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Flashcards in Neural Communication Deck (75):
1

What are the three fundamental characteristics of a channel?


its gating

its selectivity

whether or not it can be inactivated

2

What are the three ways channels can be gated?


mechanically

ligand

voltage

3

What is a rectifier?


A rectifier basically is what returns the system to the resting potential

so if the membrane is depolarized, the rectifier will repolarize it

if the membrane is hyperpolarize it, it will depolarize back to the RMP

K+ channels are often rectifiers

4

WHat channels establish the RMP?


the leak channels - the ones that are open at rest

5

voltage gates channels have __ subunits and ligand gated channels have __ subunits.


voltage = 4

ligand = 5

6


Which leak channels are primarily resonsible for the RMP in a neuron?


open K+ leak channels

some Na+, but mostly K+

7


In a neuron, which type of channel can be inactivated, Na+ or K+?


Na+

that's why there's an overshoot hyperpolarization at the end of an action potential - the K+ channels can't be inactivated, so it takes longer for them to close,

8


At what membrane potential will an ion stop flowing in either direction?


At the reveral potential (or equilibrium potential) for that specific ion.

this is essentially when the chemical and electrical forces are in balance

calculated by the Nernst equation

9

What is the Erev for Na+, K+, and Cl-?


Na+ = 60 mV

K+ = -88 mV

Cl- = -61 mV

10

What is the average RMP in a neuron?


about -70 mV relative to the outside of the membrane

11


Besides the resting membrane potential, what are the other two types of potentials?


action potential

graded potential

12


In which type of potential is the amplitude of the change proportion to the magnitude of the input?


Graded potentials (higher input, higher membrane change)

Action potentials are all or none

13

True or false, graded potentials can only be depolarizing.


False

graded potentials can either be depolarizing or hyperpolarizing

unlike action potentials, which are always depolarizing at first, followed by a hyperpolarization

14


What is the cell's resistance based on?

How does resistance related to voltage change?


the resistance is based on the number of open channels = more open channels = less resistance

the higher the resistance, the greater the voltage change will be (V = IR)

 

15

True or false:

THe more channels that are open, the greater the voltage change across the membrane will be.


False

It goes back to resistance.

Fewer channels open = greater resistance = greater voltage change

16


What does it mean to say that graded potentials are passive?


they will travel equally in all directions and decrease in amplitude with distance

17


What are the 3 types of graded potentials


1. post-synaptic potentials - in neurons (EPSPs and IPSPs)

2. End plate potentials in muscle cells

3. receptor potentials in sensory systems

18


What is the length constant?


an expression of how far a graded potential can be transmitted along a membrane

it's equal to the distance where the amplitude has decayed to 37% of the original amplitude

19


What affects the length constant, in what way?


1. membrane resistance: higher resistance, higher the length constant

2. axial resistance (the diameter of the axon): higher diameter, lower resistance, higher the length constant

20

Neuronal regions with high membrane resistance and low axial resistance (myelinated asons) have ____ length constans, so they can transmit potential changes over ___ distances


long length constants

long distance

21


What is the temporal and spatial relationship between graded potentials and action potentials?


the graded potentials occur first. If they can depolarize the membrane to threshold (-40 mV), they will trigger an action potential that will travel further down the axon

22

what channels are opened at threshold?


the voltage gated Na+ channels, so Na+ floods into the cell, causing rapid depolarization

23


As the Na+ channels start to be inactivated, what open?


the voltage gated K+ channels (the delayed channels)

24


what is threshold in a neuron?


usually -40 mV

25


true or false: once initiated, all action potentials will be identical.


false - they can be different shapes and sizes depending on what channels and neurotransmitters are involved

26


In general, which channels areresponsible for depolarization and which are responsible for repolarization?


Na+ is depolarization

K+ is repolarizing (and hyperpolarizing)

27


Why does the action potential peak at +40 mV and not +60 mV, which is the Erev for Na+? 4 reasons...


1. the Na+ channels become inactivated

2. As Na+ enters the cell, you get a decrease in the electrical driving force for more Na+ to enter, so it slows down

3. Cl- channels become involved as the membrane potential leaves -06 mV, so Cl- will move into the cell and play a role in the hyperpolarization

4. the rectifier VG K+ channels open and K+ leaves the cell, causiong hyperpolarization

28


At what point do the Na+ channels go back from inactivated to closed?


during the relative refractory period - as the K+ channels are closing

29


Why is hyperkalemia such an issue?


