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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
How is the RMP determined?
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)
26
Which cells in the body can change membrane potential and why?
neurons, muscle fibres, some endocrine cells | Due to stimulis
27
How much can stimulus cause/can change it? (range)
Between -100 and +50mV
28
What are the 2 ways RMP can be measured?
Intracellular recording technique | Patch clamp technique
29
What is the main physical difference between these 2 techniques?
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
30
What do they both (techniques) measure?
Membrane pot Action pot Synaptic pot
31
What is the advantage of patch clamp?
It can also meaure the current or voltage across cell membrane (channel kinetics)
32
What is the approx. conc of K+ and Na+ in cell?
``` K = 100mM Na= 15mM ```
33
What is the approx. conc of K and Na outside of cell?
``` K = 5mM Na = 150mM ```
34
How is teh conc gradient of Na and K maintained?
Na?/ pump
35
What is the ration of Na and K in the Na/K pump thing?
3 Na pump ion 2 K pump out
36
What are the results of the pump thing?
A positive charge out of the cell and a negative charge inside of the cell
37
What happens if Na+ leaves?
Leaves behind negativecharge
38
What else is found on the cell membrane of neurons?
Ion channels
39
What are the 2 main types of ions channels?
Gated - closed at rest Non-gated (leak( - open at rest
40
What do non gated channels do?
Diffusion of ions so ions flow down conc grad (important for maintaining RMP)
41
Which ones are found in neurons and how are they different>
Many leak K+ channels (important for neuroglia cells as RMP depends only on leak K+ channels) Very few Na+ leak channels
42
Therefore what this man (the difference no of K and Na leak channels?)
Cell membrane is more permeable to K+ than Na+
43
How can this be shown with values?
PK+ / PNa+ = 40 / 1
44
What does unequal conc and unequal cell membrane permeability of Na and K result in?
``` P = membrane permeability A = negative RMP ``` Equilibrium potential
45
What is equilibrium potential?
An intracellular potential at which the net flow of ions is 0 in spite of conc grad and permeability
46
How does equilibrium potential occur?
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
How do we calculate the EP for each ion?
Nernst Equation E ion = RT / zF x log [ion]o/[ion]i
48
What does RT / zF equal?
61.5mV
49
What is EP for equilibrium potential for K+ and Na+
Ek = -80mV ENa = +60mV
50
What are the limitations of the Nernst equation?
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
Give an example of a cell which is only permeable to one ion
Neuroglia cells --> K+ therfore RMP = -80mV
52
How is the RMP for neurons calculated?
The Goldman equation - takes conc gradient and relative permeability into account
53
Why is this:
Because in neurons not only K+ leak channels bu Na+ leak channels also affect the RMP
54
What is the rule regarding this?
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
Therefore, what is the RMP for neurons?
It's much higher to K+ than Na+ therfore, RMP is closer to the EP of K+ ~65mV (40:1)
56
Compare the RMP of neurons and neuroglia
Neurons - less negative because of small contribution of leak Na+
57
What is the Goldman equation ?
RMP = 65.1 x log pk[K]o + p[Na]o / pk[k]i + pk[Na}i
58
Goldman equation refer to neurons - Na and K
RMP = 65.1 x log 40[5] + 1[150]/ 40[100]i + 1[15} RMP = -65mV
59
What can occur to the potential inside the neuron?
Change: Become more negative o less negative
60
Why does it become more or less negative?
When membrane permeability or ion conc change
61
What is it called when it becomes more negative?
Hyperpolarisation (movels closer to EK+
62
What is it called when it becomes more positive?
Depolarisation (moves away from EK+ to ENa+
63
What are the different names for an action potential?
Spike, nerve impulese, discharge
64
What is an action potential?
A brief flactuation caysed by transient opening of voltage gated ion channels which spreads like a wave along the axon of the neuron
65
How is the action potential triggered?
After the membrane potential reaches the threshold (-55mV)
66
Why is action potential important?
It encodes information = how neurons communicate key elements in the signal transmission process along axons
67
What pushes RMP to threshold?
A stimulus (slow depolarization to threshold)
68
What are the three stages of the action potential after pushing the RMP threshold with a stimulus?
1. Fast depolarisation to = 30mV 2. Rpolarisation 3. After = hyperpolarisation (AHP)
69
What is the 1 and 2 stage often referred to?
Absolute refractory period
70
What does the absolute refractory period mean?
If there is a 2nd stimulus soon after the first, the neuron will not repond bc its already in refractory period (resistant)
71
What is stage 3 referred to?
Relative refractory period
72
What is the relative refractory period?
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
What can stimulus be?
Physical (current electrical, light, stretch) | Chemical (drug or synaptic extension)
74
What occurs in the first stage?
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
How does MP shift towards Na+?
Na+ move into cell; conc and electrical graient as well
76
Why does influx of Na+ slow down and stop?
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
What occurs in 3 stage?
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
What is an important feature of action potentials?
It is an all or none event
79
What is the amplitude?
100mV (from RMP to peak) | - does not respond to stimulus intensity
80
What can it be contrasted to?
Small (subthreshold) depolarisation or hyperpolarisations which are graded (change) e.g. flowing in CSF electrolyte
81
How does an electrical stimulus evoke an action potential (unatural conditions)
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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