
Q

define waveform

A

shape and form of a signal

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10
Q

define wavelength

A

length from the crest of one peak to the crest of the next peak

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11
Q

what are the three muscle tissue types

A
  • skeletal
  • smooth
  • cardiac
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12
Q

what do the prefixes myo-, mys-, and sarco- mean

A

muscle

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13
Q

what percent of your cell mass is made up of skeletal muscle

A

40%

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14
Q

which muscle tissue type does most of the work for locomotion and support of the skeleton

A

skeletal muscle

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15
Q

list the components of a muscle organizationally from smallest to largest

A
  • sarcomeres
  • muscle fibers
  • fascicles
  • muscle
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16
Q

what is an individual muscle cell

A

a muscle fiber (made of sarcomeres)

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17
Q

define upper motor neuron lesions

A
  • damaged neurons in the brain
  • cause loss of muscle function
  • often caused by strokes
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18
Q

describe how skeletal muscles compare in strength and stamina

A
  • powerful compared to other muscle types
  • can rapidly contract
  • tires rapidly
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19
Q

what are the 4 properties of muscle

A
  • excitability
  • contractility
  • extensibility
  • elasticity
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20
Q

define excitability

A

muscle cell membranes have an electric charge differential which can be changed upon stimulation to produce an intracellular muscle response

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21
Q

define contractility

A

muscle cells shorten when stimulated

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22
Q

define extensibility

A

muscle cells can be stretched, sometimes more than their resting length

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23
Q

define elasticity

A

muscles cells can recoil to their resting cell length after being stretched

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24
Q

what are all of the components of a muscle

A
  • nerves
  • blood vessels
  • connective tissue
  • muscle fibers
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25
Q

where do nerves and blood vessels enter the muscle

A

near its center

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26
Q

define epimysium

A
  • connective tissue
  • surrounds the muscle
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27
Q

define perimysium

A
  • connective tissue
  • surrounds the fascicles
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28
Q

define endomysium

A
  • connective tissue
  • surrounds the muscle fibers
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29
Q

define tendon

A
  • rope-like extensions of a muscle’s connective tissue
  • mostly collagen
  • attach muscle to bone
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30
Q

define aponeurosis

A
  • connective tissue
  • similar to tendons
  • sheet-like extension (rather than the tendon rope-like extension)
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31
Q

define the muscle insertion

A

the bone or structure that is moving

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32
Q

define the muscle origin

A

the bone or structure that mostly does not move

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33
Q

what are the two types of muscle attachments

A
  • direct
  • indirect
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34
Q

define direct muscle attachment

A

the periosteum or perichondrium is fused with the muscle’s epimysium

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35
Q

define indirect muscle attachment

A
  • the periosteum or perichondrium is NOT fused with the muscle’s epimysium directly
  • more durable, smaller, and more common than direct muscle attachments
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36
Q

describe what is means for muscles to work anatogonistically

A

as one muscle contracts and shortens, its antagonist relaces and elongates

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37
Q

define sarcolemma

A

plasma membrane of a muscle fiber

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38
Q

define sarcoplasm

A

cytoplasm in a muscle fiber

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39
Q

define myoglobin

A
  • stores oxygen
  • muscle cells contain lots of myoglobin
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40
Q

define glycosomes

A
  • granules of glycogen that can be broke down to supply ATP from glucose for energy
  • muscle cells contain lots of glycosomes
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41
Q

define myofibrils

A
  • take up most of the intracellular volume of skeletal muscle cells
  • organelles that are repeating units of sarcomeres
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42
Q

define sarcomeres

A
  • smallest atomic contractile units of skeletal muscle fibers
  • runs from Z line to Z line
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43
Q

why are skeletal muscles striated

A

the dark A bands and light I bands within the sarcomeres are perfectly lined beside one another

