Nerve Signaling Flashcards
1
Q
biology voltage definition
A
- the difference in electrical potential (charge separation)
- the difference in the amount of energy in charged ions between two points
2
Q
membrane potential
A
the voltage across a membrane
3
Q
What is the charge state outside the nerve cell in a membrane potential?
A
there is an excess of cations so positive
4
Q
What is the charge state inside the nerve cell in a membrane potential?
A
there is an excess of anions so negative
5
Q
what do you use to measure a membrane potential?
A
a voltmeter
6
Q
what is resting potential and its value
A
membrane potential of a neuron at rest usually - 70mV
7
Q
how do you calculate membrane potential?
A
Vm = Vin - Vout
membrane potential = potential inside of cell - potential outside of cell
8
Q
which cells have a membrane potential?
A
ALL
9
Q
which cells can generate a large enough change in membrane potential?
A
neurons and muscle cells
10
Q
what factors maintain the resting potential neurons?
A
- the ion distribution
- membrane permeability
- Na+/K+ pumps
11
Q
what is the ion distribution in the maintenance of resting potential of neurons?
A
a large pool of negatively charge molecules inside the neuron
12
Q
what is the membrane permeability in the maintenance of resting potential of neurons?
A
- there are only Na+ and K+ leak channels
- more permeable to K+ (efflux) than Na+ (influx
13
Q
what is the Na+/K+ exchange rate in the maintenance of resting potential of neurons?
A
moves 3 Na+ out for every 2 K+ in
14
Q
what types of molecules make up the large internal pool that is negatively charged in the ion distribution?
A
- proteins
- amino acids
- sulfate
- phosphate
15
Q
Describe the molecules that make up the large internal pool that is negatively charged.
A
large molecules that cannot cross the membrane via diffusion
16
Q
What regulates the movement of ions?
A
transmembrane proteins (leak channels)
17
Q
How do the transmembrane transport proteins work?
A
- facilitated diffusion (passive transport)
- does not determine the direction or rate of flow
18
Q
Which has more leak channels? K+ or Na+
A
K+
19
Q
what is equilibrium potential?
A
potential at which there is no net movement of an ion at equilibrium
20
Q
What causes the equilibrium potential?
A
passive movement of ions that is dependent on electrochemical gradient
21
Q
what is the electrochemical gradient composed of?
A
the chemical gradient and electrical gradient
22
Q
describe the chemical gradient
A
- concentration gradient
- chemical force
- movement from high to low ion concentration
23
Q
describe the electrical gradient
A
- ion gradient
- electrical force
- movement of positive ion to area of negative ion concentration and vice versa
24
Q
what type of movement does the K+ channel have with the chemical gradient?
A
passive movement OUT of the cell
25
what type of movement does the na+ channel have with the **chemical** gradient?
poassive moment INTO the cell
26
what type of movement does the Cl- channel have with the **chemical** gradient?
passive movement INTO the cell
27
what type of movement does the K+ channel have with the **electrical** gradient?
passive movement INTO cell
28
what type of movement does the Na+ channel have with the **electrical** gradient?
passive movement INTO the cell
29
what type of movement does the Cl- channel have with the **electrical** gradient?
passive movement OUT of cell
30
what is the net movement of the K+ with the electrochemical gradient?
out of the cell
31
what is the net movement of the Na+ with the electrochemical gradient?
into the cell
32
how does K+ establish equilibrium?
- a chemical force causes K+ diffusion out of the cell making the inside of the cell more negative
the electrical force will pull the K+ back into the cell
33
When does equilibrium with chemical and electrical forces happen?
when chemical and electrical forces are in opposite directions and equal in magnitude
34
what happens with the cell is left unchecked?
- influx of Na+ makes cell less negative
- drives steady efflux of K+
- concentration gradient dissipates
YOU DIE
35
What drives the Na+/K+ pump ?
uses ATP to drive active transport to maintain ionic gradients
36
How many Na+ vs K+ get transported by the Na+/K+ pump?
3 Na+ out of cell
2 K+ into the cell
more positive ions leaving cell than entering contributing to the -70 mV resting potential
37
what is hyperpolarization?
an increase in voltage across the membrane
38
how does the Na+/K+ pump work?
