Week 2 - Cell Receptors, Membrane Potentials, & Action Potentials Flashcards
(147 cards)
1
Q
Membrane Potential
A
Electrical potential or electrical difference across cell membrane
2
Q
Membrane potential exists across _____ cell membranes.
A
All
(cell membranes)
3
Q
What does it mean when “some cells are excitable”?
A
They can generate action potentials or electrical impulses.
They can conduct the electrical impulses along their cell membrane.
4
Q
Name 5x types of cells that are excitable. (all are fibers)
A
1) Nerve fibers
2) Skeletal muscle fibers
3) Cardiac muscle fibers
4) Smooth muscle fibers
5) Cardiac electrical fibers
5
Q
Resting Membrane Potential
A
Electrical difference/gradient across the cell membrane in the resting, undisturbed state
6
Q
Cell membranes are polarized or non-polarized?
A
Polarized
7
Q
What direction do you compare cell membranes?
A
ALWAYS compare “inside” of the cell membrane to “outside” of the cell membrane
Inside –> Outside
8
Q
In large nerve fibers, skeletal muscle fibers, and some cardiac fibers, the membrane potential is what mV?
A
-90 mV
9
Q
When the membrane potential is -90 mV, INSIDE of the cell membrane is what?
A
90 mV more negative relative to the outside of that cell membrane
10
Q
What does each cell establish and maintain?
A
Its own specific membrane potential
11
Q
Where is the electrical difference of the cell membrane?
A
Just inside and just outside (RIGHT ON) the cell membrane
12
Q
Intracellular and Extracellular body fluids are electrically _____
A
NEUTRAL
(Cations = Anions)
13
Q
What are the 4x main contributors to the cell membrane potential?
A
1) Potassium Leak Channels
2) Sodium Leak Channels
3) Sodium - Potassium Pump
4) Accumulation of negatively charged proteins along the inside of the cell membrane
14
Q
Which contributor contributes most to the cell membrane potential?
A
Potassium Leak Channels
(always open and the leakiest of the leak channels)
15
Q
If only potassium leak channels were present on the cell membrane, what would the resting potential be?
A
-94 mV
16
Q
If potassium & sodium leak channels were present on the cell membrane, what would the resting potential be?
A
-86 mV
17
Q
How many mV’s do sodium leak channels contribute to the cell membrane?
A
+8 mV
18
Q
If potassium leak channels, sodium leak channels, and the primary active sodium potassium pump were present on the cell membrane, what would the resting potential be?
A
-90 mV
19
Q
How many mV’s does the primary active sodium potassium pump contribute to the cell membrane?
A
-4 mV
20
Q
Action Potentials
A
Transmission of electrical impulses along the membranes of excitable cells
21
Q
Name 4x main components of an action potential (remember the curve picture)
A
1) Resting membrane potential
2) Threshold potential
3) Depolarization
4) Repolarization
22
Q
The UPSTROKE of an action potential is ________
A
Depolarization
23
Q
The DOWNSTROKE of an action potential is ________
A
Repolarization
24
Q
What is another name for “overshoot” on an action potential curve?
A
Peak Amplitude of Depolarization
25
What is happening in the resting phase of an action potential?
The cell is in an undisturbed state of -90 mV
26
What leads to an influx of sodium into the cell?
An Initial Stimulus
27
When sodium moves into the cell, the cell membrane potential becomes what?
Less Negative
(sodium is positively charged)
28
What happens at the threshold potential?
Voltage Gated Sodium Channels OPEN
29
Usually, how many mV's is the Overshoot or Peak Amplitude of Depolarization?
+20 mV
(can be more than this though)
30
When do voltage gated sodium channels close?
Peak Amplitude of Depolarization
31
When voltage gated sodium channels close, what other channel opens?
Voltage Gated Potassium Channels OPEN
32
What causes the end of Depolarization?
The closing of voltage gated sodium channels
33
What causes the start of Repolarization?
The opening of voltage gated potassium channels
34
What is the movement of potassium through Voltage Gated Potassium Channels?
WITH its electrochemical gradient
Inside --> Outside of the cell
35
The cell membrane potential becomes more _______ during Repolarization
NEGATIVE (-)
36
The cell membrane potential becomes more _______ during Depolarization
POSITIVE (+)
37
Voltage Gated Potassium Channels ______ when the cell membrane reaches the resting state
Close
38
What are the 4x steps of Depolarization?
