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BIOSCI 107 > Neurons > Flashcards

Neurons Flashcards

1
Q

What is the role of neurons?

A

principal building blocks and instruments of communication of the CNS and PNS

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2
Q

What are the roles of the networks formed by these two systems?

A

Communication
So organism can interact in appropriate ways with its internal (contents in the body) and external (the world outside of the body) environments

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3
Q

What are the three types of components found in the nervous system?

A

Sensory
Motor
Integrative

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4
Q

What is the role of the sensory components?

A

Monitor environmental and internal events

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5
Q

What is the role of the motor components?

A

Generate responses to sensory inours or voluntary commands

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6
Q

What is the role of the intgratice component?

A

Process and store sensory and other info

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7
Q

What is the role of rapid communication in neurons?

A

For integration and to control the active lifestyles of humans and animals

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8
Q

How many neurons are foun in the human brain

A

100 billion

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9
Q

What does each neuron do, physically?

A

Make synaptic connections with large number of other neurons (10,000)

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10
Q

How does each neuron do this (synaptic connections)

A

Defined by genetic factors and other cues

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11
Q

Ehat are the features of a typical neuron?

A

Soma (cell body)
2 processes
- dendrites
-axon (single)

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12
Q

Wher do neurons first recieve their input from other neurons?

A

Dendritic tree and soma

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13
Q

What are these inputs called?

A

Synaptic inputs/potentials

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14
Q

What the occurs? in syanpsis.

A

It goes down to the cell body where it make the decsiion to respond or not

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15
Q

If it does respond, what occurs>

A

The axon conducts the messages away from the soma to the tips of the axons where their synaptic ‘boutons’ 1 axon terminal communicate with other neurons

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16
Q

What are these mesgs called?

A

Aetnon potentials

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17
Q

What are the 2 types of signals in communication?

A

Electrical

Chemical

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18
Q

Which components of the neuron conducts chemical signals?

A

Synapses (where is transfers info) contact points

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19
Q

Which comp of the neuron conducts electrical signals?

A

Dendrites, soma, axon

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20
Q

Wjat are 2 eg of neurons?

A

Pukinje cell in cerbellum
Pyramidial cell in cerebral cortex

Both multipolar

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21
Q

What does RMP stand for>

A

Resting membrane potential

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22
Q

What is the RMP in all cells?

A

The voltage across the cell membrane at rest (absence of synaptic potentials and action potentials)

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23
Q

What is the value of RMP usually>

A

Between -50 to 70 mV

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24
Q

What does the value mean

A

The cytoplasm in the neuron has a potential that is 50 to 70 mV lower (more neg) than the potential of the extracellular space: resulting from separation of charge

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25
Q

How is the RMP determined?

A
  1. Unequal conc of Na+ and K+ iside and outside the cell -> electrochemical gradient driving movement of ions
  2. Unequal permeability of cell membrane (p) to these ions
  3. Electrigenic action fo the NaK pump (small contribution)
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26
Q

Which cells in the body can change membrane potential and why?

A

neurons, muscle fibres, some endocrine cells

Due to stimulis

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27
Q

How much can stimulus cause/can change it? (range)

A

Between -100 and +50mV

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28
Q

What are the 2 ways RMP can be measured?

A

Intracellular recording technique

Patch clamp technique

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29
Q

What is the main physical difference between these 2 techniques?

A

Microelectrode: 0.1 microtip –> electrode touches membrane

Patch clamp: 1 micro tip –> electrode sealed or patched on membrane - can burst it so the cytoplasm becomes continuous with solution in electrode

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30
Q

What do they both (techniques) measure?

A

Membrane pot
Action pot
Synaptic pot

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31
Q

What is the advantage of patch clamp?

A

It can also meaure the current or voltage across cell membrane (channel kinetics)

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32
Q

What is the approx. conc of K+ and Na+ in cell?

A 
K = 100mM
Na= 15mM
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33
Q

What is the approx. conc of K and Na outside of cell?

A 
K = 5mM 
Na = 150mM
34
Q

How is teh conc gradient of Na and K maintained?

A

Na?/ pump

35
Q

What is the ration of Na and K in the Na/K pump thing?

A

3 Na pump ion

2 K pump out

36
Q

What are the results of the pump thing?

A

A positive charge out of the cell and a negative charge inside of the cell

37
Q

What happens if Na+ leaves?

A

Leaves behind negativecharge

38
Q

What else is found on the cell membrane of neurons?

A

Ion channels

39
Q

What are the 2 main types of ions channels?

A

Gated - closed at rest

Non-gated (leak( - open at rest

40
Q

What do non gated channels do?

A

Diffusion of ions so ions flow down conc grad (important for maintaining RMP)

41
Q

Which ones are found in neurons and how are they different>

A

Many leak K+ channels (important for neuroglia cells as RMP depends only on leak K+ channels)

Very few Na+ leak channels

42
Q

Therefore what this man (the difference no of K and Na leak channels?)

A

Cell membrane is more permeable to K+ than Na+

43
Q

How can this be shown with values?

A

PK+ / PNa+ = 40 / 1

44
Q

What does unequal conc and unequal cell membrane permeability of Na and K result in?