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44
Q

define thick filaments

A
  • contain the protein myosin
  • myosin has protruding globular heads
  • run the length of the A band
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45
Q

how many light chains does each myosin globular head associate with

A

2

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46
Q

where do thick filaments connect

A

the M line

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47
Q

where are myosin heads located on thick filaments

A

where actin proteins of the thin filament and myosin heads of the thick filament overlap

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48
Q

how many myosin molecules are om each thick filament

A

over 300

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49
Q

define thin filaments

A
  • helix of two actin subunit strands
  • proteins tropomyosin and troponin
  • each actin subunit contains active sites where myosin heads attach
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50
Q

what does tropomyosin do

A
  • blocks actin’s myosin-binding site in relaxed muscle
  • move to expose the myosin-binding site during muscle contraction
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51
Q

describe the components of troponin

A
  • 3 globular polypeptides:
  • one binds to actin
  • middle one binds to calcium ions
  • one binds to tropomyosin
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52
Q

define elastic filaments

A
  • made of the protein titin
  • run from the Z line to the thick filaments
  • hold thick filaments in place and provide flexible recoil to the sarcomeres
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53
Q

how do myosin-binding sites on actin filaments become exposed

A
  • tropomyosin blocks the binding sites during relaxation
  • 2 calcium ions bind to troponin which displaces the tropomyosin
  • the binding site will now be exposed
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54
Q

what are the 4 steps of the cross bridge cycle

A
  • binding
  • power stroke
  • detaching
  • cocking
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55
Q

describe the first step of the cross bridge cycle (binding)

A
  • a myosin-head is in its high energy configuration (with ADP and P)
  • myosin head binds to an exposed myosin-binding site on the actin filament
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56
Q

describe the second step of the cross bridge cycle (power stroke)

A
  • ADP and inorganic phosphate are released from the myosin head
  • myosin head returns to its low energy state
  • results in a power stroke as myosin strokes from its high energy to low energy state
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57
Q

what happens to the actin filaments during a power stroke

A

actin filaments pulled towards to M line

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58
Q

describe the third step of the cross bridge cycle (detaching)

A
  • ATP binds to the myosin head
  • myosin head detaches form the actin filaments
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59
Q

describe the fourth step of the cross bridge cycle (cocking)

A
  • hydrolysis of ATP into ADP and inorganic phosphate on the myosin head
  • myosin head will be repositioned into its high-energy configuration
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60
Q

define sarcoplasmic reticulum

A
  • smooth endoplasmic reticulum in muscle cells
  • surrounds each myofibril
  • controls calcium levels within the sarcoplasm
  • stores and releases calcium to control muscle fiber contraction
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61
Q

define terminal cisterns

A
  • large perpendicular cross channels
  • always found in pairs surrounding T tubules
  • formed by the sarcoplasmic reticulum
  • at the A band and I band junction
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62
Q

where are mitochondria and glycogen highly abundant

A

near the sarcoplasmic reticulum

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63
Q

define T tubules

A
  • at the A band and I band junction
  • elongated tubular extensions of the sarcolemma
  • dive deep into the cell
  • surrounded by terminal cisterns
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64
Q

define a triad

A

the T tubule and terminal cisterns on either side

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65
Q

what is the major function of T tubules

A

as extensions of the sarcolemma, electrical signals can travel down them and deep into the muscle to every sarcomere

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66
Q

what do the membrane proteins protruding from the T tubules and terminal cisterns do

A
  • proteins of the T tubules function as voltage sensors
  • proteins of the terminal cisterns cerate gated channels for the release of calcium
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67
Q

describe the polarization of all plasma membranes of all human cells

A
  • all carry a resting charge (polarization)
  • inside of the cell is more negative relative to the outside
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68
Q

what are the 3 steps of the initiation and propagation of a muscle action potential

A
  • end plate potential
  • muscle action potential
  • repolarization
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69
Q

describe the first step of the initiation and propagation of a muscle action potential (end plate potential)

