Membrane & Muscle Flashcards
(152 cards)
1
Q
What are 4 functions of the plasma membrane?
A
1) Separate ICF from ECF
2) Selective barrier to diffusion
3) Selective transporter of nutrients and ions
4) Interpret and carry signals
2
Q
What do proteins function as in the plasma membrane?
A
Channels, carriers, receptors, and enzymes
3
Q
What are important factors for passive transport?
A
- Lipid solubility
- Concentration gradient
- Size
4
Q
Does the rate of passive transport depend on temperature?
A
Nope
5
Q
What are 4 characteristics of carrier-mediated transport?
A
1) Specificity
2) Saturation (waiting time)
3) Competition
4) Temperature-sensitivity
6
Q
What are the 2 types of carrier-mediated transport?
A
1) Passive (facilitated diffusion)
2) Active (“pumps”)
7
Q
What is primary active transport?
A
When the mechanism uses ATP directly
8
Q
What is secondary active transport?
A
When the mechanism is powered by a mechanism that directly uses ATP
9
Q
What is the relationship between solutes and water concentration?
A
Inverse – less solutes means a higher concentration of water
10
Q
Define isotonic in regards to a cell
A
- A solution in which the cell retains its original volume because it does not gain or lose water
- Impermeable solutes = 300 mOsm
11
Q
Define isosmotic
A
A solution in which the TOTAL solutes (impermeable and permeable) = 300 mOsm
12
Q
Do permeable solutes contribute to the dilution of water?
A
Nope
13
Q
What happens when concentration gradient equals electrical gradient?
A
The ion will stop moving down its concentration gradient
14
Q
What is resting membrane potential?
A
A dynamic steady state in which inward current is exactly matched by outward current
15
Q
What impact will increasing extracellular potassium have on Em?
A
It will raise Em, resulting in depolarization
16
Q
What impact will increasing permeability of potassium have on Em?
A
It will decrease Em, resulting in hyperpolarization
17
Q
What impact will increasing permeability of sodium have on Em?
A
Raise Em, resulting in depolarization
18
Q
What impact will decreasing sodium potassium pumping have on Em?
A
Raise Em, resulting in depolarization
19
Q
What impact will increasing the permeability of chlorine have on Em?
A
No impact
20
Q
Uncharged and nonpolar molecules are highly ___ soluble
A
Lipid
21
Q
Charge and polar molecules are highly ___ soluble
A
Water
22
Q
What is equilibrium potential?
A
When the concentration gradient and the net electrical gradient become balanced
23
Q
What direction is the sodium gradient?
A
Into the cell
24
Q
What direction is the potassium gradient?
A
Outside of the cell
25
What causes Em to change?
Any change in ionic current
26
When do aquaporins close?
Never
27
When do voltage-gated sodium channels open?
Upon depolarization
28
What is the speed of the response from a voltage-gated sodium channel?
Very fast
29
How long does it take for voltage-gated sodium channels to self-inactivate?
Very short time
30
What happens when a cell becomes depolarized?
1) Potassium current increases through aquaporin channels, tending to repolarize
2) Voltage-gated sodium channels open, producing a sodium current
3) If the current of sodium is more than the potassium current an action potential starts
31
What does the peak of an action potential represent?
When the sodium current equals the potassium current
32
When do voltage-gated potassium channels open?
Upon depolarization
33
What is the speed of the response from a voltage-gated potassium channel?
Slow
34
How long do voltage-gated potassium channels stay open?
As long as depolarization persists
35
What is the membrane considered during the downstroke (repolarization)?
Refractory
36
What happens with progressive repolarization?
- Sodium channels reset
- Potassium current decreases as Em approaches Ek
- Potassium channels begin to close
- Excitability is restored
37
What is the absolute refractory period?
When not enough sodium channels are open to make the sodium current greater than the potassium current, results in total inexcitability
38
What is the relative refractory period?
When there are less sodium channels and/or more potassium channels open than normal, the threshold is higher than normal and can still be excited
39
What impact does increasing extracellular potassium have on an action potential?
Potassium from inside the cell with leak outside, inhibiting repolarization
40
What effect does decreasing temperature have on an action potential?
Stops the Na/K pump, which stops membranes from getting excited
41
What effect does increasing extracellular calcium have on an action potential?
Calcium stabilizes sodium channels, so more depolarization would be needed to excite
42
What effect does local anesthetic have on an action potential?
"Super calcium"; will cause threshold to increase dramatically
43
What are 3 characteristics of local circuits?
1) Depolarize adjacent membranes, causing an action potential
2) Decay with distance
3) Slow
44
What is the velocity of conduction determined by?
Spatial extent of local circuits
45
What is the relationship between threshold and velocity of conduction?
Inverse
46
What is the relationship between height and velocity of conduction?
Direct
47
What is the relationship between membrane resistance and velocity of conduction?
Direct
48
What is the relationship between fibre diameter and velocity of conduction?
Direct
49
Why does decreasing diameter result in a lower velocity?