A 
P = membrane permeability 
A = negative RMP

Equilibrium potential

45
Q

What is equilibrium potential?

A

An intracellular potential at which the net flow of ions is 0 in spite of conc grad and permeability

46
Q

How does equilibrium potential occur?

A

Due to conc grad, ions flow out.

Due to electrical grad, ions flow (as ions flow out, a negative charge is left behind) until it all balances out = E ion

47
Q

How do we calculate the EP for each ion?

A

Nernst Equation

E ion = RT / zF x log [ion]o/[ion]i

48
Q

What does RT / zF equal?

A

61.5mV

49
Q

What is EP for equilibrium potential for K+ and Na+

A

Ek = -80mV

ENa = +60mV

50
Q

What are the limitations of the Nernst equation?

A

Does not consider permeability for the ion. Applies only to striation when a cell membrane is only permeable to one ion )has 1 leak channel)

51
Q

Give an example of a cell which is only permeable to one ion

A

Neuroglia cells –> K+ therfore RMP = -80mV

52
Q

How is the RMP for neurons calculated?

A

The Goldman equation - takes conc gradient and relative permeability into account

53
Q

Why is this:

A

Because in neurons not only K+ leak channels bu Na+ leak channels also affect the RMP

54
Q

What is the rule regarding this?

A

The higher the permeability (more leak channels) of the cell membrane to a particular ion, the greater the ability of this ion to shift the RMP towards its equilibrium potential

55
Q

Therefore, what is the RMP for neurons?

A

It’s much higher to K+ than Na+ therfore, RMP is closer to the EP of K+

~65mV (40:1)

56
Q

Compare the RMP of neurons and neuroglia

A

Neurons - less negative because of small contribution of leak Na+

57
Q

What is the Goldman equation ?

A

RMP = 65.1 x log pk[K]o + p[Na]o / pk[k]i + pk[Na}i

58
Q

Goldman equation refer to neurons - Na and K

A

RMP = 65.1 x log 40[5] + 1[150]/ 40[100]i + 1[15}

RMP = -65mV

59
Q

What can occur to the potential inside the neuron?

A

Change: Become more negative o less negative

60
Q

Why does it become more or less negative?

A

When membrane permeability or ion conc change

61
Q

What is it called when it becomes more negative?

A

Hyperpolarisation (movels closer to EK+

62
Q

What is it called when it becomes more positive?

A

Depolarisation (moves away from EK+ to ENa+

63
Q

What are the different names for an action potential?

A

Spike, nerve impulese, discharge

64
Q

What is an action potential?

A

A brief flactuation caysed by transient opening of voltage gated ion channels which spreads like a wave along the axon of the neuron

65
Q

How is the action potential triggered?

A

After the membrane potential reaches the threshold (-55mV)

66
Q

Why is action potential important?

A

It encodes information = how neurons communicate key elements in the signal transmission process along axons

67
Q

What pushes RMP to threshold?

A

A stimulus (slow depolarization to threshold)

68
Q

What are the three stages of the action potential after pushing the RMP threshold with a stimulus?

A
  1. Fast depolarisation to = 30mV
  2. Rpolarisation
  3. After = hyperpolarisation (AHP)
69
Q

What is the 1 and 2 stage often referred to?

A

Absolute refractory period

70
Q

What does the absolute refractory period mean?

A

If there is a 2nd stimulus soon after the first, the neuron will not repond bc its already in refractory period (resistant)

71
Q

What is stage 3 referred to?

A

Relative refractory period

72
Q

What is the relative refractory period?

A

If a second stimulus is present in 3 it will induce an actio potential but it has to be stronger as the membrane potential is even lower than RMP

73
Q

What can stimulus be?

A

Physical (current electrical, light, stretch)

Chemical (drug or synaptic extension)

74
Q

What occurs in the first stage?

A

Voltage gated Na+ channels open very fast therfore PK+/Na+ is noe 1:20 so is very permeable to Na+, so MP shifts to Na+ = OVERSHOOT

75
Q

How does MP shift towards Na+?

A

Na+ move into cell; conc and electrical graient as well

76
Q

Why does influx of Na+ slow down and stop?

A
  1. The middle potential becomes less positive and thus attracts Na+ ions less
  2. Na+ channels inactivate before it reaches +6-mV
    Na channels inactivate, K+ gated channels activate, becomes PK+/PNa+ = 100:1
    Mp shifts towards EK+
77
Q

What occurs in 3 stage?

A

Voltage-gated K+ channels remain open for a while.

MP decreases below RMP then close until it reaches back to RMP (PK/PNa = 40:1)

78
Q

What is an important feature of action potentials?

A

It is an all or none event

79
Q

What is the amplitude?

A

100mV (from RMP to peak)

- does not respond to stimulus intensity

80
Q

What can it be contrasted to?

A

Small (subthreshold) depolarisation or hyperpolarisations which are graded (change) e.g. flowing in CSF electrolyte

81
Q

How does an electrical stimulus evoke an action potential (unatural conditions)

A

When a current generated from an outside source flows through the cell membrane from outside to inside = hyperpolarisation

Inside to outside - Depolarisation

CHANGES RMP

BIOSCI 107 (8 decks)

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