A
  • acetylcholine binds to its receptor opening chemical ligan-gated ion channels for sodium
  • sodium enters the cell
  • the inner surface of the sarcolemma becomes less negative (depolarization)
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70
Q

describe the second step of the initiation and propagation of a muscle action potential (muscle action potential)

A
  • sodium channels on surrounding sarcolemma respond to the change in charge of another sarcolemma and the channels open
  • sodium enters more cells
  • more sodium channels will continue to open
  • depolarization will spread in a wave along the sarcolemma
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71
Q

describe the third step of the initiation and propagation of a muscle action potential (repolarization)

A
  • voltage-gated sodium channels close when the voltage becomes sufficiently positive
  • voltage-gated potassium channels open
  • potassium flows out of the cell
  • the membrane becomes more negative (repolarizes)
  • once the membrane is sufficiently negative, the potassium channels will close
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72
Q

define refractory period

A
  • the period of time between when a muscle cell can be stimulated a second time
  • while repolarizing
  • cell cannot be stimulated again until the membrane is sufficiently negative
73
Q

how long are the electrical events leading to muscle contraction

A

1 millisecond

74
Q

how long can muscle contraction last

A

100x the duration of the electrical signal (usually around 100 milliseconds)

75
Q

describe what happens to calcium as the muscle action potential travels down the T tubules

A
  • depolarization causes calcium release channels to open in the terminal cisterns
  • calcium moves into the sarcoplasm where it removes the inhibitory action of tropomyosin
76
Q

define excitation-contraction coupling

A

events leading to the contraction of the muscle

77
Q

describe why subsequent contractions may be stronger and/or more sustained

A

if the nerve impulses arrive at the muscle in rapid succession, intracellular calcium will elevate and be sustained leading to another contraction before the muscle was completely relaxed

78
Q

how often does cross bridge cycling occur during a single muscle contraction

A

many times

79
Q

define muscle tension

A

force exerted by a contracting muscle on an object

80
Q

define load

A

the opposing force applied on the muscle by the mass of the object being moved

81
Q

what is each individual muscle fiber innervated by

A

a branch of a motor axon

82
Q

define motor unit

A
  • motor neuron and all the individual muscle fibers that it innervates
  • vary greatly in size
83
Q

what is the difference between a small motor unit and a large motor unit

A
  • small motor unit: innervates a few muscle fibers
  • large motor unit: innervates thousands of muscle fibers
84
Q

which has finer control of movement in a muscle: small or large motor units

A

small motor units

85
Q

which muscles have small motor units

A
  • those needing finer control
  • muscles of the fingers and eyes
86
Q

which muscles have large motor units

A

large muscles controlling limbs

87
Q

what size motor units do most muscles contain

A

most muscles consist of a range of motor unit sizes

88
Q

how many neurons are in a motor unit

A

1

89
Q

how are the muscle fibers of a single motor unit usually spread and why

A
  • spread throughout the entire muscle (not clustered together)
  • allows for nearly simultaneous contraction of all muscle fibers
90
Q

what happens to the thick and thin filaments during muscle contraction

A
  • do not change length
  • thin filaments are pulled past the stationary thick filaments by the power stroke
91
Q

what happens to the Z lines during muscle contraction

A

the Z lines are pulled towards the M line which shortens the sarcomere

92
Q

describe where the thick and thin filaments overlap in a relaxed and contracted muscle