1) Inward diffusion of sodium ions until the resting membrane potential reaches the threshold potential
2) Voltage-gated sodium channels open at the threshold potential, followed by rapid influx of sodium ions inward
3) Voltage-gated sodium channels suddenly close when full amplitude of depolarization is achieved (about +20 mV)
4) Influx of sodium ceases
*Since the membrane potential has been reversed, the INSIDE is now more POSITIVE relative to outside of the cell membrane
39
What are the 2x steps of Repolarization?
1) Voltage-gated potassium channels open at about the exact same time that voltage-gated sodium channels close
2) Rapid outflux of potassium causes return of membrane potential to the resting membrane potential
40
Refractory Period of Action Potentials
Built in protective mechanisms that allow the membrane potential to return to resting membrane potential and recover before another action potential can occur
*EX: Cardiac Action Potential waveform*
41
Name the 3x refractory periods of action potentials
1) Absolute
2) Relative
3) Supernormal/Vulnerable
42
Absolute Refractory Period
Cell will NOT depolarize again, regardless of how strong the stimulus
(another action potential cannot occur)
43
Relative Refractory Period
An EXTRA STRONG stimulus is needed to depolarize the cell again
(if this happens, it's an abnormal occurrence)
44
Supernormal/Vulnerable Refractory Period
Even a MILD stimulus may cause another depolarization
(if this happens, it's an abnormal occurrence)
45
What is another name for Absolute Refractory Period?
Effective Refractory Period (ERP)
46
Where does the Absolute Refractory Period start?
At threshold
47
On an EKG, if there is a depolarization during the relative refractory period, what do you see?
A QRS sitting on top of the previous T-wave
48
On an EKG, if there is a depolarization during the supernormal/vulnerable refractory period, what do you see?
A QRS sitting on the down-slope of the previous T-wave
49
If the supernormal period allows the cell to depolarize very easily because it's closer to threshold, why does this not apply to the relative refractory period?
- During the relative refractory period, the voltage gated sodium channels have not completely reset themselves
- It's harder to open them up
- That's why it takes an extra strong stimulus to create another depolarization in the relative refractory period
- By the time we get to the supernormal period, the voltage gated sodium channels have had time to completely reset themselves
50
The longer repolarization is, the _______ the refractory period is.
Longer
51
True or False: The longer the refractory period is, the lesser the chance that an ectopic stimulus will initiate an early abnormal depolarization.
False
*The GREATER the chance*
52
What are the 3x types of stimuli that can initiate an action potential? (influx of sodium)
1) Chemical
2) Electrical
3) Mechanical
53
What is an example of a Chemical Stimulus?
Acetylcholine Gated Sodium Channel
54
What is an example of a Electrical Stimulus?
Electrical conduction system of the heart
55
What is an example of a Mechanical Stimulus?
Touch, pressure, or vibration
56
What type of event must cause enough influx of sodium for the resting membrane potential to reach the threshold potential?
Initial Event
57
"All or None" Phenomenon (3x)
1) If resting membrane potential does NOT reach threshold, depolarization will NOT occur
2) If the initial event DOES cause the resting membrane potential to reach the threshold potential, then depolarization WILL occur
3) Suprathreshold stimulus (a very strong stimulus that causes a lot of sodium influx) will NOT cause greater amplitude of depolarization than a threshold stimulus
58
Suprathreshold Stimulus
A very strong stimulus that causes a lot of sodium influx
59
Most action potentials begin at _______ on the cell membrane.
A single point
60
What direction does the action potential move in across the cell membrane?
Bi-directional Propagation (wide spreading)
From the site of the stimulus, outward across the cell membrane
61
What type of polarization does Hyperkalemia cause on the resting membrane potential?
HYPOpolarization
62
What type of polarization does Hypokalemia cause on the resting membrane potential?
HYPERpolarization
63
How difficult is it to open voltage-gated Na+ channels in Hypocalcemia?
Easier to open
64
How difficult is it to open voltage-gated Na+ channels in Hypercalcemia?
Harder to open
65
Is it harder or easier to initiate depolarization (threshold potential closer to resting membrane potential) in Hypocalcemia?
Easier to depolarize
66
Is it harder or easier to initiate depolarization (threshold potential farther to resting membrane potential) in Hypercalcemia?
Harder to depolarize
67
When potassium is high (K+ = 7 mEq/L), what type of polarization happens?
Hypopolarization
(resting membrane potential is closer to threshold; ex: -90 mV --> -80 mV)
68
When potassium is low (K+ = 2 mEq/L), what type of polarization happens?
Hyperpolarization
(resting membrane potential is farther from threshold; ex: -90 mV --> -100 mV)
69
When the potassium gradient is less (inside cell = 140 mEq/L; outside cell = 7 mEq/L), what is the speed of ions in potassium leak channels?
