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
2
Q
define transducer
A
device that converts the signal of interest (blood pressure, body temperature, etc.) into an analog voltage
3
Q
define signal conditioning
A
modifies the analog voltage by amplifying, filtering, and zeroing
4
Q
define zeroing
A
the removal of unwanted steady offset voltage from a transducer’s output
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
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
7
Q
define frequency
A
number of occurrences of a repeating event per unit time
8
Q
define amplitude
A
height of the wave from baseline to crest
9
Q
define waveform
A
shape and form of a signal
10
Q
define wavelength
A
length from the crest of one peak to the crest of the next peak
11
Q
what are the three muscle tissue types
A
- skeletal
- smooth
- cardiac
12
Q
what do the prefixes myo-, mys-, and sarco- mean
A
muscle
13
Q
what percent of your cell mass is made up of skeletal muscle
A
40%
14
Q
which muscle tissue type does most of the work for locomotion and support of the skeleton
A
skeletal muscle
15
Q
list the components of a muscle organizationally from smallest to largest
A
- sarcomeres
- muscle fibers
- fascicles
- muscle
16
Q
what is an individual muscle cell
A
a muscle fiber (made of sarcomeres)
17
Q
define upper motor neuron lesions
A
- damaged neurons in the brain
- cause loss of muscle function
- often caused by strokes
18
Q
describe how skeletal muscles compare in strength and stamina
A
- powerful compared to other muscle types
- can rapidly contract
- tires rapidly
19
Q
what are the 4 properties of muscle
A
- excitability
- contractility
- extensibility
- elasticity
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
21
Q
define contractility
A
muscle cells shorten when stimulated
22
Q
define extensibility
A
muscle cells can be stretched, sometimes more than their resting length
23
Q
define elasticity
A
muscles cells can recoil to their resting cell length after being stretched
24
Q
what are all of the components of a muscle
A
- nerves
- blood vessels
- connective tissue
- muscle fibers
25
where do nerves and blood vessels enter the muscle
near its center
26
define epimysium
- connective tissue
- surrounds the muscle
27
define perimysium
- connective tissue
- surrounds the fascicles
28
define endomysium
- connective tissue
- surrounds the muscle fibers
29
define tendon
- rope-like extensions of a muscle's connective tissue
- mostly collagen
- attach muscle to bone
30
define aponeurosis
- connective tissue
- similar to tendons
- sheet-like extension (rather than the tendon rope-like extension)
31
define the muscle insertion
the bone or structure that is moving
32
define the muscle origin
the bone or structure that mostly does not move
33
what are the two types of muscle attachments
- direct
- indirect
34
define direct muscle attachment
the periosteum or perichondrium is fused with the muscle's epimysium
35
define indirect muscle attachment
- the periosteum or perichondrium is NOT fused with the muscle's epimysium directly
- more durable, smaller, and more common than direct muscle attachments
36
describe what is means for muscles to work anatogonistically
as one muscle contracts and shortens, its antagonist relaces and elongates
37
define sarcolemma
plasma membrane of a muscle fiber
38
define sarcoplasm
cytoplasm in a muscle fiber
39
define myoglobin
- stores oxygen
- muscle cells contain lots of myoglobin
40
define glycosomes
- granules of glycogen that can be broke down to supply ATP from glucose for energy
- muscle cells contain lots of glycosomes
41
define myofibrils
- take up most of the intracellular volume of skeletal muscle cells
- organelles that are repeating units of sarcomeres
42
define sarcomeres
- smallest atomic contractile units of skeletal muscle fibers
- runs from Z line to Z line
43
why are skeletal muscles striated
the dark A bands and light I bands within the sarcomeres are perfectly lined beside one another
44
define thick filaments
- contain the protein myosin
- myosin has protruding globular heads
- run the length of the A band
45
how many light chains does each myosin globular head associate with
2
46
where do thick filaments connect
the M line
47
where are myosin heads located on thick filaments
where actin proteins of the thin filament and myosin heads of the thick filament overlap
48
how many myosin molecules are om each thick filament
over 300
49
define thin filaments
- helix of two actin subunit strands
- proteins tropomyosin and troponin
- each actin subunit contains active sites where myosin heads attach
50
what does tropomyosin do
- blocks actin's myosin-binding site in relaxed muscle
- move to expose the myosin-binding site during muscle contraction
51
describe the components of troponin
- 3 globular polypeptides:
- one binds to actin
- middle one binds to calcium ions
- one binds to tropomyosin
52
define elastic filaments
- 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
53
how do myosin-binding sites on actin filaments become exposed
- tropomyosin blocks the binding sites during relaxation
- 2 calcium ions bind to troponin which displaces the tropomyosin
- the binding site will now be exposed
54
what are the 4 steps of the cross bridge cycle