A
  • relaxed: overlap only at the ends of the A bands
  • contracted: overlap through the entire A band
93
Q

do the A bands change in length during muscle contraction

A

no

94
Q

when do skeletal muscles contract

A
  • when a motor nerve stimulates an electrical action potential that originates at the neuromuscular junction
  • electrical action potential propagates along the sarcolemma leading to rises of intracellular calcium and excitation-contraction coupling
95
Q

what type of neurons activate skeletal muscle

A

somatic (voluntary) motor neurons

96
Q

where are the cell bodies of somatic (voluntary) motor neurons located

A

brain or spinal cord

97
Q

how many neuromuscular junctions does each muscle fiber have

A

one

98
Q

where does the neuromuscular junction join with the muscle fiber

A

about halfway down the muscle fiber

99
Q

define synaptic end bulb/axon terminal

A
  • synonyms
  • meaning the end of the axon
100
Q

define synaptic cleft

A
  • the space between the end of the axon and the muscle fiber
  • filled with extracellular fluid containing collagen fibers and glycoproteins
101
Q

what neurotransmitter is contained in vesicles at the axon terminal of the neuromuscular junction

A

acetylcholine (ACh)

102
Q

describe the structure and function of the sarcolemma at the neuromuscular junction

A
  • sarcolemma is folded greatly
  • increases surface area for acetylcholine receptors
103
Q

describe the process of acetylcholine moving from the axon terminal to the sarcolemma and the change from electrical to chemical to electrical signals

A
  • nerve action potential (electrical signal) reaches the axon terminal and depolarizes the membrane
  • calcium increases in the axon terminal leading to acetylcholine vesicles to fuse with the axon terminal membrane and enter the synaptic cleft (chemical signal)
  • acetylcholine moves across the synaptic cleft and attaches to receptors on the sarcolemma which opens sodium channels
  • the influx of sodium depolarizes the sarcolemma and causes muscle action potential (electrical signal)
104
Q

define acetylcholinesterase

A
  • enzyme in the synaptic cleft
  • breaks down acetylcholine to acetic acid and choline to terminate the signal
  • allows for fine control of muscle activation
105
Q

define isometric muscle contraction

A
  • muscles contract but joints do not move and muscle fibers stay the same length
  • muscle tension increases but muscle length does not change
106
Q

what exercises cause isometric muscle contraction

A
  • those performed against an immovable object
  • maintenance of upright balanced posture and stable joints
107
Q

define isotonic muscle contraction

A
  • a body part is moved
  • muscle fibers shorten or lengthen
  • muscle tension remains constant but muscle length changes
108
Q

define concentric isotonic contraction

A
  • muscle length decreases
  • ex: biceps while curling barbell
109
Q

define eccentric isotonic contraction

A
  • muscle length increases
  • ex: uncurling the barbell by slowly extending your arm from the original curled position
110
Q

define motor end plate

A

the area of the sarcolemma that is folded at the neuromuscular junction

111
Q

what happens after a single action potential in one motor neuron

A

leads to synchronous excitation and contraction of all muscle fibers in its motor unit

112
Q

define electromyogram (EMG)

A
  • measures the electrical activity of muscles and the nerves controlling the muscles
  • observing compounds muscle potential
113
Q

define compound muscle potential (CMP)

A

sum of the electrical activity of many individual muscle fibers all firing at once

114
Q

define the magnitude of the CMP

A

reflects the number and size of motor units that are active

115
Q

define a muscle twitch

A

a motor unit’s reaction to a single action potential of its motor neuron

116
Q

what are the three parts/periods of every twitch

A
  • latent period
  • period of contraction
  • period of relaxation
117
Q

what occurs during the latent period

A
  • excitation-contraction coupling
  • cross bridges begin to form but measurable tension has not been achieved
118
Q

what happens to the latent period as the load increases

A

as load increases, latent period will be longer

119
Q

when does the period of contraction last

A

from once tension is measurable until tension peaks

120
Q

what occurs during the period of contraction

A
  • cross bridges are cycling
  • the muscle will shorten as the force being generated by the contraction exceeds the resistance applied to the muscle
121
Q

when does the period of relaxation begin

A

when calcium levels drop in the sarcoplasm

122
Q

what occurs during the period of relaxation

A
  • calcium levels drop in the sarcoplasm
  • number of cycling cross bridges decreases
  • muscle tension declines
123
Q

contrast the time is takes for a muscle to contract and relax

A

a muscle can contract rapidly but will relax more slowly in comparison

124
Q

why do some muscles twitch and relax more rapidly than others

A

due to the differences in the enzyme composition and metabolic properties of different muscles in the body