If there's too much extracellular K+, the E rev and Vm of K+ changes and the VG K+ channels won't close again - this means you won't be able to fire anymore action potentials - the RMP will be too hyperpolarized.

30


What does poisoning with tetrodotoxin, saxitosin and brevitoxin do?


They block the VG Na+ channels so that you don't get action potentials in the nerves going to the lungs and you die from respiratory depression

31


What is hyperkalemic periodic paralysis?

It's an autosomal dominant mutation in muscle VG Na+ channels, such that they get less Na+ entering their cells during exercise and the muscles can't fire = paralysis

32

In what state are the VG Na+ channels during the absolute refractory period?


the majority of the Na+ channels are inactivated

this means that the cell membrane cannot immediately produce a second AP

33


In what state are the VG Na+ channels during the relative refractory period?


they are transitioning baack from the inactivated to the closed state

in other words, they become capable of opening again

this menas it's possible to have another action potential, but it takes a greater stimulus to do so

34


True or false, the action potential fired during the relative refractory period will be the same as the first.


False - it will be smaller

35

Why is the propagation of an action potential unidirectional?


the absolute refractory period prevents the initiation of an AP in the region of membrane that has just produce one (can't go backwards).

36


How does AP propagation occur in myelinated axons?


its through saltatory conduction...

depolarization only occurs at the nodes

the signal propagates down the axon under the myelin (higher resistance = longer length constant) and triggers the sodium channels to open at the node, causing depolarization

then it jumps to the next node

37

What two things determine the conduction velocity of nerve fibers?


the diameter and degree of myelination

more myelination = faster

greater diameter = faster

38

WHat are the subcategories of nerve fibers arranged from fastest conduciton to slowest conduction?


A-alpha (motor neurons)

A-beta (sensory neurons)

A-gamma (sensory neurons)

B (autonomic nervous system)

C (sensory)

39


What are the two types of synapses?


chemical and electrica

40


What are the properties of an electrical synapse?


1. it's the passage of a graded potential from one cell to another

2. they're passive, so the signal will decay with distance

3. they'll be extremely rapid

4 will be bidirectional

41


What are the properties of chemical synapses?


1. similarly to an AP, a weak signal can be transferred in an all-or-none way

2. slower because of synaptic delay

3. use NTs

4. unidirectional (pre to post synaptic)

42


What are the 3 fundamental steps in chemical neurotransmission?


1. NT release

2. receptor activation

3. NT inactivation

43


How often does a synapse actually fire an action potential when it's signalled to?


It depends on the tissue, but electrical and chemical synapses in the brain actually fail about 50% of the time!

44

 

WHat are the steps in neurotransmitter release coupling?


1. depolarization reaches the terminal membrane

2. activation of voltage gated Ca2+ channels

3. Ca2+ enters the cell

4. Ca2+ causes a conformational change in the docking proteins

5. The vesicles fuse to the plasma membrane

6. NT is released into the synaptic cleft

45


the amount of Ca2+ that enters the cell depends on what?


the size and shape of the action potential

 

46

If you _____ the terminal membrane, you will de-inactivate the VG Ca2+ channels, making them more likely to ____ if threshold is reached, and therefmore making it ____  likely NTs will be released.


If you hyperpolarize the membrane, you'll be de-inactivating the VG Ca2+ channels, making them more likely to open if threhold is reached, and therefore making it more likely NTs will be released

47


What happens in Lambert-Eton Syndrome?


It's an autoimmune disorder that attacks some VG Ca2+ channels in the periphery

this means you get less Ca2+ triggered NT release in the periphery

this manifests in muscle weakness that will go away the more you try to contract the muscle (because the Ca2+ will eventually build up- it just takes longer)

48

What is the treatment for Lambert-Eton Syndrome?


Diaminopyridine

It's a K+ channel blocker that serves to prolong the action potential and therefore increase the liklihood that the Ca2+ channels will open to allows Ca2+ to enter the cell and trigger NT release

49


WHat does botox do?


It destroyes the docking proteins in cholinergic nerves

this means you don't get NT release and thus muscle contraction is decreased = less wrinkles, less twitches

50


What does tetanus \do?


it's retrogradely transported back to inhibitory nerves

it dcreases the inhibitory nerve's ability to send inhibitory signals and thus you get an INCREASE in muscle contraction

51


What is a quantum?


1 quantum = the amount of NT held in 1 vesicle

52

What does Dale's prinicple say?


In general, all axonal branches of a neuron release the same NT substances from each nerve terminal.