Decreasing the diameter means an increase in axoplasmic resistance
50
What is the immediate effect of temperature on rate of activation of channels?
Cooling decreases fluidity of membranes which slows opening of sodium channels
51
What is the progressive effect of temperature on rate of activation of channels?
Cooling slows rate of Na/K pumping, which means a loss of sodium and potassium gradients, resulting in depolarization, which raises threshold, decrease action potential height, and decreases membrane resistance. These altogether decrease conduction velocity
52
Why can a "backward" current flow NOT reexcite old active areas?
Because these areas are in a refractory period
53
What are 5 events of neuromuscular transmission?
1) Release of acetylcholine
2) Acetylcholine diffuses across cleft
3) Acetylcholine binds to Ach receptors
4) End-plate potential spreads via local circuits to adjacent excitable sarcolemma
5) Hydrolysis of Ach
54
What causes acetylcholine to be released?
Motor action potential arrives at nerve terminal, depolarizes, activates voltage-gated calcium channels, causing a calcium influx, which causes packets of Ach to be released
55
What happens when Ach binds to receptors?
Permeability of sodium AND potassium increases
56
How much does end-plate potential depolarize to?
Threshold
57
What happens when voltage-gated calcium channels are blocked?
Voluntary muscles (lungs) will no longer work
58
Is a membrane more permeable to K or Na?
K
59
How does a membrane being more permeable to potassium impact Em?
Em will be affected more dramatically by changes in K permeability than by changes in Na permeability
60
Is the sodium/potassium needed to keep up concentration gradients after every action potential and why?
No because very few sodium and potassium ions are needed to cause an action potential
61
What is the charge of a cell that is experiencing an action potential?
Positive
62
What is the charge of a cell that is at resting potential?
Negative
63
Does the original action potential travel along a membrane?
No, it triggers an identical new action potential in the adjacent area
64
What must happen for a sodium channel to be triggered a second time?
Resting potential must be restored and the channels must be reset to their original positions
65
How are refractory period and action potentials related?
The longer the refractory period the greater delay between action potentials
66
Describe the all-or-none fashion of an action potential
An excitable membrane responds to a triggering event with either a maximal AP, or it does not respond with an AP at all
67
What is the effect of a stronger stimulus on an AP, and what will it not do?
- It will produce a greater number of AP's per second
| - It will not produce a larger AP
68
What causes striations?
Acto-myosin organization
69
Between skeletal and cardiac muscle, which one controls voluntary movement and which one controls involuntary movement?
- Skeletal -- voluntary
| - Cardiac -- involuntary
70
Which types of muscle have striations?
Skeletal & cardiac
71
Does smooth muscle control voluntary or involuntary movement?
Involuntary
72
How is skeletal muscle attached to the skeleton?
Tendons
73
Define isometric
Force generated without change in length
74
Define isotonic in regards to skeletal muscle
Length change at steady force
75
What is concentric contraction?
Tension during shortening motion
76
What is eccentric contraction?
Tension during lengthening motion
77
What is each muscle cell/fiber innervated by and where?
By an alpha motor neuron in a neuromuscular junction or "end plate"
78
Where is the efferent motor neuron cell body found?
Ventral horn of spinal cord
79
Where is the afferent motor neuron found?
Dorsal horn
80
How do neurons leave the spinal cord and what do they form?
- By the ventral root
| - Form mixed peripheral nerves
81
What is a motor unit?
A motor nerve and all the muscle fibers it innervates
82
What does it mean when a motor unit is described as a functional contractile unit?
All of the fibers contract synchrously
83
How is motor unit size related to muscle function?
- The motor unit gets larger as more fibers are needed
| - Large motor units are needed for limbs that facilitate large movements with high force
84
Where are neurotransmitters released?
Neuromuscular junctions
85
What is epimysium and what does it do?
Epimysium is a mixture of elastin and collagen that surrounds muscle and prevents it from falling apart
86
What is a fasciculus?
A bundle of muscle fibers
87
What does perimysium surround?
Fasciculus'
88
What does endomysium surround?
Muscle fibers
89
What are myofibrils?
Bundles of actin and myosin filaments running along the long axis of cells
90
What are the Z lines?
The beginning and ending of a sarcomere
91
What is the I band composed of, and is it light or dark?
- Actin filaments
| - Light
92
What is the A band composed of, and is it light or dark?
- Myosin and actin filaments
| - Dark
93
What is the H band composed of and where is it found?
- Only myosin
| - Centre of sarcomere
94
What does the M line do?
Organize and align thick filaments
95
What are myofibrils surrounded by?
Calcium ion rich sarcoplasmic reticulum
96
What is a T tubule?
Essentially the plasma membrane, hollow and filled with ECF
97
What direction do actin filaments extend and from where?
Inward from the Z-disk
98
What does it mean when myosin filaments are described as bipolar?
The heads are oriented in opposite directions at each end of the sarcomere
99
Describe the organization of a thick filament
- Hexamer with 2 heavy chains and 2 pairs of light chains
| - Heavy chain has coiled tail with 2 globular heads
100
What is a cross bridge?