- binding
- power stroke
- detaching
- cocking
55
describe the first step of the cross bridge cycle (binding)
- 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
56
describe the second step of the cross bridge cycle (power stroke)
- 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
57
what happens to the actin filaments during a power stroke
actin filaments pulled towards to M line
58
describe the third step of the cross bridge cycle (detaching)
- ATP binds to the myosin head
- myosin head detaches form the actin filaments
59
describe the fourth step of the cross bridge cycle (cocking)
- hydrolysis of ATP into ADP and inorganic phosphate on the myosin head
- myosin head will be repositioned into its high-energy configuration
60
define sarcoplasmic reticulum
- smooth endoplasmic reticulum in muscle cells
- surrounds each myofibril
- controls calcium levels within the sarcoplasm
- stores and releases calcium to control muscle fiber contraction
61
define terminal cisterns
- large perpendicular cross channels
- always found in pairs surrounding T tubules
- formed by the sarcoplasmic reticulum
- at the A band and I band junction
62
where are mitochondria and glycogen highly abundant
near the sarcoplasmic reticulum
63
define T tubules
- at the A band and I band junction
- elongated tubular extensions of the sarcolemma
- dive deep into the cell
- surrounded by terminal cisterns
64
define a triad
the T tubule and terminal cisterns on either side
65
what is the major function of T tubules
as extensions of the sarcolemma, electrical signals can travel down them and deep into the muscle to every sarcomere
66
what do the membrane proteins protruding from the T tubules and terminal cisterns do
- proteins of the T tubules function as voltage sensors
- proteins of the terminal cisterns cerate gated channels for the release of calcium
67
describe the polarization of all plasma membranes of all human cells
- all carry a resting charge (polarization)
- inside of the cell is more negative relative to the outside
68
what are the 3 steps of the initiation and propagation of a muscle action potential
- end plate potential
- muscle action potential
- repolarization
69
describe the first step of the initiation and propagation of a muscle action potential (end plate potential)
- 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)
70
describe the second step of the initiation and propagation of a muscle action potential (muscle action potential)
- 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
71
describe the third step of the initiation and propagation of a muscle action potential (repolarization)
- 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
72
define refractory period
- 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
how long are the electrical events leading to muscle contraction
1 millisecond
74
how long can muscle contraction last
100x the duration of the electrical signal (usually around 100 milliseconds)
75
describe what happens to calcium as the muscle action potential travels down the T tubules
- 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
define excitation-contraction coupling
events leading to the contraction of the muscle
77
describe why subsequent contractions may be stronger and/or more sustained
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
how often does cross bridge cycling occur during a single muscle contraction
many times
79
define muscle tension
force exerted by a contracting muscle on an object
80
define load
the opposing force applied on the muscle by the mass of the object being moved
81
what is each individual muscle fiber innervated by
a branch of a motor axon
82
define motor unit
- motor neuron and all the individual muscle fibers that it innervates
- vary greatly in size
83
what is the difference between a small motor unit and a large motor unit
- small motor unit: innervates a few muscle fibers
- large motor unit: innervates thousands of muscle fibers
84
which has finer control of movement in a muscle: small or large motor units
small motor units
85
which muscles have small motor units
- those needing finer control
- muscles of the fingers and eyes
86
which muscles have large motor units
large muscles controlling limbs
87
what size motor units do most muscles contain
most muscles consist of a range of motor unit sizes
88
how many neurons are in a motor unit
1
89
how are the muscle fibers of a single motor unit usually spread and why
- spread throughout the entire muscle (not clustered together)
- allows for nearly simultaneous contraction of all muscle fibers
90
what happens to the thick and thin filaments during muscle contraction
- do not change length
- thin filaments are pulled past the stationary thick filaments by the power stroke
91
what happens to the Z lines during muscle contraction
the Z lines are pulled towards the M line which shortens the sarcomere
92
describe where the thick and thin filaments overlap in a relaxed and contracted muscle
- relaxed: overlap only at the ends of the A bands
- contracted: overlap through the entire A band
93
do the A bands change in length during muscle contraction
no
94
when do skeletal muscles contract
- 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
