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1 NAS > Lectures 1-5 > Flashcards

Lectures 1-5 Flashcards

1
Q

What is the permiability of a membrane dependent on?

A

The number of channels for each ion

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2
Q

What two factors do ion flux depend on?

A

Chemical gradient

Electrical force

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3
Q

If a membrane were only surrounded by Na+, what would

happen

A

Na+ influx into the negatively charged area, down the chemical gradient

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4
Q

What is the equilibrium potential of an ion?

A

The voltage at which there is no net movement of a specific ion (when chemical and electrical forces are in equilibrium.
This is given by the Nernst equation.

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5
Q

What is the ionic driving force?

A

The net result of the chemical gradient and electrical force on ions

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6
Q

At rest, what are the relative permeabilities to Na+ and K+ across the axon membrane?

A

40 times more permeable to K+

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7
Q

What do ion pumps do?

A

THEY DON’T CONTROL MEMBRANE POTENTIAL
They top up the Em
catalyse ATP breakdown, efflux 2Na+ for 3K+ influx (electrogenic)

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8
Q

How does the influx of Na+ compare to the efflux of K+ at rest?

A

they are equal

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9
Q

Essentially, what is conductance?

A

permeability
It treats the membrane as an electrical resistor
g=1/R

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10
Q

When do Na+ Voltage gated ion channels open and close?

A

open gradually in depolarisation and close in repolarisation

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11
Q

What is the effect of depolarisation?

A

Em approaches E(Na)

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12
Q

What stops the influx of Na+ at the end of depolarisation?

A

Na+ channels undergo a conformational change

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13
Q

What causes repolarisation?

A

K+ VGC’s open as a delyaed response, allowing K+ efflux.

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14
Q

What causes hyperpolarisation?

A

conductance for K+ increases after Em returns to rest.

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15
Q

How is Em returned to -65mV?

A

K+ VGC’s close, using leak channels to establish resting potential

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16
Q

In what circumstances would Na+ influx lead to depolarisation?

A

If Na+ influx is greater than K+ efflux

The threshold potential is the Em value where this is established

17
Q

What is the difference between the types of refractory periods?

A

Absolute refractory periods - impossible for another AP to be generated (most Na+ channels inactivated)
Relative refractory periods - a stronger stimulus is required to open enough Na+ channels to overcome the increased K+ conductance.

18
Q

What prevents AP’s from travelling backwards?

A

local current flow to adjacent membranes

19
Q

Are most neurones in the CNS or PNS?

A

They are normally straddling both, as the systems are in continuum

20
Q

Where is the boundary between CNS and PNS?

A

the Pia mater (formally the Redlich-Obsteiner’s zone, where myelin sheathing changes)

21
Q

What kind of state is the somatic system in?

A

bi-stable, it’s partially paralysed in REM sleep

22
Q

What does the axon hillock do?

A

generate the action potential

23
Q

What is the fastest type of synapse?

Why?

A

The Gap junction (electrical)

uses the direct transfer of ion currents

24
Q

What is the function of the gap junction

A

It permits synchronous activity between cells, by allowing communication bidirectionally

25
Q

What is the structure of the gap junction?

A

has one connexon made of 6 connexins, hemichannels form a pore junction

26
Q

What triggers the exocytosis of neurostransmitter in the chemical synapse?

A

depolarisation oppens Ca2+ channel proteins, Ca2+ influx triggers exocytosis

27
Q

What are the kinds of ionotropic signalling mechanisms at the synapse?

A

Excitatory - Na+ influx depolarises the membrane, forming a small excitatory post synaptic potential (EPSP)
Inhibitory - Cl- influx causes hyperpolarisation (small inhibitory post-synaptic potential (IPSP)

28
Q

How does transmision and effect duration differ between ionotropic and metabotropic receptor signalling mechanisms?

A

metabotropic offer a slower transmission, but longer-lasting effects

29
Q

what is special summation?

What is another kind of summation?

A

multiple EPSP may increase the likelihood of a threshold potential being reached, or EPSP and IPSP cancel each other out

Temporal summation

1 NAS (12 decks)

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