1. binding of the cytoplasmic Na+ to the protein causes phsohorylation by ATP
2. phosphorylation causes the protein to change its conformation
3. the conformational change expels Na+ to the outside and extracellular K+ binds
4. K+ binding triggers release of a phosphate group
5. loss of phosphate restores original conformation
6. K+ is released into the cell and Na+ sites are receptive again CYCLE REPEATS
39
what is depolarization?
reduction in voltage across the membrane
40
describe the ions in hyperpolarization
K+ outflow, Cl- inflow
more negative
41
describe the ions in depolarization
increase Na+ flow, less negative + more positive
42
what are the types of potentials?
- graded potential
- threshold potential
- action potential
43
what is the graded potential?
all membrane potentials are below the threshold
44
What is the magnitude of a membrane potential affected by?
- strength of stimulus
- distance that stimulus travels
45
what happens with a stronger stimulus?
- more channels open
- increase cells permeability for the ion
- producing a larger change in membrane potential
46
what does it mean to be decremental?
the magnitude decays/degenerates as it spreads
47
what is the threshold potential?
the potential at which an action potential occurs
48
what happens with the threshold is reached?
the graded potential becomes an action potential
stimulus intensity plays no role in the magnitude
49
what is the action potential?
a large depolarization followed by repolarizing back to resting
50
where is the action potential generated?
in the axon
51
what is the axon hillock?
an anatomical description site where the axon begins
52
what is the trigger zone?
a functional description that refers to the region on the axon in which the first action potential occurs - often the same place as the axon hillock
53
what are the types of channels on neurons?
- ungated, leak
- voltage-gated
- chemically-gated
54
describe the state of the ungated, leak channels
open at all times
55
describe the state of the voltage-gated channels
open or close in response to changes in membrane potential
56
describe the state of the chemically-gated channels
open or close in response to chemicals
57
where are chemically-gated channels located on a neuron?
at dendrites
58
where are voltage-gated channels located on a neuron?
- on the axon at the notes of ranvier
- the synaptic terminal
59
where are ungated, leak channels located on a neuron?
all over the cell
60
what are examples of ungated, leak channels?
Na+ and k+ channels involved maintaining resting potential
61
what are examples of voltage-gated channels?
- Na+ and K+ channels involved in an action potential
- Ca+ channels involved in a synapse
62
what are examples of chemically-gated channels?
receptors open when neurotransmitters bind
63
Describe the K+ Channel.
- resting position
- depolarization stimulus
- speed
- resting position: closed
- depolarization stimulus: opens
- speed: slow
64
Describe the Na+ activation Channel.
- resting position
- depolarization stimulus
- speed
- resting position: closed
- depolarization stimulus: opens
- speed: rapid
65
Describe the Na+ inactivation channel.
- resting position
- depolarization stimulus
- speed
- resting position: open
- depolarization stimulus: closes
- speed: slow
66
what are the phases of an action potential?
1. rapid depolarization
2. rapid repolarization
3. undershoot
4. return to resting
5. threshold
67
what happens during the resting state
nothing - only ungated leak channel open
68
What happens during Step 2 - threshold?
- depolarization stimulus open some Na gates
- results in a graded potential that reaches threshold
69
What happens during Step 3 - depolarization phase?
- the depolarization opens NA gates resulting in more depolarization
- stimulates other Na gates to open until all are open
- positive feedback bc depolarization potential triggers a larger depolarization to action potential
70
What happens during Step 4 - repolarizing phase?
- closing sodium inactivationg gates so there nore entry of Na+
- opening of potassium channels so K+ moves out of cell
- cell becomes more negative
71
What happens during Step 5 - the undershoot?
- closing K+ gates means too many K+ can get out of the cell resulting in hyperpolarization
- reestablish resting potential with the Na+ and K+ leak channels
72
propagation
an action potential "travels" by repeated regeneration along the axon
73
what direction does propagation occur in?
unidirectional
74
what is the refractory period?
period when neuron is insensitive to depolarization
75
what causes the refractory period?
a closed Na activation gate
76
When does the refractory period happen?
during the repolarization and undershoot phases
77
What is the purpose of the refractory period?
prevents the action potential from moving backwards
it limits the maximum frequency with which action potential can be generated
78
What factors affect the speed of conduction?