what type of neurons activate skeletal muscle
somatic (voluntary) motor neurons
96
where are the cell bodies of somatic (voluntary) motor neurons located
brain or spinal cord
97
how many neuromuscular junctions does each muscle fiber have
one
98
where does the neuromuscular junction join with the muscle fiber
about halfway down the muscle fiber
99
define synaptic end bulb/axon terminal
- synonyms
- meaning the end of the axon
100
define synaptic cleft
- the space between the end of the axon and the muscle fiber
- filled with extracellular fluid containing collagen fibers and glycoproteins
101
what neurotransmitter is contained in vesicles at the axon terminal of the neuromuscular junction
acetylcholine (ACh)
102
describe the structure and function of the sarcolemma at the neuromuscular junction
- sarcolemma is folded greatly
- increases surface area for acetylcholine receptors
103
describe the process of acetylcholine moving from the axon terminal to the sarcolemma and the change from electrical to chemical to electrical signals
- 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
define acetylcholinesterase
- 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
define isometric muscle contraction
- muscles contract but joints do not move and muscle fibers stay the same length
- muscle tension increases but muscle length does not change
106
what exercises cause isometric muscle contraction
- those performed against an immovable object
- maintenance of upright balanced posture and stable joints
107
define isotonic muscle contraction
- a body part is moved
- muscle fibers shorten or lengthen
- muscle tension remains constant but muscle length changes
108
define concentric isotonic contraction
- muscle length decreases
- ex: biceps while curling barbell
109
define eccentric isotonic contraction
- muscle length increases
- ex: uncurling the barbell by slowly extending your arm from the original curled position
110
define motor end plate
the area of the sarcolemma that is folded at the neuromuscular junction
111
what happens after a single action potential in one motor neuron
leads to synchronous excitation and contraction of all muscle fibers in its motor unit
112
define electromyogram (EMG)
- measures the electrical activity of muscles and the nerves controlling the muscles
- observing compounds muscle potential
113
define compound muscle potential (CMP)
sum of the electrical activity of many individual muscle fibers all firing at once
114
define the magnitude of the CMP
reflects the number and size of motor units that are active
115
define a muscle twitch
a motor unit's reaction to a single action potential of its motor neuron
116
what are the three parts/periods of every twitch
- latent period
- period of contraction
- period of relaxation
117
what occurs during the latent period
- excitation-contraction coupling
- cross bridges begin to form but measurable tension has not been achieved
118
what happens to the latent period as the load increases
as load increases, latent period will be longer
119
when does the period of contraction last
from once tension is measurable until tension peaks
120
what occurs during the period of contraction
- cross bridges are cycling
- the muscle will shorten as the force being generated by the contraction exceeds the resistance applied to the muscle
121
when does the period of relaxation begin
when calcium levels drop in the sarcoplasm
122
what occurs during the period of relaxation
- calcium levels drop in the sarcoplasm
- number of cycling cross bridges decreases
- muscle tension declines
123
contrast the time is takes for a muscle to contract and relax
a muscle can contract rapidly but will relax more slowly in comparison
124
why do some muscles twitch and relax more rapidly than others
due to the differences in the enzyme composition and metabolic properties of different muscles in the body
125
define recruitment
nervous system adjusts that number of motor axons firing thus controlling the number of twitching muscle fibers
126
define threshold stimulus
stimulus is just strong enough to generate an observable contraction
127
define Henneman's size principle
- 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
what excitability of neurons control smaller and larger motor units
- 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
what explains how the same muscle can control dine delicate movements and also perform powerful heavy maneuvers
Henneman's size principle
130
what happens to intracellular calcium levels and muscle contraction at stimulation intervals greater than 200 ms
- intracellular calcium is restored to baseline levels between action potentials
- contraction consists of separate twitches
131
what happens to intracellular calcium levels and muscle contraction at stimulation intervals between 200 and 75 ms
- 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
what happens to the degree of summation at higher stimulation frequencies (stimulation intervals less than 75 ms)
degree of summation increases
132
define summation
- 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
define unfused or incomplete tetanus
- occurs when there is a high degree of summation (high stimulation frequencies)