The interaction between myosin heads with thin filaments
101
Describe the troponin-tropomyosin complex
- Tropomyosin binds actin and blocks myosin head binding
- Troponin T binds tropomyosin
- Troponin I facilitates inhibition myosin binding
- Troponin C binds calcium ions, changes shape, and causes releases of troponin I and exposes myosin binding sites
102
Describe the sliding filament theory
Muscle contraction is caused by the sliding of actin filaments past myosin filaments with no change in filament length
103
What gets pulled together in the sliding filament theory?
Z-lines
104
In the crossbridge cycle, does actin or myosin move?
Actin
105
How does elevating cellular calcium enable cross bridge cycling?
Calcium binds troponin C, causing release of troponin I, and movement of tropomyosin to expose myosin binding sites
106
Describe excitation-contraction coupling
1) Motor neuron releases synaptic vesicle at end plate
2) Ach from vesicles activates channels enriched on the facing sarcolemma
3) Short AP transmitted along the sarcolemma and down T tubules
4) AP changes conformation of DHPR leading to calcium release from SR terminal cisternae via RYR into myoplasm
5) Increased calcium promotes actin-myosin interaction (binds troponin C to move tropomyosin), thus inducing a twitch
6) Intracellular calcium re-sequestered to the SR via SERCA to cause relaxation
107
What is DHPR?
A protein in the T tubule
108
What is RYR?
A protein in the terminal cisternae
109
What does an AP in the T tubule cause?
A conformational change in DHPR
110
What does a DHPR shape change cause?
The RYR to open and allow SR calcium to be released
111
What is SERCA?
A calcium-ATPase pump that re-sequesters intracellular calcium
112
What is passive tension?
Resistance to stretch of a muscle at rest
113
What is active tension?
New tension is developed after the muscle is stimulated
114
What is Lo?
The optimal length to develop active tension
115
What is the ideal Lo?
2.0 - 2.2 micrometers
116
What is Vo (maximum shortening velocity)?
Velocity in the absence of a load
117
What is Po (maximum isometric tension)?
Load at which stimulated muscle no longer shortens
118
What is the relationship between load and shortening?
Inverse -- increasing load decreases shortening
119
What type of skeletal muscle is considered type 2?
Fast twitch
120
How is a fiber determined to be fast or slow?
Innervation
121
What type of activity is high for fast fibers?
Glycolytic
122
What type of activity is high for slow fibers?
Oxidative
123
Between fast and slow fibers, which has more mitochondria?
Slow
124
Between fast and slow fibers, which has more capillaries?
Slow
125
Between fast and slow fibers, which has a more extensive SR?
Fast
126
Between fast and slow fibers, which is innervated by alpha 1 motor neurons?
Fast
127
Between fast and slow fibers, which is innervated by alpha 2 motor neurons?
Slow
128
Describe the diameter, excitability, and conduction velocity of alpha 1 motor neurons
- Large diameter
- Low excitability
- Very fast conduction velocity
129
Describe the diameter, excitability, and conduction velocity of alpha 2 motor neurons
- Small diameter
- High excitability
- Fast conduction velocity
130
Between fast and slow fibers, which fatigues faster?
Fast
131
Between fast and slow fibers, which is used for sustained activities?
Slow
132
What are 3 energy sources used during contraction?
1) ATP
2) Creatine phosphate
3) Glycogen & glucose
133
What is oxygen debt?
When rate of energy use exceeds rate of production by oxidative metabolism
134
How is oxygen debt payed back?
Increased respiration and cardiac work during recovery
135
Can the ATP pool ever be reduced to zero?
No
136
How is the force of contraction increased?
Recruiting more fibers
137
How are cardiac muscle cells connected?
End-to-end
138
Do smooth muscle cells have sarcomeres?
Nope
139
Do smooth muscle cells have neuromuscular junctions?
No
140
What are the 2 types of smooth muscle cells?
1) Phasic (single unit)
| 2) Tonic (multi-unit)
141
Describe phasic smooth muscle cells
- Cells contract together and are normally relaxed
| - Cells coupled for free flow of ions and AP
142
Describe tonic smooth muscle cells
- Cells operate independently, normally contracted
- Each cell innervated by a nerve ending
- Little cell-cell communication
143
What are muscle fibres made up of?
Myofibrils
144
What are the outer limits of the A band determined by?
The 2 ends of the thick filaments
145
What make up cross bridges?
Myosin heads
146
What happens when troponin is not bound to calcium?
It stabilizes tropomyosin in its blocking position over actin's cross-bridge binding sites
147
What happens when troponin is bound to calcium?
The calcium's shape changes, which allows tropomyosin to slip away from it's blocking position
148
When the sarcomere shortens, do the thick and thin filaments decrease in length?
No
149
Where are T tubules found?
Every junction of an A band and I band
150
What do terminal cisternae store?
Calcium
151
How many muscle fibres does one axon terminal supply?
One
152
As a motor unit increases in size, what happens to its ability to become activated?
The ability decreases (gets harder to activate)