53

What are some of the NT and substances that can be released from nerve terminals?


- it will release the primary NT

- then it will release neuromodulators that influence the action of the primary NT

classic NTs: ACh, NE, GABA, 5HT, glutamate, glycine, ATP

peptides: endorphins, insulin, enkaphalins

gases: NO

54


Receptor mecanisms can be classified in what two ways?


Speed (fast or slow) and action (excitatory or inhibitory)

55

What is the difference between an ionotropic receptor and a metabortropic receptor?


An ionotropic receptor itself is the ion channel, so its action is very fast

A metabotropic receptor involves a 2nd messenger to act as the ligand to open the ion channels, so it's slower

56

What are the 5 ionotropic receptors that cause excitatory signals?


nicotinic (ACh)

AMPA (glutamate)

NMDA (glutamate)

5HT3 (5HT)

P2X (ATP)

57


What are the two inhibitory ionotropic receptors we talked about?


GABA

Glycine

58


What do agaonists do?

What do antagonists do?


Agonists will bind tot he active site and produce the same effect as the native NT
 

An antagonis will bind the active site and have NO effect, thus preventing the effect of the native NT

59


What type of receptor is the nicotinic receptor?


it's a 5-subunit ligand gated receptor (Ach) that, when open, acts as a nonselective cation channel that allows K+, Na+ and Ca2+ to go through

 

60


At rest, if the nictoinic receptor opens, which ion is more likely to flow through the fastest and why?


the Na+ because at the resting membrane potential of -70 mV, Na+ is the ion that is furthest away from its Erev (+60 mv), so it will flow through the fastest and you'll get Na+ entry/depolarization

61


As Na+ rushes into the cell through the nicotnic receptor, what will happen as it depolarizes?


the membrane potential will get further away from the Erev for K+ (-88 mv), so K+ will begin to exit the cell, meaning the EPSPs will be self-limiting (and won't reach the Erev of Na+)

62

What happens in myasthenia gravis?


it's an autoimmune disease against he nicotinic ACh receptors

patients get rapid muscle fatigue because the nicotinic receptors won't open for the ions to enter = no EPSPs

63

What is the treatment for myasthenia gravis?


give an acetylcholinesterase inhibitor to block the degradation of ACh

64


What are thet wo glutaminergic receptors we talked about?


the AMPA and NMDA

65


Describe the AMPA channel.


It's a non-selective cation channel

when opened at rest, Na+ will enter the cell first, then K+ will leave

it will open and close quickly due to desentitization

66


Describe the NMDA receptor. WHy is it unique?


The NMDA receptor is unique in that it is both voltage AND ligand gated

1. At rest, the receptor is blocked by MG2+, so even if it opens, no ions will go through at the restine membrane potential

2. WHen the membrane depolarizes (through AMPA usually), the inside becomes more negative and the Mg2+ is pushed out

3. when glutamate binds without Mg2+ inside, the channel will open and the cations will be able to flow (Na+ and Ca2+ in and K+ out)

67


WHy is the NMDA receptor considered activaty dependent activation?


it takes depolarization to get more depolarization

the Na+ influx keeps the channels open in a positive feedback loop.

68

WHat role does Ca2+ play in the NMDA receptor?


it will enter the cell when the receptor is open and you get calcium induced calcium release, which alters channel function

69


What HUGELY IMPORTANT role does the NMDA receptor play?


It's the underlying cause of learning and memory because it's pivitol in long term potantial and changing gene expression with anatomical remodeling

70


Describe the GABA receptors


they are the predominant inhibitory receptor in the brain

it's a chloride channel that produces inhibition by basically stabilizing the RMP around -61 mV

If the membrane is hyperpolarized, the Cl- will leave the cell, bringing it back to RMP

If the membrane is depolarized, the Cl- will enter the cell, bringing it back to RMP

71

What are the 3 mechanisms for NT inactivation?


1. diffusion (glutamate and GABA)

2. enzymatic degradation (ACh)

3. Reuptake (monoamines and 5HT)

72

What breaks down ACh?


acetylcholinesterase in the synaptic cleft

73


Individual ESPs are generally too small to trigger an AP, so what has to happen?


synaptic summation or integration

74


What are the two types of synaptic summation?


1. temporal summation - summate the output of a single (or multiple) pre-synaptic neuron EPSPs that are occuring in quick temporal succession)

2. Spatial summation - integrate the EPSPs from multiple pre-synaptic neurons on the same post-synaptic neuron

75