Slows down
70
When the potassium gradient is more (inside cell = 140 mEq/L; outside cell = 2 mEq/L), what is the speed of ions in potassium leak channels?
Faster
71
On an EKG, when a patient is Hyperkalemic, what type of waves do you see and why?
Peaked T-waves
Because of Rapid Repolarization
72
Why is there rapid repolarization in hyperkalemia?
More potassium goes through voltage gated potassium channels quickly
73
Other than peaked T-waves, what do you see on an EKG for hyperkalemia?
Conduction blocks
(widened PR interval, P-wave lost, QRS complex widen and flatten)
74
What type of rhythms would you see in a patient with Hypokalemia?
Irritable dysrhythmias
75
True or False: The higher the extracellular calcium level, the harder it is to open voltage gated sodium channels.
True
76
True or False: The lower the extracellular calcium level, the harder it is to open voltage gated sodium channels.
False
*The EASIER it is to open*
77
What membrane potential does Potassium move?
Resting Membrane Potential
78
What membrane potential does Calcium move?
Threshold Potential
79
Why would you give calcium as a temporary treatment to a patient who is Hyperkalemic?
Hyperkalemia moves the resting membrane potential closer to the threshold potential.
[RMP --> TP]
Giving calcium will move the threshold potential away from the resting potential, which re-establishes a normal gradient between the two potentials
[RMP ------------> TP]
80
What 5x temporary treatments can you use for Hyperkalemia?
1) Give calcium
2) Hyperventilate
3) Give bicarbonate
4) Give insulin & dextrose
5) Give a beta-2 agonist (albuterol)
81
How does hyperventilation help decrease potassium levels?
Causes an alkalotic state
Makes hydrogen move out of the cell and potassium into the cell
82
How do you truly treat hyperkalemia?
Dialysis and Giving Kayexalate*
*Binds potassium to the lumen of the gut so it cannot be reabsorbed, then excreted through the feces
83
Signal Transduction
What happens inside the cell after a cell receptor is activated
Eventually leads to the target cell response
84
What is the purpose of cell receptors and signal transduction?
To allow extracellular substances (hormones, neurotransmitters, neuromodulators, etc.) to regulate the activity of cells through one or more intermediate mechanisms
85
True or False: The extracellular substance does not actually enter into the cell.
False
*The extracellular substance MAY OR MAY NOT actually enter into the cell*
86
True or False: Many drugs can also bind with these receptors and bring about a cell response by an agonist or antagonist effect on the receptors.
True
87
What are the 3x cascading set of events of cell receptor mechanisms and signal transductions?
1) Extracellular substance (little amount)
2) Binds to a few receptors
3) Activates numerous intracellular mediators that actually bring about target cell response to the extracellular substance
88
What does an "agonist effect" mean?
Activates the receptor
89
What does an "antagonist effect" mean?
Inhibits the receptor
90
What are the 3x locations of receptors?
1) Membrane-bound
2) Intracellular
3) Combination of membrane-bound and intracellular
91
Where are Membrane-Bound Receptors found? (2x)
1) Incorporated into phospholipid cell membrane
2) Integrated with a number of intracellular proteins, enzymes, second messengers, and protein kinases
92
Where are Intracellular Receptors found? (2x)
1) Cytoplasm
2) Nucleus
93
What 2x properties does a chemical signal need to have in order to completely move through the phospholipid bilayer?
1) Lipid soluble
2) Electrically neutral
94
What 2x types of hormones are lipid soluble?
1) Thyroid-based hormones
2) Steroid-based hormones
95
What are the 5x cascading sequence of events of a hormone & receptor from the extracellular area to activating protein kinase enzymes?
1) Hormone attaches to the receptor at the plasma membrane
2) Activated G-proteins
3) Activated adenylate cyclase
4) cAMP
5) Activated protein kinase enzymes
96
What membrane bound receptor opens an ion channel in the cell membrane? (think neuro)
Acetylcholine
(Acetylcholine Gated Channel)
97
When sodium (+) moves into the cell, does it have an excitatory or inhibitory effect on the cell?
Excitatory
98
When a ligand opens a chloride (-) channel and moves into the cell, does it have an excitatory or inhibitory effect on the cell?
Inhibitory
99
What is a group of drugs that opens chloride channels and leads to hyperpolarization of cell membranes?
Benzodiazepines
*Binds with GABA receptors, which opens chloride channels, and inhibits action potentials
100
What is the fastest of all the cell receptor mechanisms?