125
Q

define recruitment

A

nervous system adjusts that number of motor axons firing thus controlling the number of twitching muscle fibers

126
Q

define threshold stimulus

A

stimulus is just strong enough to generate an observable contraction

127
Q

define Henneman’s size principle

A
  • central nervous system signals small motor units to be recruited first followed by larger and larger motor units until all motor units are recruited
  • smooth increase in muscle contraction
128
Q

what excitability of neurons control smaller and larger motor units

A
  • smaller motor units are controlled by low threshold and easily excitable motor neurons
  • larger motor units are controlled by high threshold and less excitbale motor neurons
129
Q

what explains how the same muscle can control dine delicate movements and also perform powerful heavy maneuvers

A

Henneman’s size principle

130
Q

what happens to intracellular calcium levels and muscle contraction at stimulation intervals greater than 200 ms

A
  • intracellular calcium is restored to baseline levels between action potentials
  • contraction consists of separate twitches
131
Q

what happens to intracellular calcium levels and muscle contraction at stimulation intervals between 200 and 75 ms

A
  • calcium in the muscle is still above baseline levels when the next action potential arrives
  • the muscle fiber has not completely relaxed and the next contraction will be stronger
132
Q

what happens to the degree of summation at higher stimulation frequencies (stimulation intervals less than 75 ms)

A

degree of summation increases

132
Q

define summation

A
  • additive effect of muscle contractions getting stronger as more action potentials arrive
  • the muscle has not been able to completely relax before the next action potential arrives so the next contraction will be stronger
133
Q

define unfused or incomplete tetanus

A
  • occurs when there is a high degree of summation (high stimulation frequencies)
  • sustained graded contractions that can increase in size and length
134
Q

define complete or fused tetanus

A
  • occurs when there is a very high degree of summation (very high stimulation frequencies)
  • the muscle has no time to relax at all between successive stimuli
  • results in smooth contraction called a tetanic contraction
135
Q

define tetanic contraction

A
  • smooth contraction may time stronger than a single twitch
  • occurs when the muscle is in a state of complete or fused tetanus
136
Q

describe the baseline tone of skeletal muscles

A
  • always maintain a baseline tine
  • even relaxed muscles will be in a state of slight contraction
  • does not give rise to movements
137
Q

why are skeletal muscles always in a state of slight contraction (even relaxed muscles)

A
  • keeps muscles healthy, firm, and primed to respond
  • generates posture and stabilizes joints
138
Q

when is an EMG usually performed in a clinical setting

A

when a patient has symptoms of weakness and an examination shows impaired muscles strength

139
Q

when can an EMG help to differentiate between

A

muscle weakness caused by neurological disorders or caused by another condition

140
Q

what does the raw surface EMG signal reflect

A

the muscle fibers active at that time

141
Q

can you detect the contributions of individual motor units on an EMG

A

sometimes, with exceedingly weak contractions

142
Q

how is the raw EMG signal processed in the experiment done in lab

A
  • the negative-going portions of the EMG are inverted
  • the whole signal is integrated to smooth out individual spikes
  • makes the time course of changing activity much clearer
143
Q

define coactivation

A

a phenomenon in which contraction of a muscle leads to some minor contractile activity in the antagonist muscle

144
Q

what is the physiological significance of coavtivation

A
  • not entirely clear
  • likely helps to stabilize the joint and generate smooth contractions and relaxations against the load on the muscle
145
Q

how many seconds worth of ATP is stored by muscle

A

5 seconds worth

146
Q

what are the 3 main mechanisms that ATP is generated in muscle

A
  • creatine phosphate directly phosphorylating ADP to ATP
  • anaerobic glycolysis
  • aerobic respiration
147
Q

describe the timing of creatine phosphate reacting with ADP to form ATP and creatine

