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PSYC-2900 > Chapter 2: Computing with Neurons > Flashcards

Chapter 2: Computing with Neurons Flashcards

1
Q

Camillo golgi developed the golgi stain that would only stain a handful of neurons at a time, but believed that the building block of the nervous system was a nerve net, aka a ____-

A

reticulum

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2
Q

in addition to thinking of the neuron hypothesis, ramon cajal also believed that neurons were ____ ____, which oriented them in a specific direction.

A

ramon cajal noted that dendrites were THICKER and directed towards a sensory input, but axons were THINNER, and facing toward the brain center, showing that neurons were FUNCTIONALLY POLARLIZED.

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3
Q

Sherrington’s findings

A

found that reflex pathways are uni-directional and stimulation at a sensory end of sensory pathway elicits activity on the motor end.
he also coined the term SYNAPSE: tiny one way vallves that connect neurons together to function in a directional manner.

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4
Q

Neuron doctrine

A

concept that the nervous system is made up of discrete individual cells, which connect (synapse) together to propagate information in a directional manner.

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5
Q

Nissl Substance

A

special rough ER only found in neurons that can be stained with NISSL stain to locate cell bodies.

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6
Q

the brain uses 40% of glucose in the body. Why does it need so much energy?

A

uses a lot of energy maintaining ion gradients and myelin sheaths of neuronss

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7
Q

dendrites tend to start ____ and become ___ with distance from the cell body, whereas axons are uniformly ____ compared to dendrites.

A

dendrites tend to start THICK and become THINNER with distance from the cell body, whereas axons are uniformly THIN compared to dendrites.

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8
Q

axon collateral

A

branches off the main axon that may terminate in alternative locations

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9
Q

axonal-plasmic transport

A

system that allows materials produced by the cell body to be efficiently moved down the axon to the terminals.

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10
Q

neurotransmitters in vesicles get transported very fast down the axon via ___ and ____ protein carriers.

A

dynein and kinesin

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11
Q

a ____ measures the potential difference between 2 points. Can also used microelectrodes in and out of the cell in order to see the separation of charges that is causing the difference

A

voltmeter

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12
Q

resting potential

A

voltage difference between inside and outside of the neural membrane when it is not firing

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13
Q

action potential

A

the reversal of negative polarity that allows excitable cells to transmit information along their axons.

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14
Q

intracellular recording vs extracellular recording

A

using an intracellular microelectrode to record the membrane potential at rest and during an AP. more accurate than extracellular recording of potentials becasue extracellular probes only measure changes NEAR the neuronal membrane and not across.

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15
Q

there are high ___ and ___ concentrations INSIDE THE CELL, and high __ and ___ OUTSIDE THE CELL

A

there are high K+ and A- concentrations INSIDE THE CELL, and
high Na+ and Cl- OUTSIDE THE CELL

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16
Q

the principle reason as to why a neuron is negatively charged. how is the membrane potential maintained?

A

K+ concentrated inside the cell flows out through LEAK channels, creating a more positive ECF and negative ICF. The Na+/K+ ATPase pump MAINTAINS the Na+/L+ concentration gradient of neurons, pumping sodium out while K+ is pumped in(and leaves again via leak channels)

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17
Q

how does the concentration and electrochemical gradient of potassium work against each other?

A

initially, K+ will flow out of the cell according to its concentration gradient, making the cell increasingly negative. however, as the cell reaches the Ek+ (equilibrium potential), the potassium efflux will slow, as the A- in the cell draws potassium in and the positive ECF prevents it from moving out.

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18
Q

an equilibrium potential of an ion has been reached when:

A

ion efflux =ion influx

concentration gradient effects= electrochemical gradient effects.

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19
Q

why does K+ play a more major role in setting the neurons membrane potential than sodium?

A

because it is more permeable and can thus exert larger effects on the membrane compared to sodium

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20
Q

why is the resting potential of the cell not entirely the equilibrium potential of potassium?

A

because sodium electrochemical and concentration effects are slightly affecting the cell as well, not as much as apotassium though because the cell is not as permeable to sodium

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21
Q

how does the lipid bilayer act as a capacitor?

A

it is an INSULATOR and prevents the ions from flowing past it unless a channel is present. it therefore STORES CHARGE on either side.

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22
Q

a hyperpolarization is an ____ in membrane potential, exceeding the normal resting potential

A

INCREASE in membrane potential.

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23
Q

electrolyte

A

aqueous solution of ions, typically acids, bases and salts.

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24
Q

electrostatic pressure

A

attractive forces between oppositely charged particles, or repulsive forces between same charged particles

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25
Q

ion must ___ ___ a ____ in order to go past a membrane

A

PASS THROUGH a CHANNEL

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26
Q

two types of membrane channels

A

1) leak channels

2) gated channels: open and close to a different stimuli (ex/ voltage gated channels)

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27
Q

voltage gated channel

A

an ion channel that opens and clsoes according to the value of the membrane potential

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28
Q

patch clamp technique

A

using a micropipette to isolate a specific portion of a membrane containing an ion channel, forming a tight seal known as a GIGASEAL. after forming a tight seal around a membrane portion, the opening and closing of the isolated ion channel is recorded to see how that one channel AFFECTS the depolarization or hyperpolarization of the cell. An amplifier is used to allow recording with greater clarity.