Membrane receptors that open ion channels
(milliseconds)
101
What is the step-by-step process of an atrial natriuretic hormone binding to a receptor to an increase in sodium secretion by the kidney's? (5x)
1) Atrial natriuretic hormone binds to the receptor site
2) Ligand is bound and activates the membrane bound receptor, which is attached to a peripheral protein -- guanylate cyclase
3) Guanylate cyclase converts GTP to cyclic GMP (second messenger)
4) Cyclic GMP (cGMP) activates protein kinase G
5) Protein kinase G brings about the cell response -- Increases Na+ excretion by kidney cells and increases urine volume
102
Peripheral proteins are often what?
Enzymes
103
What inactivates/stops cGMP?
Phosphodiesterase
(breaks cGMP to just GMP)
104
If you gave a drug that inhibits phosphodiesterase, what happens?
The cGMP, protein kinase G, and cell response pathway will last longer
(EX: patient will continue to excrete Na+ in kidney's and increase urine volume)
105
What is a G-Protein?
Complexes that are composed of an alpha, beta, and gamma subunit and widely distributed throughout the body
106
What 2x things are attached to each other when the G-protein is in an inactive state?
Alpha subunit & GDP
107
What 3x things happen when the chemical binds to the receptor site and the G-protein couple receptor is activated?
1) G-protein breaks away from the receptor
2) Alpha subunit breaks away from the beta and gamma subunits
3) GDP is replaced by GTP (phosphorylated)
108
What 2x things can an alpha-GTP complex do?
1) Open an ion channel
2) Activate secondary messengers
109
Alpha subunits contain what?
De-phosphorylating enzyme called Phosphatase
110
What does Phosphatase do?
De-phosphorylates GTP back to GDP
111
How do you recombine the alpha subunit back to the beta and gamma subunits?
Once the GTP is de-phosphorylated back to GDP (alpha subunit & GDP, inactive state)
112
What 3x types of receptors does Norepinephrine bind to?
1) Alpha-1
2) Alpha-2
3) Beta-adrenergic receptors
113
What is the complete process of Norepinephrine binding with ALPHA-1 target cell receptors? (9x)
1) Norepinephrine binds to the alpha-1 receptor
2) The alpha subunit breaks away from the G-protein
3) The GDP is replaced by GTP
4) The alpha subunit is phosphorylated
5) The alpha GTP complex actives the phospholipase-C enzyme
6) Phospholipase-C converts PIP2 into two substances (IP3 and Diacylglycerol)
7) IP3 causes a calcium release from the endoplasmic or sarcoplasmic reticulum to increase intracellular calcium levels
8) The calcium ions increase intracellular protein kinase C
9) Protein kinase C brings about the physiologic response
114
What are the 2x bodily responses to Norepinephrine activating ALPHA-1 receptors?
1) Vascular smooth muscle contraction
2) Blood vessel constriction
115
What is the purpose of Norepinephrine activating the ALPHA-1 receptors?
To increase blood pressure
116
What is the complete process of Norepinephrine binding with BETA target cell receptors? (7x)
1) Norepinephrine binds to the beta receptor
2) The alpha subunit breaks away from the G-protein
3) GDP is replaced by GTP
4) Alpha GTP complex activates the adenylyl cyclase enzyme
5) Adenylyl cyclase enzyme converts ATP to cyclic AMP (cAMP)
6) cAMP activates protein kinase A
7) Protein kinase A brings about the physiologic response
117
What are the 3x bodily responses to Norepinephrine activating BETA-1 receptors?
1) SA node increases heart rate
2) AV node increases speed of conduction
3) Ventricular contractile fibers increase strength of contraction
118
What is the purpose of Norepinephrine activating the BETA-1 receptors?
To increase cardiac output
119
What are the 2x bodily responses to Norepinephrine activating BETA-2 receptors?
1) Bronchiolar smooth muscle relaxation
2) Bronchiolar dilation
120
What is the purpose of Norepinephrine activating the BETA-2 receptors?
To improve gas exchange
121
Where do you find Alpha-1 receptors?
Vascular smooth muscle
122
Other than Norepinephrine, what 2x other drugs are used to activate Beta receptors? (these are better for Beta receptor activation too)
Epinephrine & Isoproterenol
123
Where do you find Beta-1 receptors? (3x)
In the HEART!
1) SA node
2) AV node
3) Ventricular contractile fibers
124
Where do you find Beta-2 receptors?
Bronchiolar smooth muscle
125
What is an example of a membrane-bound receptor and signal transduction that phosphorylates intracellular proteins?
Insulin that binds to an insulin receptor
126
How does insulin phosphorylate intracellular proteins? (2x)
1) Insulin binds to the insulin receptor
2) Phosphorylates specific sites on the receptor and specific intracellular proteins
127
In most cases, phosphorylation activates enzymes and causes an excitatory response. But in some instances, phosphorylation can ________ enzymes.