A

rapid

148
Q

how much more creatine phosphate than ATP do muscles store

A

3x more creatine phosphate than ATP

149
Q

how long can stored ATP and creatine phosphate power a muscle during vigorous activity

A

10 seconds

150
Q

can muscles revert ATP and creatine to ADP and creatine phospahte

A

yes, they will do this during periods of rest

151
Q

what is the first phase of glucose breakdown

A

glycolysis

152
Q

does glycolysis require oxygen

A

no

153
Q

is glycolysis aerobic or anaerobic

A

anaerobic (does not require oxygen)

154
Q

how much ATP is formed from one glucose molecule during glycolysis

A

2 ATP

155
Q

what happens after glycolysis if sufficient oxygen is available

A
  • pyruvate enters the TCA cycle and oxidative phosphorylation
  • aerobic respiration
  • produces substantially more ATP
156
Q

what happens at 70% maximal contraction of a muscle

A

the muscle will become so bulged that it compresses blood vessels which decreases oxygen delivery

157
Q

what happens after glycolysis if sufficient oxygen is not available

A
  • pyruvate is converted to lactic acid
  • anaerobic glycolysis
  • lactic acid will exit the muscle and can be converted to glucose by the liver
158
Q

how long can anaerobic glycolysis power a muscle

A

40 seconds

159
Q

what is produced during aerobic respiration

A
  • carbon dioxide
  • water
  • 34 ATP (per glucose)
160
Q

how can free fatty acids be burned

A

aerobically

161
Q

when are free fatty acids used as a major source of energy

A

after 30 minutes of contractile activity

162
Q

why is aerobic metabolism slow

A

there are many steps and intermediaries required

163
Q

when will muscles perform aerobic pathyways

A

so long as oxygen is available

164
Q

define aerobic endurance

A

the amount of time a muscle can contract using aerobic pathways

165
Q

define anaerobic threshold

A

the point at which metabolism in a muscle switches to anaerobic glycolysis

166
Q

what are surges of intense activity powered by

A
  • stored ATP
  • creatine phosphate
167
Q

what are longer duration and high intensity exercises powered by

A

anaerobic glycolysis

168
Q

what leads to muscle fatigue

A
  • depletion of energy and metabolite stores
  • ionic imbalances across the muscle cell membrane (ex: potassium accumulation)
  • lactic acid accumulation
  • motor drive from the brain is reduced
169
Q

are some muscle fibers more resistant to fatigue than others

A

yes, they have a greater capacity for oxidative metabolism

170
Q

what affects the force of a muscle contraction

A
  • number of motor units recruited
  • size of the muscle fiber
  • contraction summation due to increased stimulation
  • extent of stretch to the muscle
171
Q

how does exercise increase the force of muscle contraction

A
  • exercise causes muscles fibers to hypertrophy
  • larger muscle fibers create more force during contraction
172
Q

describe slow and fast muscle fibers

A
  • refers to how fast and for how long muscle fibers can contract before fatigue sets in
  • determined by responsiveness of their motor neurons and speed at which myosin ATPases can split ATP in the muscle fibers
173
Q

what is contraction duration influenced by

A

how fast a muscle type can pump calcium back into the sarcoplasmic reticulum

174
Q

what are the classifications of muscles in terms of the metabolic pathway they mainly use during contraction

A
  • oxidative fibers
  • glycolytic fibers
175
Q

define oxidative fibers

A

muscle fibers that rely mainly on aerobic pathways during contraction

176
Q

define glycolytic fibers

A

muscle fibers that rely mainly on anaerobic glycolysis and creatine phosphate during contraction

177
Q

what are the 3 main muscle fiber types

A
  • slow oxidative fibers
  • fast oxidative glycolytic fibers
  • fast glycolytic fibers

BIOL 319 (15 decks)

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