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29
Q

Difference between Nernst and Goldman Equation

A

A nernst equation can determine an ions EQUILIBRIUM POTENTIAL (the potential where there is no longer any net movement across the membrane)

a Goldman equation can determine the CELL’S MEMBRANE POTENTIAL by taking account the permeabilities of ALL IONS involved with the membrane (includes chlrine, Na+ and K+ all in one equation)

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30
Q

hodgkin Huxley Model of AP:

A

an AP is triggered due to rapid influx of sodium, which generates a conventional inward current into the cell and causes a depolarization.

  • the voltage gated Na+ channels open more quickly and close more quickly than voltage-gated potassium channels, and the concentration and electrochemical forces later cause sodium to stop influxing into the cells.
31
Q

How did Hodgkin and Huxley get their findings about how an AP works?

A

used VOLTAGE CLAMPING TECHNIQUE (not patch clamp)

32
Q

how does voltage clamping work

A

uses 2 sets of electrodes: one set records potential across the membrane, and the second set injects current via specific ions into the neuron to set an internal voltage.

when the cell naturally depolarizes, the first set recognizes the change in membrane potential and causes the SECOND set to compensate for the depolarization.

essentially, wthe membrane potential is maintained at a specific level. researchers can then infer how much current is moving across the membrane, because this current is exactly the INVERSE of the current needed to clamp the membrane at desired voltage.

by varying command voltage and ion concentrations, experiments can deduce how much the different ions contribute to overall current at various membrane voltages.

33
Q

explain how a sodium voltage gated channel is a positive feedback loop

A

the more the membrane is depolarized, the more Na+ flows in (from ligand gated channels), causing even more depolarization, which can trigger voltage gated channels to open and cause a mass influx of Na+ (Explosive depolarization)

34
Q

Undershoot portion of an AP

A

membrane potential that occurs at the end of each AP when voltage gated Na+ channels are inactivated, but the VG channels are still open, resulting in the + ion efflux. Causes the membrane the be hyperpolarized compared to resting

35
Q

All or none law

A

an Ap is always the same magnitude and same shape. as long as threshold is met, the same AP will be elicited

36
Q

Cable properties

A

the PASSIVE conduction of electrical current in a decremental fasio.

(no voltage gated channels to help propagate the membrane potential change, the current just spreads down the axon decrementally).

37
Q

a Neuron has _____ properties at the dendrite, but ____ properties at the axon hillock.

A

a Neuron has CABLE properties at the dendrite, but AP properties at the axon hillock.

38
Q

Saltatory conduction

A

conduction of APs by myelinated axons in which the AP jumps from one node of Ranvier to the next.

39
Q

Rate Law

A

principle that variations in the intesnity of a stimulus is represented by the variations in the RATE at which an axon fires.

large stimulus DOES NOT EQUAL large AP
large stimulus = frequency increase of APs

40
Q

Why is it beneficial that K+ channels open and close later than sodium VG channels?

A

if they opened and closed at the same time, it would cause a permeability overlap. Na+ would influx the same time K+ would efflux and the 2 currents would cancel each other out.

41
Q

how does an AP spread to surrounding areas?

A

na+ influx through one channel helps to depolarize the membrane around it, thus opening neighboring Na+ channels and propagating the AP to adjacent locations.

42
Q

Why is there no back flow of an AP?

A

becasue the axonal membrane has a refractory period where its Na+ channesl are inactive and K+ channels are open, resulting in inability to conduct AP.

43
Q

2 main methods of speeding up conduction

A

1) increase the diameter: the thicker the axon, the less INTERNAL resistance there is, allowing the AP to propagate faster
2) myelin increases speed of conduction by allowing for saltatory conduction. All the nodes of ranvier have concentrated areas of Na+ VG channels and act as sites of AP generation.

44
Q

length constant and how does it affect speed of AP conduction

A

Length constant is the DISTANCE over which the voltage change generated by an injected current decays to 37% of its max value.

LCs are dependent on the number of leak channels and internal resistance. if there is less internal resistance (ie/ larger diameter of axon), the AP can be propagated further without losing current

45
Q

how does myelin speed up AP conduction

A

changes both length constant and its capacitance. mylination acts as a larger layer of electrical INSULATION and PREVENTS CURRENT LOSS thorugh leak channels.

Myelin DECREASES CAPACITANCE, allowing MORE CURRENT to be propagated INTERNALLY at long distances.

a time consuming aspect of AP propagation is the depolarization of a membrane patch to the threshold for AP triggering. having mylein reduces the area that needs to be depolarized by restricting AP sites to only nodes of ranvier, allowing for saltatory conduction and faster propagation.