Inhibit
128
If insulin binds to its receptor and causes Glycogenesis, are the enzymes activated or inhibited?
Activated
(insulin favors storing energy for later)
(Glucose --> Glycogen)
129
If insulin binds to its receptor and causes Glycogenolysis, are the enzymes activated or inhibited?
Inhibited
(Glycogen --> Free Glucose)
130
If insulin binds to its receptor and causes Glycolysis, are the enzymes activated or inhibited?
Inhibited
(Glucose --> Pyruvic Acid)
131
If insulin binds to its receptor and causes Lipogenesis, are the enzymes activated or inhibited?
Activated
(insulin favors storing up fat to be used later for energy)
(Glucose --> Fatty Acids)
132
What is an example of an intracellular receptor and signal transduction mechanism?
Aldosterone (steroid-based hormone) binding to an intracellular aldosterone receptor
133
What is the complete process of Aldosterone producing a cellular response? (9x)
1) Aldosterone (steroid-based hormone) passes directly through the phospholipid plasma membrane
2) Aldosterone binds to the aldosterone receptor in the cytoplasm
3) Aldosterone-receptor complex passes through nuclear pores into the nucleus
4) Aldosterone-receptor complex binds to DNA
5) Transcriptase enzymes are activated
6) mRNA synthesis occurs with the attached complex
7) mRNA moves out into the cytoplasm and delivers the complex code to a ribosome
8) Ribosome translates the code into a protein
9) Proteins produce a cell response
134
Name 5x steroid-based hormones that use intracellular receptors
1) Aldosterone
2) Testosterone
3) Estrogen
4) Progesterone
5) Cortisol
135
What is the other type of hormone that can use intracellular receptors?
Thyroid hormones (T3 & T4)
136
What does Transcriptase do?
An enzyme that regulates the transcription of DNA to mRNA
137
What is an example of a combined membrane-bound and intracellular receptor & signal transduction mechanism?
Acetylcholine to an endothelial cell (lines a blood vessel) and a smooth muscle cell
138
What is the complete process of Acetylcholine producing a cellular response in a smooth muscle cell? (9x)
1) Acetylcholine binds to a membrane-bound receptor
2) Membrane-bound receptor causes the Calcium channel to open
3) Calcium diffuses with it's electrochemical gradient from outside the cell to inside the cell
4) Calcium channel activates the enzyme Nitric Oxide synthase
5) Nitric Oxide diffuses out of the endothelial cell into the smooth muscle
6) Nitric Oxide activates guanylate cyclase
7) Guanylate cyclase converts GTP to cyclic GMP (cGMP)
8) cGMP increases the activity of protein kinase G
9) Protein kinase G causes smooth muscle cell relaxation and blood vessel dilation
139
What does Nitric Oxide Synthase do?
An enzyme that converts the amino acid, Arginine, into Nitric Oxide
140
What does protein kinase G do in smooth muscle cells?
Inhibits smooth muscle contraction
141
What does Guanylate cyclase do in smooth muscle cells?
Converts GTP to cGMP
142
How does Nitroprusside and Nitroglycerin work in the combined membrane-bound and intracellular receptor & signal transduction mechanism? (2x)
1) Nitroprusside & Nitroglycerin enzymatically converts into nitric oxide in the plasma/bloodstream
2) Nitric oxide that is formed diffuses across the endothelial cell, into the smooth muscle, and binds to guanylate cyclase
143
What 2x things can stop the sequence of events for cell receptor & signal transduction mechanisms?
1) Initial stimulus is removed from the receptor (i.e. norepinephrine, acetylcholine, etc.)
2) Phosphodiesterase enzyme
144
What are 3x phosphodiesterase inhibitor drugs that are commonly used? (penile drugs, lol)
1) Viagra (sildenafil)
2) Levitra (vardenafil)
3) Cialis (tadalafil)
*Inhibits phosphodiesterase #5, which is found in the smooth muscle of penile blood vessels
*Improves blood flow
145
How fast are directly regulated (open or close) cell membrane ion channels?
Milliseconds
*Fastest one*
146
How fast are intracellular receptors?
Minutes, hours, or days
Usually long-lasting target cell response
*Slowest one*
147
Name the 5x types of cell receptors and signal transduction mechanisms from FASTEST to SLOWEST.
1) Directly regulate (open or close) cell membrane ion channels
2) Receptors coupled with intracellular enzymes and second messengers
3) Receptors coupled with G-proteins
4) Phosphorylation of intracellular proteins/enzymes
5) Intracellular receptors (minutes, hours, or days for target cell effect -- usually long lasting target cell response)