- sustained graded contractions that can increase in size and length
134
define complete or fused tetanus
- 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
define tetanic contraction
- smooth contraction may time stronger than a single twitch
- occurs when the muscle is in a state of complete or fused tetanus
136
describe the baseline tone of skeletal muscles
- always maintain a baseline tine
- even relaxed muscles will be in a state of slight contraction
- does not give rise to movements
137
why are skeletal muscles always in a state of slight contraction (even relaxed muscles)
- keeps muscles healthy, firm, and primed to respond
- generates posture and stabilizes joints
138
when is an EMG usually performed in a clinical setting
when a patient has symptoms of weakness and an examination shows impaired muscles strength
139
when can an EMG help to differentiate between
muscle weakness caused by neurological disorders or caused by another condition
140
what does the raw surface EMG signal reflect
the muscle fibers active at that time
141
can you detect the contributions of individual motor units on an EMG
sometimes, with exceedingly weak contractions
142
how is the raw EMG signal processed in the experiment done in lab
- 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
define coactivation
a phenomenon in which contraction of a muscle leads to some minor contractile activity in the antagonist muscle
144
what is the physiological significance of coavtivation
- not entirely clear
- likely helps to stabilize the joint and generate smooth contractions and relaxations against the load on the muscle
145
how many seconds worth of ATP is stored by muscle
5 seconds worth
146
what are the 3 main mechanisms that ATP is generated in muscle
- creatine phosphate directly phosphorylating ADP to ATP
- anaerobic glycolysis
- aerobic respiration
147
describe the timing of creatine phosphate reacting with ADP to form ATP and creatine
rapid
148
how much more creatine phosphate than ATP do muscles store
3x more creatine phosphate than ATP
149
how long can stored ATP and creatine phosphate power a muscle during vigorous activity
10 seconds
150
can muscles revert ATP and creatine to ADP and creatine phospahte
yes, they will do this during periods of rest
151
what is the first phase of glucose breakdown
glycolysis
152
does glycolysis require oxygen
no
153
is glycolysis aerobic or anaerobic
anaerobic (does not require oxygen)
154
how much ATP is formed from one glucose molecule during glycolysis
2 ATP
155
what happens after glycolysis if sufficient oxygen is available
- pyruvate enters the TCA cycle and oxidative phosphorylation
- aerobic respiration
- produces substantially more ATP
156
what happens at 70% maximal contraction of a muscle
the muscle will become so bulged that it compresses blood vessels which decreases oxygen delivery
157
what happens after glycolysis if sufficient oxygen is not available
- pyruvate is converted to lactic acid
- anaerobic glycolysis
- lactic acid will exit the muscle and can be converted to glucose by the liver
158
how long can anaerobic glycolysis power a muscle
40 seconds
159
what is produced during aerobic respiration
- carbon dioxide
- water
- 34 ATP (per glucose)
160
how can free fatty acids be burned
aerobically
161
when are free fatty acids used as a major source of energy
after 30 minutes of contractile activity
162
why is aerobic metabolism slow
there are many steps and intermediaries required
163
when will muscles perform aerobic pathyways
so long as oxygen is available
164
define aerobic endurance
the amount of time a muscle can contract using aerobic pathways
165
define anaerobic threshold
the point at which metabolism in a muscle switches to anaerobic glycolysis
166
what are surges of intense activity powered by
- stored ATP
- creatine phosphate
167
what are longer duration and high intensity exercises powered by
anaerobic glycolysis
168
what leads to muscle fatigue
- 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
are some muscle fibers more resistant to fatigue than others
yes, they have a greater capacity for oxidative metabolism
170
what affects the force of a muscle contraction
- number of motor units recruited
- size of the muscle fiber
- contraction summation due to increased stimulation
- extent of stretch to the muscle
171
how does exercise increase the force of muscle contraction
- exercise causes muscles fibers to hypertrophy
- larger muscle fibers create more force during contraction
172
describe slow and fast muscle fibers
- 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
what is contraction duration influenced by
how fast a muscle type can pump calcium back into the sarcoplasmic reticulum
174
what are the classifications of muscles in terms of the metabolic pathway they mainly use during contraction
- oxidative fibers
- glycolytic fibers
175
define oxidative fibers
muscle fibers that rely mainly on aerobic pathways during contraction
176
define glycolytic fibers
muscle fibers that rely mainly on anaerobic glycolysis and creatine phosphate during contraction
177
what are the 3 main muscle fiber types
- slow oxidative fibers
- fast oxidative glycolytic fibers
- fast glycolytic fibers