46
Q

myelin is made by ____ in CNS and ____ in PNS

A

oligodendrocytes in CNS and Schwann cells in PNS

47
Q

most excitatory neurotransmitter in CNS

A

glutamate

48
Q

Mechanism for neurotransmitter release

A

1) AP from axon activates voltage gated Ca2+ channels, resulting in an influx of Ca2+
2) calmodium triggers vesicle fusing and content release via exocytosis, pushing neurotransmitters from the terminal bulbs into the synapse.

49
Q

Rate Coding

A

changing in firing and AP propagation. belief that strong stimulus = more APs, allows for efficient long distance transmission.

50
Q

EPSP. What causes EPSP?

A

depolarization of membrane caused by changes in ion permeability; summation of EPSP can lead to an AP/ increase in firing rate. EPSP usually caused by Na+ influx

51
Q

_____ EPSPS are more likely to elicit an AP and are LARGER than _____ EPSPs.

A

PROXIMAL EPSPS are more likely to elicit an AP and are LARGER than DISTAL EPSPs.

52
Q

Spatial Summation

A

when two EPSP inputs are activated simultaenously in DIFFERENT SYNAPSES, and are added together to create a net depolarization

53
Q

temporal summation

A

the addition of EPSPS from the SAME synapse; can occur as long as the synapse fires multiple times extremely fast. ie/ summation of EPSPs over time (rather than summation of EPSPs from multiple sources)

54
Q

the more rapidly a pre-synaptic cell fires, the more likely it is to :

A

push the post synaptic cell above the action potential threshold

55
Q

the membrane potential at the axon hillock represents:

A

the SUM of all the EPSPS that have arrived within 10-30ms.

56
Q

what does it mean by “neurons are leaky”

A

EPSPs decay over time because the dendrite and cell body is not myelinated (has cable properties) and thus an EPSP is decremental. if they are not summated soon, a single EPSP effect will belost.

57
Q

If an excitatory synpatic input is activated in rapid succession, what might happen to the amplitude of the EPSPs over time? why?

A

the first time, the EPSP will increase in magnitude and probably trigger an AP due to temporal summation.

later, the EPSP will decrease in amplitude because the constant firing will cause a neurotransmitter depletion. the pre synaxon may be firing but not releasing as much NT, resulting in a decrease in EPSP signals at the post syn neuron.

AKA SYNAPTIC DEPRESSION

58
Q

what is synaptic depression

A

a decrease in EPSP amplitude or power due to a decrease in neurotransmitter out put from the pre synaptic cell.

59
Q

interneurons

A

contact neurons nearby and have SHORT AXONS

60
Q

projection neurons

A

long axons that branch away to distant brain regions. some neurons may have both interneuron and projection neuron qualities by using axon collaterals

61
Q

recurrent collateral

A

branches off a main axon that synapses and sends the outputs back onto themselves.

62
Q

why do IPSPs become smaller as the membrane potential approaches -70mV ?

A

because that’s the equilibrium potential for chloride, and thus less cl- will flow into the cell.

63
Q

what is IPSP reversal potential?

A

at a specific negative membrane potential, an IPSP can SWITCH THEIR POLARITY and actually cause a depolarization. Happens when the membrane potential is MORE NEGATIVE THAN THE Ecl-, causing Cl- to acutually efflux out of the cell when the ion channels open.

64
Q

EPSPs tend to become more smaller at _____ membrane voltages because the Na+ influx is balanced by K+ efflux

A

positive membrane voltages

65
Q

a number of APs a neuron fires in response to stimulation is proportional to:

A

the degree of depolarization to the axon hillock

66
Q

how is info encoded in a neuron?

A

primarily in their AP firing rate (RATE CODING)

67
Q

Spike rate

A

degree of deplarization, the number of APs fired by unit time

68
Q

Spike rate code:

A

the number of APs per unit time being passed from one neuron to another. Essentially the method of info encoding and transmssion

69
Q

spike timing

A

the rhythym of AP firing

70
Q

response profile

A

how a neuron responds to various stimuli

71
Q

when no stimuli is present, the neuron typically fires at ____ ___ ___

A

low background rate

72
Q

spatial receptive field

A

preferred location of stimuli at which neurons respond. neurons can be TUNED to different stimuli if it reponds to a specific stimuli more often than others.

73
Q

action potentials are metabolically costly to produce. ATP is required to maintain gradients. How do neurons economize their use of APs?

A

by habituating to persistant stimuli but firing when a stimuli changes.

74
Q

two main differences between computers and brains

A

brains are capable to PARALLEL PROCESSING: multiple neurons carry out identical computations. energetically costly BUT produces less faults and mistakes than a typical computer that uses serial processing (one part of the computer responsible for one computation)

neurons also have function specialization for computing efficiency–> anatomically adapted for specific functions.

PSYC-2900 (12 decks)

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