- axon diameter
- myelination
79
How does a larger axon diameter affect the speed of conduction? Why?
larger makes it faster as there is less resistance
80
what is saltatory conduction?
when the current generated by action potential at a node "leaps" to next node to stimulate new action potential
81
An action potential is All-or-Nothin. What does this mean?
magnitude of action independent of stimulus strength once threshold is reached
82
How is stimulus strength translated into an action potential if the stimulus strength can't change the magnitude?
Frequency coding
83
what is frequency coding?
stimulus strength & duration correlates to frequency of action potential
84
what is a synapse
a cell junction that controls communication between a neuron and another cell
85
describe an electrical synapse
current from presynaptic cell flows directly to the postsynaptic cell through gap junctions - direct communication through physical connection
86
What types of species have electrical synapses?
- found in giant axons in crustaceans
- not common in vertebrates
87
what is the advantage of an electrical synapse?
rapid transmission of action potential from cell to cell
88
what is the disadvantage of an electrical synapse?
more difficult to regulate
89
what is a synaptic cleft?
a narrow gap separating pre and postsynaptic cell
90
what are the steps of a chemical synapse?
1. presynaptic membrane depolarized by action potential
2. voltage-gated Ca2+ channels open
3. Ca2+ enters cell
4. stimulates exocytosis of synaptic vesicles
91
what is a synaptic vesicles?
sacs at the synaptic terminal that contains neurotransmitters
92
what is a neurotransmitter?
substance released by presynaptic cell as an intercellular messenger into synaptic cleft
93
each neuron usually secretes only one type of neurotransmitter
94
What is the effect of changing the Ca levels in the chemical synapse? Steps
- Voltage-gated Ca2+ channels close soon after opening
- Ca2+ actively transported out of axon terminal bringing it back to resting level
- but if another action potential arrives soon after previous, then Ca2+ levels continue to increase
- frequency of AP -> [Ca] -> [NT]
95
What happens when a neurotransmittter (NT) binds to a receptor?
gates open allowing in a specific ion (I.i. Na, K, Cl)
96
what are the receptors a part of?
a gated ion channel
97
Each type of receptor on the post-synaptic membrane specifically recognize one neurotransmitter
98
what are postsynaptic potentials? (PSP)
graded potentials that start at the dendrites and progress to the axon hillock on the post-synaptic neuron
are decremental
99
what are the two types of PSP?
- excitatory (EPSP)
- inhibitory (IPSP)
100
what's an excitatory synapse?
- an increased chance of generating an action potential
- depolarization
- net flow of positive charge into cell
101
What is an inhibitory synapse?
- a decrease in the chance of generating an AP
- hyperpolarization
- net flow of negative charge into the cell
102
what is an example of an excitatory synapse?
neurotransmitter binding to receptor which open the gated Na+ channels causing Na+ to enter
103
What is an example of an inhibitory synapse?
neurotransmitters binding to receptor that open gated K+ and Cl- channels and the diffusion down electrochemical gradients K+ leaves and Cl- enters
104
What is summation?
the additive effects of postsynaptic potentials
105
How/Why does summation work?
a single EPSP is usually not strong enough to trigger an action potential so you needed several EPSPs working together on the same postsynaptic cell to have a cumulative impact
106
Where does summation occur?
at the axon hillock
107
What are the different types of summation?
- spatial summation
- temporal summation
108
what is spatial summation?
when several different synaptic terminals (usually from different presynaptic cells) stimulate the same postsynaptic cell at the same time
109
What is temporal summation?
a chemical transmission form one or more synaptic terminal occuring close together in time affecting membrane on postsynaptic membrane before the voltage can return to resting potential
110
how are neutrotransmitter's removed?
enzymatic degradation
111
What is the consequence of removing a neurotransmitter?
- ensuring the effect of NT is bried and precise
- allows transmission of the next action potential
112
what are other possible fates for the neurotransmitter?
- reuptake into the presynaptic cell
- diffusion out of the synaptic cleft
113
